No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Targeting tumors with hypoxia-activated cytotoxins
Abstract
This review focuses on the recent development of hypoxia-activated cytotoxins. Such drugs are prodrugs activated to cytotoxic products in the hypoxic environment of solid tumors (so-called "bioreductive prodrugs"), but can also be activated by radiation (radiation-activated prodrugs). These compounds grew out of research on hypoxic radiosensitizers, which are compounds that can overcome the radiation resistance of hypoxic cells, and we will discuss this area also. The advantages and limitations of each class of the hypoxia-activated cytotoxins are discussed. In addition we will discuss a novel method of targeting drugs to tumors based on anaerobic bacteria, the so-called "clostridia-directed enzyme prodrug therapy" or CDEPT, which also exploits the hypoxic environment of solid tumors.
... They are generally classified under three major groups: the quinones, nitroaromatics and N-oxides. These have been extensively reviewed [73,158,159]. All require hypoxic conditions and the presence of specific reductases for activation. ...
... Another promising group of bioreductives are the organic nitroxides, of which the lead compound is tirapazamine, a benzotriazene di-N-oxide [158]. This hypoxiaactivated prodrug not only shows selective toxicity to hypoxic cells, but can substantially enhance radiation damage to tumours in vivo [167]. ...
... Overall, despite the excellent preclinical data and the subsequent hype surrounding these various hypoxiaactivated prodrugs [73,158,159], the clinical studies were generally disappointing. It has been suggested that the lack of clinical progress with such agents can probably be attributed to a failure to pre-select those patients in which hypoxia is an issue [159]. ...
Regions of reduced oxygenation (hypoxia) are a characteristic feature of virtually all animal and human solid tumours. Numerous preclinical studies, both in vitro and in vivo, have shown that decreasing oxygen concentration induces resistance to radiation. Importantly, hypoxia in human tumours is a negative indicator of radiotherapy outcome. Hypoxia also contributes to resistance to other cancer therapeutics, including immunotherapy, and increases malignant progression as well as cancer cell dissemination. Consequently, substantial effort has been made to detect hypoxia in human tumours and identify realistic approaches to overcome hypoxia and improve cancer therapy outcomes. Hypoxia-targeting strategies include improving oxygen availability, sensitising hypoxic cells to radiation, preferentially killing these cells, locating the hypoxic regions in tumours and increasing the radiation dose to those areas, or applying high energy transfer radiation, which is less affected by hypoxia. Despite numerous clinical studies with each of these hypoxia-modifying approaches, many of which improved both local tumour control and overall survival, hypoxic modification has not been established in routine clinical practice. Here we review the background and significance of hypoxia, how it can be imaged clinically and focus on the various hypoxia-modifying techniques that have undergone, or are currently in, clinical evaluation.
... The failure of radiotherapy in killing the hypoxic tumor cells is largely because of DNA damage produced by ionizing radiation can be repaired by hydrogen donation from cellular nonprotein sulfhydryls. Whereas, in the well-oxygenated aerobic cells, oxygen reacts extremely rapidly with the single electron of the free radical, formed on DNA by ionizing radiation, and converts it into a permanent damage which is lethal to the cell (see the reviews by Brown, 1999;Brown and Wilson, 2004;Ahn and Brown, 2007). Tumor hypoxia is also a problem for chemotherapy. ...
... Because the hypoxic tumor cells which are usually far away from nutritive blood vessels do not receive adequate anticancer drug concentrations. In addition, because hypoxic tumor cells are nonproliferating cells, the chemotherapeutic agents that target rapidly dividing cells may be less effective on this population of cells (Ahn and Brown, 2007). Furthermore, hypoxia has been shown to promote tumor progression through inducing gene amplification that results in resistance to common antineoplastic agents (Sartorelli, 1988). ...
... Furthermore, hypoxia has been shown to promote tumor progression through inducing gene amplification that results in resistance to common antineoplastic agents (Sartorelli, 1988). This is mainly the result of overexpression of hypoxia-inducible factor 1 (HIF-1) transcription factor which stimulates the increased expression of a large number of genes involved in cellular metabolism and survival under hypoxic conditions (Ahn and Brown, 2007). ...
Idarubicin (IDA) and mitomycin C (MC) are clinically effective quinone-containing anticancer agents used in the treatment of several human cancers. Quinone-containing anticancer drugs have the potential to undergo bioreduction by oxidoreductases to reactive species, and thereby exert their cytotoxic effects. In the present study, we investigated, for the first time, the potential of IDA, in comparison to MC, to undergo reductive activation by NADPH-cytochrome P450 reductase (P450R), NADH-cytochrome b5 reductase (b5R) and P450R-cytochrome P4502B4 (CYP2B4) system by performing both in vitro plasmid DNA damage experiments and enzyme assays. In addition, we examined the potential protective effects of some antioxidants against DNA damaging effects of IDA and MC resulting from their reductive activation. To achieve these goals, we obtained P450R from sheep lung, beef liver and PB-treated rabbit liver microsomes, b5R from beef liver microsomes
and CYP2B4 from PB-treated rabbit liver microsomes in highly purified forms.
The plasmid DNA damage experiments demonstrated that P450R is capable of effectively reducing IDA to DNA-damaging species. The effective protections provided by antioxidant enzymes, SOD and catalase, as well as scavengers of hydroxyl radical, DMSO and thiourea, revealed that the mechanism of DNA damage by IDA involves the generation of ROS by redox cycling of IDA with P450R under aerobic conditions. The extent of DNA damages by both IDA and MC were found to increase with increasing concentrations of the drug or the enzyme as well as with increasing incubation time. IDA was found to have a greater ability to induce DNA damage at high drug concentrations than MC. The plasmid DNA experiments using b5R, on the other hand, showed that, unlike P450R, b5R was not able to reduce IDA to DNA-damaging reactive species. It was also found that in the presence of b5R and cofactor NADH, MC barely induced DNA strand breaks. All the purified P450Rs reduced IDA at about two-fold higher rate than that of MC as shown by the measurement of drug-induced cofactor consumption. This indicates that IDA may be a more potent cytotoxic drug than MC in terms of the generation of reactive metabolites. The results obtained from enzyme assays confirmed the finding obtained from plasmid DNA experiments that while MC is a very poor substrate for b5R, IDA is not a suitable substrate for this enzyme unlike P450R. The reconstitution experiments carried out under both aerobic and anaerobic conditions using various amounts of CYP2B4, P450R and lipid DLPC revealed that reconstituted CYP2B4 produced about 1.5-fold and 1.4-fold rate enhancements in IDA and MC reduction catalyzed by P450R alone, respectively. The present results also showed that among the tested dietary antioxidants, quercetin, rutin, naringenin, resveratrol and trolox, only quercetin was found to be highly potent in preventing DNA damage by IDA.
These results may have some practical implications concerning the potential use of P450R as therapeutic agent on their own in cancer treatment strategies. Selective targeting of tumor cells with purified P450R by newly developed delivery systems such as using polymers, liposomes or antibodies may produce greater reductive activation of bioreductive drugs in tumor cells. Consequently, this strategy has a high potential to increase the efficacy and selectivity of cancer chemotherapy.
... The enhanced activities of reducing enzymes in hypoxic regions of solid tumors, such as the nitroreductases, provide means for site-specific conversion of prodrugs to yield the cytotoxic products. Selectivity for hypoxia is usually a result of a futile redox cycling in which oxygen is able to reverse or inhibit reduction to the one-electron radial intermediate thereby regenerating the non-toxic parent drug (Rauth et al. 1984;Ahn & Brown, 2007;Wilson & Hay, 2011). Four classes of bioreductive compounds, quinones, nitroaromatics, aliphatic and heteroaromatic N-oxides, have been developed. ...
... Four classes of bioreductive compounds, quinones, nitroaromatics, aliphatic and heteroaromatic N-oxides, have been developed. These have been extensively reviewed (McKeown et al., 2007, Ahn & Brown, 2007Wilson & Hay, 2011;Guise et al., 2014). All require hypoxic conditions and the presence of specific reductases for activation. ...
... The latter, a 2-nitroimidazole-based nitrogen mustard prodrug, releases bromoisophosphoramide mustard (Duan et al., 2008) and shows significant selectivity for hypoxic cells (Meng et al., 2012). The most advanced of the aromatic N-oxides class of bioreductive agents is tirapazamine (Ahn & Brown, 2007). This agent has shown HCR values of up to 200 in murine and 50 in human cell lines (Zeman et al., 1986). ...
