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ABSTRACT: Abstract Achieving high-efficiency tumor targeting after systemic delivery is a considerable challenge facing oncolytic gene therapists. Efficient retargeting should be combined with efforts to improve in vivo safety, reduce hepatotoxicity, minimize off-target interactions, and improve antitumoral potency and efficacy. We previously described the successful retargeting of adenovirus serotype 5 (Ad5) to α(v)β(6), an integrin that is highly overexpressed in numerous human carcinomas. In this study, we have further modified this construct by introducing mutations that ablate coxsackievirus-adenovirus receptor (CAR) binding and putative interactions with factor IX (FIX)/C4b-binding protein (C4BP). We have found that the resulting vector, Ad5-477dlTAYT(A20), displays a desirable in vivo safety profile. This vector does not agglutinate human erythrocytes, fails to cause thrombocytopenia after intravenous delivery, has limited induction of proinflammatory cytokines, and results in low-level toxicity (aspartate aminotransferase/alanine aminotransferase) when compared with Ad5-EGFP(WT). Furthermore, it has reduced accumulation in Kupffer cells (1 hr) and limited hepatocyte transduction at later time points (24 and 96 hr). The parental vector, Ad5-EGFP(A20), also displayed many of these desirable properties. As a result of the improved safety profile of both A20-modified vectors, we escalated the dose from 2×10(10) to 4×10(10) viral particles in an antitumoral efficacy study. We observed improvements in reducing percent tumor growth at early time points (96 hr) when compared with Ad5-EGFP(WT), although increasing the dose did not affect the therapeutic outcome beneficially. On completion of the experiment, we detected increased E1A staining in the tumors of all A20-treated groups and we determined that E1A expression was localized largely within α(v)β(6)(+) tumor cells. However, in spite of apparently efficient tumor transduction, this did not result in enhanced antitumoral efficacy as the virus failed to disseminate effectively throughout the tumor mass, presumably due to physical intratumoral restrictions. This highlights a remaining challenge that needs to be overcome before such vectors can be developed for future cancer gene therapy applications.
Human gene therapy 06/2012; 23(9):960-79. · 4.20 Impact Factor
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ABSTRACT: Calcium channel blockers including verapamil have been proposed to enhance release and antitumor efficacy of oncolytic adenoviruses in preclinical studies but this has not been studied in humans before. Here, we studied if verapamil leads to increased replication of oncolytic adenovirus in cancer patients, as measured by release of virions from tumor cells into the systemic circulation. The study was conducted as a matched case-control study of advanced cancer patients treated with oncolytic adenoviruses with or without verapamil. We observed that verapamil increased mean virus titers present in blood after treatment (P < 0.05). The frequency or severity of adverse events was not increased, nor were cytokine responses or neutralizing antibody levels different between groups. Signs of possible treatment-related clinical benefits were observed in both groups, but there was no significant difference in responses or survival. Thus, our data suggests that the combination of verapamil with oncolytic adenoviruses is safe and well tolerated. Moreover, verapamil treatment seems to result in higher virus titers in blood, indicating enhanced overall replication in tumors. A randomized trial is needed to confirm these findings and to study if enhanced replication results in benefits to patients.
Molecular Therapy 11/2011; 20(1):221-9. · 6.87 Impact Factor
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ABSTRACT: Tumor-associated stromal cells constitute a major hurdle in the antitumor efficacy with oncolytic adenoviruses. To overcome this biological barrier, an in vitro bioselection of a mutagenized AdwtRGD stock in human cancer-associated fibroblasts (CAFs) was performed. Several rounds of harvest at early cytopathic effect (CPE) followed by plaque isolation led us to identify one mutant with large plaque phenotype, enhanced release in CAFs and enhanced cytotoxicity in CAF and several tumor cell lines. Whole genome sequencing and functional mapping identified the truncation of the last 17 amino acids in C-terminal end of the i-leader protein as the mutation responsible for this phenotype. Similar mutations have been previously isolated in two independent bioselection processes in tumor cell lines. Importantly, our results establish the enhanced antitumor activity in vivo of the i-leader C-terminal truncated mutants, especially in a desmotic fibroblast-embedded lung carcinoma model in mice. These results indicate that the i-leader truncation represents a promising trait to improve virotherapy with oncolytic adenoviruses.
