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The induction of autophagy by gamma-radiation contributes to the radioresistance of glioma stem cells
International Journal of Cancer
Abstract
Malignant gliomas are characterized by a short median survival which is largely impacted by the resistance of these tumors tochemo- and radiotherapy. Recent studies suggest that a small subpopulation of cancer stem cells, which are highly resistant to gamma-radiation, has the capacity to repopulate the tumors and contribute to their malignant progression. gamma-radiation activates the process of autophagy and inhibition of this process increases the radiosensitivity of glioma cells; however, the role of autophagy in the resistance of glioma stem cells (GSCs) to radiation has not been yet reported. In this study we examined the induction of autophagy by gamma-radiation in CD133+ GSCs. Irradiation of CD133+ cells induced autophagy within 24-48 hr and slightly decreased the viability of the cells. gamma-radiation induced a larger degree of autophagy in the CD133+ cells as compared with CD133- cells and the CD133+ cells expressed higher levels of the autophagy-related proteins LC3, ATG5 and ATG12. The autophagy inhibitor bafilomycin A1 and silencing of ATG5 and beclin1 sensitized the CD133+ cells to gamma-radiation and significantly decreased the viability of the irradiated cells and their ability to form neurospheres. Collectively, these results indicate that the induction of autophagy contributes to the radioresistance of these cells and autophagy inhibitors may be employed to increase the sensitivity of CD133+ GSCs to gamma-radiation.
... Currently, the role of autophagy in cancer cells in response to radiotherapy is not completely understood; also in the case of malignant brain tumors, the outcome of radiation-induced autophagy is bifunctional, including both protective and cytotoxic effects [151,152]. Several studies support the fact that IR at a clinically relevant dose can induce autophagy in tumor cells [153][154][155][156]. Autophagy is thought to assist tumor cells to evade cell death through the cooperative crosstalk between the apoptotic signaling pathways [91,157]. ...
... Owing to progress in the cellular and cancer biology methods of investigation, the mechanisms of glioblastoma resistance were uncovered in the last decade, with several studies showing that glioblastoma heterogeneity influences the unequal response of cancer cells to therapy [178]. Cancer stem cells (CSCs) are a subtype of the tumor population that plays a central role in glioma progression and resistance to therapy [155]. Previously, it has been shown that CSCs can produce neurospheres in vitro, forming tumors in an immunocompromised animal model in vivo, and showed resistance to TMZ and ionizing radiation [78,179]. ...
... Simultaneously, the same study showed that GSCs exhibit low levels of phosphorylated mTOR and AKT, noting a connection between the activation statuses of mTOR or AKT with autophagy [198]. Enrichment of GSCs with CD133 marker allows autophagy induction, which results in the expression of isoform II of LC3, ATG5 and ATG12 in comparison with the CD133-negative subtype [155]. In that study, the isolated glioma cells expressed high viability, which correlated with the expression of isoform II of LC3, ATG5 and ATG12, known for their contribution to prosurvival autophagy. ...
Autophagy is a process essential for cellular energy consumption, survival, and defense mechanisms. The role of autophagy in several types of human cancers has been explicitly explained ; however, the underlying molecular mechanism of autophagy in glioblastoma remains ambiguous. Autophagy is thought to be a "double-edged sword", and its effect on tumorigenesis varies with cell type. On the other hand, autophagy may play a significant role in the resistance mechanisms against various therapies. Therefore, it is of the utmost importance to gain insight into the molecular mechanisms deriving the autophagy-mediated therapeutic resistance and designing improved treatment strategies for glioblastoma. In this review, we discuss autophagy mechanisms, specifically its pro-survival and growth-suppressing mechanisms in glioblastomas. In addition, we try to shed some light on the autophagy-mediated activation of the cellular mechanisms supporting radioresistance and chemoresistance in glioblastoma. This review also highlights autophagy's involvement in glioma stem cell behavior, underlining its role as a potential molecular target for therapeutic interventions.
... Chaachouas et al. analyzed both radioresistant and radiosensitive breast cancer cells and revealed that radioresistant cells exhibit a strong post-irradiation induction of autophagy, which consequently serves as a protective and prosurvival mechanism in radioresistance 19 . Furthermore, Lomonaco et al. 20 analyzed two different GBM specimens and revealed that CD133 + glioma stem cells (GSCs) exhibited a higher level of autophagy and increased radioresistance. Although radiation-induced autophagy mediates radioresistance in GBM, the specific molecular mechanisms of autophagy remain unclear. ...
... The correlation between therapy resistance and autophagy in GBM, another malignant tumor, has not been studied as well as in PDAC, but recent studies suggest that there is a close relationship between the two phenomena. Based on these outcomes, a study was conducted based on the hypothesis that the autophagy mechanism is crucial for acquiring radiation resistance in GBM 20,28,29 . Initially, microarray analysis was performed to identify key factors related to autophagy that were altered after radiation treatment in GBM orthotopic xenograft mice (GEO accession number: GSE117126) ( Fig. 1a, b). ...
Overcoming therapeutic resistance in glioblastoma (GBM) is an essential strategy for improving cancer therapy. However, cancer cells possess various evasion mechanisms, such as metabolic reprogramming, which promote cell survival and limit therapy. The diverse metabolic fuel sources that are produced by autophagy provide tumors with metabolic plasticity and are known to induce drug or radioresistance in GBM. This study determined that autophagy, a common representative cell homeostasis mechanism, was upregulated upon treatment of GBM cells with ionizing radiation (IR). Nuclear receptor binding factor 2 (NRBF2)—a positive regulator of the autophagy initiation step—was found to be upregulated in a GBM orthotopic xenograft mouse model. Furthermore, ATP production and the oxygen consumption rate (OCR) increased upon activation of NRBF2-mediated autophagy. It was also discovered that changes in metabolic state were induced by alterations in metabolite levels caused by autophagy, thereby causing radioresistance. In addition, we found that lidoflazine—a vasodilator agent discovered through drug repositioning—significantly suppressed IR-induced migration, invasion, and proliferation by inhibiting NRBF2, resulting in a reduction in autophagic flux in both in vitro models and in vivo orthotopic xenograft mouse models. In summary, we propose that the upregulation of NRBF2 levels reprograms the metabolic state of GBM cells by activating autophagy, thus establishing NRBF2 as a potential therapeutic target for regulating radioresistance of GBM during radiotherapy.
... In both human patients and mouse models, therapeutic resistance occurs due to a variety of mechanisms, including enhanced DNA damage response and drug efflux pumps. 4,[26][27][28][29][30][31][32] In addition, several signaling pathways, cellular processes, and cell states have been linked to resistance, including autophagy, 33 gap junction proteins, 34,35 activation of the Wnt and Notch pathways directly or via prosurvival proteins, [36][37][38] and activation of the mesenchymal program. [39][40][41][42] CSC mosaicism adds an additional layer to the numerous underlying mechanisms of therapy resistance in GBM ( Fig. 1). ...
... For instance, CD133+ GBM cells express higher levels of autophagy related proteins LC3, ATG5, and ATG12, radiation specifically prompted LC3-II expression in CD133+ GBM cells, and inhibition of autophagy sensitized cells to radiation. 33 Inhibition of the gap junction protein connexin-46 or -43 sensitized TMZ resistant cells to TMZmediated apoptosis. 34,35 Activation of the Wnt and Notch pathways have been described in radioresistant GBM CSCs, and radiosensitization could be achieved by inhibiting Wnt signaling or with gamma secretase inhibitors, which target the Notch pathway. ...
Cellular heterogeneity is a hallmark of advanced cancers and has been ascribed to a population of self-renewing, therapeutically resistant cancer stem cells (CSCs). Glioblastoma (GBM), the most common primary malignant brain tumor, has been a paradigm for the study of CSCs and has helped to define key aspects of the disease as well as served as the basis for the development of next-generation therapies. While there continues to be an expansion in our knowledge of how CSCs contribute to GBM progression, opportunities have emerged to revisit this conceptual framework. In this review, we will summarize the current state of CSCs in GBM using key concepts of evolution as a paradigm (variation, inheritance, selection, and time) to describe how the CSC state is subject to alterations of cell intrinsic and extrinsic interactions that shape their evolutionarily trajectory. We identify emerging areas for future consideration, including moving beyond a single CSC population to appreciate CSCs as a cell state that is subject to plasticity, as opposed to a discrete population. These future considerations will not only have an impact on our understanding of this ever-expanding field but will also provide an opportunity to inform future therapies to effectively target this complex and devastating disease.
... However, at later stages, it induces tumor survival and growth and promotes invasion and metastasis formation [54]. Thus, cancer cells can exploit the benefits of autophagy by inducing cell survival associated with the stressful tumor microenvironment [55], as well as damage caused by chemo-and radiotherapies [56]. ...
Hyponatremia is the prevalent electrolyte imbalance in cancer patients, and it is associated with a worse outcome. Notably, emerging clinical evidence suggests that hyponatremia adversely influences the response to anticancer treatments. Therefore, this study aims to investigate how reduced extracellular [Na+] affects the responsiveness of different cancer cell lines (from human colon adenocarcinoma, neuroblastoma, and small cell lung cancer) to cisplatin and the underlying potential mechanisms. Cisplatin dose–response curves revealed higher IC50 in low [Na+] than normal [Na+]. Accordingly, cisplatin treatment was less effective in counteracting the proliferation and migration of tumor cells when cultured in low [Na+], as demonstrated by colony formation and invasion assays. In addition, the expression analysis of proteins involved in autophagosome–lysosome formation and the visualization of lysosomal areas by electron microscopy revealed that one of the main mechanisms involved in chemoresistance to cisplatin is the promotion of autophagy. In conclusion, our data first demonstrate that the antitumoral effect of cisplatin is markedly reduced in low [Na+] and that autophagy is an important mechanism of drug escape. This study indicates the role of hyponatremia in cisplatin chemoresistance and reinforces the recommendation to correct this electrolyte alteration in cancer patients.
... Augmentation of autophagy results in increased cervical cancer cell death under radiation (Roy et al., 2022;Wu et al., 2023). Autophagy occurs to maintain stability and promote cell survival against radiation, thus contributing to cells' radioresistance (Lomonaco et al., 2009;Saleh et al., 2022). However, when autophagic activity becomes excessive and degradation overwhelms the cell's capacity, autophagy can lead to the death of irradiated cells and cells in the microenvironment (Zein et al., 2021). ...
In the course of radiation therapy, normal cells surrounding the tumor are also irradiated. During and after irradiation, they undergo a series of structural and metabolic changes, which can lead to cell death or transformation. Therefore, when planning and conducting radiation therapy, the effects of radiation on normal cells are taken into account with the aim of predicting and further correcting post-radiation complications, including the development of radiation burns and ulcers. Radiation skin burns are characterized by a prolonged course of the wound healing process, which is accompanied by a sharp decrease in the number of viable cells in the affected tissue from the first hours of irradiation. The type of cell death can significantly impact the effectiveness of radiation therapy and post-radiation complication correction. Therefore, it is important to study the type of their death in irradiated three-dimensional culture on a model of irradiated dermal equivalent, which is widely used today for modeling biological processes. To detect the pathways of cell death, the levels of reactive oxygen species, cell viability, number of cells undergoing autophagy, apoptosis, and necrosis, the content of active caspases 3, 8, and 9 was fluorometrically measured in the irradiated 3D cell culture by laser scanning confocal microscopy. It was determined that the transplantation of fibroblasts and keratinocytes into the irradiated dermal equivalent contributed to an increase in the overall viability of cells of the equivalent and led to a significant decrease in the concentration of free oxygen forms in the irradiated equivalent. Cells within the irradiated equivalent were not evenly distributed in terms of their quantity and viability, with an overall decrease in the cell count over time. A cluster of equivalent cells with significantly higher viability was formed around the transplant. At the same time, the fibroblasts of the transplant were found to be more resistant to the cytotoxic factors of the post-irradiation culture environment compared to keratinocytes. It was demonstrated that non-irradiated dermal equivalent cells predominantly undergo cell death through autophagy, irradiated equivalent cells primarily undergo necrosis, and after the introduction of the transplant, cell death predominantly occurs through apoptosis. In irradiated culture, both with and without transplantation, there is an increase in the content of effector caspase 3. Cells in irradiated culture undergo apoptosis through the mitochondrial mechanism (with a predominance of active caspase 9), while in irradiated culture with the introduction of the transplant, the receptor-mediated mechanism of apoptosis dominates (with a predominance of active caspase 8). The obtained results can be important for the development of new effective methods of therapy for radiation burns, chronic ulcers and wounds of various etiologies.
... To that end, cellular mechanisms that confer resistance to TMZ by augmenting DNA repair may be induced and rapidly confer resistance to ionizing radiation and TTF therapy. Of the multiple pathways initiated by DNA damage in glioma cells, principle among them is the induction of cytoprotective autophagy (Kanzawa et al., 2004;Ito et al., 2005;Lomonaco et al., 2009;Lin et al., 2012;Knizhnik et al., 2013;Zou et al., 2014;Hori et al., 2015;Lee et al., 2015;Ye et al., 2016;Shteingauz et al., 2018). Autophagy has not only been implicated in resistance to TMZ, radiation and TTF, but also supports tumor cell survival in areas of hypoxia (Hu et al., 2012;Jawhari et al., 2016;Abdul Rahim et al., 2017) and dampens anti-tumor immune responses (Liang et al., 2012;DeVorkin et al., 2019;Valdor et al., 2019;Sharma et al., 2020;Kim et al., 2021). ...
Glioblastoma (GBM) is the most frequently diagnosed primary CNS tumor in adults. Despite the standard of care therapy which includes surgical resection, temozolomide chemotherapy, radiation and the newly added tumor treating fields, median survival remains only ~20 months. Unfortunately, GBM has a ~100% recurrence rate, but after recurrence there are no FDA-approved therapies to limit tumor growth and enhance patient survival, as these tumors are resistant to TMZ. Recently, our laboratory reported that lucanthone slows GBM by inhibiting autophagic flux through lysosome targeting and decreases the number of Olig2+ glioma stem-like cells (GSC) in vitro and in vivo. We now additionally report that lucanthone efficiently abates stemness in patient-derived GSC and reduces tumor microtube formation in GSC, an emerging hallmark of treatment resistance in GBM. In glioma tumors derived from cells with acquired resistance to TMZ, lucanthone retains the ability to perturb tumor growth, inhibits autophagy by targeting lysosomes and reduces Olig2 positivity. We also find that lucanthone may act as an inhibitor of protein palmitoyl thioesterase 1 (PPT1). Our results suggest that lucanthone may function as a potential treatment option for GBM tumors that are not amenable to TMZ treatment. Significance Statement We report that the anti-schistosome agent lucanthone impedes tumor growth in a preclinical model of temozolomide-resistant glioblastoma, and reduces the numbers of stem-like glioma cells. It acts as an autophagy inhibitor and its mechanism of action may be via inhibition of palmitoyl protein thioesterase 1. As there are no defined therapies approved for recurrent, TMZ-resistant tumor, lucanthone could emerge as a treatment for glioblastoma tumors that may not be amenable to TMZ both in the newly diagnosed and recurrent settings.
... Treatment with autophagy inhibitor, bafilomycin A1 enhanced the cytotoxic effect of gamma radiation on CD133 + cells and exerted a inhibitory effect on neurosphere formation of gamma irradiated cells, showing the potential of autophagy inhibitors to radiosensitize CD133 + glioma stem cells. 26 ...