The tumor microenvironment is increasingly recognized as a major factor influencing the success of therapeutic treatments and has become a key focus for cancer research. The progressive growth of a tumor results in an inability of normal tissue blood vessels to oxygenate and provide sufficient nutritional support to tumor cells. As a consequence the expanding neoplastic cell population initiates its own vascular network which is both structurally and functionally abnormal. This aberrant vasculature impacts all aspects of the tumor microenvironment including the cells, extracellular matrix, and extracellular molecules which together are essential for the initiation, progression and spread of tumor cells. The physical conditions that arise are imposing and manifold, and include elevated interstitial pressure, localized extracellular acidity, and regions of oxygen and nutrient deprivation. No less important are the functional consequences experienced by the tumor cells residing in such environments: adaptation to hypoxia, cell quiescence, modulation of transporters and critical signaling molecules, immune escape, and enhanced metastatic potential. Together these factors lead to therapeutic barriers that create a significant hindrance to the control of cancers by conventional anticancer therapies. However, the aberrant nature of the tumor microenvironments also offers unique therapeutic opportunities. Particularly interventions that seek to improve tumor physiology and alleviate tumor hypoxia will selectively impair the neoplastic cell populations residing in these environments. Ultimately, by combining such therapeutic strategies with conventional anticancer treatments it may be possible to bring cancer growth, invasion, and metastasis to a halt.
Copyright © 2015. Published by Elsevier Inc.
... Because hypoxia (low in oxygen tension) has been shown to be a common feature in all solid tumors of humans as well as animals [4], this oxygen-dependency for IR-induced cell kill allows hypoxic cancer cells to selectively resist against cytotoxic action of RT [4]. To overcome this problem of tumor hypoxia, numerous attempts have been made including the use of hyperbaric oxygen (100% O2) or carbogen (95% O2/5% CO2) breathing, radiosensitizers, and hypoxia-selective cytotoxins [4,5], although none of these strategies has made to the clinic. ...
... This suggests that tumor hypoxia may remain as a major factor contributing to the treatment failure by FLASH RT. Much attempts have been made to overcome tumor hypoxia with CONV RT, for example, the use of radiosensitizers, compounds that acts like oxygen thereby fixing the IR-induced DNA damage ( Fig. 1) [5]. Although this may work with CONV RT, it should not be used with FLASH RT because such agent can also sensitize normal tissues (if the normal tissues becomes severely hypoxic by FLASH RT) as well as tumors. ...
FLASH radiotherapy (FLASH RT) is a technique to deliver ultra-high dose rate in a fraction of a second. Evidence from experimental animal models suggest that FLASH RT spares various normal tissues including the lung, gastrointestinal track, and brain from radiation-induced toxicity (a phenomenon known as FLASH effect), which is otherwise commonly observed with conventional dose rate RT. However, it is not simply the ultra-high dose rate alone that brings the FLASH effect. Multiple parameters such as instantaneous dose rate, pulse size, pulse repetition frequency, and the total duration of exposure all need to be carefully optimized simultaneously. Furthermore it is critical to validate FLASH effects in an in vivo experimental model system. The exact molecular mechanism responsible for this FLASH effect is not yet understood although a number of hypotheses have been proposed including oxygen depletion and less reactive oxygen species (ROS) production by FLASH RT, and enhanced ability of normal tissues to handle ROS and labile iron pool compared to tumors. In this review, we briefly overview the process of ionization event and history of radiotherapy and fractionation of ionizing radiation. We also highlight some of the latest FLASH RT reviews and results with a special interest to neurocognitive protection in rodent model with whole brain irradiation. Lastly we discuss some of the issues remain to be answered with FLASH RT including undefined molecular mechanism, lack of standardized parameters, low penetration depth for electron beam, and tumor hypoxia still being a major hurdle for local control. Nevertheless, researchers are close to having all answers to the issues that we have raised, hence we believe that advancement of FLASH RT will be made more quickly than one can anticipate.
... Chronic hypoxia, a common feature in solid tumor tissue, has been associated with therapeutic resistance, tumor progression, and metastatic potential (8)(9)(10). In vitro studies have further demonstrated that cultured lung cancer cells subject to intermittent hypoxia are more resistant to radiation and apoptosis and are more prone to metastasis (11). ...
... However, our observations are consistent with our a priori hypothesis, grounded on evidence from recent in vitro and animal studies on the effects of hypoxia in cancer progression. Cancer cells subjected to either chronic (8)(9)(10) or intermittent hypoxia (11) show increased resistance to therapy (e.g., radiation) and malignant progression. Furthermore, recent experiments in a melanoma-injected mouse model demonstrate that intermittent hypoxia mimicking sleep apnea in humans increases tumor growth (12). ...
Sleep-disordered breathing (SDB) has been associated with total and cardiovascular mortality, but an association with cancer mortality has not been studied. Results from in vitro and animal studies suggest that intermittent hypoxia promotes cancer tumor growth.
The goal of the present study was to examine whether SDB is associated with cancer mortality in a community-based sample.
We used 22-year mortality follow-up data from the Wisconsin Sleep Cohort sample (n = 1,522). SDB was assessed at baseline with full polysomnography. SDB was categorized using the apnea-hypopnea index (AHI) and the hypoxemia index (percent sleep time below 90% oxyhemoglobin saturation). The hazards of cancer mortality across levels of SDB severity were compared using crude and multivariate analyses.
Adjusting for age, sex, body mass index, and smoking, SDB was associated with total and cancer mortality in a dose-response fashion. Compared with normal subjects, the adjusted relative hazards of cancer mortality were 1.1 (95% confidence interval [CI], 0.5-2.7) for mild SDB (AHI, 5-14.9), 2.0 (95% CI, 0.7-5.5) for moderate SDB (AHI, 15-29.9), and 4.8 (95% CI, 1.7-13.2) for severe SDB (AHI ≥ 30) (P-trend = 0.0052). For categories of increasing severity of the hypoxemia index, the corresponding relative hazards were 1.6 (95% CI, 0.6-4.4), 2.9 (95% CI, 0.9-9.8), and 8.6 (95% CI, 2.6-28.7).
Our study suggests that baseline SDB is associated with increased cancer mortality in a community-based sample. Future studies that replicate our findings and look at the association between sleep apnea and survival after cancer diagnosis are needed.
... Since Thomlinson and Gray proposed the existence of hypoxic cells in solid tumors half a century ago, these hypoxic tumor cells have been recognized as potential problems of resistance to chemo-and radiotherapy and predictors of poor prognosis and recurrence. At first, strategies of cancer therapy that target hypoxia focused on sensitizing the tumor response to cancer therapy by developing oxygen-mimic chemical modifiers and hypoxia-selective cytotoxic prodrugs (4,5). Key mechanisms of hypoxia selectivity are bioreductions to generate active species in hypoxic tissue, which have long been studied (Fig. 1). ...
... By using bioreductive activation mechanisms, not only various hypoxia-selective prodrugs but also hypoxia-imaging agents have been developed (6). Especially, nitro aromatic compounds (e.g., nitroimidazoles) and electron-deficient aromatic heterocycles (e.g., quinones and benzotriazine di-N-oxides) are typical scaffolds for hypoxia-selective compounds due to their appropriate reduction potentials (5). Although no new agents have been approved for clinical use, several hypoxia-selective prodrugs, such as EO9, CB1954, RP104, tirapazamine (TPZ), and AQ4N, are in various stages of clinical trials (7). ...
The tumor microenvironment, characterized by regions of hypoxia, low nutrition, and acidosis due to incomplete blood vessel networks, has been recognized as a major factor that influences not only the response to conventional anti-cancer therapies but also malignant progression and metastasis. However, exploiting such a cumbersome tumor microenvironment for cancer treatment could provide tumor-specific therapeutic approaches. In particular, hypoxia is now considered a fundamentally important characteristic of the tumor microenvironment in which hypoxia inducible factor (HIF)-1-mediated gene regulation is considered essential for angiogenesis and tumor development. Additional oxygen sensitive signaling pathways including mammalian target of rapamycin (mTOR) signaling and signaling through activation of the unfolded protein response (UPR) also contribute to the adaptation in the tumor microenvironment. This in turn has led to the current extensive interest in the signal molecules related to adaptive responses in the tumor microenvironment as potential molecular targets for cancer therapy against refractory cancer and recurrence in preparation for the aging society. Therefore, we should focus on the drug discovery for targeting the tumor microenvironment to develop tumor-specific cytostatic agents including angiogenesis inhibitors. In this paper, the development of hypoxia-selective prodrugs, HIF-1 inhibitors, and modulators of the tumor microenvironment will be discussed.
... These prodrugs are reduced by concerted mechanisms, which involve either oneelectron reductases followed by fragmentation or further reduction of the initially formed prodrug radicals; or two-electron reductions of specific prodrugs. In normoxic conditions, the initial reaction is reversible, while under hypoxic conditions these prodrugs become stable cytotoxins, and act as mono−/di-functional DNA alkylators, intra-and interstrand crosslinkers, and DNAstrandbreakers or additionally poison specific enzymes involved in correct DNA-replication and repair, such as topoisomerase II by TPZ [5,189]. ...