Molecular Therapy 08/2011; 20(1):54-62. · 6.87 Impact Factor
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ABSTRACT: Replication-competent adenoviruses armed with thymidine kinase (TK) combine the concepts of virotherapy and suicide gene therapy. Moreover TK-activity can be detected by noninvasive positron emission-computed tomography (PET) imaging, what could potentially facilitate virus monitoring in vivo. Here, we report the generation of a novel oncolytic adenovirus that incorporates the Tat8-TK gene under the control of the Major Late Promoter in a highly selective backbone thus providing selectivity by targeting the retinoblastoma pathway. The selective oncolytic TK virus, termed ICOVIR5-TK-L, showed reduced potency compared to a non-selective counterpart. However the combination of ICOVIR5-TK-L with ganciclovir (GCV) induced a potent antitumoural effect similar to that of wild type adenovirus in a preclinical model of pancreatic cancer. Although the treatment with GCV provoked a reduction in the viral yield, both in vitro and in vivo, a two-cycle treatment of virus and GCV resulted in an enhanced antitumoral response that correlated with high TK-activity, based on microPET measurements. Thus, TK-expressing oncolytic adenoviruses can be traced by PET imaging providing real time information on the activity of the virus and its antitumoral potency can be optimized by GCV dosing.
PLoS ONE 01/2011; 6(10):e26142. · 4.09 Impact Factor
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ABSTRACT: The most efficient system to introduce genes of interest within the adenovirus genome is by homologous recombination in microorganisms. In this chapter, the most popular procedures are described: two for homologous recombination in Escherichia coli, and one in yeast. Main differences between procedures are found in the plasmids needed as well as in the selection system used to rapidly identify newly generated recombinant adenovirus. The adenovirus genomes are then analyzed to confirm their identity and integrity, and further linearized to generate a viral pre-stock in permissive human cells. Finally, as a previous step before its amplification at medium or large scale, the viral pre-stock must be analyzed to quantify its potency and infectivity as well as to exclude the presence of unwanted replication competent particles.
Methods in molecular biology (Clifton, N.J.) 01/2011; 737:117-38.
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ABSTRACT: Oncolytic adenoviruses are promising anticancer agents due to their ability to self-amplify at the tumor mass. However, tumor stroma imposes barriers difficult to overcome by these agents. Transgene expression is a valuable strategy to counteract these limitations and to enhance antitumor activity. For this purpose, the genetic backbone in which the transgene is inserted should be optimized to render transgene expression compatible with the adenovirus replication cycle and to keep genome size within the encapsidation size limit. In order to design a potent and selective oncolytic adenovirus that keeps intact all the viral functions with minimal increase in genome size, we inserted palindromic E2F-binding sites into the endogenous E1A promoter. The insertion of these sites controlling E1A-Δ24 results in a low systemic toxicity profile in mice. Importantly, the E2F-binding sites also increased the cytotoxicity and the systemic antitumor activity relative to wild-type adenovirus in all cancer models tested. The low toxicity and the increased potency results in improved antitumor efficacy after systemic injection and increased survival of mice carrying tumors. Furthermore, the constrained genome size of this backbone allows an efficient and potent expression of transgenes, indicating that this virus holds promise for overcoming the limitations of oncolytic adenoviral therapy.
Molecular Therapy 11/2010; 18(11):1960-71. · 6.87 Impact Factor
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Petri Nokisalmi,
Sari Pesonen,
Sophie Escutenaire,
Merja Särkioja,
Mari Raki,
Vincenzo Cerullo,
Leena Laasonen, Ramon Alemany,
Juan Rojas,
Manel Cascallo, [......],
Maria Rajecki,
Lotta Kangasniemi,
Elina Haavisto,
Aila Karioja-Kallio,
Päivi Hannuksela,
Minna Oksanen,
Anna Kanerva,
Timo Joensuu,
Laura Ahtiainen,
Akseli Hemminki
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ABSTRACT: Twenty-one patients with cancer were treated with a single round of oncolytic adenovirus ICOVIR-7.
ICOVIR-7 features an RGD-4C modification of the fiber HI-loop of serotype 5 adenovirus for enhanced entry into tumor cells. Tumor selectivity is mediated by an insulator, a modified E2F promoter, and a Rb-binding site deletion of E1A, whereas replication is optimized with E2F binding hairpins and a Kozak sequence. ICOVIR-7 doses ranged from 2 x 10(10) to 1 x 10(12) viral particles. All patients had advanced and metastatic solid tumors refractory to standard therapies.