Reactive oxygen species (ROS) and its related signaling pathways and regulating molecules play a major role in the growth and development of cancer stem cells. The concept of ROS and cancer stem cells (CSCs) has been gaining much attention since the past decade and the evidence show that these CSCs possess robust self-renewal and tumorigenic potential and are resistant to conventional chemo-and radiotherapy and believed to be responsible for tumor progression, metastasis, and recurrence. It seems reasonable to say that cancer can be cured only if the CSCs are eradicated. ROS are Janus-faced molecules that can regulate cellular physiology as well as induce cytotoxicity, depending on the magnitude, duration, and site of generation. Unlike normal cancer cells, CSCs expel ROS efficiently by upregulating ROS scavengers. This unique redox regulation in CSCs protects them from ROS-mediated cell death and nullifies the effect of radiation, leading to chemoresistance and radioresistance. However, how these CSCs control ROS production by scavenging free radicals and how they maintain low levels of ROS is a challenging to understand and these attributes make CSCs as prime therapeutic targets. Here, we summarize the mechanisms of redox regulation in CSCs, with a focus on therapy resistance, its various pathways and microRNAs regulation, and the potential therapeutic implications of manipulating the ROS levels to eradicate CSCs. A better understanding of these molecules, their interactions in the CSCs may help us to adopt proper control and treatment measures.
... The radioresistance of CSCs is associated with intrinsic properties such as DNA repair, ROS removal capacity, enhanced inhibition of apoptosis and induction of survival pathways, and adaptive properties due to IR and the microenvironment (Fig. 2) 12,13,[142][143][144][145][146][147][148][149][150] . CSCs generally express high levels of DNA repair genes and contribute to radioresistance 12,[144][145][146][147] . ...
The development of high-precision dose calculation techniques for the radiotherapy of tumors has enabled treatment with fewer side effects in normal tissues. However, a crucial problem remains wherein some cancer cells may acquire radioresistance or cancer stem cell (CSC) characteristics and cause recurrence and metastasis. The acquisition of these phenotypes is associated with complex molecular signaling and biological processes that remain unclear. In addition, these phenotypes are originally inherent within the tumor and are induced by external factors such as radiation. Therefore, a better understanding of the mechanisms underlying radiosensitization and how these phenotypes are acquired is essential for improving radiotherapy outcomes. This review outlines the current findings on the association of radiotherapy with CSC induction, signaling pathways and radioresistance processes, as well as therapeutic strategies aimed at the radiosensitization of these phenotypes.
... Finally, autophagy is suspected to play a role in radioresistance. As a defense mechanism, autophagy is triggered by cell stress such as hypoxia or elevated ROS and markers for autophagy such as LP3 and ATG5 and ATG12 increase in CD133 + cells following IR therapy 162 . ...
Malignant brain tumors are aggressive and difficult to treat. Glioblastoma is the most common and lethal form of primary brain tumor, often found in patients with no genetic predisposition. The median life expectancy for individuals diagnosed with this condition is 6 months to 2 years and there is no known cure. New paradigms in cancer biology implicate a small subset of tumor cells in initiating and sustaining these incurable brain tumors. Here, we discuss the heterogenous nature of glioblastoma and theories behind its capacity for therapy resistance and recurrence. Within the cancer landscape, cancer stem cells are thought to be both tumor initiators and major contributors to tumor heterogeneity and therapy evasion and such cells have been identified in glioblastoma. At the cellular level, disruptions in the delicate balance between differentiation and self-renewal spur transformation and support tumor growth. While rapidly dividing cells are more sensitive to elimination by traditional treatments, glioblastoma stem cells evade these measures through slow division and reversible exit from the cell cycle. At the molecular level, glioblastoma tumor cells exploit several signaling pathways to evade conventional therapies through improved DNA repair mechanisms and a flexible state of senescence. We examine these common evasion techniques while discussing potential molecular approaches to better target these deadly tumors. Equally important, the presented information encourages the idea of augmenting conventional treatments with novel glioblastoma stem cell-directed therapies, as eliminating these harmful progenitors holds great potential to modulate tumor recurrence.
... Autophagy has two opposing roles. One is to kill cells by differentiating, which leads to radio sensitizing them (Zhuang et al., 2011(Zhuang et al., , 2012 and the other is a process of resistance to cell death (Lomonaco et al., 2009;Chang et al., 2012;Zhuang and Qin, 2009). Finally, resveratrol can interfere with the DNA repair progression in cells with radiation-induced DNA damage . ...
Glioblastoma multiforme (GBM) is one of the most aggressive brain and spinal cord tumors. Despite the significant development in application of antitumor drugs, no significant increases have been observed in the survival rates of patients with GBM, as GBM cells acquire resistance to conventional anticancer therapeutic agents. Multiple studies have revealed that PI3K/Akt, MAPK, Nanog, STAT 3, and Wnt signaling pathways are involved in GBM progression and invasion. Besides, biological processes such as anti-apoptosis, autophagy, angiogenesis, and stemness promote GBM malignancy. Resveratrol (RESV) is a non-flavonoid polyphenol with high antitumor activity, the potential of which, regulating signaling pathways involved in cancer malignancy, have been demonstrated by many studies. Herein, we present the potential of RESV in both single and combination therapy- targeting various signaling pathways- which induce apoptotic cell death, re-sensitize cancer cells to radiotherapy, and induce chemo-sensitizing effects to eventually inhibit GBM progression.
... Despite all the progress made, therapeutic interventions do have a downside. Recent studies have shown that they are drivers for molecular changes and differentiations within these tumors that help tumor cells to evade these therapies [17,24,25]. Therefore, treatment regimes effective on the initial tumor might be rendered insufficient in the recurrent situation. ...
In general, cancer is one of the most frequent causes of death [...]
... A recent study illustrated that both the inhibition and induction of autophagy may be used as therapeutic approaches to high-grade malignant GBM (72). There is increasing evidence that autophagy inhibition can sensitize CD133+ to radiotherapy and chemotherapy, while the induction of autophagy can be beneficial by increasing cell apoptosis during treatment (73,74). The use and balancing of autophagy inducers and inhibitors presents as a promising combinatorial therapy to target gamma-radiation resistance in GBM. ...
Glioblastoma multiforme (GBM) is the most common malignant primary brain tumor, known for its poor prognosis and high recurrence rate. Current standard of care includes surgical resection followed by combined radiotherapy and chemotherapy. Although immunotherapies have yielded promising results in hematological malignancies, their successful application in GBM remains limited due to a host of immunosuppressive factors unique to GBM. As a result of these roadblocks, research efforts have focused on utilizing combinatorial immunotherapies that target networks of immune processes in GBM with promising results in both preclinical and clinical trials, although limitations in overcoming the immunosuppressive factors within GBM remain. In this review, we aim to discuss the intrinsic and adaptive immune resistance unique to GBM and to summarize the current evidence and outcomes of engineered and non-engineered treatments targeted at overcoming GBM resistance to immunotherapy. Additionally, we aim to highlight the most promising strategies of targeted GBM immunotherapy combinatorial treatments and the insights that may directly improve the current patient prognosis and clinical care.
... However, radioresistance is a crucial challenge in the usage of radiotherapy in clinical practice, so identifying the underlying mechanisms associated with radioresistance is urgently needed. Radioresistance is considered to be related to multiple elements, including microenvironmental hypoxia, 15 activation of DNA repair, 16,17 autophagy induced by radiotherapy or hypoxia, 18,19 aberrant pathway activation such as PI3K/ ...
Background:
Metastasis-associated lung adenocarcinoma transcript 1 (MALAT1), a conserved transcript with 8000 nt, is highly associated with malignancy of numerous cancer types. However, the function of MALAT1 plays in regulating the response to radiotherapy in colorectal cancer (CRC) remains unclear. Thus, the object of this study is to investigate the functions of MALAT1 in CRC radioresistance.
Methods:
First, the expression of MALAT1 in colon adenocarcinoma (COAD) was analyzed through the Cancer Genome Atlas (TCGA) database. Then, we detected the expression level of MALAT1 in tumor tissues and CRC cell lines and analyzed the relevance of MALAT1 and clinicopathological parameters. In the end, the effect of silencing MALAT1 on the radiosensitivity of CRC cells was investigated, and its potential mechanism was preliminarily illustrated.
Results:
The analysis of TCGA data showed that MALAT1 was closely related to the type of tumor, and high expression of MALAT1 was remarkably relevant to poor outcome. MALAT1 was highly expressed in CRC tissues and cell lines and related to tumor stages. Knockdown of MALAT1 could significantly suppress colony survival, proliferation, and migration and increase apoptosis, G2/M phase arrest, and formation of gamma-H2AX foci in HCT116, whether in combination with X-rays or not. Moreover, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis demonstrated that the regulated proteins were principally enriched in the glycosaminoglycan degradation pathway after silencing MALAT1.
Conclusion:
Our results implied that MALAT1 was highly expressed in CRC and associated with tumor stage and prognosis. Silencing MALAT1 can increase HCT116 cell radiosensitivity, which may be potentially influenced by glycosaminoglycan degradation pathway.
... La sur-réparation des cassures double brin par recombinaison homologue (HR), médiée par la protéine RAD51 notamment, est aussi responsable de la radiorésistance des CSG (Balbous et al., 2016;Tachon et al., 2018). Au niveau cellulaire, Lomonaco et al. ont démontré que l'augmentation de l'autophagie contribuait à la radiorésistance de CSG CD133 + et que l'inhibition de l'autophagie supprimait la radiorésistance (Lomonaco et al., 2009). D'autres voies de signalisation sont responsables de résistance aux radiations ionisantes, notamment la voie de l'EGFR (Chakravarti et al., 2002), NOTCH ou AKT (Eyler et al., 2008) mais aussi l'environnement tumoral qui peut offrir aux CSG des conditions de réparation de l'ADN plus favorables (Jamal et al., 2010). ...
L’expression de facteurs de transcription (FT), aux rôles clés dans l’embryogénèse, semble être une caractéristique importante des gliomes et particulièrement des glioblastomes (GBM). Le FT MEOX2 n’a jamais été étudié dans les gliomes/glioblastomes et encore moins dans les cellules souches de glioblastomes (CSG) bien que ces dernières soient au cœur du caractère récidivant des gliomes. Les objectifs de mon travail de thèse étaient d’explorer les bases de données publiques pour trouver un ou plusieurs FT clés impliqués dans la survie des patients porteurs d’un gliome, pour ensuite confirmer l’impact diagnostique et pronostique du FT trouvé, MEOX2, à partir d’une cohorte locale. Le rôle de ce FT a ensuite été étudié dans les cellules souches de GBM. Parmi les gènes différentiellement exprimés entre les gliomes de grade II ou III mutés IDH1/2 et codélétés 1p/19q, ou mutés IDH1/2 non-codélétés, ou IDH1/2 sauvages, et les GBM IDH sauvages, MEOX2 était un FT négativement corrélé à la survie globale et à la survie sans progression. L’étude des bases de données publiques, et d’une cohorte interne de 112 gliomes a permis de montrer que MEOX2 était enrichi dans les gliomes les plus agressifs (GBM et gliomes de grade II ou III IDH sauvage) et était associé au statut IDH sauvage, indépendamment du statut de codélétion 1p19q. Son expression serait sous la dépendance de son nombre de copie chromosomique et de l’état de méthylation de son promoteur. L’analyse des courbes de survie a montré que la forte expression de MEOX2 était associée à un mauvais pronostic pour les patients. Concernant son rôle biologique, l’expression de MEOX2 était nucléaire et hétérogène entre les CSG. MEOX2 avait un effet anti-prolifératif via la voie des MAPK et sa perte d’expression corrélait avec la différenciation des CSG et l’acquisition de caractéristiques du lignage neuronal. L’inhibition de MEOX2 régulait un réseau de gènes restreint comprenant la cadhérine CDH10. Plus particulièrement, l’inhibition de MEOX2 corrélait avec une augmentation d’un acteur de la voie des cadhérines, CDH10, et avec une diminution de plusieurs acteurs de la voie des intégrines. MEOX2 est encore un acteur très peu connu et étudié dans la carcinogénèse et notre travail apporte une contribution à la compréhension de son rôle dans les gliomes et dans les CSG.
... Moreover, loss of PTEN contributes to an increase in the cellular motility of neural precursor cells, alteration in Chk1 localization, and genetic instability, conferring radioresistance in GBM cells [320,321]. It has been established that the radiosensitivity of GSCs can be increased by inhibiting Becline-1 and ATG5, autophagy-related proteins, indicating that the induction of autophagy contributes to radioresistance in GSC [322]. The PI3K/Akt/mTOR pathway has been suggested to play an important role in IR-induced autophagy in GBM cells [323]. ...
Ionizing radiation (IR) has been shown to play a crucial role in the treatment of glioblastoma (GBM; grade IV) and non-small-cell lung cancer (NSCLС). Nevertheless, recent studies have indicated that radiotherapy can offer only palliation owing to the radioresistance of GBM and NSCLС. Therefore, delineating the major radioresistance mechanisms may provide novel therapeutic approaches to sensitize these diseases to IR and improve patient outcomes. This review provides insights into the molecular and cellular mechanisms underlying GBM and NSCLC radioresistance, where it sheds light on the role played by cancer stem cells (CSCs), as well as discusses comprehensively how the cellular dormancy/non-proliferating state and polyploidy impact on their survival and relapse post-IR exposure.
... It has been widely demonstrated that low pH reduces uptake and efficacy of weak base chemotherapeutics such as anthracyclines, anthraquinones and vinca alkaloids [95,96], thus alkalisation could be useful to restore cell drug sensitivity. Autophagy, a self-digestive process that cells perform in response to nutrient stress, is now considered a mechanism of drug resistance in cancer; indeed, it has been found to maintain cancer stem cell phenotype and correlates with chemo-and radio-resistance [89,[97][98][99][100]. It was demonstrated that hypoxia can induce autophagy in different cellular settings [76,101], acting as a survival mechanism for hypoxic cells through the recycling of cellular components. ...
Tumour vascularisation is vital for cancer sustainment representing not only the main source of nutrients and oxygen supply but also an escape route for single or clustered cancer cells that, once detached from the primary mass, enter the blood circulation and disseminate to distant organs. Among the mechanisms identified to contribute to tumour vascularisation, vasculogenic mimicry (VM) is gaining increasing interest in the scientific community representing an intriguing target for cancer treatment. VM indeed associates with highly aggressive tumour phenotypes and strongly impairs patient outcomes. Differently from vessels of healthy tissues, tumour vasculature is extremely heterogeneous and tortuous, impeding efficient chemotherapy delivery, and at the meantime hyperpermeable and thus extremely accessible to metastasising cancer cells. Moreover, tumour vessel disorganisation creates a self-reinforcing vicious circle fuelling cancer malignancy and progression. Because of the inefficient oxygen delivery and metabolic waste removal from tumour vessels, many cells within the tumour mass indeed experience hypoxia and acidosis, now considered hallmarks of cancer. Being strong inducers of vascularisation, therapy resistance, inflammation and metastasis, hypoxia and acidosis create a permissive microenvironment for cancer progression and dissemination. Along with these considerations, we decided to focus our attention on the relationship between hypoxia/acidosis and VM. Indeed, besides tumour angiogenesis, VM is strongly influenced by both hypoxia and acidosis, which could potentiate each other and fuel this vicious circle. Thus, targeting hypoxia and acidosis may represent a potential target to treat VM to impair tumour perfusion and cancer cell sustainment.