Hypoxia in solid tumors is an important predictor of treatment resistance and poor clinical outcome. The significance of hypoxia in the development of resistance to radiotherapy has been recognized for decades and the search for hypoxia-targeting, radiosensitizing agents continues. This review summarizes the main hypoxia-related processes relevant for radiotherapy on the subcellular, cellular and tissue level and discusses the significance of hypoxia in radiation oncology, especially with regard to the current shift towards hypofractionated treatment regimens. Furthermore, we discuss the strategies to interfere with hypoxia for radiotherapy optimization, and we highlight novel insights into the molecular pathways involved in hypoxia that might be utilized to increase the efficacy of radiotherapy.
... The combination of ionizing radiation (IR) with a Hypoxia-Activated Prodrug (HAP), targeting hypoxic tumor cells and thereby complementing the effect of IR in well-oxygenated cells, nicely represents the concept of biological cooperation [5]. Originally, nitrobenzenes, followed by the nitroimidazoles (misonidazole, etanidazole, pimonidazole) [6], were proposed to act as oxygen mimetic agents and to generate together with short-lived IR-induced free DNA radicals cytotoxic DNA strand breaks [7,8]. Unfortunately, and despite the clarity of the concept, severe toxicities of these www.impactjournals.com/oncotarget/ ...
The promising treatment combination of ionizing radiation (IR) with a hypoxia-activated prodrug (HAP) is based on biological cooperation. Here we investigated the hypoxia-activated prodrug evofosfamide in combination with different treatment regimens of IR against lung A549- and head&neck UT-SCC-14-derived tumor xenografts. DNA damage-related endpoints and clonogenic cell survival of A549 and UT-SCC-14 carcinoma cells were probed under normoxia and hypoxia.
Evofosfamide (TH-302) induced DNA-damage and a dose-dependent antiproliferative response in A549 cells on cellular pretreatment under hypoxia, and supra-additively reduced clonogenic survival in combination with IR. Concomitant treatment of A549-derived tumor xenografts with evofosfamide and fractionated irradiation induced the strongest treatment response in comparison to the corresponding neoadjuvant and adjuvant regimens. Adjuvant evofosfamide was more potent than concomitant and neoadjuvant evofosfamide when combined with a single high dose of IR. Hypoxic UT-SCC-14 cells and tumor xenografts thereof were resistant to evofosfamide alone and in combination with IR, most probably due to reduced P450 oxidoreductase expression, which might act as major predictive determinant of sensitivity to HAPs.
In conclusion, evofosfamide with IR is a potent combined treatment modality against hypoxic tumors. However, the efficacy and the therapeutic outcome of this combined treatment modality is, as indicated here in preclinical tumor models, dependent on scheduling parameters and tumor type, which is most probably related to the status of respective HAP-activating oxidoreductases. Further biomarker development is necessary for the launch of successful clinical trials.
... However, unlike O 2 , these agents are not being metabolized by cells through which they penetrate thus able to diffuse beyond the oxygen diffusion distance [19]. With misonidazole and metronidazole being the prototype members of nitroimidazole class of hypoxic radiosensitizers (other classes of radiosensitizers are reviewed elsewhere by Ahn and Brown [20]) (Fig. 2B), many clinical studies were conducted but revealed rather disappointing results. They had very little efficacy in improving the clinical response while there was a high incidence of peripheral neuropathy when multiple doses were given [21]. ...
Tumor hypoxia, a common feature occurring in nearly all human solid tumors is a major contributing factor for failures of anticancer therapies. Because ionizing radiation depends heavily on the presence of molecular oxygen to produce cytotoxic effect, the negative impact of tumor hypoxia had long been recognized. In this review, we will highlight some of the past attempts to overcome tumor hypoxia including hypoxic radiosensitizers and hypoxia-selective cytotoxin. Although they were (still are) a very clever idea, they lacked clinical efficacy largely because of 'reoxygenation' phenomenon occurring in the conventional low dose hyperfractionation radiotherapy prevented proper activation of these compounds. Recent meta-analysis and imaging studies do however indicate that there may be a significant clinical benefit in lowering the locoregional failures by using these compounds. Latest technological advancement in radiotherapy has allowed to deliver high doses of radiation conformally to the tumor volume. Although this technology has brought superb clinical responses for many types of cancer, recent modeling studies have predicted that tumor hypoxia is even more serious because 'reoxygenation' is low thereby leaving a large portion of hypoxic tumor cells behind. Wouldn't it be then reasonable to combine hypoxic radiosensitizers and/or hypoxia-selective cytotoxin with the latest radiotherapy? We will provide some preclinical and clinical evidence to support this idea hoping to revamp an enthusiasm for hypoxic radiosensitizers or hypoxia-selective cytotoxins as an adjunct therapy for radiotherapy.
... One of these methods is the creation of a temporary intermediate (usually a one-electron product) in reductive reaction, which is able to back-oxidized to the original form by the molecular oxygen present in normoxic condition. In the other method, the HAP can compete directly with oxygen at the active site of the reducing enzyme (64). HAPs include metal complexes, nitrocyclic compounds, aliphatic N-oxides, aromatic Noxides, and Quinone (65). ...
Hypoxia is a common feature of malignant tumors. There is an interactive connection between hypoxia and chemoresistance, radioresistance, invasiveness, and angiogenesis. Therefore, tumor hypoxia has been considered as a validated target for treating cancer. This review focuses on the role of hypoxia on chemoresistance and radioresistance. In addition, we address several approaches targeting tumor hypoxia, known as hypoxia-targeted therapy.
... Non-invasive clinical imaging has potential to improve patient care by producing biomarkers that alter clinical decision making (40,41). In the case of hypoxia, a clinically translational imaging biomarker has potential to be prognostic and/or predictive (identifying presence of hypoxia and quantifying hypoxic fraction/volume prior to therapy), to assist treatment planning (mapping targets for radiation boost or adaptive therapy) (42), or to monitor therapy induced changes in tumor hypoxia, for example following radiosensitisation or hypoxia activated cytotoxic therapy (10,43). ...
There is a clinical need for non-invasive biomarkers of tumor hypoxia for prognostic and predictive studies, radiotherapy planning and therapy monitoring. Oxygen enhanced MRI (OE-MRI) is an emerging imaging technique for quantifying the spatial distribution and extent of tumor oxygen delivery in vivo. In OE-MRI, the longitudinal relaxation rate of protons (∆R1) changes in proportion to the concentration of molecular oxygen dissolved in plasma or interstitial tissue fluid. Therefore, well-oxygenated tissues show positive ∆RR1. We hypothesized that the fraction of tumor tissue refractory to oxygen challenge (lack of positive ∆RR1, termed "Oxy-R fraction") would be a robust biomarker of hypoxia in models with varying vascular and hypoxic features. Here we demonstrate that OE-MRI signals are accurate, precise and sensitive to changes in tumor pOR2 in highly vascular 786-0 renal cancer xenografts. Furthermore, we show that Oxy-R fraction can quantify the hypoxic fraction in multiple models with differing hypoxic and vascular phenotypes, when used in combination with measurements of tumor perfusion. Finally, Oxy-R fraction can detect dynamic changes in hypoxia induced by the vasomodulator agent hydralazine. In contrast, more conventional biomarkers of hypoxia (derived from blood oxygenation-level dependent MRI and dynamic contrast-enhanced MRI) did not relate to tumor hypoxia consistently. Our results show that the Oxy-R fraction accurately quantifies tumor hypoxia non-invasively and is immediately translatable to the clinic.
... The majorities of HAPs described to date are designed to release DNA damaging cytotoxin and thus killed cancer cells [37]. Among these HAPs, PR-104 and NLCQ-1 are DNA crosslinker and intercalator, respectively [38,39]; while AQ4N as well as TPZ were revealed to be topo II poisons [8,40]. ...
In spite of the tremendous efforts dedicated to developing hypoxia-activated prodrugs, no agents yet have been approved for clinical therapy. In the present study, the hypoxic selective anti-cancer activity as well as the cellular target of a novel tirapazamine (TPZ) analogue, 7-methyl-3-(3-chlorophenyl)-quinoxaline-2-carbonitrile 1,4-dioxide (Q6) were investigated. Q6 implemented anti-cancer effects via poisoning topoisomerase II (topo II) under hypoxia. Modified trapped in agarose DNA immunostaining (TARDIS) assay showed more topo II-DNA cleavage complexes trapped by Q6 than TPZ at even lower concentration. In addition, by introducing ataxia-telangiectasia-mutated (ATM) kinase inhibitors caffeine and KU-60019, we displayed that Q6-triggered apoptosis was attributed, at least partially, to DNA double-strand breaks generated by the topo II-targeting effect. Collectively, Q6 stood out for its better hypoxia-selectivity and topo II-poisoning than the parental compound TPZ. All these data shed light on the research of Q6 as a promising hypoxia-activated prodrug candidate for human hepatocellular carcinoma therapy.