ICOVIR-7 treatment was well tolerated with mild to moderate fever, fatigue, elevated liver transaminases, chills, and hyponatremia. One patient had grade 3 anemia but no other serious side effects were seen. At baseline, 9 of 21 of patients had neutralizing antibody titers against the ICOVIR-7 capsid. Treatment resulted in neutralizing antibody titer induction within 4 weeks in 16 of 18 patients. No elevations of serum proinflammatory cytokine levels were detected. Viral genomes were detected in the circulation in 18 of 21 of patients after injection and 7 of 15 of the samples were positive 2 to 4 weeks later suggesting viral replication.
Overall, objective evidence of antitumor activity was seen in 9 of 17 evaluable patients. In radiological analyses, 5 of 12 evaluable patients had stabilization or reduction in tumor size. These consisted of one partial response, two minor responses and two cases of stable disease, all occurring in patients who had progressive disease before treatment. In summary, ICOVIR-7 treatment is apparently safe, resulting in anticancer activity, and is therefore promising for further clinical testing.
Clinical Cancer Research 06/2010; 16(11):3035-43. · 7.74 Impact Factor
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ABSTRACT: Successful virotherapy requires efficient virus spread within tumors. We tested whether the expression of hyaluronidase, an enzyme which dissociates the extracellular matrix (ECM), could enhance the intratumoral distribution of an oncolytic adenovirus and improve its therapeutic activity. As a proof of concept, we demonstrated that intratumoral coadministration of hyaluronidase in mice-bearing tumor xenografts improves the antitumor activity of an oncolytic adenovirus. Next, we constructed a replication-competent adenovirus expressing a soluble form of the human sperm hyaluronidase (PH20) under the control of the major late promoter (MLP) (AdwtRGD-PH20). Intratumoral treatment of human melanoma xenografts with AdwtRGD-PH20 resulted in degradation of hyaluronan (HA), enhanced viral distribution, and induced tumor regression in all treated tumors. Finally, the PH20 cDNA was inserted in an oncolytic adenovirus that selectively kills pRb pathway-defective tumor cells. The antitumoral activity of the novel oncolytic adenovirus expressing PH20 (ICOVIR17) was compared to that of the parental virus ICOVIR15. ICOVIR17 showed more antitumor efficacy following intratumoral and systemic administration in mice with prestablished tumors, along with an improved spread of the virus within the tumor. Importantly, a single intravenous dose of ICOVIR17 induced tumor regression in 60% of treated tumors. These results indicate that ICOVIR17 is a promising candidate for clinical testing.
Molecular Therapy 05/2010; 18(7):1275-83. · 6.87 Impact Factor
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ABSTRACT: The therapeutic potential of oncolytic adenoviruses is limited by the rate of adenovirus release. Based on the observation that several viruses induce cell death and progeny release by disrupting intracellular calcium homeostasis, we hypothesized that the alteration in intracellular calcium concentration induced by verapamil could improve the rate of virus release and spread, eventually enhancing the antitumoral activity of oncolytic adenoviruses. Our results indicate that verapamil substantially enhanced the release of adenovirus from a variety of cell types resulting in an improved cell-to-cell spread and cytotoxicity. Furthermore, the combination of the systemic administration of an oncolytic adenovirus (ICOVIR-5) with verapamil in vivo greatly improved its antitumoral activity in two different tumor xenograft models without affecting the selectivity of this virus. Overall, our findings indicate that verapamil provides a new, safe, and versatile way to improve the antitumoral potency of oncolytic adenoviruses in the clinical setting.
Molecular Therapy 02/2010; 18(5):903-11. · 6.87 Impact Factor
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ABSTRACT: Thymidine kinase (TK)-mediated suicide gene therapy has been considered for the treatment of pancreatic cancer. However, despite a bystander effect, the proportion of transduced tumor cells has proven too low to result in efficacy. We propose the use of a drug-selectable marker (MDR1) to enrich TK-expressing cells using chemotherapy. This enrichment or positive selection phase may increase the efficacy of suicide gene therapy. To test this strategy, we generated stable NP18MDR/TK-GFP transfectants and showed docetaxel resistance in vivo. Mixed tumors of MDR/TK-expressing cells and parental NP18 cells were established and docetaxel was used to increase the proportion of TK-expressing cells. After this positive selection phase, suicide gene therapy with ganciclovir was applied. Upon positive selection, the proportion of TK-expressing cells increased from 4% to 22%. Subsequent suicide gene therapy was more effective compared with a control group without positive selection. Starting with 10% of TK-expressing cells the positive-negative selection strategy completely inhibited tumor growth. Taken together, these results suggest that a positive-negative selection strategy based on MDR and TK genes represents an efficient way to increase the proportion of TK-expressing cells in the tumor and the efficacy of TK-mediated suicide gene therapy.