... Autophagy refers to the lysosomal-mediated degradation of unwanted and nonessential cellular components, and has been recognized as a survival mechanism that cells use to adapt to hostile environments including hypoxia and in response to IR. GBM cells have been reported to employ autophagy to reutilize unwanted or damaged proteins to aid in the progressive growth of the tumor. 26 Exposure of CD133 + GSCs to IR was found to activate autophagy, whereas inhibition of autophagy using the autophagic inhibitor bafilomycin A1, caused radiosensitization and decreased the ability of GSCs to form neurospheres. 27 Cathepsin D is a class of cysteine proteases that demonstrates a positive correlation with autophagic markers such as LC3A and LC3B in GBM. Overexpression of cathepsin D has been associated with radioresistance and poor survival of GBM patients, and inhibiting cathepsin D by small interfering RNA (siRNA) or by the inhibitor pepstatin-A was found to suppress autophagy and sensitize GBM cells to IR. 28 These data point to the involvement of autophagy in the radioresistant phenotype of GBM. ...
Glioblastoma (GBM) is a highly invasive primary brain tumour in adults with a 5-year survival rate of less than 10%. Conventional radiotherapy with photons, along with concurrent and adjuvant temozolomide, is the mainstay for treatment of GBM although no significant improvement in survival rates has been observed over the last twenty years. Inherent factors such as tumour hypoxia, radioresistant GBM stem cells, and upregulated DNA damage response (DDR) mechanisms are well established as contributing to treatment resistance and tumour recurrence. While it is understandable that efforts have focussed on targeting these factors to overcome this phenotype, there have also been striking advances in precision radiotherapy techniques, including proton beam therapy (PBT) and carbon ion radiotherapy (CIRT). These enable higher doses of radiation to be delivered precisely to the tumour while minimising doses to surrounding normal tissues and organs at risk. These alternative radiotherapy techniques also benefit from increased biological effectiveness, particularly in the case of CIRT. Although not researched extensively to date, combining these new radiation modalities with radio-enhancing agents may be particularly effective in improving outcomes for patients with GBM.
... Combination treatment with radiation, CQ, and PI-103, a dual inhibitor of phosphatidylinositol 3-kinase and mTOR, synergistically induces apoptosis and suppresses tumorsphere formation in GSCs [114]. Similarly, inhibition of autophagy by bafilomycin A1 sensitizes GSCs to radiotherapy and significantly decreases their ability to form tumorspheres [85]. In contrast, adjunctive treatment with quinacrine, an autophagy inhibitor capable of crossing the BBB, enhances the anti-tumor effect of TMZ in primary cultured GSCs, but not in orthotopic xenograft mouse models [86]. ...
Glioblastoma (GBM) is the most malignant primary brain tumor. The current standard approach in GBM is surgery, followed by treatment with radiation and temozolomide (TMZ); however, GBM is highly resistant to current therapies, and the standard of care has not been revised over the last two decades, indicating an unmet need for new therapies. GBM stem cells (GSCs) are a major cause of chemoresistance due to their ability to confer heterogeneity and tumorigenic capacity. To improve patient outcomes and survival, it is necessary to understand the properties and mechanisms underlying GSC chemoresistance. In this review, we describe the current knowledge on various resistance mechanisms of GBM to therapeutic agents, with a special focus on TMZ, and summarize the recent findings on the intrinsic and extrinsic mechanisms of chemoresistance in GSCs. We also discuss novel therapeutic strategies, including molecular targeting, autophagy inhibition, oncolytic viral therapy, drug repositioning, and targeting of GSC niches, to eliminate GSCs, from basic research findings to ongoing clinical trials. Although the development of effective therapies for GBM is still challenging, this review provides a better understanding of GSCs and offers future directions for successful GBM therapy.
... Cancer propagating/progenitor cells have been suggested to resist conventional radiotherapy due to high free-radical scavenger levels [38], activation of the WNT/β-catenin signaling pathway [39], effective DNA damage repair mechanisms [2], and induction of autophagy [40]. Our data indicate that sub-lethal fractionated radiation can select for GPCs with intrinsic or acquired radio-resistance as well as GPCs with enhanced colony-formation capacities. ...
Simple Summary
Stem cell-like glioma-propagating cells (GPCs) are crucial for initiation, growth, and treatment resistance of glioblastoma multiforme. Due to their strong immunosuppressive activities, they essentially limit immunotherapeutic approaches. This study offers a new model of radio-selected patient-derived GPCs mimicking a clinical treatment regime of tumor irradiation which is especially useful for immunotherapeutic studies. We provide evidence that clinically relevant, sub-lethal fractions of γ radiation select for a more radio-resistant GPC phenotype with lower immunogenic potential, potentially hampering the success of adjuvant T-cell-based immunotherapies. The immune evasion in GPCs was characterized by quantitative proteomics. It revealed a marked downregulation of the antigen processing machinery in lipid rafts of these cells, leading to reduced MHC surface expression and weaker cytotoxic T lymphocyte (CTL) recognition.
Abstract
Glioblastoma multiforme is the most common and devastating form of brain tumor for which only palliative radio- and chemotherapy exists. Although some clinical studies on vaccination approaches have shown promising efficacy due to their potential to generate long-term immune surveillance against cancer cells, the evasion mechanisms preventing therapy response are largely uncharacterized. Here, we studied the response of glioblastoma-propagating cells (GPCs) to clinically relevant doses of γ radiation. GPCs were treated with 2.5 Gy of γ radiation in seven consecutive cellular passages to select for GPCs with increased colony-forming properties and intrinsic or radiation-induced resistance (rsGPCs). Quantitative proteomic analysis of the cellular signaling platforms of the detergent-resistant membranes (lipid rafts) in GPCs vs. rsGPCs revealed a downregulation of the MHC class I antigen-processing and -presentation machinery. Importantly, the radio-selected GPCs showed reduced susceptibility towards cytotoxic CD8+ T-cell-mediated killing. While previous studies suggested that high-dose irradiation results in enhanced antigen presentation, we demonstrated that clinically relevant sub-lethal fractionated irradiation results in reduced expression of components of the MHC class I antigen-processing and -presentation pathway leading to immune escape.
... Studies have indicated that the relatively radio-sensitive cells or small radiotherapy fraction (2 Gy) displays enhanced autophagic flux, while more radio-resistant cells or largeer radiotherapy fraction exhibited an inhibition of autophagic flux [56] . Regarding the glioma stem-like cells, it was reported the subsets were enhanced for autophagy after radiation to promote metabolism, anti-apoptosis and stemness [57] , while the other reports showed that CD133 + cells or sphere cells from one patient have a lower level of autophagy [58,59] . Notably, it is also found that CD133 + glioma stem-like cells can be resensitized to radiation treatment by using autophagy inhibitors (bafilomycin) or down-regulation of ATG protein levels [60] . ...
Patients with glioblastoma (GBM), a malignant brain tumor, exhibit a mean survival of less than 1.5 years. Despite treatment, the disease eventually develops resistance, resulting in disease relapse. Autophagy is a process of degradation and clearance that is activated to maintain cellular homeostasis. Its roles in cancer disease course and the treatment response, however, are controversial. In GBM, accumulating evidence has indicated that autophagy can protect cells, especially those with stemness features, causing the development of cell resistance. In this review, we discuss the impact of the cell reaction to currently active treatments, including temozolomide, radiation, tumor treating fields, bevacizumab (Avastin), etoposide (VP-16), cisplatin (CDDP), and carmustine (BCNU). Most of these induce the up-regulation of autophagy through signaling pathways of DNA damage response, reactive oxygen species, hypoxia, retinoblastoma, AMP-activated protein kinase, AKT/mTOR and MST4 kinase affecting cell fate by altering cell metabolism, cell death, and DNA repair. Treatment-related autophagy may be modulated by combining autophagy inhibitors such as chloroquine or antioxidants to prevent the development of resistance, thus improving cancer treatment.
... IR also triggers autophagy in GSCs, and CD133+ GSC cells express higher levels of LC3, ATG5, and ATG12, and an increased autophagy frequency compared to the CD133negative GBM fraction. Autophagy obstruction by inhibition with 3-MA and b-A1 or by ATG5 and beclin1 (BECN1, allows the assembly of the autophagosome from pre-autophagic structures) silencing leads to reduced cellular viability of irradiated cells and decreased neurospheres formation [270]. In normal GBM cells, beside the impairment of autophagy and radiosensitization, the knockdown of BECN1 also resulted in the disruption of nuclear translocation and DNA binding activity of Ku proteins with consequent attenuation of DSB repair, providing evidence of the association of autophagy and repair [271,272]. ...
Simple Summary
Glioblastoma is a type of brain cancer that remains incurable. Despite multiple past and ongoing preclinical studies and clinical trials, involving adjuvants to the conventional therapy and based on molecular targeting, no relevant benefit for patients’ survival has been achieved so far. The current first-line treatment regimen is based on ionizing radiation and the monoalkylating compound, temozolomide, and has been administered for more than 15 years. Glioblastoma is extremely resistant to most agents due to a mutational background that elicits quick response to insults and adapts to microenvironmental and metabolic changes. Here, we present the most recent evidence concerning the molecular features and their alterations governing pathways involved in GBM response to the standard radio-chemotherapy and discuss how they collaborate with acquired GBM’s resistance.
Abstract
Glioblastoma multiforme (GBM) is a brain tumor characterized by high heterogeneity, diffuse infiltration, aggressiveness, and formation of recurrences. Patients with this kind of tumor suffer from cognitive, emotional, and behavioral problems, beyond exhibiting dismal survival rates. Current treatment comprises surgery, radiotherapy, and chemotherapy with the methylating agent, temozolomide (TMZ). GBMs harbor intrinsic mutations involving major pathways that elicit the cells to evade cell death, adapt to the genotoxic stress, and regrow. Ionizing radiation and TMZ induce, for the most part, DNA damage repair, autophagy, stemness, and senescence, whereas only a small fraction of GBM cells undergoes treatment-induced apoptosis. Particularly upon TMZ exposure, most of the GBM cells undergo cellular senescence. Increased DNA repair attenuates the agent-induced cytotoxicity; autophagy functions as a pro-survival mechanism, protecting the cells from damage and facilitating the cells to have energy to grow. Stemness grants the cells capacity to repopulate the tumor, and senescence triggers an inflammatory microenvironment favorable to transformation. Here, we highlight this mutational background and its interference with the response to the standard radiochemotherapy. We discuss the most relevant and recent evidence obtained from the studies revealing the molecular mechanisms that lead these cells to be resistant and indicate some future perspectives on combating this incurable tumor.
... Ionising radiation (IR) is a common treatment for cancer and is known to induce autophagy in malignant cells [138,139]. Although TP53-mediated autophagy was shown to promote tumour cell killing [140,141], it can also contribute to protection against radiotherapy [142,143]. ...
The tumour suppressor TP53 is a master regulator of several cellular processes that collectively suppress tumorigenesis. The TP53 gene is mutated in ~50% of human cancers and these defects usually confer poor responses to therapy. The TP53 protein functions as a homo-tetrameric transcription factor, directly regulating the expression of ~500 target genes, some of them involved in cell death, cell cycling, cell senescence, DNA repair and metabolism. Originally, it was thought that the induction of apoptotic cell death was the principal mechanism by which TP53 prevents the development of tumours. However, gene targeted mice lacking the critical effectors of TP53-induced apoptosis (PUMA and NOXA) do not spontaneously develop tumours. Indeed, even mice lacking the critical mediators for TP53-induced apoptosis, G1/S cell cycle arrest and cell senescence, namely PUMA, NOXA and p21, do not spontaneously develop tumours. This suggests that TP53 must activate additional cellular responses to mediate tumour suppression. In this review, we will discuss the processes by which TP53 regulates cell death, cell cycling/cell senescence, DNA damage repair and metabolic adaptation, and place this in context of current understanding of TP53-mediated tumour suppression.
... Another aspect by which autophagy favors the tumor development concern its impact on the resistance to antitumor treatments. In various tumor models (e.g., ovarian, colon, or osteosarcoma tumors), autophagy has been demonstrated to be an important actor of chemoresistance, leading to an increase of the survival of tumor cells under treatment of salt-based chemotherapies (204)(205)(206)(207)(208). Autophagy has also been observed to be an important promoter of resistance to radiotherapy in various tumor models, including lung, glioma, pancreatic, and colorectal cancer (209)(210)(211)(212). Interestingly, in order to overcome this resistance, several therapeutic approaches consisting in combining chemotherapy and radiotherapy with autophagy inhibitors have emerged with very promising results (213,214). ...
Autophagy is a self-degradative process important for balancing cellular homeostasis at critical times in development and/or in response to nutrient stress. This is particularly relevant in tumor model in which autophagy has been demonstrated to have an important impact on tumor behavior. In one hand, autophagy limits tumor transformation of precancerous cells in early stage, and in the other hand, it favors the survival, proliferation, metastasis, and resistance to antitumor therapies in more advanced tumors. This catabolic machinery can be induced by an important variety of extra- and intracellular stimuli. For instance, viral infection has often been associated to autophagic modulation, and the role of autophagy in virus replication differs according to the virus studied. In the context of tumor development, virus-modulated autophagy can have an important impact on tumor cells’ fate. Extensive analyses have shed light on the molecular and/or functional complex mechanisms by which virus-modulated autophagy influences precancerous or tumor cell development. This review includes an overview of discoveries describing the repercussions of an autophagy perturbation during viral infections on tumor behavior.
... L'autophagie permet de lyser les protéines et organelles endommagées tout en recyclant les nutriments ce qui permet à la cellule de se protéger en réponse aux rayonnements. Il a ainsi été proposé de bloquer l'autophagie pour radiosensibiliser les tumeurs dans les traitements par radiothérapie (Lomonaco et al. 2009;Ko et al. 2014;Yang et al. 2015;Maier et al. 2016;He et al. 2017;X. Chen et al. 2017). ...
La radiothérapie est un traitement majeur dans la lutte contre le cancer, avec plus de 50% des patients atteints d’un cancer qui en bénéficie, et pouvant à elle seule conduire à une rémission complète. Bien que les avancées technologiques aient diminuées considérablement les effets secondaires, 5 à 15 % des patients traités par radiothérapie souffrent d’effets secondaires sévères au niveau des tissus sains, limitant ainsi l’application de ce traitement. Ces effets secondaires sévères sont variés dans leur forme (desquamation, nécrose, fibrose), dans leur intensité (certains peuvent conduire à une nouvelle hospitalisation) ainsi que dans leur temps d’apparition (de quelques jours à plusieurs années après la radiothérapie). L’apparition de ces effets secondaires sévères chez certains patients de radiothérapie alors que les protocoles sont standardisés met à jour l’existence d’une radiosensibilité propre à chacun : la radiosensibilité individuelle. Malheureusement, à ce jour, il n’existe pas de test clinique applicable en routine qui fasse consensus, permettant de mesurer la radiosensibilité individuelle des patients atteints d’un cancer afin d’individualiser les protocoles de radiothérapie. D’autre part, les mécanismes moléculaires conduisant à ces effets secondaires restent encore mal connus. Nous avons donc étudié le transcriptome et le méthylome de fibroblastes dermiques de patients ayant souffert d’effets secondaires sévères de radiothérapie afin d’identifier une signature de la radiosensibilité individuelle et également de mieux comprendre les bases moléculaires sous-jacentes. Nous avons ainsi observé dans une 1ère cohorte que les fibroblastes cutanés des patients radiosensibles présentaient un profil transcriptomique et méthylomique spécifique. A l’aide d’une approche de machine learning, nous avons pu mettre à jour, une signature composée de 5 gènes dont l’expression nous a permis d’identifier les patients ayant souffert d’effets secondaires de radiothérapie dans une 2ème cohorte indépendante. De plus, nous avons observé que les fibroblastes des patients ayant souffert d’effets secondaires de radiothérapie présentaient un défaut de réparation de l’ADN ainsi qu’une toxicité accrue après irradiation. Finalement, nous avons identifié le facteur de transcription NFATc2 comme un acteur de la réponse aux radiations ionisantes dont la déficience peut entraîner un défaut de réparation de l’ADN et augmenter la radiosensibilité cellulaire. Ce travail de thèse a donc permis de révéler une signature moléculaire des cellules de patients ayant souffert d’effets secondaires sévères de radiothérapie, une première étape vers la mise au point d’un nouveau test clinique, et ouvre la voie à une meilleure compréhension des mécanismes de la radiosensibilité individuelle
... Cell pellet preparation and Western blot analyses were performed as previously described (Lomonaco et al., 2009). Equal loading was verified using an anti-b-actin or tubulin antibodies as described (Giladi et al., 2015;Bier et al., 2018). ...