... 27 Hypoxic tumour cells can be directly targeted using cytotoxic agents that induce DNA damage only under low oxygen; these include the bioreductive drugs, tirapazamine and apaziquone. 66,67 A newer drug, TH-302 (a 2-nitroimidazole triggered hypoxia-activated cytotoxin) directly decreases the hypoxic fraction in xenografts of varying histology and is undergoing Phase II-III clinical trials in combination with chemotherapy. 68 Additional targeting of hypoxic subregions can be achieved by targeting HIF-1-dependent transcription or targeting the unfolded protein response, which controls gene translation under cellular stress (e.g. ...
Abstract Prostate cancer (CaP) is the most commonly diagnosed malignancy in males in the Western world with one in six males diagnosed in their lifetime. Current clinical prognostication groupings use pathologic Gleason score, pre-treatment prostatic-specific antigen and Union for International Cancer Control-TNM staging to place patients with localized CaP into low-, intermediate- and high-risk categories. These categories represent an increasing risk of biochemical failure and CaP-specific mortality rates, they also reflect the need for increasing treatment intensity and justification for increased side effects. In this article, we point out that 30-50% of patients will still fail image-guided radiotherapy or surgery despite the judicious use of clinical risk categories owing to interpatient heterogeneity in treatment response. To improve treatment individualization, better predictors of prognosis and radiotherapy treatment response are needed to triage patients to bespoke and intensified CaP treatment protocols. These should include the use of pre-treatment genomic tests based on DNA or RNA indices and/or assays that reflect cancer metabolism, such as hypoxia assays, to define patient-specific CaP progression and aggression. More importantly, it is argued that these novel prognostic assays could be even more useful if combined together to drive forward precision cancer medicine for localized CaP.
... A related approach is based on the targeting of hypoxia. Hypoxia-activated prodrugs or bioreductive drugs are designed to deliver a cytotoxic agent to hypoxic areas within a tumour [140][141][142][143]. Several clinical trials have shown promising results for this class of drugs, e.g. a phase IIb trial of TH-302, a hypoxia-activated prodrug, in combination with gemcitabine in patients with pancreatic cancer [144]. ...
Major changes in intra- and extracellular pH homoeostasis are shared features of most solid tumours. These changes stem in large part from the metabolic shift of most cancer cells towards glycolytic metabolism and other processes associated with net acid production. In combination with oncogenic signalling and impact from factors in the tumour microenvironment, this upregulates acid-extruding plasma membrane transport proteins which maintain intracellular pH normal or even more alkaline compared with that of normal cells, while in turn acidifying the external microenvironment. Mounting evidence strongly indicates that this contributes significantly to cancer development by favouring e.g. cancer cell migration, invasion and chemotherapy resistance. Finally, while still under-explored, it seems likely that non-cancer cells in the tumour microenvironment also exhibit altered pH regulation and that this may contribute to their malignant properties. Thus, the physical tumour microenvironment and the cancer and stromal cells within it undergo important reciprocal interactions which modulate the tumour pH profile, in turn severely impacting on the course of cancer progression. Here, we summarize recent knowledge of tumour metabolism and the tumour microenvironment, placing it in the context of tumour pH regulation, and discuss how interfering with these properties may be exploited clinically.
... The present study has implications for targeted anticancer prodrug approaches, as most are limited by spatial heterogeneity in prodrug activation (3,4,88). The approach is also potentially applicable to hypoxia-targeting strategies that utilize prodrugs such as gene-directed enzyme prodrug therapy approaches in which the prodrug-activating enzyme is delivered using macrophages that accumulate in hypoxic tumor regions (89), or obligate anaerobic bacteria (90). In approaches with a different spatial distribution of prodrug-activating regions relative to non-activating regions and blood vessels the optimum conditions may differ and could be identified in the future using SR-PK/PD modeling. ...
Hypoxia contributes to resistance of tumors to some cytotoxic drugs and to radiotherapy, but can in principle be exploited with hypoxia-activated prodrugs (HAP). HAP in clinical development fall into two broad groups. Class I HAP (like the benzotriazine N-oxides tirapazamine and SN30000), are activated under relatively mild hypoxia. In contrast, Class II HAP (such as the nitro compounds PR-104A or TH-302) are maximally activated only under extreme hypoxia, but their active metabolites (effectors) diffuse to cells at intermediate O2 and thus also eliminate moderately hypoxic cells. Here, we use a spatially resolved pharmacokinetic/pharmacodynamic (SR-PK/PD) model to compare these two strategies and to identify the features required in an optimal Class II HAP. The model uses a Green's function approach to calculate spatial and longitudinal gradients of O2, prodrug, and effector concentrations, and resulting killing in a digitized 3D tumor microregion to estimate activity as monotherapy and in combination with radiotherapy. An analogous model for a normal tissue with mild hypoxia and short intervessel distances (based on a cremaster muscle microvessel network) was used to estimate tumor selectivity of cell killing. This showed that Class II HAP offer advantages over Class I including higher tumor selectivity and greater freedom to vary prodrug diffusibility and rate of metabolic activation. The model suggests that the largest gains in class II HAP antitumor activity could be realized by optimizing effector stability and prodrug activation rates. We also use the model to show that diffusion of effector into blood vessels is unlikely to materially increase systemic exposure for realistic tumor burdens and effector clearances. However, we show that the tumor selectivity achievable by hypoxia-dependent prodrug activation alone is limited if dose-limiting normal tissues are even mildly hypoxic.
... In this study, the observation that the prognostic value of low pO 2 and increased expression of hypoxia-associated markers in situ are independent of radiation dose suggest that eradication of the aggressive hypoxic subfraction may require escalation in both local and systemic therapies. For example, this could lead to the use of combined modality therapies using precision surgery or radiotherapy plus androgen deprivation therapy ) and/or selective and hypoxia-targeted systemic agents Ahn and Brown 2007 ;Meng et al. 2012 ;Chan and Bristow 2010 ). ...
Intratumoral hypoxia is prevalent in many solid tumors and is a marker of poor clinical prognosis in prostate cancer. The presence of hypoxia is associated with increased chromosomal instability, gene amplification, downregulation of DNA damage repair pathways, and altered sensitivity to agents that damage DNA. These genomic changes could also lead to oncogene activation or tumor suppressor gene inactivation during prostate cancer progression. We review here the concept of repair-deficient hypoxic tumor cells that can adapt to low oxygen levels and acquire an aggressive "unstable mutator" phenotype. We speculate that hypoxia-induced genomic instability may also be a consequence of aberrant mitotic function in hypoxic cells, which leads to increased chromosomal instability and aneuploidy. Because both hypoxia and aneuploidy are prognostic factors in prostate cancer, a greater understanding of these biological states in prostate cancer may lead to novel prognostic and predictive tests and drive new therapeutic strategies in the context of personalized cancer medicine.
... [10] At the same time the presence of more severe and extensive hypoxia in tumours than in normal tissues provides a physiological target that can potentially be exploited as a basis for tumour selectivity. [3,111213141516 Several prodrugs that are selectively activated under hypoxia are currently in clinical or preclinical development,17181920 including the benzotriazine-di-N-oxide tirapazamine (TPZ;Fig. 1). ...
he therapeutic activity of anticancer agents depends critically on their ability to penetrate through tumour tissue to reach their target cells, a requirement that is especially important for hypoxia-activated prodrugs. Here we use multicellular layers (MCL) grown in vitro from HT29 colon carcinoma cells to measure tissue diffusion coefficients (Dmcl) of 67 structurally diverse benzotriazine di-N-oxides (analogues of the hypoxia-activated prodrug tirapazamine) plus four miscellaneous compounds. An algorithm was developed to predict Dmcl from physicochemical parameters (molecular weight, octanol/water partition coefficient at pH 7.4, number of hydrogen bond donors and acceptors); the fitted multivariate relationship had an explained variance (R2) of 0.907 and predictive power (Q2) of 0.879. Using a subset of nine compounds tested as a single cassette, the algorithm was shown to apply, with some adjustment of coefficients, to MCLs from three other tumour cell lines with differing cell packing densities (SiHa, HCT8-Ea, and HCT8-Ra). The demonstrated relationships provide tools for optimizing extravascular transport of anticancer agents during lead optimization.
... Hypoxic cancer cells are also responsible for tumor vasculature and growth (Vaupel and Mayer, 2007). Although certain drugs are used to target hypoxic cancer cells, there still remains a great need for a fast cytotoxic assay to measure hypoxic resistance that will be useful to screen better hypoxic drugs (Ahn and Brown, 2007). The results demonstrated that HEDS assay can be used to measure the hypoxic resistance of cancer cells to radiation. ...