Molecular Cancer Therapeutics 11/2009; 8(11):3098-107. · 5.23 Impact Factor
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ABSTRACT: Oncolytic adenoviruses are emerging as a promising alternative therapy for glioma patients and are currently being tested in clinic. In this review, we summarize our experience with gene-based therapy targeting RB pathway in gliomas. Our study has evolved from the development of RB-expressing adenoviral vectors to the characterization of the oncolytic effects on gliomas of the replication competent adenoviruses Delta-24, Delta-24-RGD and ICOVIR. We also review the successful combination of the viruses with chemotherapies that are routinely used in glioma patients, the efficacy of Delta-24-RGD against brain tumor stem cells, the newly described adenovirus-induced autophagy and the potential for the systemic delivery of the oncolytic viruses with human mesenchymal stem cells. Finally, we comment on the preclinical and clinical studies of p53 expressing adenoviral vector and the lessons learned from the experience of Onyx-015, the first oncolytic adenovirus tested in clinical setting.
Current Gene Therapy 10/2009; 9(5):422-7. · 3.39 Impact Factor
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ABSTRACT: Tumor targeting on systemic adenovirus administration is key to improve the prospects of adenovirus-mediated gene therapy and virus therapy of cancer. Despite many genetic and ligand conjugation approaches this objective remains elusive. Ablation of human adenovirus type 5 (Ad5) binding to its natural receptors in airway epithelial cells, that is, the coxsackievirus and adenovirus receptor (CAR) and integrins, does not impact on the preeminent liver tropism of adenovirus in the bloodstream. This is explained by a distinct entry pathway mediated by blood factors and heparan sulfates. Mutation of the KKTK heparin sulfate-binding domain of the fiber shaft to GATK results in liver transduction detargeting, but it is not compatible with otherwise useful HI-loop tumor-targeting ligand insertions such as the insertion of Arg-Gly-Asp (RGD). To circumvent this problem we have mutated the KKTK domain to RGDK, and analyzed the liver-detargeting and tumor-targeting transduction properties of this replacement mutant. Similar to RGD at the HI-loop, RGD at this new shaft location efficiently enhances the infectivity of adenovirus and improves the tumor-to-liver transduction ratio in vivo.
Human gene therapy 07/2009; 20(10):1214-21. · 4.20 Impact Factor
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ABSTRACT: Cancer treatment with oncolytic viruses is at a crucial intersection from where two very different routes can be taken. The key role of the immune system needs to be addressed proactively to succeed. An immunocentric point of view posits that the intense immunosuppression induced by tumors can be outbalanced by the natural immunogenicity of viruses. To their advantage, viruses can be safely armed to be even more immunostimulatory. The microbe-associated inflammatory response is optimal for antigen presentation and helps to reveal the hidden tumor antigens. The induced immune effector cells patrol the organs to destroy disseminated tumor cells out of the reach of the oncolytic virus. However, as tumor immunosuppression is localized, this concept needs to be revisited because every tumor focus will have to be reached by the oncolytic virus. By contrast, virocentrics see the immune system as an obstacle to virotherapy. A virus is so immunogenic that it dominates all the elicited immunity to the detriment of a response towards tumor antigens. For them immunosuppression is the way to go, and the intense immunosuppression in and around the tumor is now an advantage, offering a privileged site for virus replication. A better oncolytic virus evades the immune system, but such a virus should be very tumor-selective to be safe. Although the trend favors immunocentrics, clinical results have been more often documented in immunocompromised patients. Trials of comparative interventions on the immune system will validate immunocentrism or virocentrism. What seems clear is that at this intersection one should take one route or the other to overcome the current limitations of virotherapy.