Inactivating mutations in the Methyl-CpG Binding Protein 2 (MECP2) gene are the main cause of Rett syndrome (RTT). Despite extensive research into MECP2 function, no treatments for RTT are currently available. Here, we used an evolutionary genomics approach to construct an unbiased MECP2 gene network, using 1028 eukaryotic genomes to prioritize proteins with strong co-evolutionary signatures with MECP2. Focusing on proteins targeted by FDA-approved drugs led to three promising targets, two of which were previously linked to MECP2 function (IRAK, KEAP1) and one that was not (EPOR). The drugs targeting these three proteins (Pacritinib, DMF, and EPO) were able to rescue different phenotypes of MECP2 inactivation in cultured human neural cell types, and appeared to converge on Nuclear Factor Kappa B (NF-κB) signaling in inflammation. This study highlights the potential of comparative genomics to accelerate drug discovery, and yields potential new avenues for the treatment of RTT.
... (4) CSCs have enhanced self-renewal ability (Woodward et al., 2007;Batlle and Clevers, 2017). (5) CSCs have an increased autophagy level (Lomonaco et al., 2009). Among them, in recent years, some studies have shown that lysosomes and autophagy may be related to the radio-resistance of CSC Zhang et al., 2018). ...
Cancer stem cell (CSC) is thought to be the major cause of radio-resistance and relapse post radiotherapy (RT). Recently ultra-high dose rate “FLASH-RT” evokes great interest for its decreasing normal tissue damages while maintaining tumor responses compared with conventional dose rate RT. However, the killing effect and mechanism of FLASH irradiation (FLASH-IR) on CSC and normal cancer cell are still unclear. Presently the radiation induced death profile of CSC and normal cancer cell were studied. Cells were irradiated with FLASH-IR (∼109 Gy/s) at the dose of 6–9 Gy via laser-accelerated nanosecond particles. Then the ratio of apoptosis, pyroptosis and necrosis were determined. The results showed that FLASH-IR can induce apoptosis, pyroptosis and necrosis in both CSC and normal cancer cell with different ratios. And CSC was more resistant to radiation than normal cancer cell under FLASH-IR. Further experiments tracing lysosome and autophagy showed that CSCs had higher levels of lysosome and autophagy. Taken together, our results suggested that the radio-resistance of CSC may associate with the increase of lysosome-mediated autophagy, and the decrease of apoptosis, necrosis and pyroptosis. To our limited knowledge, this is the first report shedding light on the killing effects and death pathways of CSC and normal cancer cell under FLASH-IR. By clarifying the death pathways of CSC and normal cancer cell under FLASH-IR, it may help us improve the understanding of the radio-resistance of CSC and thus help to optimize the future clinical FLASH treatment plan.
... Recent studies suggest that autophagy has been recognized as frequently activated in cancer and mediates tumor cells' response to anticancer therapy, especially radiotherapy, decreasing its efficacy by contributing to GSC maintenance and reducing ROS-associated DNA damage [65,66]. Moreover, radiation preferentially activates autophagy in CD133 + cells and increases the levels of the autophagy-related proteins LC3, ATG5, and ATG12 [67]. The same was found in the radioresistant cell line, in which enhanced autophagic flux and silencing of the LC3A gene sensitized mouse xenografts to radiation [68]. ...
Glioblastoma (GBM) is the highest-grade form of glioma, as well as one of the most aggressive types of cancer, exhibiting rapid cellular growth and highly invasive behavior. Despite significant advances in diagnosis and therapy in recent decades, the outcomes for high-grade gliomas (WHO grades III-IV) remain unfavorable, with a median overall survival time of 15–18 months. The concept of cancer stem cells (CSCs) has emerged and provided new insight into GBM resistance and management. CSCs can self-renew and initiate tumor growth and are also responsible for tumor cell heterogeneity and the induction of systemic immunosuppression. The idea that GBM resistance could be dependent on innate differences in the sensitivity of clonogenic glial stem cells (GSCs) to chemotherapeutic drugs/radiation prompted the scientific community to rethink the understanding of GBM growth and therapies directed at eliminating these cells or modulating their stemness. This review aims to describe major intrinsic and extrinsic mechanisms that mediate chemoradioresistant GSCs and therapies based on antineoplastic agents from natural sources, derivatives, and synthetics used alone or in synergistic combination with conventional treatment. We will also address ongoing clinical trials focused on these promising targets. Although the development of effective therapy for GBM remains a major challenge in molecular oncology, GSC knowledge can offer new directions for a promising future.
... The main reason for hypoxic radiation sensitization induced by siNPS is the promotion of cell apoptosis and the enhancement of destructive autophagy, suggesting that AgNPs can be used as excellent radiosensitizers in the treatment of hypoxic glioma. Paradoxically, earlier studies have found that gamma-rayinduced autophagy contributes to the radioresistance of these cells, and autophagy inhibitors may be employed to increase the sensitivity of GSCs to gamma-radiation (83). ...
Glioma is the most common intracranial malignant tumor, and its specific pathogenesis has been unclear, which has always been an unresolved clinical problem due to the limited therapeutic window of glioma. As we all know, surgical resection, chemotherapy, and radiotherapy are the main treatment methods for glioma. With the development of clinical trials and traditional treatment techniques, radiotherapy for glioma has increasingly exposed defects in the treatment effect. In order to improve the bottleneck of radiotherapy for glioma, people have done a lot of work; among this, nano-radiosensitizers have offered a novel and potential treatment method. Compared with conventional radiotherapy, nanotechnology can overcome the blood–brain barrier and improve the sensitivity of glioma to radiotherapy. This paper focuses on the research progress of nano-radiosensitizers in radiotherapy for glioma.
... Autophagy plays a role in maintaining stem cells in normal stem cells and CSCs [53,94,95]. Exposure to IR leads to an increase in autophagy marker protein expression in CSCs [96]. Moreover, there is now increasing evidence that autophagy signaling and EMT are interlinked, and the autophagy is often highly expressed in tumor cells carrying a mesenchymal signature [36]. ...
Ionizing radiation (IR) is used for patients diagnosed with unresectable non-small cell lung cancer (NSCLC). However, radiotherapy remains largely palliative due to the survival of specific cell subpopulations. In the present study, the sublines of NSCLC cells, A549IR (p53wt) and H1299IR (p53null) survived multifraction X-ray radiation exposure (MFR) at a total dose of 60 Gy were investigated three weeks after the MFR course. We compared radiosensitivity (colony formation), expression of epithelial-mesenchymal transition (EMT) markers, migration activity, autophagy, and HR-dependent DNA double-strand break (DSB) repair in the bulk and entire CD44high/CD166high CSC-like populations of both parental and MFR survived NSCLC cells. We demonstrated that the p53 status affected: the pattern of expression of N-cadherin, E-cadherin, Vimentin, witnessing the appearance of EMT-like phenotype of MFR-surviving sublines; 1D confined migratory behavior (wound healing); the capability of an irradiated cell to continue to divide and form a colony of NSCLC cells before and after MFR; influencing the CD44/CD166 expression level in MFR-surviving NSCLC cells after additional single irradiation. Our data further emphasize the impact of p53 status on the decay of γH2AX foci and the associated efficacy of the DSB repair in NSCLC cells survived after MFR. We revealed that Rad51 protein might play a principal role in MFR-surviving of p53 null NSCLC cells promoting DNA DSB repair by homologous recombination (HR) pathway. The proportion of Rad51 + cells elevated in CD44high/CD166high population in MFR-surviving p53wt and p53null sublines and their parental cells. The p53wt ensures DNA-PK-mediated DSB repair for both parental and MFR-surviving cells irrespectively of a subsequent additional single irradiation. Whereas in the absence of p53, a dose-dependent increase of DNA-PK-mediated non-homologous end joining (NHEJ) occurred as an early post-irradiation response is more intensive in the CSC-like population MFR-surviving H1299IR, compared to their parental H1299 cells. Our study strictly observed a significantly higher content of LC3 + cells in the CD44high/CD166high populations of p53wt MFR-surviving cells, which enriched the CSC-like cells in contrast to their p53null counterparts. The additional 2 Gy and 5 Gy X-ray exposure leads to the dose-dependent increase in the proportion of LC3 + cells in CD44high/CD166high population of both parental p53wt and p53null, but not MFR-surviving NSCLC sublines. Our data indicated that autophagy is not necessarily associated with CSC-like cells’ radiosensitivity, emphasizing that careful assessment of other milestone processes (such as senescence and autophagy-p53-Zeb1 axis) of primary radiation responses may provide new potential targets modulated for therapeutic benefit through radiosensitizing cancer cells while rescuing normal tissue. Our findings also shed light on the intricate crosstalk between autophagy and the p53-related EMT, by which MFR-surviving cells might obtain an invasive phenotype and metastatic potential.
... Hypoxic microenvironments preferentially contribute to GCS growth, which can reduce oxidative-stress produced by radiation (46). GSC radioresistance is also conferred by both the hypoxia-mediated activation of DNA damage checkpoint response enzymes Chk 1/2 (47) as well as by induction of autophagy to process and eliminate constituent parts of cells damaged by radiation (48). ...
Glioblastoma is the most common and lethal primary brain malignancy. Despite major investments in research into glioblastoma biology and drug development, treatment remains limited and survival has not substantially improved beyond 1–2 years. Cancer stem cells (CSC) or glioma stem cells (GSC) refer to a population of tumor originating cells capable of self-renewal and differentiation. While controversial and challenging to study, evidence suggests that GCSs may result in glioblastoma tumor recurrence and resistance to treatment. Multiple treatment strategies have been suggested at targeting GCSs, including immunotherapy, posttranscriptional regulation, modulation of the tumor microenvironment, and epigenetic modulation. In this review, we discuss recent advances in glioblastoma treatment specifically focused on targeting of GCSs as well as their potential integration into current clinical pathways and trials.
... Several studies reported that the initiation of autophagy causes radiation sensitization in radioresistant and malignant glioma cells. Studies have also shown that certain chemotherapeutic drugs may destroy tumor cells through intrinsic pathway of apoptosis initiated by autophagy [125,126]. ...
Autophagy, a catabolic process, degrades damaged and defective cellular materials through lysosomes, thus working as a recycling mechanism of the cell. It is an evolutionarily conserved and highly regulated process that plays an important role in maintaining cellular homeostasis. Autophagy is constitutively active at the basal level; however, it gets enhanced to meet cellular needs in various stress conditions. The process involves various autophagy-related genes that ultimately lead to the degradation of targeted cytosolic substrates. Many factors modulate both upstream and downstream autophagy pathways like nutritional status, energy level, growth factors, hypoxic conditions, and localization of p53. Any problem in executing autophagy can lead to various pathological conditions including neurodegeneration, aging, and cancer. In cancer, autophagy plays a contradictory role; it inhibits the formation of tumors, whereas, during advanced stages, autophagy promotes tumor progression. Besides, autophagy protects the tumor from various therapies by providing recycled nutrition and energy to the tumor cells. Autophagy is stimulated by tumor suppressor proteins, whereas it gets inhibited by oncogenes. Due to its dynamic and dual role in the pathogenesis of cancer, autophagy provides promising opportunities in developing novel and effective cancer therapies along with managing chemoresistant cancers. In this article, we summarize different strategies that can modulate autophagy in cancer to overcome the major obstacle, i.e., resistance developed in cancer to anticancer therapies.
... Lactate has been implicated in tumor angiogenesis and the expression of GSC markers (Hjelmeland et al., 2011). Exposure to acidic conditions could result in autophagy, which, as stated earlier, is connected with the preservation of the GSC phenotype and resistance to therapy (Lomonaco et al., 2009;Peppicelli et al., 2017). Acidosis could also neutralize ROS associated with radiotherapy, inhibit radiationinduced apoptosis, enhance the activity of P-glycoprotein (P-gp), and/or reduce the rate of proliferation of tumor cells (Peppicelli et al., 2017). ...
Glioblastomas (GBM) are the most common primary brain tumor with a median survival of 15 months. A population of cells with stem cell properties (glioblastoma stem cells, GSCs) drives the initiation and progression of GBM and is localized in specialized microenvironments which support their behavior. GBM are characterized as extremely resistant to therapy, resulting in tumor recurrence. Reactive oxygen species (ROS) control the cellular stability by influencing different signaling pathways. Normally, redox systems prevent cell oxidative damage; however, in gliomagenesis, the cellular redox mechanisms are highly impaired. Herein we review the dual nature of the redox status in drug resistance. ROS generation in tumor cells affects the cell cycle and is involved in tumor progression and drug resistance in GBM. However, excess ROS production has been found to induce cell death programs such as apoptosis and autophagy. Since GBM cells have a high metabolic rate and produce high levels of ROS, metabolic adaptation in these cells plays an essential role in resistance to oxidative stress-induced cell death. Finally, the microenvironment with the stromal components participates in the enhancement of the oxidative stress to promote tumor progression and drug resistance.
... In this case, proteins are either protected by the current redox state of the cytoplasm upon irradiation, or they are all damaged and the cell dies. On the other hand, autophagy, which allows cells to turnover damaged macromolecules, may affect IR resistance in eukaryotic cells (Lomonaco et al., 2009;Chaachouay et al., 2011;Höhn et al., 2013). In S. cerevisiae, a specific pathway of autophagy was recently found to contribute to DNA repair, and one of the genes involved in that study (ATG8) was also shown to be highly induced here (Eapen et al., 2017). ...
Fungi can tolerate extremely high doses of ionizing radiation compared with most other eukaryotes, a phenomenon encompassing both the recovery from acute exposure and the growth of melanized fungi in chronically contaminated environments such as nuclear disaster sites. This observation has led to the use of fungi in radiobiology studies, with the goal of finding novel resistance mechanisms. However, it is still not entirely clear what underlies this phenomenon, as genetic studies have not pinpointed unique responses to ionizing radiation in the most resistant fungi. Additionally, little work has been done examining how fungi (other than budding yeast) respond to irradiation by ionizing particles (e.g., protons, α-particles), although particle irradiation may cause distinct cellular damage, and is more relevant for human risks. To address this paucity of data, in this study we have characterized the phenotypic and transcriptomic response of the highly radioresistant yeast Exophiala dermatitidis to irradiation by three separate ionizing radiation sources: protons, deuterons, and α-particles. The experiment was performed with both melanized and non-melanized strains of E. dermatitidis , to determine the effect of this pigment on the response. No significant difference in survival was observed between these strains under any condition, suggesting that melanin does not impart protection to acute irradiation to these particles. The transcriptomic response during recovery to particle exposure was similar to that observed after γ-irradiation, with DNA repair and replication genes upregulated, and genes involved in translation and ribosomal biogenesis being heavily repressed, indicating an attenuation of cell growth. However, a comparison of global gene expression showed clear clustering of particle and γ-radiation groups. The response elicited by particle irradiation was, in total, more complex. Compared to the γ-associated response, particle irradiation resulted in greater changes in gene expression, a more diverse set of differentially expressed genes, and a significant induction of gene categories such as autophagy and protein catabolism. Additionally, analysis of individual particle responses resulted in identification of the first unique expression signatures and individual genes for each particle type that could be used as radionuclide discrimination markers.