Cell viability assays have a variety of well known practical and technical limitations. All the available approaches have disadvantages, such as non-linearity, high background and cumbersome protocols. Several commonly used tetrazolium chemicals rely upon generation of a colored formazan product formed by mitochondrial reduction of these compounds via phenazine methosulfate (PMS). However, sensitivity is inherently limited because their reduction relies on mitochondrial bioreduction and cellular transport of PMS, as well as accessibility to tetrazolium chemicals. In this study, we identify hydroxethyldisulfide (HEDS) as an inexpensive probe that can measure cellular metabolic activity without the need of PMS. In tissue culture medium, HEDS accurately quantitated metabolically active live cells in a linear manner superior to tetrazolium based and other assays. Cell toxicity produced by chemotherapeutics (cisplatin, etoposide), oxidants (hydrogen peroxide, acetaminophen), toxins (phenyl arsine oxide, arsenite) or ionizing radiation was rapidly determined by the HEDS assay. We found that HEDS was superior to other commonly used assays for cell viability determinations in its solubility, membrane permeability, and intracellular conversion to a metabolic reporter that is readily transported into the extracellular medium. Our findings establish the use of HEDS in a simple, rapid and low cost assay to accurately quantify viable cells.
... Steep oxygen gradients in the tissue adjacent to blood vessels result in near-zero partial pressures of oxygen (pO 2 ) at distances as short as 100μm from the nearest blood vessel [53][54][55]. The development of prodrugs that reversibly release highly cytotoxic compounds under hypoxic conditions is a promising anticancer strategy that may overcome the inherent resistance of cells in hypoxic regions in solid tumors [56,57], while anaerobic microbial spores that germinate under hypoxic conditions are also being explored in preclinical models [57]. ...
The proliferative cancer cell paradigm that has driven cancer drug development for the past 50 years has failed to generate treatments that cure most metastatic adult cancers. This view is supported not only by cumulative experience with conventional cytotoxic anticancer drugs, but also by the application of highly-targeted anticancer compounds against, for example, BCR-ABL in CML and mutant BRAF in metastatic melanoma. Such drugs often send their respective cancers into complete molecular remission but fail to effect cures because a small population of quiescent or slowly self-renewing cancer cells that are drug and radiation resistant survive treatment indefinitely. This review explores the grounds for an emerging cancer paradigm that views cancer as a disorganized tissue with hierarchical cellular compartments in which the boudaries are less well-defined than in normal tissues with plasticity controlled by epigenetic changes mediated by the local microenvironment. Increased metabolic flexibility and adaptability give cancer cells an additional survival advantage that may be able to be targeted with drugs like metformin. Combining approaches that target the increased metabolic flexibility of cancer cells as well as ablating rapidly-proliferating cells and self-renewing cancer stem cells in individual cancers are needed to address the holy grail of cancer cure.
... Attempts to target tumor hypoxia currently focus on agents that exploit the molecular phenotype of hypoxic cells, especially stabilized HIF-1 and its transcriptional targets (5), and on hypoxia-activated prodrugs (HAP, also called hypoxic cytotoxins or bioreductive drugs). The latter are reduced enzymatically to DNA-reactive cytotoxins via pathways that are inhibited by molecular oxygen (3,(6)(7)(8). A complicating factor in targeting HIF-1 is that its activity is subject to complex oxygen-independent regulation (9)(10)(11). ...
PR-104, currently in clinical trial, is converted systemically to the dinitrobenzamide nitrogen mustard prodrug PR-104A, which is reduced selectively in hypoxic cells to cytotoxic hydroxylamine (PR-104H) and amine (PR-104M) metabolites. Here, we evaluate the roles of this reductive metabolism, and DNA interstrand cross-links (ICL), in the hypoxic and aerobic cytotoxicity of PR-104. Using a panel of 9 human tumor cell lines, cytotoxicity was determined by clonogenic assay after a 2-hour aerobic or hypoxic exposure to PR-104A. PR-104H and PR-104M were determined by high performance liquid chromatography/mass spectrometry, and ICL with the alkaline comet assay. Under hypoxia, the relationship between ICL and cell killing was similar between cell lines. Under aerobic conditions, there was a similar relationship between ICL and cytotoxicity, except in lines with very low rates of aerobic reduction of PR-104A (A2780, C33A, H1299), which showed an ICL-independent mechanism of PR-104A cytotoxicity. Despite this, in xenografts from the same lines, the frequency of PR-104-induced ICL correlated with clonogenic cell killing (r(2) = 0.747) with greatest activity in the fast aerobic metabolizers. In addition, changing levels of hypoxia in SiHa tumors modified both ICL frequency and tumor growth delay in parallel. We conclude that both aerobic and hypoxic nitroreduction of PR-104A contribute to the monotherapy antitumor activity of PR-104 in human tumor xenografts, and that ICL are responsible for its antitumor activity and represent a broadly applicable biomarker for tumor cell killing by this novel prodrug.
Hypoxia, or low oxygen tension, is a universal feature of solid tumors. The tumor microenvironment consists of regions of chronic and acute hypoxia that develop due to the irregular distribution of tumor vessels and limited oxygen diffusion within tumor tissue. While exposure to prolonged or severe hypoxia can be toxic to both normal and cancer cells, cancer cells take particular advantage of their ability to initiate a transcriptional program that allows them to adapt and thrive under these harsh conditions. Importantly, hypoxia upregulates a wide array of signal transduction pathways that drive angiogenesis, cell survival, metabolism, immune evasion, invasion and metastasis. For these reasons, the presence of intratumoral hypoxia is an adverse prognostic factor for patients with solid tumors and is a key component contributing to therapeutic resistance and metastasis. Understanding of the signaling mechanisms and physiological changes that occur in response to hypoxia will lead to alternative and more efficient therapeutic approaches.
Bromohexitols represent a potent class of DNA‐alkylating carbohydrate chemotherapeutics that has been largely ignored over the last decades due to safety concerns. The limited structure−activity relationship data available reveals significant changes in cytotoxicity with even subtle changes in stereochemistry. However, no attempts have been made to improve the therapeutic window by rational drug design or by using a prodrug approach to exploit differences between tumour physiology and healthy tissue, such as acidic extracellular pH and hypoxia. Herein, we report the photochemical synthesis of highly substituted endoperoxides as key precursors for dibromohexitol derivatives and investigate their use as microenvironment‐activated prodrugs for targeting cancer cells. One endoperoxide was identified to have a marked increased activity under hypoxic and low pH conditions, indicating that endoperoxides may serve as microenvironment‐activated prodrugs.
3838
Poster Board III-774
Hypoxia is known to be linked to increased metastatic potential and a treatment-resistant phenotype leading to rapid progression and poor prognosis in solid tumors. We confirmed previous data[1] on hypoxia in human multiple myeloma (MM) in the 5T33MM syngeneic murine model of MM by using H&E staining and Hypoxyprobe (Pimonidazole) staining on consecutive serial sections from both naive mice and 5T33MMvv diseased mice. We observed a physiological hypoxic situation in MM diseased bone marrow. Given the contribution of hypoxia to tumor progression and drug resistance, a number of hypoxia-targeted therapeutics are under development. TH-302 is a new hypoxia-activated prodrug (HAP) that is currently being evaluated in the clinical trials as monotherapy and in combination with standard chemotherapy regimens for the treatment of solid tumors. The aims of the current study are (1) to demonstrate the effects of TH302 on MM cells in hypoxic conditions, focusing on apoptosis and cell cycle and associated signaling pathways and (2) to evaluate potential therapeutic effects when used in an experimental mouse MM model. We evaluated the effects of TH-302 in vitro on the murine 5T33MMvt cell line and the human LP-1, MMS-1, RPMI-8226, Karpas MM cell lines. Flow cytometry analysis revealed that TH-302 (0.5-50μM) can induce significant Go/G1 cell cycle phase arrest and apoptosis in hypoxic conditions (both 1% and 0% O2) in a concentration dependent manner, in contrast to normoxic conditions (20% O2) (p<0.001). Western blot confirmed that treatment with TH-302 in hypoxic conditions down-regulates cyclin D1/2/3, CDK4/6 and pRb expressions, but CDK2 expression was not disturbed. Furthermore, treatment with TH-302 in hypoxic conditions down-regulates the anti-apoptotic proteins BCL-2 and BCL-xL, as well as up-regulates the expression of three proapoptotic proteins: cleaved caspase-3, 9 and PARP. The expression pattern of Bax was however not influenced. The expression of p21 and p27 decreased in hypoxic condition after treatment with TH-302. Further studies conducted in the 5T33MMvv mouse model demonstrated that animals treated prophylactically with TH-302 (12.5 mg/kg, 25 mg/kg and 50 mg/kg, i.p.) for 3 weeks from day 1 after tumor inoculation showed decreased serum paraprotein (12.5 mg/kg, 32% decrease, p<0.05; 25 mg/kg, 77% decrease, p<0.001; 50 mg/kg, 54% decrease, p<0.001), compared to vehicle-treated 5T33MMvv mice (n=10). The frequency of apoptotic multiple myeloma cells in bone marrow sections was also significantly increased (12.5 mg/kg, 2.5 fold, p<0.05; 25mg/kg, 2.1 fold, p<0.05; 50mg/kg, 3.1 fold, p<0.01). Treatment with TH-302 resulted in no adverse events, any observable detriment to the mice or weight loss (p>0.05). In conclusion, these results show that hypoxia-activated treatment with TH-302 activates apoptosis and induces cell cycle arrest in MM cells, under hypoxic conditions, both in vitro and in vivo and therefore represents a promising therapeutic approach for multiple myeloma. Reference [1] Simona Colla, Paola Storti, Gaetano Donofrio, et al. Hypoxia and Hypoxia Inducible Factor (HIF)-1α in Multiple Myeloma: Effect on the Pro-Angiogenic Signature of Myeloma Cells and the Bone Marrow Microenvironment, 50th ASH annual meeting, http://ash.confex.com/ash/2008/webprogram/Paper13156.html
Disclosures
Handisides: Treshold Pharmaceuticals: Employment. Liu:Treshold Pharmaceuticals: Employment. Sun:Treshold Pharmaceuticals: Employment. Hart:Treshold Pharmaceuticals: Employment. Vanderkerken:Treshold Pharmaceuticals: Research Funding.