Future Microbiology 07/2009; 4(5):527-36. · 3.82 Impact Factor
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ABSTRACT: Treatment options for pancreatic cancer have shown limited success mainly owing to poor selectivity for pancreatic tumor tissue and to a lack of activity in the tumor. In this study, we describe the ability of the urokinase-type plasminogen activator receptor (uPAR) promoter to efficiently and selectively target pancreatic tumors and metastases, which enables the successful management of pancreatic cancer. We have generated a replication-defective reporter adenovirus, AduPARLuc, and a conditionally replicating adenovirus, AduPARE1A, and we have studied the selectivity and antitumoral efficacy in pancreatic tumors and metastases. Toxicity was studied on intravascular delivery. We demonstrate that the uPAR promoter is highly active in pancreatic tumors but very weak in normal tissues. Tumor specificity is evidenced by a 100-fold increase in the tumor-to-liver ratio and by selective targeting of liver metastases (P < .001). Importantly, the AduPARE1A maintains the oncolytic activity of the wild-type virus, with reduced toxicity, and exhibits significant antitumoral activity (25% tumor eradication) and prolonged survival in pancreatic xenograft models (P < .0001). Furthermore, upon intravascular delivery, we demonstrate complete eradication of liver metastasis in 33% of mice, improving median survival (P = 5.43 x 10(-5)). The antitumoral selective activity of AduPARE1A shows the potential of uPAR promoter-based therapies in pancreatic cancer treatment.
Neoplasia (New York, N.Y.) 06/2009; 11(6):518-28, 4 p following 528. · 5.48 Impact Factor
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ABSTRACT: A major obstacle for the efficacy of cancer gene therapy is the need to transduce a high proportion of tumor cells with genes that directly or indirectly cause their death. During the formation of certain organs, cells compete among themselves to colonize the whole tissue. We reasoned that cell competition could be used to increase the proportion of cells that become transfected in a tumor. For this, a transgene that provides a selective advantage to the transfected cells should be used. If the same gene conferred a suicide mechanism the tumor could be eradicated after a period of selection. Bystander effect of transfected cells over neighboring nonmodified cells may eliminate tumors even with incomplete replacement of tumor cells. To test this strategy a competitive advantage was provided to colon cancer cells, using a gene encoding a fusion protein of dihydrofolate reductase (DHFR) and thymidine kinase (TK). DHFR confers resistance to methotrexate (MTX) and TK confers sensitivity to ganciclovir (GCV). Modified cells were also transduced with green fluorescent protein and parental cells with red fluorescent protein. In vitro and in vivo experiments were performed, using various proportions of modified cells and applying positive selection with MTX followed by negative selection with GCV. In vitro, cell competition was evident. Under MTX treatment, tumor cells transfected with the DHFR-TK fusion gene efficiently replaced the parental cells (from 0.1 to 90% in 35 days). After this positive selection period, negative selection with GCV eliminated the transfected cells. In vivo, positive selection was also achieved and resulted in a statistically significant therapeutic effect.
Human gene therapy 04/2009; 20(7):728-38. · 4.20 Impact Factor
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ABSTRACT: Genetic bioselection of a mutagenized Ad5wt stock in human tumor xenografts led us to isolate AdT1, a mutant displaying a large-plaque phenotype in vitro and an enhanced systemic antitumor activity in vivo. AdT1 phenotype correlates with an increased progeny release without affecting total viral yield in different human tumors and cancer-associated fibroblasts. An approach combining hybrid Ad5/AdT1 recombinants and sequencing identified a truncating insertion in the endoplasmic reticulum retention domain of the E3/19K protein (445A mutation) which relocates the protein to the plasma membrane and is responsible for AdT1's enhanced release. E3/19K-445A phenotype does not correlate with the protein's ability to interact with MHC-I or induce apoptosis. Intracellular calcium measurement revealed that the 445A mutation induces extracellular Ca(2+) influx, deregulating intracellular Ca(2+) homeostasis and inducing membrane permeabilization, a viroporin-like function. E3/19K-445A mutants also display enhanced antitumoral activity when injected both intratumorally and systemically in different models in vivo. Our results indicate that the inclusion of mutation 445A in tumor-selective adenoviruses would be a very powerful tool to enhance their antitumor efficacy.
Cancer Research 12/2008; 68(21):8928-37. · 7.86 Impact Factor
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ABSTRACT: A critical obstacle for efficient gene therapy and virotherapy of cancer with adenoviral vectors and oncolytic adenoviruses is to target tumor cells in vivo. Recent reports indicate that, contrary to the natural airborne infection of epithelial cells with adenovirus type 5 mediated by coxsackievirus B and adenovirus receptor (CAR) and integrins, blood-borne adenovirus infects hepatocytes mainly through an indirect pathway that involves blood coagulation factors. In this report we have studied whether adenovirus also infects tumor cells in vivo by this pathway. In vitro and in vivo analyses show that vitamin K-dependent coagulation zymogens mediate tumor transduction and that the elimination of these factors abrogates tumor transduction. This finding imposes new challenges to retarget adenoviruses in vivo.