Tumors are composed of heterogeneous populations of dysregulated cells that grow in specialized niches that support their growth and maintain their properties. Tumor heterogeneity and metastasis are among the major hindrances that exist while treating cancer patients, leading to poor clinical outcomes. Although the factors that determine tumor complexity remain largely unknown, several genotypic and phenotypic changes, including DNA mutations and metabolic reprograming provide cancer cells with a survival advantage over host cells and resistance to therapeutics. Furthermore, the presence of a specific population of cells within the tumor mass, commonly known as cancer stem cells (CSCs), is thought to initiate tumor formation, maintenance, resistance, and recurrence. Therefore, these CSCs have been investigated in detail recently as potential targets to treat cancer and prevent recurrence. Understanding the molecular mechanisms involved in CSC proliferation, self-renewal, and dormancy may provide important clues for developing effective therapeutic strategies. Autophagy, a catabolic process, has long been recognized to regulate various physiological and pathological processes. In addition to regulating cancer cells, recent studies have identified a critical role for autophagy in regulating CSC functions. Autophagy is activated under various adverse conditions and promotes cellular maintenance, survival, and even cell death. Thus, it is intriguing to address whether autophagy promotes or inhibits CSC functions and whether autophagy modulation can be used to regulate CSC functions, either alone or in combination. This review describes the roles of autophagy in the regulation of metabolic functions, proliferation and quiescence of CSCs, and its role during therapeutic stress. The review further highlights the autophagy-associated pathways that could be used to regulate CSCs. Overall, the present review will help to rationalize various translational approaches that involve autophagy-mediated modulation of CSCs in controlling cancer progression, metastasis, and recurrence.
BACKGROUND
Prevalence of hepatocellular carcinoma (HCC) is increasing, especially in patients with metabolic dysfunction-associated steatotic liver disease (MASLD).
AIM
To investigate rifaximin (RIF) effects on epigenetic/autophagy markers in animals.
METHODS
Adult Sprague-Dawley rats were randomly assigned (n = 8, each) and treated from 5-16 wk: Control [standard diet, water plus gavage with vehicle (Veh)], HCC [high-fat choline deficient diet (HFCD), diethylnitrosamine (DEN) in drinking water and Veh gavage], and RIF [HFCD, DEN and RIF (50 mg/kg/d) gavage]. Gene expression of epigenetic/autophagy markers and circulating miRNAs were obtained.
RESULTS
All HCC and RIF animals developed metabolic-dysfunction associated steatohepatitis fibrosis, and cirrhosis, but three RIF-group did not develop HCC. Comparing animals who developed HCC with those who did not, miR-122, miR-34a, tubulin alpha-1c (Tuba-1c) , metalloproteinases- 2 (Mmp2) , and metalloproteinases- 9 (Mmp9) were significantly higher in the HCC-group. The opposite occurred with Becn1 , coactivator associated arginine methyltransferase-1 (Carm1 ), enhancer of zeste homolog-2 (Ezh2 ) , autophagy-related factor LC3A/B (Map1 Lc3b) , and p62/ sequestosome-1 (p62/ SQSTM1)- protein. Comparing with controls, Map1 Lc3b , Becn1 and Ezh2 were lower in HCC and RIF-groups (P < 0.05). Carm1 was lower in HCC compared to RIF (P < 0.05). Hepatic expression of Mmp9 was higher in HCC in relation to the control; the opposite was observed for p62/Sqstm1 (P < 0.05). Expression of p62/SQSTM1 protein was lower in the RIF-group compared to the control (P = 0.024). There was no difference among groups for Tuba-1c , Aldolase-B, alpha-fetoprotein, and Mmp2 (P > 0.05). miR-122 was higher in HCC, and miR-34a in RIF compared to controls (P < 0.05). miR-26b was lower in HCC compared to RIF, and the inverse was observed for miR-224 (P < 0.05). There was no difference among groups regarding miR-33a, miR-143, miR-155, miR-375 and miR-21 (P > 0.05).
CONCLUSION
RIF might have a possible beneficial effect on preventing/delaying liver carcinogenesis through epigenetic modulation in a rat model of MASLD-HCC.
Head and neck squamous cell carcinoma (HNSCC) is a very heterogeneous cancer with a poor overall response to therapy. One of the reasons for this therapy resistance could be cancer stem cells (CSCs), a small population of cancer cells with self-renewal and tumor-initiating abilities. Tumor cell heterogeneity represents hurdles for therapeutic elimination of CSCs. Different signaling pathway activations, such as Wnt, Notch, and Sonic-Hedgehog (SHh) pathways, lead to the expression of several cancer stem factors that enable the maintenance of CSC features. Identification and isolation of CSCs are based either on markers (CD133, CD44, and aldehyde dehydrogenase (ALDH)), side populations, or their sphere-forming ability. A key challenge in cancer therapy targeting CSCs is overcoming chemotherapy and radiotherapy resistance. However, in novel therapies, various approaches are being employed to address this hurdle such as targeting cell surface markers, other stem cell markers, and different signaling or metabolic pathways, but also, introducing checkpoint inhibitors and natural compounds into the therapy can be beneficial.
Colorectal cancer (CRC) is the most common digestive malignancy across the world. Its first-line treatments applied in the routine clinical setting include surgery, chemotherapy, radiotherapy, targeted therapy, and immunotherapy. However, resistance to therapy has been identified as the major clinical challenge that fails the treatment method, leading to recurrence and distant metastasis. An increasing number of studies have been attempting to explore the underlying mechanisms of the resistance of CRC cells to different therapies, which can be summarized into two aspects: (1) The intrinsic characters and adapted alterations of CRC cells before and during treatment that regulate the drug metabolism, drug transport, drug target, and the activation of signaling pathways; and (2) the suppressive features of the tumor microenvironment (TME). To combat the issue of therapeutic resistance, effective strategies are warranted with a focus on the restoration of CRC cells' sensitivity to specific treatments as well as reprogramming impressive TME into stimulatory conditions. To date, nanotechnology seems promising with scope for improvement of drug mobility, treatment efficacy, and reduction of systemic toxicity. The instinctive advantages offered by nanomaterials enable the diversity of loading cargoes to increase drug concentration and targeting specificity, as well as offer a platform for trying the combination of different treatments to eventually prevent tumor recurrence, metastasis, and reversion of therapy resistance. The present review intends to summarize the known mechanisms of CRC resistance to chemotherapy, radiotherapy, immunotherapy, and targeted therapy, as well as the process of metastasis. We have also emphasized the recent application of nanomaterials in combating therapeutic resistance and preventing metastasis either by combining with other treatment approaches or alone. In summary, nanomedicine is an emerging technology with potential for CRC treatment; hence, efforts should be devoted to targeting cancer cells for the restoration of therapeutic sensitivity as well as reprogramming the TME. It is believed that the combined strategy will be beneficial to achieve synergistic outcomes contributing to control and management of CRC in the future.
Background:
Pediatric high-grade glioma (pHGG) is largely incurable and accounts for most brain tumor-related deaths in children. Radiation is a standard therapy, yet the benefit from this treatment modality is transient, and most children succumb to disease within 2 years. Recent large-scale genomic studies suggest that pHGG have alterations in DNA damage response (DDR) pathways that induce resistance to DNA damaging agents. The aim of this study was to evaluate the therapeutic potential and molecular consequences of combining radiation with selective DDR inhibition in pHGG.
Methods:
We conducted an unbiased screen in pHGG cells that combined radiation with clinical candidates targeting the DDR and identified the ATM inhibitor AZD1390. Subsequently, we profiled AZD1390 + radiation in an extensive panel of early passage pHGG cell lines, mechanistically characterized response to the combination in vitro in sensitive and resistant cells and evaluated the combination in vivo using TP53 wild-type and TP53 mutant orthotopic xenografts.
Results:
AZD1390 significantly potentiated radiation across molecular subgroups of pHGG by increasing mutagenic non-homologous end joining and augmenting genomic instability. In contrast to previous reports, ATM inhibition significantly improved the efficacy of radiation in both TP53 wild-type and TP53 mutant isogenic cell lines and distinct orthotopic xenograft models. Furthermore, we identified a novel mechanism of resistance to AZD1390 + radiation that was marked by an attenuated ATM pathway response which dampened sensitivity to ATM inhibition and induced synthetic lethality with ATR inhibition.
Conclusions:
Our study supports the clinical evaluation of AZD1390 in combination with radiation in pediatric patients with HGG.
Cancer stem cells (CSCs) are self-renewing and slow-multiplying micro subpopulations in tumour microenvironments. CSCs contribute to cancer's resistance to radiation (including radiation) and other treatments. CSCs control the heterogeneity of the tumour. it alters the tumour's microenvironment cellular singling and promotes epithelial-to-mesenchymal transition (eMT). Current research decodes the role of extracellular vesicles (evs) and CSCs interlink in radiation resistance. exosome is a subpopulation of evs and originated from plasma membrane. it is secreted by several active cells. it involed in cellular communication and messenger of healthly and multiple pathological complications. exosomal biological active cargos (DNA, RNA, protein, lipid and glycan), are capable to transform recipient cells' nature. The molecular signatures of CSCs and CSC-derived exosomes are potential source of cancer theranostics development. This review discusse cancer stem cells, radiation-mediated CSCs development, eMT associated with CSCs, the role of exosomes in radioresistance development, the current state of radiation therapy and the use of CSCs and CSCs-derived exosomes biomolecules as a clinical screening biomarker for cancer. This review gives new researchers a reason to keep an eye on the next phase of scientific research into cancer theranostics that will help mankind.
Cancer stem cells (CSCs) are self-renewing and slow-multiplying micro subpopulations in tumor microenvironments. CSCs contribute to cancer's resistance to radiation (including radiation) and other treatments. CSCs control the heterogeneity of the tumor. It alters the tumor's microenvironment cellular singling and promotes epithelial-to-mesenchymal transition (EMT). Current research decodes the role of extracellular vesicles (EVs) (exosomes a subpopulation of EVs) and CSCs interlink in radiation resistance. This review discusses cancer stem cells, radioresistance-mediated CSCs development, EMT associated with CSCs, the role of exosomes in radioresistance development, the current state of radiation therapy, and the use of CSCs and CSCs derived exosomes biomolecules as a clinical screening biomarker for cancer. This review gives new researchers a reason to keep an eye on the next phase of scientific research into cancer therapies that will help mankind.
High-grade glioma (HGG) such as glioblastoma multiforme (GBM) is an aggressive brain tumor that is still associated with poor prognosis. With the discovery and advancement in understanding of cancer stem cells (CSC) in glioma, these cells have emerged as seed cells for tumor growth and recurrence and appear as a potential target for therapeutics. Glioma stem cells (GSCs) demonstrate capacity of self-renewal, proliferation, and differentiation into multiple cell types and can contribute to tumor heterogeneity. Their role is established in tumorigenesis, metastasis, chemo- and radio-resistance and appears as a major cause for tumor recurrence. Thus, targeting GSCs by various therapeutics may improve effectiveness of the drugs in use alone or in combination to significantly improve patient survival outcome in GBM cases. In this chapter, we have discussed various mechanisms that drive GSC including signaling pathways and tumor microenvironment. We have also discussed the mechanism behind resistance of GSCs toward therapeutics and the pathways that can be targeted to improve the outcome of the patients.
Glioblastoma (GBM) is a highly malignant brain tumor characterized by a heterogeneous population of genetically unstable and highly infiltrative cells that are resistant to chemotherapy. Although substantial efforts have been invested in the field of anti-GBM drug discovery in the past decade, success has primarily been confined to the preclinical level, and clinical studies have often been hampered due to efficacy-, selectivity-, or physicochemical property-related issues. Thus, expansion of the list of molecular targets coupled with a pragmatic design of new small-molecule inhibitors with central nervous system (CNS)-penetrating ability is required to steer the wheels of anti-GBM drug discovery endeavors. This Perspective presents various aspects of drug discovery (challenges in GBM drug discovery and delivery, therapeutic targets, and agents under clinical investigation). The comprehensively covered sections include the recent medicinal chemistry campaigns embarked upon to validate the potential of numerous enzymes/proteins/receptors as therapeutic targets in GBM.
Capacity of tumor niche chemotaxis and long-term persistency making macrophage as great vehicles for anti-tumor factor delivery. Macrophages-based delivery of chemokines or cytokines have been tested for tissue homeostasis and cancer repression. TRAIL as a promising anti-tumor cytokine, made little clinical progress due to limited stability and off-target toxicity. Here we engineered macrophages with tumor micro-environment (TME)-induced trimerized CP1-TRAIL secretion under the TME specific promoter Arg1 (Tri-TRAIL-iM). The Tri-TRAIL-iM cells displayed high specific inducible activity in both cell-based co-culture assay and in tumor baring mice models. Compared to normal TRAIL over-expressed macrophages under none-inducible promoter, Tri-TRAIL-iM infiltrated to tumor sites and showed superior apoptosis induction of cancer cells and tumor growth repression as well as less systemic side effect. This inducible delivery TRAIL strategy can be effectively further applied in clinical studies and can be coupled with other engineered methods to maximize the therapeutic outcomes for solid tumors.
Background: Metastasis-associated lung adenocarcinoma transcript 1 (MALAT1), a conserved transcript with 8,000 nt, is highly associated with malignancy of numerous cancer types. However, the function of MALAT1 plays in regulating the response to radiotherapy in colorectal cancer (CRC) remains unclear. Thus, the object of this study is to investigate the functions of MALAT1 in CRC radioresistance.
Methods: First, the expression of MALAT1 in colon adenocarcinoma (COAD) was analyzed through the Cancer Genome Atlas (TCGA) database. Then, we detected the expression level of MALAT1 in tumor tissues and CRC cell lines and analyzed the relevance of MALAT1 and clinicopathological parameters. In the end, the effect of silencing MALAT1 on the radiosensitivity of CRC cells was investigated, and its potential mechanism was preliminarily illustrated.
Results: The analysis of TCGA data showed that MALAT1 was closely related to the type of tumor, and high expression of MALAT1 was remarkably relevant to poor outcome. MALAT1 was highly expressed in CRC tissues and cell lines and related to tumor stages. Knockdown of MALAT1 could significantly suppress colony survival, proliferation, and migration and increase apoptosis, G2/M phase arrest, and formation of gamma-H2AX foci in HCT116, whether in combination with X-rays or not. Moreover, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis demonstated that the regulated proteins were principally enriched in the glycosaminoglycan degradation pathway after silencing MALAT1.
Conclusion: Our results implied that MALAT1 was highly expressed in CRC and associated with tumor stage and prognosis. Silencing MALAT1 can increase HCT116 cell radiosensitivity, which may be potentially influenced by glycosaminoglycan degradation pathway.