Hypoxia is a typical feature of solid tumors. To detect hypoxic tumor cells, we designed new selective turn-on probes by conjugating (1-methyl-2-nitro-1H-imidazol-5-yl)methanol to the near-infrared fluorescence probe DCPO through an ether linkage and bis-carbamate linkage specifically. The proposed activation mechanism was demonstrated through the nitroreductase and cytochrome P450 assays in vitro. However, two probes revealed different hypoxia selectivities when evaluated on H460, HeLa and A549 cell lines. The hypoxia selectivity of IOD was higher than that of IND. The probe IOD (containing the ether linkage) was considered to be a promising hypoxia-selective fluorescent probe.
Radiotherapy is one of the most effective treatment modalities to cure cancer. It has been estimated that radiotherapy used alone or in combination with other modalities was responsible for almost 40% of cancer cures. There is compelling experimental evidence that the DNA is the principal target for radiation-induced cell killing. There is increasing awareness that radiotherapy, although a very effective form of cancer therapy, is associated with a range of both acute and long-term side effects. The International Commission on Radiation Units and Measurements (ICRU) has developed guidelines for prescribing, recording and reporting the dose of the radiation therapy. For small tumours, radiotherapy is typically delivered as a single modality, whereas for locally advanced stages, it is most frequently delivered in association with radiosensitizing agents such as chemotherapy. Brachytherapy is commonly used to treat cervical, uterine and prostate cancers.
We designed new hypoxia-activated prodrugs by conjugating (1-methyl-2-nitro-1H-imidazol-5-yl)methanol with 7-ethyl-10-hydroxy camptothecin (SN-38). Initially, we improved the method of multi-gram scale synthesis of (1-methyl-2-nitro-1H-imidazol-5-yl)methanol, which increased the yield to 42% compared to 8% by the original synthesis method. The improved method was used to synthesize evofosfamide (TH-302) and hypoxia-activated prodrugs of SN-38. Two different linkages between (1-methyl-2-nitro-1H-imidazol-5-yl)methanol and SN-38 were evaluated that afforded different hypoxia-selectivity and toxicity. Compound 16 (IOS), containing an ether linkage, was considered to be a promising hypoxia-selective antitumor agent.
Radiotherapy is one of the most effective treatment modalities to cure cancer. It has been estimated that radiotherapy used alone or in combination with other modalities was responsible for almost 40% of cancer cures. There is compelling experimental evidence that the DNA is the principal target for radiation-induced cell killing. There is increasing awareness that radiotherapy, although a very effective form of cancer therapy, is associated with a range of both acute and long-term side effects. The International Commission on Radiation Units and Measurements (ICRU) has developed guidelines for prescribing, recording and reporting the dose of the radiation therapy. For small tumours, radiotherapy is typically delivered as a single modality, whereas for locally advanced stages, it is most frequently delivered in association with radiosensitizing agents such as chemotherapy. Brachytherapy is commonly used to treat cervical, uterine and prostate cancers.
Tumour hypoxia is a critically important, but elusive, target in cancer therapy; the importance of eliminating hypoxic cells is underscored by their central roles in tumour progression and resistance to cytotoxic chemotherapy and radiotherapy. While many molecular targets may offer synthetic lethal interactions with hypoxia, the development of prodrugs that are activated to generate cytotoxins by one-electron (1e) reduction in hypoxic cells represents a more direct approach. Although conceptually simple, significant challenges need to be overcome to achieve useful therapeutic activity. These include designing prodrugs able to diffuse efficiently into hypoxic tissue, avoidance of off-target (oxygen-insensitive) two-electron (2e) reduction, maximizing bystander effects from diffusion of the active metabolites to exploit severely hypoxic regions in tumours and (critically) the development of predictive biomarkers for what is in fact a multifaceted target (comprising hypoxia, activating reductases and the molecular determinants of sensitivity to the active metabolites). Here we provide an overview of recent progress towards these goals in the context of four classes of hypoxia-activated prodrugs (HAPs) in clinical trial or in advanced preclinical development, namely benzotriazine di-oxides (tirapazamine and SN30000), the dinitrobenzamide mustard (DNBM) PR-104, the phosphoramidate mustard TH-302 and nitrochloromethylbenzindoline (nitroCBI) prodrugs of potent DNA minor groove alkylators.
Survival and maintenance of normal hematopoietic stem cells (HSCs) are regulated by bone marrow (BM) microenvironment. The experimental evidence indicates the vital role of hypoxia in maintenance of the primitive quiescent HSCs within the discrete subendosteal BM niches. Recent findings demonstrate that in the setting of hematologic malignancies BM is highly hypoxic, and that progression of the disease is associated with expansion of hypoxic niches and stabilization of the oncogenic hypoxia-inducible factor-1α (HIF-1α). This chapter will provide an overview of normal and leukemic BM microenvironment with an especial emphasis on pathological hypoxia. We will further describe the development of the hypoxia-activated prodrugs (HAPs) and their applicability in hematological malignancies.
Medicinal Chemistry of Anticancer Drugs, Second Edition, provides an updated treatment from the point of view of medicinal chemistry and drug design, focusing on the mechanism of action of antitumor drugs from the molecular level, and on the relationship between chemical structure and chemical and biochemical reactivity of antitumor agents. Antitumor chemotherapy is a very active field of research, and a huge amount of information on the topic is generated every year. Cytotoxic chemotherapy is gradually being supplemented by a new generation of drugs that recognize specific targets on the surface or inside cancer cells, and resistance to antitumor drugs continues to be investigated. While these therapies are in their infancy, they hold promise of more effective therapies with fewer side effects. Although many books are available that deal with clinical aspects of cancer chemotherapy, this book provides a sorely needed update from the point of view of medicinal chemistry and drug design. • Presents information in a clear and concise way using a large number of figures • Historical background provides insights on how the process of drug discovery in the anticancer field has evolved • Extensive references to primary literature.
PGRMC1 (progesterone receptor membrane component 1) は1996年にブタの肝細胞膜から発見されたプロゲステロンレセプターの一つであり, ヒトの腎臓や肝臓, 子宮内膜, 卵巣に比較的発現が強くみられ, ホルモンや電解質などの代謝作用や, アポトーシスを抑制することなどが様々な細胞で解明された. 癌細胞では乳癌や甲状腺癌, 大腸癌, 肺癌, 卵巣癌などにも発現を認め, 特に乳癌では予後因子との関連を示唆する報告があった.
ヒト子宮内膜癌細胞Ishikawa cellにおいてもPGRMC1は発現を強く認め, PGRMC1をノックダウンするとPI3K/AKT経路においてリン酸化AKTとPDK1の発現低下を認めたが, MAPK経路には影響を及ぼさなかった.
またPGRMC1をノックダウンしたIshikawa cellではアポトーシスが誘導され, 低酸素ストレス下では細胞活性が抑制され抗腫瘍効果を示した.
子宮内膜癌細胞株Ishikawa cellにおいてPGRMC1はその細胞維持にPI3K/AKT経路のPDK1-AKT間でクロストークしており, PGRMC1を抑制することでIshikawa cellを制御できることが解明され, PGRMC1は子宮内膜癌の治療において一つの分子標的となり得ることが示唆された.
There are some data to suggest that insufficient sleep, including short sleep duration and sleep disruption, may be associated with an increased risk of cancer. We investigated the association between sleep duration and sleep disruption and risk of prostate cancer.
Prospective cohort study.
Sweden.
A total of 14,041 men in the Swedish National March Cohort.
None.