Human gene therapy 10/2008; 19(12):1415-9. · 4.20 Impact Factor
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ABSTRACT: Cancer arises as a result of a stepwise accumulation of genetic changes. One of these changes, deregulation of the Rb/E2F1 pathway resulting from alterations in members of the pathway, is a hallmark of all human cancers. These mutations promote tumor development by deregulating the E2F family of transcription factors, which results in uncontrolled cell cycle progression. The E2F1 protein functions as a transcription factor that enhances cell proliferation by binding to the promoter region of several genes, including those that are involved in cell cycle regulatory activities and DNA replication. It is now becoming clear that the role of E2F1 in regulating transcription and cell growth is also highly dependent on the cellular context. This complexity is also evident from analyses of perturbations in E2F-modulated tumor development. For example, deregulated E2F1 expression can either promote or inhibit tumorigenesis depending on the nature of the other oncogenic mutations that are present. This explains the ability of E2F1 to behave as both an oncogene and tumor suppressor gene. Here we focus on reviewing the most recent evidence supporting the "addiction" of gliomas to this versatile transcription factor. We also consider the clinical relevance of this by examining the role of E2F1 as a prognosis factor and as a target for the development of novel strategies.
Cancer Letters 06/2008; 263(2):157-63. · 4.24 Impact Factor
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ABSTRACT: E2F acts as a transcriptional repressor when bound to unphosphorylated RB during the G(1) or G(0) phase. Upon phosphorylation, E2F is released from the E2F-RB complexes to activate transcription. Tumor cells are characterized by an increase in the level of "free" E2F as a consequence of the absence or hyperphosphorylation of RB. The E2F-1 promoter is a well-characterized E2F-responsive promoter, and it can be used to control adenovirus E1a gene expression as a strategy to achieve tumor-selective expression and replication of an adenovirus. ICOVIR-5 (Ad-DM-E2F-K-Delta24RGD) is an optimized oncolytic adenovirus that combines E1a transcriptional control by an insulated form of the E2F promoter with the Delta24 mutation of E1a to improve the therapeutic index of AdDelta24RGD. ICOVIR-5 also contains the Kozak sequence at the E1a start codon, which is important to restore E1a expression and viral replication to AdwtRGD levels in tumor cells. The unique combination of genetic elements in ICOVIR-5 allows the selectivity for cells with a deregulated E2F-RB pathway to be increased and potent anti-tumoral activity to be maintained. Dose-response toxicological and efficacy studies after a single systemic administration in pre-clinical models in mice are presented to demonstrate that this virus holds promise for treatment of disseminated cancer.
Molecular Therapy 10/2007; 15(9):1607-15. · 6.87 Impact Factor
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ABSTRACT: During 2007, approximately 200,000 people in the United States will be diagnosed with brain tumors. Gliomas account for 77% of primary malignant brain tumors, and the prognosis has hardly changed in the past 20 years, with only 30% of patients with malignant glioma surviving 5 years after diagnosis. Oncolytic adenoviruses are promising therapies for the treatment of gliomas. Here, report the antiglioma activity of the tumor-selective ICOVIR-5 adenovirus, which encompasses an early 1A adenoviral (E1A) deletion in the retinoblastoma (Rb) protein-binding region, substitution of the E1A promoter for E2F-responsive elements, and an RGD-4C peptide motif inserted into the adenoviral fiber to enhance adenoviral tropism. Mechanistic studies showed a dramatic addiction of ICOVIR-5 to the E2F1 oncogene in vitro and in vivo. This addiction was mediated by the occupancy of the ectopic adenoviral E2F1-responsive elements by the endogenous E2F1 protein resulting in high level of E1A expression in cancer cells and potent antiglioma effect. Importantly, we showed for the first time the ability of oncolytic adenoviruses to enhance E2F transcriptional activity in vivo, and we provided direct evidence of the interaction of the E2F1 protein with native and ectopic adenovirus promoters. Restoration of Rb function led to the association of Rb/E2F1 repressor complexes with ICOVIR-5 ectopic E2F1 promoter and subsequent down-modulation of E1A, dramatically impairing adenoviral replication. In xenografted mice, intratumoral injection of ICOVIR-5 resulted in a significant improvement of the median survival (P < 0.0001), and furthermore, led to 37% of long-term survivors free of disease. The antitumor activity of ICOVIR-5 suggests that it has the potential to be an effective agent in the treatment of gliomas.
Cancer Research 09/2007; 67(17):8255-63. · 7.86 Impact Factor