ABSTRACT Glioblastoma remains among the most lethal of human malignancies. The current standard of care prolongs life expectancy about 2 months on average compared to from radiation therapy alone, leading to a median patient survival of 14.6 months. Glioblastoma is heterogenous tumor at various levels, and intrinsically resistance to radiation and chemotherapy. These limits therapeutic options for both primary and recurrent tumors. Importantly, glioblastoma progression is often accompanied by cerebral edema, a significant cause of morbidity that influences the clinical course and prognosis of the disease. Immunosuppressive corticosteroids have been the primary treatment for glioblastoma-associated edema. However, the effect is temporary and accompanied by adverse effects due to the action of corticosteroids outside of the targeted area. Research over the past two decades has unveiled a significant role for metabolic reprogramming that confers a survival advantage during gliomagenesis and therapeutic resistance. This chapter introduces the recent discoveries of two energy metabolism pathways: AMP-activated kinase-mediated stress-resilient glioblastoma growth, and Guanosine-5’-triphosphate (GTP)- metabolic reprogramming that renders anabolic growth and radioresistance. We discuss the potential clinical utility of currently available medicine that could target these metabolic pathways to suppress malignant growth of glioblastoma and increase the efficacy of the current glioblastoma therapy.
Tumor cells can undergo diverse responses to cancer therapy. While apoptosis represents the most desirable outcome, tumor cells can alternatively undergo autophagy and senescence. Both autophagy and senescence have the potential to make complex contributions to tumor cell survival via both cell autonomous and cell non-autonomous pathways. The induction of autophagy and senescence in tumor cells, preclinically and clinically, either individually or concomitantly, has generated interest in the utilization of autophagy modulating and senolytic therapies to target autophagy and senescence, respectively. This chapter summarizes the current evidence for the promotion of autophagy and senescence as fundamental responses to cancer therapy and discusses the complexity of their functional contributions to cell survival and disease outcomes. We also highlight current modalities designed to exploit autophagy and senescence in efforts to improve the efficacy of cancer therapy.
Tumor recurrence is one of the major obstacles to overcome in the future to improve the overall survival of patients with colon cancer. High rates and patterns of therapeutic failure seen in patients are consistent with a steady accumulation of drug-resistant cancer stem cells (CSCs). Here, we demonstrate that the nuclear receptor PXR (NR1I2) acts as a key regulator of colon CSC chemoresistance and of their ability to generate post-treatment tumor relapse. We first determined that the enrichment of PXR paralleled that of CSC markers upon treatment of colon cancer cells with the standard of care chemotherapy. We found that PXR was highly expressed in colorectal cancer cells displaying CSC markers and function and that it was instrumental for the emergence of CSCs following chemotherapy in vitro and in vivo. mRNA profiling experiments in colon CSCs indicated that PXR transcriptionally controls a large network of genes including markers of stemness, genes involved in resistance to drug/apoptosis or migration/invasion. Finally, PXR down-regulation altered the survival and self-renewal of colon CSCs in vitro and hampered their capacity to resist chemotherapy in vivo, leading to significant delays of post-chemotherapy tumor relapse. Clinically, we observed that patients bearing tumors with high PXR expression display a lower probability of recurrence-free survival, while a molecular signature associated with poor progression-free survival was specifically enriched in PXRoverexpression LS174T cells and was decreased in patient-derived CSC cells after PXR depletion. This study
strongly suggests that targeting PXR may represent a novel treatment strategy to prevent drug resistance and recurrence through the sensitization of CSCs to standard chemotherapy. Taken together, our data strongly suggest that PXR plays an instrumental role in the so-called "intrinsic" pan-resistance of CSCs against therapy.
Keywords: Colon Cancer, PXR, Drug resistance, Tumor Recurrence
Inactivating mutations in the Methyl-CpG Binding Protein 2 (MECP2) gene are the main cause of Rett syndrome (RTT). Despite extensive research into MECP2 function, no treatments for RTT are currently available. Here we use an evolutionary genomics approach to construct an unbiased MECP2 gene network, using 1,028 eukaryotic genomes to prioritize proteins with strong co-evolutionary signatures with MECP2. Focusing on proteins targeted by FDA approved drugs led to three promising candidates, two of which were previously linked to MECP2 function (IRAK, KEAP1) and one that was not (EPOR). We show that each of these compounds has the ability to rescue different phenotypes of MECP2 inactivation in cultured human neural cell types, and appear to act on Nuclear Factor Kappa B (NF-κB) signaling in inflammation. This study highlights the potential of comparative genomics to accelerate drug discovery, and yields potential new avenues for the treatment of RTT.
Abstract Figure
Malignant brain tumors strike deep into the psyche of those receiving and those delivering the diagnosis. Ma- lignant gliomas, the most common subtype of primary brain tumors, are aggressive, highly invasive, and neuro- logically destructive tumors considered to be among the deadliest of human cancers. In its most aggressive mani- festation, glioblastoma (GBM), median survival ranges from 9 to 12 months, despite maximum treatment ef- forts—a statistical fact that has changed little over sev- eral decades of technological advances in neurosurgery, radiation therapy, and clinical trials of conventional and novel therapeutics. Over the same time period, there has been an explosion of knowledge in cancer biology and basic science discovery that has fueled meaningful prog- ress in the treatment of many common human cancers, including those of the breast, lung, and prostate. It is perplexing that therapies used effectively in the treat- ment of these solid tumors are overwhelmingly ineffec- tive in the treatment of GBM, perhaps reflecting the ec- centric biology and cellular origin of this neoplasm. To date, only one new agent has been documented to have modest activity against intermediate-grade gliomas, whereas no effective agents have emerged for the treat- ment of GBM, despite 20 years of enrolling patients in clinical trials. It is ironic that although a comprehensive view of the genetic lesions encountered in malignant gliomas has been compiled, substantive conceptual and practical barriers remain in assigning functional signifi- cance to these genetic changes and in harnessing this basic information into the development of drugs that make a difference in patient care. The history of treating malignant gliomas dates back to the middle of the 19th century and parallels landmark advances in modern surgical technique and the clinical discipline of neurology. The first brain tumor surgery of the modern era was performed in 1884 by Rickman
Most current research on human brain tumors is focused on the molecular and cellular analysis of the bulk tumor mass. However, there is overwhelming evidence in some malignancies that the tumor clone is heterogeneous with respect to proliferation and differentiation. In human leukemia, the tumor clone is organized as a hierarchy that originates from rare leukemic stem cells that possess extensive proliferative and self-renewal potential, and are responsible for maintaining the tumor clone. We report here the identification and purification of a cancer stem cell from human brain tumors of different phenotypes that possesses a marked capacity for proliferation, self-renewal, and differentiation. The increased self-renewal capacity of the brain tumor stem cell (BTSC) was highest from the most aggressive clinical samples of medulloblastoma compared with low-grade gliomas. The BTSC was exclusively isolated with the cell fraction expressing the neural stem cell surface marker CD133. These CD133+ cells could differentiate in culture into tumor cells that phenotypically resembled the tumor from the patient. The identification of a BTSC provides a powerful tool to investigate the tumorigenic process in the central nervous system and to develop therapies targeted to the BTSC.
Malignant cells often display defects in autophagy, an evolutionarily conserved pathway for degrading long-lived proteins and cytoplasmic organelles. However, as yet, there is no genetic evidence for a role of autophagy genes in tumor suppression. The beclin 1 autophagy gene is monoallelically deleted in 40-75% of cases of human sporadic breast, ovarian, and prostate cancer. Therefore, we used a targeted mutant mouse model to test the hypothesis that monoallelic deletion of beclin 1 promotes tumorigenesis. Here we show that heterozygous disruption of beclin 1 increases the frequency of spontaneous malignancies and accelerates the development of hepatitis B virus-induced premalignant lesions. Molecular analyses of tumors in beclin 1 heterozygous mice show that the remaining wild-type allele is neither mutated nor silenced. Furthermore, beclin 1 heterozygous disruption results in increased cellular proliferation and reduced autophagy in vivo. These findings demonstrate that beclin 1 is a haplo-insufficient tumor-suppressor gene and provide genetic evidence that autophagy is a novel mechanism of cell-growth control and tumor suppression. Thus, mutation of beclin 1 or other autophagy genes may contribute to the pathogenesis of human cancers.
Autophagy is originally named as a process of protein recycling. It begins with sequestering cytoplasmic organelles in a membrane vacuole called autophagosome. Autophagosomes then fuse with lysosomes, where the materials inside are degraded and recycled. To date, however, little is known about the role of autophagy in cancer therapy. In this study, we present that temozolomide (TMZ), a new alkylating agent, inhibited the viability of malignant glioma cells in a dose-dependent manner and induced G2/M arrest. At a clinically achievable dose (100 microM), TMZ induced autophagy, but not apoptosis in malignant glioma cells. After the treatment with TMZ, microtubule-associated protein light-chain 3 (LC3), a mammalian homologue of Apg8p/Aut7p essential for amino-acid starvation-induced autophagy in yeast, was recruited on autophagosome membranes. When autophagy was prevented at an early stage by 3-methyladenine, a phosphatidylinositol 3-phosphate kinase inhibitor, not only the characteristic pattern of LC3 localization, but also the antitumor effect of TMZ was suppressed. On the other hand, bafilomycin A1, a specific inhibitor of vacuolar type H(+)-ATPase, that prevents autophagy at a late stage by inhibiting fusion between autophagosomes and lysosomes, sensitized tumor cells to TMZ by inducing apoptosis through activation of caspase-3 with mitochondrial and lysosomal membrane permeabilization, while LC3 localization pattern stayed the same. These results indicate that TMZ induces autophagy in malignant glioma cells. Application of an autophagy inhibitor that works after the association of LC3 with autophagosome membrane, such as bafilomycin A1, is expected to enhance the cytotoxicity of TMZ for malignant gliomas.
Autophagy is characterized by sequestration of bulk cytoplasm and organelles in double or multimembrane autophagic vesicles, and their delivery to and subsequent degradation by the cell's own lysosomal system. Autophagy has multiple physiological functions in multicellular organisms, including protein degradation and organelle turnover. Genes and proteins that constitute the basic machinery of the autophagic process were first identified in the yeast system and some of their mammalian orthologues have been characterized as well. Increasing lines of evidence indicate that these molecular mechanisms may be recruited by an alternative, caspase-independent form of programmed cell death, named autophagic type II cell death. In some settings, autophagy and apoptosis seem to be interconnected positively or negatively, introducing the concept of 'molecular switches' between them. Additionally, mitochondria may be central organelles integrating the two types of cell death. Malignant transformation is frequently associated with suppression of autophagy. The recent implication of tumor suppressors like Beclin 1, DAP-kinase and PTEN in autophagic pathways indicates a causative role for autophagy deficiencies in cancer formation. Autophagic cell death induction by some anticancer agents underlines the potential utility of its induction as a new cancer treatment modality.
Most current research on human brain tumors is focused on the molecular and cellular analysis of the bulk tumor mass. However, evidence in leukemia and more recently in solid tumors such as breast cancer suggests that the tumor cell population is heterogeneous with respect to proliferation and differentiation. Recently, several groups have described the existence of a cancer stem cell population in human brain tumors of different phenotypes from both children and adults. The finding of brain tumor stem cells (BTSCs) has been made by applying the principles for cell culture and analysis of normal neural stem cells (NSCs) to brain tumor cell populations and by identification of cell surface markers that allow for isolation of distinct tumor cell populations that can then be studied in vitro and in vivo. A population of brain tumor cells can be enriched for BTSCs by cell sorting of dissociated suspensions of tumor cells for the NSC marker CD133. These CD133+ cells, which also expressed the NSC marker nestin, but not differentiated neural lineage markers, represent a minority fraction of the entire brain tumor cell population, and exclusively generate clonal tumor spheres in suspension culture and exhibit increased self-renewal capacity. BTSCs can be induced to differentiate in vitro into tumor cells that phenotypically resembled the tumor from the patient. Here, we discuss the evidence for and implications of the discovery of a cancer stem cell in human brain tumors. The identification of a BTSC provides a powerful tool to investigate the tumorigenic process in the central nervous system and to develop therapies targeted to the BTSC. Specific genetic and molecular analyses of the BTSC will further our understanding of the mechanisms of brain tumor growth, reinforcing parallels between normal neurogenesis and brain tumorigenesis.
The cancer stem cell (CSC) hypothesis suggests that neoplastic clones are maintained exclusively by a rare fraction of cells with stem cell properties. Although the existence of CSCs in human leukaemia is established, little evidence exists for CSCs in solid tumours, except for breast cancer. Recently, we prospectively isolated a CD133+ cell subpopulation from human brain tumours that exhibited stem cell properties in vitro. However, the true measures of CSCs are their capacity for self renewal and exact recapitulation of the original tumour. Here we report the development of a xenograft assay that identified human brain tumour initiating cells that initiate tumours in vivo. Only the CD133+ brain tumour fraction contains cells that are capable of tumour initiation in NOD-SCID (non-obese diabetic, severe combined immunodeficient) mouse brains. Injection of as few as 100 CD133+ cells produced a tumour that could be serially transplanted and was a phenocopy of the patient's original tumour, whereas injection of 10(5) CD133- cells engrafted but did not cause a tumour. Thus, the identification of brain tumour initiating cells provides insights into human brain tumour pathogenesis, giving strong support for the CSC hypothesis as the basis for many solid tumours, and establishes a previously unidentified cellular target for more effective cancer therapies.
Glial neoplasms represent 0.5-1% of all cancers in most Western countries. Malignant gliomas are among the most devastating cancers, leading to death in most cases. They present unique challenges due to their location, aggressive biological behavior and diffuse infiltrative growth. Notwithstanding the development of new surgical and radiation techniques in the last thirty years, a cure for malignant gliomas remains elusive. In this article, we will review the standard and new therapies used for malignant gliomas. As standard therapies, surgery, radiation therapy and systemic chemotherapy, are in a continuous process of evolution. Multiple chemotherapies have been used in malignant gliomas, as single agents, in combination, or with different modes of administration, including high-dose chemotherapy with stem cell rescue and intra-arterial chemotherapy. The last decade has been noticeable for the advent of a better understanding of the biology of malignant gliomas. This has stimulated active research in multiples areas and the advent of new treatment strategies. Techniques to circumvent the resistance mechanisms to chemotherapy have been evaluated, tyrosine kinase inhibitors have shown activity in malignant primary brain tumors and radioimmunotherapy remains an area of active research. In this article, we review the past, present and future treatments of malignant gliomas with a special interest on chemotherapy, resistance mechanisms and tyrosine kinase inhibitors.
Macroautophagy is a vacuolar, self-digesting mechanism responsible for the removal of long-lived proteins and damaged organelles by the lysosome. The discovery of the ATG genes has provided key information about the formation of the autophagosome, and about the role of macroautophagy in allowing cells to survive during nutrient depletion and/or in the absence of growth factors. Two connected signaling pathways encompassing class-I phosphatidylinositol 3-kinase and (mammalian) target of rapamycin play a central role in controlling macroautophagy in response to starvation. However, a considerable body of literature reports that macroautophagy is also a cell death mechanism that can occur either in the absence of detectable signs of apoptosis (via autophagic cell death) or concomitantly with apoptosis. Macroautophagy is activated by signaling pathways that also control apoptosis. The aim of this review is to discuss the signaling pathways that control macroautophagy during cell survival and cell death.