Habitual sleep duration and sleep disruption were self-reported in 1997. Prostate cancer diagnoses, including lethal (metastases at diagnosis or death from prostate cancer) and advanced (stage T4, N1, or M1 at diagnosis or death from prostate cancer), were determined from linkage to nationwide cancer registries through 2010. We conducted Cox proportional hazards regression adjusted for potential confounding variables. During 13 years of follow-up, we identified 785 cases of incident prostate cancer, including 118 lethal and 127 advanced cases. Four percent of men reported sleeping 5 h or less a night, and 2% reported sleeping 9 h or more per night. We found no association between sleep duration and risk of prostate cancer overall or for advanced/lethal disease. We also did not find an association between prostate cancer and sleep disruption, as defined by difficulty falling asleep, difficulty maintaining sleep, sleep quality, and restorative power of sleep.
In this large prospective study from Sweden, we found no association between habitual sleep duration or sleep disruption and risk of prostate cancer.
Copyright © 2015 Associated Professional Sleep Societies, LLC. All rights reserved.
Hypoxia in solid tumors is one of the seminal mechanisms for developing aggressive trait and treatment resistance in solid tumors. This evolutionarily conserved biological mechanism along with derepression of cellular functions in cancer, although resulting in many challenges, provide us with opportunities to use these adversities to our advantage. Our ability to use molecular imaging to characterize therapeutic targets such as hypoxia and apply this information for therapeutic interventions is growing rapidly. Evaluation of hypoxia and its biological ramifications to effectively plan appropriate therapy that can overcome the cure-limiting effects of hypoxia provides an objective means for treatment selection and planning. Fluoromisonidazole (FMISO) continues to be the lead radiopharmaceutical in PET imaging for the evaluation, prognostication, and quantification of tumor hypoxia, one of the key elements of the tumor microenvironment. FMISO is less confounded by blood flow, and although the images have less contrast than FDG-PET, its uptake after 2 hours is an accurate reflection of inadequate regional oxygen partial pressure at the time of radiopharmaceutical administration. By virtue of extensive clinical utilization, FMISO remains the lead candidate for imaging and quantifying hypoxia. The past decade has seen significant technological advances in investigating hypoxia imaging in radiation treatment planning and in providing us with the ability to individualize radiation delivery and target volume coverage. The presence of widespread hypoxia in the tumor can be effectively targeted with a systemic hypoxic cell cytotoxin or other agents that are more effective with diminished oxygen partial pressure, either alone or in combination. Molecular imaging in general and hypoxia imaging in particular will likely become an important in vivo imaging biomarker of the future, complementing the traditional direct tissue sampling methods by providing a snap shot of a primary tumor and metastatic disease and in following treatment response and will serve as adjuncts to personalized therapy.
Published by Elsevier Inc.
Very recent studies revealed that obstructive sleep apnoea (OSA) is a contributor of the increased incidence and mortality of cancer in humans, but mechanisms of how OSA promotes tumorigenesis remains largely unknown. We investigated whether intermittent hypoxia with and without hypercapnia plays a role in tumorigenesis.
First, Sprague-Dawley (SD) male rats (12 weeks old) were subjected to different hypoxia exposures: intermittent hypoxia and intermittent hypoxia with hypercapnia; continuous hypoxia and normal air. The systemic application of chronic fast rate hypoxia with or without hypercapnia mimicked severe OSA patients with apnoea/hypopnea index equivalent to 60 events per hour. Then routine blood tests were performed and the levels of brain derived neurotrophic factor (BDNF) and miR-34a were examined.
In contrast to intermittent hypoxia with hypercapnia, both intermittent hypoxia and continuous hypoxia treatments caused significantly higher levels of haematology parameters than normoxia treatments. Compared to normoxia, intermittent hypoxia with hypercapnia exposure resulted in substantial decrease of serum BDNF and, miR-34a in the lower brainstem, while less pronounced results were found in intermittent hypoxia and continuous hypoxia exposure.
The exposure of intermittent hypoxia with or without hypercapnia, mimicking the situations in severe OSA patients, was associated with, or even promoted tumorigenesis.
Due to the involvement of nitric oxide (NO) in numerous and diverse physiological processes, site-directed delivery of therapeutic NO in order to minimize unwanted side-effects is necessary. O(2)-(4-Nitrobenzyl) diazeniumdiolates are designed as substrates for Escherichia coli nitroreductase (NTR), an enzyme that is frequently used to facilitate directed delivery of cytotoxic species to cancers. O(2)-(4-Nitrobenzyl) diazeniumdiolates are found to be stable in aqueous buffer but are metabolized by NTR to produce NO. A cell viability assay revealed that cytotoxic effects of O(2)-(4-nitrobenzyl)1-(2-methylpiperidin-1-yl)diazen-1-ium-1,2-diolate (4b) towards two cancer cell lines is significantly enhanced in the presence of NTR suggesting the potential for use of this compound in nitric oxide-based directed prodrug therapy.
Hypoxia is an important factor in tumor growth. It is associated with resistance to conventional anticancer treatments. Gene therapy targeting hypoxic tumor cells therefore has the potential to enhance the efficacy of treatment of solid tumors. Transfection of a panel of tumor cell lines with plasmid constructs containing hypoxia-responsive promoter elements from the genes, vascular endothelial growth factor (VEGF) and erythropoietin, linked to the minimal cytomegalovirus (mCMV) or minimal interleukin-2 (mIL-2) promoters showed optimum hypoxia-inducible luciferase reporter gene expression with five repeats of VEGF hypoxic-response element linked to the mCMV promoter. Adenoviral vectors using this hypoxia-inducible promoter to drive therapeutic transgenes produced hypoxia-specific cell kill of HT1080 and HCT116 cells in the presence of prodrug with both herpes simplex virus thymidine kinase/ganciclovir and nitroreductase (NTR)/CB1954 prodrug-activating systems. Significant cytotoxic effects were also observed in patient-derived human ovarian cancer cells. The NTR/CB1954 system provided more readily controllable transgene expression and so was used for in vivo experiments of human HCT116 xenografts in nude mice. Subjects treated intratumorally with Ad-VEGFmCMV-NTR and intraperitoneal injection of CB1954 demonstrated a statistically significant reduction in tumor growth. Immunohistochemistry of treated xenografts showed a good correlation between transgene expression and hypoxic areas. Further investigation of these hypoxia-inducible adenoviral vectors, alone or in combination with existing modalities of cancer therapy, may aid in the future development of successful Gene-Directed Enzyme Prodrug Therapy systems, which are much needed for targeting solid tumors.
Hypoxia is a feature of most tumours, albeit with variable incidence and severity within a given patient population. It is a negative prognostic and predictive factor owing to its multiple contributions to chemoresistance, radioresistance, angiogenesis, vasculogenesis, invasiveness, metastasis, resistance to cell death, altered metabolism and genomic instability. Given its central role in tumour progression and resistance to therapy, tumour hypoxia might well be considered the best validated target that has yet to be exploited in oncology. However, despite an explosion of information on hypoxia, there are still major questions to be addressed if the long-standing goal of exploiting tumour hypoxia is to be realized. Here, we review the two main approaches, namely bioreductive prodrugs and inhibitors of molecular targets upon which hypoxic cell survival depends. We address the particular challenges and opportunities these overlapping strategies present, and discuss the central importance of emerging diagnostic tools for patient stratification in targeting hypoxia.
Hypoxia is a common condition found in a wide range of solid tumors and is often associated with poor prognosis. Hypoxia increases tumor glycolysis, angiogenesis, and other survival responses, as well as invasion and metastasis by activating relevant gene expressions through hypoxia-inducible factors (HIF). HIF-1α and HIF-2α undergo oxygen-dependent regulation, and their overexpression is frequently associated with metastasis and poor clinical outcomes. Recent studies show that each step of the metastasis process, from the initial epithelial-mesenchymal transition to the ultimate organotropic colonization, can potentially be regulated by hypoxia, suggesting a master regulator role of hypoxia and HIFs in metastasis. Furthermore, modulation of cancer stem cell self-renewal by HIFs may also contribute to the hypoxia-regulated metastasis program. The hypoxia-induced metastatic phenotype may be one of the reasons for the modest efficacy of antiangiogenic therapies and may well explain the recent provocative findings that antiangiogenic therapy increased metastasis in preclinical models. Multiple approaches to targeting hypoxia and HIFs, including HIF inhibitors, hypoxia-activated bioreductive prodrugs, and gene therapies may become effective treatments to prevent or reduce metastasis.