Recent clinical data shows that arsenic trioxide (As(2)O(3)) causes remission in patients with acute promyelocytic leukemia and multiple myeloma without severe side effects. Laboratory data suggest that As(2)O(3) induces apoptosis or cell differentiation of hematopoietic or solid tumor cells. To date, there has been no study on the effects of As(2)O(3) on glioma cells. In this study, we investigated the in vitro effect of As(2)O(3) on cell growth inhibition and cell death mechanisms in human glioma cells. As(2)O(3) significantly inhibited the proliferation of all six of the glioma cell lines (U373, U87, U251, GB1, A-172, and T98G) tested in this study in a dose-dependent manner. The IC(50) of As(2)O(3) for all of the tumor cell lines was <2 micro M. Previous studies have shown that this is a clinically safe concentration. Treatment with 2 micro M As(2)O(3) induced G(2)/M arrest in all of the glioma cell lines. Autophagy (programmed cell death type II), but not apoptosis (programmed cell death type I), was detected by electron microscopy in U-373-MG cells treated with 2 micro M As(2)O(3). Caspase inhibitors did not halt As(2)O(3)-induced cell death. Furthermore, combination of As(2)O(3) with bafilomycin A1 autophagy inhibitor enhanced the antitumor effect of As(2)O(3) through induction of apoptosis. These findings suggest that As(2)O(3) at a clinically safe concentration may be an effective chemotherapeutic agent for malignant gliomas.
Atg12, a post-translational modifier, is activated and conjugated to Atg5 by a ubiquitin-like conjugation system, though it has no obvious sequence homology to ubiquitin. The Atg12-Atg5 conjugate is essential for autophagy, an intracellular bulk degradation process. Here, we show that the carboxyl-terminal region of Atg12 that is predicted to fold into a ubiquitin-like structure is necessary and sufficient for both conjugation and autophagy, which indicates that the domain essential for autophagy resides in the ubiquitin-fold region. We further show that two hydrophobic residues within the ubiquitin-fold region are important for autophagy: mutation at Y149 affects conjugate formation catalyzed by Atg10, an E2-like enzyme, while mutation at F154 has no effect on Atg12-Atg5 conjugate formation but its hydrophobic nature is essential for autophagy. In response to the F154 mutation, Atg8-PE conjugation, the other ubiquitin-like conjugation in autophagy, is severely reduced and autophagosome formation fails. Gel filtration analysis suggests that F154 plays a critical role in the assembly of a functional Atg12-Atg5.Atg16 complex that is requisite for autophagosome formation.
Although autophagy enhances cell survival in nutrient-deprived cells by increasing adenosine triphosphate (ATP) production, it remains unclear if autophagy functions similarly in cells treated with cytotoxic chemotherapy agents. To address this issue, we measured both the ability of DNA damaging agents (Temozolomide, and Etoposide) to induce an autophagy-dependent production of ATP, and the effects of modulation of autophagy on drug-induced cell death. Both drugs induced an autophagy-associated increase in ATP production in multiple glioma cell lines. The drug-induced ATP surge could not be blocked by glucose starvation, but could be blocked by preincubation with the autophagy inhibitor 3-methyladenine (3-MA), an siRNA targeting beclin 1, or the mitochondrial inhibitor oligomycin. Inhibition of autophagy-induced ATP production increased non-apoptotic cell death associated with micronucleation, while restoration of the 3-MA-inhibited ATP surge by addition of pyruvate suppressed cell death. These results show that DNA damaging agents induce an autophagy-associated ATP surge that protects cells and may contribute to drug resistance.
Early signaling in camptothecin-treated MCF-7 cells followed an intrinsic pathway, but death was delayed and late events exhibited few hallmarks of apoptosis. BH3-only proteins, such as Noxa, Puma and BimEL, were activated and localized to mitochondrial sites within 24 h following drug exposure. However, caspase activity was low and death was unaffected by caspase inhibition. Transmission electron micrographs showed the presence of large vacuoles in drug-treated cells. An autophagic survival response has been attributed to MCF-7 cells following nutrient starvation or exposure to tamoxifen. Here, we show that autophagy also plays an important role in the delayed DNA damage response. Confocal microscopy revealed colocalization of mitochondria with large autophagic vacuoles and inhibitors of autophagy increased mitochondrial depolarization and caspase-9 activity, and accelerated cell death. Furthermore, downregulation of autophagy proteins, Beclin 1 and Atg7, unmasked a caspase-dependent, apoptotic response to DNA damage. We propose that a post-mitochondrial caspase cascade is delayed as a result of early disposal of damaged mitochondria within autophagosomes. Our data also suggest that the use of autophagy as a means of delaying apoptosis or prolonging survival may be characteristic of noninvasive breast tumor cells. These studies underscore a potential role for autophagy inhibitors in combination with conventional chemotherapeutic drugs in early breast cancer therapy.
Autophagy is an alternative cell death pathway that is induced by mammalian target of rapamycin (mTOR) inhibitors and up-regulated
when apoptosis is defective. We investigated radiation-induced autophagy in the presence or absence of Bax/Bak with or without
an mTOR inhibitor, Rad001. Two isogenic cell lines, wild type (WT) and Bak/Bak-/- mouse embryonic fibroblasts and tumor cell lines were used for this study. Irradiated Bak/Bak-/- cells had a decrease of Akt/mTOR signaling and a significant increase of pro-autophagic proteins ATG5-ATG12 COMPLEX and Beclin-1.
These molecular events resulted in an up-regulation of autophagy. Bax/Bak-/- cells were defective in undergoing apoptosis but were more radiosensitive than the WT cells in autophagy. Both autophagy
and sensitization of Bak/Bax-/- cells were further enhanced in the presence of Rad001. In contrast, inhibitors of autophagy rendered the Bak/Bax-/- cells radioresistant, whereas overexpression of ATG5 and Beclin-1 made the WT cells radiosensitive. When this novel concept
of radiosensitization was tested in cancer models, small interfering RNAs against Bak/Bax also led to increased autophagy
and sensitization of human breast and lung cancer cells to gamma radiation, which was further enhanced by Rad001. This is
the first report to demonstrate that inhibition of pro-apoptotic proteins and induction of autophagy sensitizes cancer cells
to therapy. Therapeutically targeting this novel pathway may yield significant benefits for cancer patients.
Ionizing radiation represents the most effective therapy for glioblastoma (World Health Organization grade IV glioma), one of the most lethal human malignancies, but radiotherapy remains only palliative because of radioresistance. The mechanisms underlying tumour radioresistance have remained elusive. Here we show that cancer stem cells contribute to glioma radioresistance through preferential activation of the DNA damage checkpoint response and an increase in DNA repair capacity. The fraction of tumour cells expressing CD133 (Prominin-1), a marker for both neural stem cells and brain cancer stem cells, is enriched after radiation in gliomas. In both cell culture and the brains of immunocompromised mice, CD133-expressing glioma cells survive ionizing radiation in increased proportions relative to most tumour cells, which lack CD133. CD133-expressing tumour cells isolated from both human glioma xenografts and primary patient glioblastoma specimens preferentially activate the DNA damage checkpoint in response to radiation, and repair radiation-induced DNA damage more effectively than CD133-negative tumour cells. In addition, the radioresistance of CD133-positive glioma stem cells can be reversed with a specific inhibitor of the Chk1 and Chk2 checkpoint kinases. Our results suggest that CD133-positive tumour cells represent the cellular population that confers glioma radioresistance and could be the source of tumour recurrence after radiation. Targeting DNA damage checkpoint response in cancer stem cells may overcome this radioresistance and provide a therapeutic model for malignant brain cancers.
Although glioblastomas show the same histologic phenotype, biological hallmarks such as growth and differentiation properties vary considerably between individual cases. To investigate whether different subtypes of glioblastomas might originate from different cells of origin, we cultured tumor cells from 22 glioblastomas under medium conditions favoring the growth of neural and cancer stem cells (CSC). Secondary glioblastoma (n = 7)-derived cells did not show any growth in the medium used, suggesting the absence of neural stem cell-like tumor cells. In contrast, 11/15 primary glioblastomas contained a significant CD133(+) subpopulation that displayed neurosphere-like, nonadherent growth and asymmetrical cell divisions yielding cells expressing markers characteristic for all three neural lineages. Four of 15 cell lines derived from primary glioblastomas grew adherently in vitro and were driven by CD133(-) tumor cells that fulfilled stem cell criteria. Both subtypes were similarly tumorigenic in nude mice in vivo. Clinically, CD133(-) glioblastomas were characterized by a lower proliferation index, whereas glial fibrillary acidic protein staining was similar. GeneArray analysis revealed 117 genes to be differentially expressed by these two subtypes. Together, our data provide first evidence that CD133(+) CSC maintain only a subset of primary glioblastomas. The remainder stems from previously unknown CD133(-) tumor cells with apparent stem cell-like properties but distinct molecular profiles and growth characteristics in vitro and in vivo.
Malignant gliomas are resistant to various proapoptotic therapies, such as radiotherapy and conventional chemotherapy. In this study, we show that selenite is preferentially cytotoxic to various human glioma cells over normal astrocytes via autophagic cell death. Overexpression of Akt, survivin, XIAP, Bcl-2, or Bcl-xL failed to block selenite-induced cell death, suggesting that selenite treatment may offer a potential therapeutic strategy against malignant gliomas with apoptotic defects. Before selenite-induced cell death in glioma cells, disruption of the mitochondrial cristae, loss of mitochondrial membrane potential, and subsequent entrapment of disorganized mitochondria within autophagosomes or autophagolysosomes along with degradation of mitochondrial proteins were noted, showing that selenite induces autophagy in which mitochondria serve as the main target. At the early phase of selenite treatment, high levels of superoxide anion were generated and overexpression of copper/zinc superoxide dismutase or manganese superoxide dismutase, but not catalase, significantly blocked selenite-induced mitochondrial damage and subsequent autophagic cell death. Furthermore, treatment with diquat, a superoxide generator, induced autophagic cell death in glioma cells. Taken together, our study clearly shows that superoxide anion generated by selenite triggers mitochondrial damage and subsequent mitophagy, leading to irreversible cell death in glioma cells.
Autophagy is a bulk degradation process in eukaryotic cells; autophagosomes enclose cytoplasmic components for degradation
in the lysosome/vacuole. Autophagosome formation requires two ubiquitin-like conjugation systems, the Atg12 and Atg8 systems,
which are tightly associated with expansion of autophagosomal membrane. Previous studies have suggested that there is a hierarchy
between these systems; the Atg12 system is located upstream of the Atg8 system in the context of Atg protein organization.
However, the concrete molecular relationship is unclear. Here, we show using an in vitro Atg8 conjugation system that the Atg12-Atg5 conjugate, but not unconjugated Atg12 or Atg5, strongly enhances the formation
of the other conjugate, Atg8-PE. The Atg12-Atg5 conjugate promotes the transfer of Atg8 from Atg3 to the substrate, phosphatidylethanolamine
(PE), by stimulating the activity of Atg3. We also show that the Atg12-Atg5 conjugate interacts with both Atg3 and PE-containing
liposomes. These results indicate that the Atg12-Atg5 conjugate is a ubiquitin-protein ligase (E3)-like enzyme for Atg8-PE
conjugation reaction, distinctively promoting protein-lipid conjugation.
This conceptual paper addresses the role of lysosomal autophagy in cellular defense against environmentally-induced oxidative stress using a marine mollusc (the blue mussel) as an experimental model. It is proposed that augmented autophagic removal of oxidatively damaged organelles and proteins provides a second level or tier of defense against oxidative stress. Age pigment or lipofuscin is a product of oxidative attack on proteins and lipids and can accumulate in lysosomes, where it may generate further reactive oxygen species (ROS) and inhibit lysosomal function, resulting in autophagic failure. The previously observed protective role of augmented autophagy, induced by nutritional deprivation, against oxidative stress can be explained by this model, where autophagy boosts "cellular housekeeping" through enhanced removal of ROS-damaged proteins and organelles minimizing formation of potentially harmful stress/age pigment, and has been proposed as an anti-aging mechanism. Finally, the probable low level triggering of autophagy in mussels by fluctuating environmental regimes is considered as a potential protective mechanism that will contribute to resistance to environmentally induced oxidative stress. It is further conjectured that organisms making up functional ecological assemblages (communities) in fluctuating environments, where upregulation of autophagy should provide a selective advantage, may be pre-selected to be tolerant of pollutant-induced oxidative stress.
Autophagy or "self eating" is frequently activated in tumor cells treated with chemotherapy or irradiation. Whether autophagy represents a survival mechanism or rather contributes to cell death remains controversial. To address this issue, the role of autophagy in radiosensitive and radioresistant human cancer cell lines in response to gamma-irradiation was examined. We found irradiation-induced accumulation of autophagosomes accompanied by strong mRNA induction of the autophagy-related genes beclin 1, atg3, atg4b, atg4c, atg5, and atg12 in each cell line. Transduction of specific target-siRNAs led to down-regulation of these genes for up to 8 days as shown by reverse transcription-PCR and Western blot analysis. Blockade of each autophagy-related gene was associated with strongly diminished accumulation of autophagosomes after irradiation. As shown by clonogenic survival, the majority of inhibited autophagy-related genes, each alone or combined, resulted in sensitization of resistant carcinoma cells to radiation, whereas untreated resistant cells but not sensitive cells survived better when autophagy was inhibited. Similarly, radiosensitization or the opposite was observed in different sensitive carcinoma cells and upon inhibition of different autophagy genes. Mutant p53 had no effect on accumulation of autophagosomes but slightly increased clonogenic survival, as expected, because mutated p53 protects cells by conferring resistance to apoptosis. In our system, short-time inhibition of autophagy along with radiotherapy lead to enhanced cytotoxicity of radiotherapy in resistant cancer cells.
Recurrence patterns of glioblastoma multiforme (25) and anaplastic astrocytoma (9) were studied using CT scans of 34 patients who received all or a portion of their surgical treatment at Memorial Sloan-Kettering Cancer Center from January 1983 through February 1987. Thirty-two patients presented with unifocal tumors and two with multifocal tumors. All patients received radiation therapy following initial surgery. Eighteen patients who underwent re-operation following CT evidence of recurrence had histologic verification of recurrent tumor; sixteen patients had radiographic evidence of recurrence only. Seventy-eight percent (25/32) of unifocal tumors recurred within 2.0 cm of the pre-surgical, initial tumor margin, defined as the enhancing edge of the tumor on CT scan. Fifty-six percent (18/32) of tumors recurred within 1.0 cm of the initial tumor margin. Tumors for which a gross total resection was accomplished tended to recur closer to the initial tumor margin than did subtotally resected tumors (p greater than 0.1). Extensive pre-operative edema was associated with a decreased distance between initial and recurrent tumor margins. Large tumors were generally not more likely to recur further from the initial tumor margin than were smaller tumors. No unifocal tumor recurred as a multifocal tumor. Only one tumor (initially near the midline) recurred in the contralateral hemisphere. The findings support the use of partial brain irradiation for post-operative treatment of glioblastoma multiforme and anaplastic astrocytomas, and may help to determine the most appropriate treatment volume for interstitial irradiation.
Macroautophagy is a dynamic process involving the rearrangement of subcellular membranes to sequester cytoplasm and organelles for delivery to the lysosome or vacuole where the sequestered cargo is degraded and recycled. This process takes place in all eukaryotic cells. It is highly regulated through the action of various kinases, phosphatases, and guanosine triphosphatases (GTPases). The core protein machinery that is necessary to drive formation and consumption of intermediates in the macroautophagy pathway includes a ubiquitin-like protein conjugation system and a protein complex that directs membrane docking and fusion at the lysosome or vacuole. Macroautophagy plays an important role in developmental processes, human disease, and cellular response to nutrient deprivation.
Autophagy is a bulk protein and organelle degradation process essential for cell maintenance and viability. Microtubule-associated protein 1 light chain 3 (LC3), the mammalian homologue of yeast Atg8, is involved in autophagosome formation during autophagy. The aim of this study was to investigate LC3 expression in gastrointestinal cancers to elucidate the role of autophagy in human cancer development. We evaluated LC3 expression by immunohistochemistry in 163 gastrointestinal cancers including 106 esophageal, 38 gastric and 19 colorectal cancers. Seventy precancerous intraepithelial neoplasias were found in esophageal cancer specimens. LC3 expression was compared with Ki-67 staining and expression of carbonic anhydrase (CA) IX, a hypoxic marker. LC3 was expressed in the cytoplasm of cancer cells, but not in noncancerous epithelial cells. A high expression of LC3 was observed in 53% of esophageal, 58% of gastric and 63% of colorectal cancers. LC3 immunoreactive score gradually increased during early esophageal carcinogenesis in low- and high-grade intraepithelial neoplasia and T1 carcinoma, while it did not change in later cancer progression (T2-T4 carcinomas). In early esophageal carcinogenesis, LC3 expression correlated with Ki-67 labeling index (p=0.0001), but showed no significant association with CAIX expression. In esophageal cancers, LC3 expression did not correlate with various clinicopathological factors, including survival. LC3 is upregulated in various gastrointestinal cancers and partly associated with Ki-67 index. Our results suggest that LC3 expression is advantageous to cancer development especially in early-phase carcinogenesis.
Recurrence patterns of glioblastoma multiforme (25) and anaplastic astrocytoma (9) were studied using CT scans of 34 patients who received all or a portion of their surgical treatment at Memorial Sloan-Kettering Cancer Center from January 1983 through February 1987. Thirty-two patients presented with unifocal tumors and two with multifocal tumors. All patients received radiation therapy following initial surgery. Eighteen patients who underwent re-operation following CT evidence of recurrence had histologic verification of recurrent tumor; sixteen patients had radiographic evidence of recurrence only. Seventy-eight percent (25/32) of unifocal tumors recurred within 2.0 cm of the pre-surgical, initial tumor margin, defined as the enhancing edge of the tumor on CT scan. Fifty-six percent (18/32) of tumors recurred within 1.0 cm of the initial tumor margin. Tumors for which a gross total resection was accomplished tended to recur closer to the initial tumor margin than did subtotally resected tumors (p greater than 0.1). Extensive pre-operative edema was associated with a decreased distance between initial and recurrent tumor margins. Large tumors were generally not more likely to recur further from the initial tumor margin than were smaller tumors. No unifocal tumor recurred as a multifocal tumor. Only one tumor (initially near the midline) recurred in the contralateral hemisphere. The findings support the use of partial brain irradiation for post-operative treatment of glioblastoma multiforme and anaplastic astrocytomas, and may help to determine the most appropriate treatment volume for interstitial irradiation.
Malignant gliomas are a heterogeneous group of tumors that are associated with significant morbidity and mortality. The development of the malignant phenotype is the result of a complex series of events that influence gene expression, angiogenesis, and invasion and favor the growth of tumor cells. Currently, the management of malignant glioma consists of symptom control and cytoreduction with a combination of surgery, radiation therapy, and chemotherapy. However, there is no satisfactory regimen available for adjuvant or salvage chemotherapy for these neoplasms. An overview of the biologic mechanisms, grading systems, and treatment options for anaplastic astrocytoma and glioblastoma multiforme is presented.
Macroautophagy is a dynamic process involving the rearrangement of subcellular membranes to sequester cytoplasm and organelles
for delivery to the lysosome or vacuole where the sequestered cargo is degraded and recycled. This process takes place in
all eukaryotic cells. It is highly regulated through the action of various kinases, phosphatases, and guanosine triphosphatases
(GTPases). The core protein machinery that is necessary to drive formation and consumption of intermediates in the macroautophagy
pathway includes a ubiquitin-like protein conjugation system and a protein complex that directs membrane docking and fusion
at the lysosome or vacuole. Macroautophagy plays an important role in developmental processes, human disease, and cellular
response to nutrient deprivation.
The new World Health Organization (WHO) classification of nervous system tumors, published in 2000, emerged from a 1999 international consensus conference of neuropathologists. New entities include chordoid glioma of the third ventricle, cerebellar liponeurocytoma, atypical teratoid/rhabdoid tumor, and perineurioma. Several histological variants were added, including tanycytic ependymoma, large cell medulloblastoma, and rhabdoid meningioma. The WHO grading scheme was updated and, for meningiomas, extensively revised. In recognition of the emerging role of molecular diagnostic approaches to tumor classification, genetic profiles have been emphasized, as in the distinct subtypes of glioblastoma and the already clinically useful 1p and 19q markers for oligodendroglioma and 22q/INI1 for atypical teratoid/rhabdoid tumors. In accord with the new WHO Blue Book series, the actual classification is accompanied by extensive descriptions and illustrations of clinicopathological characteristics of each tumor type, including molecular genetic features, predictive factors, and separate chapters on inherited tumor syndromes. The 2000 WHO classification of nervous system tumors aims at being used and implemented by the neuro-oncology and biomedical research communities worldwide.
The incidence of primary brain tumors has rapidly increased in recent years. The current standard of care for patients with high-grade malignant glioma is resection followed by radiotherapy. However, the use of adjuvant chemotherapy and the standard of care at first relapse are still under debate for patients with glioblastoma multiforme and anaplastic astrocytoma. Meta-analyses have suggested that adjuvant chemotherapy, specifically with nitrosourea-based regimens, is associated with improved survival. However, no randomized, controlled trial has shown a clear advantage for adjuvant chemotherapy in these patients. Cumulative toxicity associated with both radiotherapy and chemotherapy, as well as resistance to nitrosourea-based regimens related to exposure in the adjuvant setting, prevent the use of radiotherapy and nitrosourea-based regimens at first relapse. The combination of procarbazine, carmustine, and vincristine (PCV) has shown activity at first relapse in patients who have not received adjuvant chemotherapy. Temozolomide (Temodar [US], Temodal [international]; Schering-Plough Corporation, Kenilworth, NJ) has shown activity at both first and second relapse in patients who have received prior nitrosourea-based regimens. The better safety profile of temozolomide suggests that it may be preferred to PCV for treatment of patients with recurrent high-grade malignant glioma. Additional randomized, controlled trials are needed to fully define the best option for first-line chemotherapy in both the adjuvant and recurrent settings in patients with high-grade malignant glioma.
Autophagy (which includes macro-, micro-, and chaperone-mediated autophagy) is an important biological mechanism for degradation of damaged/obsolete macromolecules and organelles. Ageing non-dividing cells, however, progressively accumulate oxidised proteins, defective organelles and intralysosomal lipofuscin inclusions, suggesting inherent insufficiency of autophagy. To learn more about the role of macroautophagy in the turnover of organelles and lipofuscin formation, we inhibited autophagic sequestration with 3-methyladenine (3 MA) in growth-arrested human fibroblasts, a classical model of cellular ageing. Such treatment resulted in a dramatic accumulation of altered lysosomes, displaying lipofuscin-like autofluorescence, as well as in a moderate increase of mitochondria with lowered membrane potential. The size of the late endosomal compartment appeared not to be significantly altered following 3 MA exposure. The accumulation of lipofuscin-like material was enhanced when 3 MA administration was combined with hyperoxia. The findings suggest that macroautophagy is essential for normal turnover of lysosomes. This notion is supported by reports in the literature of lysosomal membrane proteins inside lysosomes and/or late endosomes, as well as lysosomes with active hydrolases within autophagosomes following vinblastine-induced block of fusion between lysosomes and autophagosomes. The data also suggest that specific components of lysosomes, such as membranes and proteins, may be direct sources of lipofuscin.
The eukaryotic cell uses an evolutionarily conserved lysosomal pathway of self-digestion (autophagy) for survival when extracellular nutrients are limited. In this issue of Cell, new evidence indicates that autophagy is used to for survival when intracellular nutrients are limited by growth factor deprivation (Lum et al., 2005). Other recent studies indicate that the autophagy machinery is also used to degrade foreign microbial invaders (xenophagy).
Autophagy is a novel response of cancer cells to ionizing radiation (IR) or chemotherapy, but its significance or mechanism remains largely elusive. Autophagy is characterized with the prominent formation of autophagic vacuoles in the cytoplasm. It is a protein degradation system that involves autophagic/lysosomal compartment. The process begins with sequestering a portion of the cytoplasm, forming the autophagosome. The autophagosome then fuses with the lysosome and lyses its contents. To study radiation-induced autophagy with specific molecules, we assessed changes in the expression of microtubule-associated protein light chain 3 (LC3) and its intracellular distribution after IR in comparison with starvation-induced autophagy. First, we showed that IR induced cell cycle arrest and autophagy, but not apoptosis, in human malignant glioma U373-MG cells. Type II LC3, that is specifically associated with the membrane of the autophagosome, increased after IR and amino acid starvation. Exogenous LC3 distributed on punctate structures, indicative of the formation of autophagosomes. Autophagy inhibitors, 3-methyladenine and bafilomycin A1, radiosensitized U373-MG cells. Furthermore, gammaH2AX foci, that show the extent of DNA double-strand breaks, were more pronounced and prolonged in the cells treated with IR and autophagy inhibitors than in those cells treated with IR only. Our results suggest that autophagy inhibitors may represent a new application of radiosensitization for malignant glioma cells.
Autophagy has been implicated in a range of disorders and hence is of major interest. However, imaging autophagy in real time has been hampered by lack of suitable markers. We have compared the potential of monodansylcadaverine, widely used as an autophagosomal marker, and the Atg8 homologue LC3, to follow autophagy by fluorescence microscopy whilst labelling late endosomes and lysosomes simultaneously using EGFP-CD63. Monodansylcadaverine labelled only acidic CD63-positive compartments in response to a range of autophagic inducers in various live or post-fixed cells, staining being identical in atg5(+/+) and atg5(-/-) MEFs in which autophagosome formation is disabled. Monodansylcadaverine staining was essentially indistinguishable from that of LysoTracker Red, LAMP-1 or LAMP-2. In contrast, 60-90% of EGFP-LC3-positive punctate organelles did not colocalise with LAMP-1/LAMP-2/CD63 and were monodansylcadaverine-negative while EGFP-LC3 puncta that did colocalise with LAMP-1/LAMP-2/CD63 were also monodansylcadaverine-positive. Hence monodansylcadaverine is no different from other markers of acidic compartments and it cannot be used to follow autophagosome formation. In contrast, fusion of mRFP-LC3-labelled autophagosomes with EGFP-CD63-positive endosomes and lysosomes and sequestration of dsRed-labelled mitochondria by EGFP-LC3- and EGFP-CD63-positive compartments could be visualized in real time. Moreover, transition of EGFP-LC3-I (45 kDa) to EGFP-LC3-II (43 kDa)-traced by immunoblotting and verified by [(3)H]ethanolamine labelling-revealed novel insights into the dynamics of autophagosome homeostasis, including the rapid activation of autophagy by the apoptotic inducer staurosporine prior to apoptosis proper. Use of fluorescent LC3 and a counter-fluorescent endosomal/lysosomal protein clearly allows the entire autophagic process to be followed by live cell imaging with high fidelity.
Addenda to:
Rapamycin-Sensitive Pathway Regulates Mitochondrial Membrane Potential, Autophagy and Survival in Irradiated MCF-7 Cells
Paglin S, Lee N-Y, Nakar C, Fitzgerald M, Plotkin J, Deuel B, Hackett N, McMahill M, Sphicas E, Lampen N and Yahalom J.
Cancer Res 2005; 65:11061-70.
In addition to their role in cellular homeostasis, pathways that regulate autophagy affect both tumorigenesis and tumor response to treatment. Therefore, understanding regulation of autophagy in treated cancer cells is relevant to discovery of molecular targets for development of anti-cancer drugs. Our recent report points to radiation-induced inactivation of mTOR pathway as an underlying mechanism of radiation-induced autophagy in the human breast cancer cell line MCF-7. Most importantly, radiation-induced inactivation of this pathway was detrimental to cell survival and was associated with reversal of mitochondrial ATPase activity and mitochondrial hyperpolarization, decreased level of eukaryotic initiation factor 4G (eIF4G) and increased phosphorylation of p53. Future analysis of the interrelationship among these events and the role each of them plays in cell survival following radiation will increase our ability to employ the mTOR pathway in anti-cancer therapy.
Autophagy plays important roles in both cell death and cell survival. Beclin-1, a key regulator of autophagy formation, has been considered as a haploinsufficient tumor suppressor. Loss of expression or point mutation could serve as a mechanism of loss of beclin-1 tumor suppressor function in cancers. However, our recent study revealed that point mutation of the beclin-1 gene is a rare event in common human cancers. In this study we investigated beclin-1 protein expression in 103 colorectal and 60 gastric carcinoma tissues by immunohistochemistry using a tissue microarray approach. In the cancers, expression of beclin-1 was detected in 95% of the colorectal carcinomas and 83% of the gastric carcinomas. In contrast, normal mucosal cells of both stomach and colon showed no or very weak expression of beclin-1. There was no significant association of beclin-1 expression with clinocopathologic characteristics, including invasion, metastasis and stage. The beclin-1 expression of colorectal and gastric cancers in the present study is quite in contrast to that of the breast cancers in the previous study, which showed a decreased beclin-1 expression in breast cancer cells compared to normal breast cells. Our data indicate that beclin-1 inactivation by loss of expression may not occur in colorectal and gastric cancers. Rather, increased expression of beclin-1 in the malignant colorectal and gastric epithelial cells compared to their normal mucosal epithelial cells suggests that neo-expression of beclin-1 may play a role in both colorectal and gastric tumorigenesis.
Autophagy is a cellular process whose primary function is to degrade long-lived proteins and recycle cellular components. Beside macroautophagy, there are several forms of selective autophagy, including chaperone-mediated autophagy (CMA), cytoplasm to vacuole targeting (Cvt), pexophagy and mitophagy. In this review, we summarize what is currently known about selective autophagy, and discuss its role in cell death and survival. We also discuss possible mechanisms underlying the selectivity of macroautophagy.
Macroautophagy is a self-digesting pathway responsible for the removal of long-lived proteins and organelles by the lysosomal compartment. Parts of the cytoplasm are first segregated in double-membrane-bound autophagosomes, which then undergo a multistep maturation process including fusion with endosomes and lysosomes. The segregated cytoplasm is then degraded by the lysosomal hydrolases. The discovery of ATG genes has greatly enhanced our understanding of the mechanisms of this pathway. Two novel ubiquitin-like protein conjugation systems were shown to function during autophagosome formation. Autophagy has been shown to play a role in a wide variety of physiological processes including energy metabolism, organelle turnover, growth regulation, and aging. Impaired autophagy can lead to diseases such as cardiomyopathy and cancer. This review summarizes current knowledge about the formation and maturation of autophagosomes, the role of macroautophagy in various physiological and pathological conditions, and the signaling pathways that regulate this process in mammalian cells.
CD133(1) and CD133(2) glioblastoma-derived cancer stem cells show differential growth characteristics and molecular profiles
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Eating oneself and uninvited guests: autophagy‐related pathways in cellular defense
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Role of autophagy in temozolomide-induced cytotoxicity for malignant glioma cells
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