Hypoxia plays an important role in the development of solid tumors and is associated with their therapeutic resistance. There exist three major forms of hypoxia: acute, chronic, and intermittent hypoxia. Previous studies have shown that cancer cells could behave in the form of adaptation to hypoxia in tumor growth, which could result in their biological changes and determine their responses to the therapies. To investigate the tumor cells' adaptation to hypoxia, we recreated two models using two lung cancer cell lines in the presence of intermittent hypoxia, which is characterized by changes in oxygen pressure within the disorganized vascular network. We investigated biological behaviors such as cell cycle, proliferation, radiation sensitivity, apoptosis and migration, hypoxia signal pathway in the lung cancer cells treated with chronic intermittent hypoxia, as well as the role of hypoxia inducible factor 1 there, hypoxia-inducible genes analyzed by real-time RT-PCR chip in H446 cells treated with the model. The results indicated the changes of some hypoxia target gene expressions of those induced by hypoxia, some of which were confirmed by real-time RT-PCR. The cells mediated by irradiation induced resistance to radiation and apoptosis and increased metastasis in lung cancer cells. It was found that such changes were related to hypoxia inducible factor 1, alpha subunit (HIF-1α).
Hypoxia is associated with increased metastatic potential and poor prognosis in solid tumors. In this study, we demonstrated in the murine 5T33MM model that multiple myeloma (MM) cells localize in an extensively hypoxic niche compared with the naive bone marrow. Next, we investigated whether hypoxia could be used as a treatment target for MM by evaluating the effects of a new hypoxia-activated prodrug TH-302 in vitro and in vivo. In severely hypoxic conditions, TH-302 induces G(0)/G(1) cell-cycle arrest by down-regulating cyclinD1/2/3, CDK4/6, p21(cip-1), p27(kip-1), and pRb expression, and triggers apoptosis in MM cells by up-regulating the cleaved proapoptotic caspase-3, -8, and -9 and poly ADP-ribose polymerase while having no significant effects under normoxic conditions. In vivo treatment of 5T33MM mice induces apoptosis of the MM cells within the bone marrow microenvironment and decreases paraprotein secretion. Our data support that hypoxia-activated treatment with TH-302 provides a potential new treatment option for MM.
The objectives of this study were to evaluate the antiproliferation effect of a synthetic quinone-containing compound bis-type triaziquone (BTZQ) on breast cancer cells BC-M1 and MCF-7. At a dose of 0.42 and 0.79 microM, BTZQ showed a 50% inhibition on BC-M1 and MCF-7 cell growth after 24 h treatment, respectively, but reduced to 0.2 and 0.61 microM after 48 h. A low toxic effect was observed for skin fibroblast cell after BTZQ treatment for 48 h at a dose from 0.0625-0.25 microM. BTZQ was more effective in inhibiting growth of breast cancer cells than tamoxifen. Additionally, BTZQ-treated BC-M1 cells under hypoxia condition for 48 h exhibited a higher cytotoxicity than under aerobic condition. Cell cycle analysis revealed the arrest of BC-M1 cells at G2/M phase, with accumulation of apoptotic cells at the sub-G1 phase being enhanced following a rise in dose. The expression levels of caspase-3, caspase-8 and caspase-9 were elevated in both dose- and time-dependent responses. Western blot analysis indicated that BTZQ may up-regulate expression of cyclin B, p21, p53 and cytochrome c, but down-regulate cdk1 expression in a dose-dependent manner, leading to apoptosis of BC-M1 cells. All these results suggested that BTZQ may be a potential anti-breast cancer drug.
Metabolic flexibility is a hallmark of cancer. Although many tumors preferentially use glycolysis in the presence of oxygen for bioenergetic purposes (Warburg effect), the effects of glycolytic metabolism on tumor metastasis have not been investigated. We have employed an extreme model of glycolytic metabolism to investigate the ability of metastatic B16 mouse melanoma cells to grow as primary subcutaneous tumors and to form lung tumors when injected intravenously into syngeneic and immunocompromised mice. Mitochondrial gene-knockout B16rho degrees cells showed delayed subcutaneous tumor growth and, surprisingly, failed to form lung tumors. The results suggest that mitochondrial reactive oxygen species (ROS) may be required for tumor metastasis.
Hypoxia is common in prostate tumours, promoting tumour progression and impairing treatment responses. Hypoxia stimulates angiogenesis but blood vessels formed in tumours are functionally abnormal so the tissue remains hypoxic. Castration treatment is the standard therapy for advanced prostate cancer. In non-malignant prostate tissue castration-induced epithelial cell death is in part mediated by vascular insult and acute hypoxia, but in prostate tumours the cell death response is less prominent and the tumours will eventually relapse. The effect of androgen ablation therapy should therefore be enhanced by additional targeting of the vasculature and hypoxic tumour cells. However if castration fails to kill a sufficiently large number of cells it could by inducing hypoxia make the situation worse. Androgen ablation treatment, may, after the initial vascular insult, result in temporary vascular normalisation and transiently increased tissue oxygen levels. During this time window, which needs to be better defined, the efficacy of cytotoxic drug and radiation treatments are probably enhanced. In order to allow development of more effective treatment strategies for advanced prostate cancer we need to understand the role of hypoxia in prostate cancer progression and treatment responses. With this knowledge we can properly tailor and time additional treatments with androgen ablation.
Conventional tumor therapy is usually based on surgery, radiation and chemotherapy. Treatment with chemotherapeutics is often impeded by dose-limiting toxicities. Therefore, medical scientists sought for tools to improve chemotherapy by directly coupling targeting molecules to cytotoxic substances. This review provides a general overview on the development of targeted drugs designed for tumor therapy. Further carrier-based delivery systems of anti-tumorigenic drugs will not be described here. The targeting moiety is usually an antibody or a fragment thereof. Growth factors, cytokines and ligands are also used as targeting moiety. The targeting moiety is coupled to the toxic moiety either chemically or both components were combined as fusion proteins. In addition to those targeted molecules containing conventional chemotherapeutics, more sophisticated targeted drugs were developed containing protein toxins, such as diphtheria toxin or Pseudomonas exotoxin. Only a small number of these protein toxins inside tumor cells results in efficient killing of the target cell. Several of these targeted toxins are currently in clinical trials. Another targeting mechanism utilizes the activation of formerly harmless substances in the vicinity of tumor cells. This mechanism is referred to as directed enzyme prodrug therapy.
Non-invasive detection of tumor hypoxia using radiolabeled 2-nitroimidazoles has been a major effort during the last two decades. Recent years have witnessed the introduction of several new compounds which are chemically related to [(18)F]fluoromisonidazole (FMISO) but show slight but distinct differences in biodistribution and metabolic clearance. Although [(18)F]FMISO has shown clinical potential it suffers from suboptimal oxygen dependent tissue contrast and newer agents seek to improve this essential feature. The limited data on other interesting tracers keeps the investigators busy at demonstrating the potential advantages over [(18)F]FMISO while efforts should start to concentrate on proving the clinical significance of such techniques in the form of outcome data from image-guided therapy modification. We review here our experiences with two hypoxia-avid agents [(18)F]fluoroerythronitromidazole (FETNIM) and [(18)F] 2-(2-nitro-1-H-imidazol-1-yl)-N-(2,2,3,3,3-pentafluoropropyl)-acetamide (EF5) and focus on the similarities and differences of these two tracers in comparison to other radiolabeled 2-nitroimidazoles. It is recognized that only [(18)F]FMISO has thus far shown clinical utility and newer tracers need to be tested against this circumstance.
The synthesis and antitumor activity in normoxic and hypoxic conditions of a series of pyrazolo[5,1-c][1,2,4]benzotriazine and its related analogues are reported. All compounds were tested on human colorectal adenocarcinoma cell line HCT-8 and for compounds 15 and 20, which show to have selective cytotoxicity in hypoxic and in normoxic conditions respectively, ROS production, cell cycle, and DNA fragmentation were measured. This preliminary study encouraged us to consider 15 and 20 as interesting leads for further optimization.
Interest in DNA binding drugs has increased in recent years due to their importance in the treatment of genome-related diseases, like cancer. A new family of water-soluble DNA binding compounds, the benzothiazolo[3,2- a]quinolinium chlorides (BQCls), is studied here as potential candidates for chemical treatment of solid tumor cells that may encounter low-oxygen environments, a condition known as hypoxia. These compounds are good DNA intercalators; however, no studies have been made of these compounds under hypoxic conditions. This work demonstrates the importance of the nitro-functionality in the DNA binding of 3-nitro-10-methylbenzothiazolo[3,2- a]quinolinium chloride (NBQ-91), which possesses nitro-functionality, and 10-methylbenzothiazolo[3,2- a]quinolinium chloride (BQ-106), which does not. Both NBQ-91 and BQ-106 have similar noncovalent binding affinity toward DNA. Dialysis experiments show that NBQ-91 binds DNA under N2-saturated conditions with increasing concentrations of reducing agent, presumably due to reduction of the nitro-functionality. Conversely, because of the lack of nitro-functionality, the presence of a reducing agent had no effect on BQ-106 binding to DNA under both aerobic and N2-saturated conditions. Clonogenic assays were performed to determine the quinolinium chloride cytotoxicities under both aerobic (95% air and 5% CO2) and hypoxic (80% N2 and 20% CO2) conditions. The calculated ratios of cellular toxicity under aerobic to hypoxic conditions caused by the same concentration of test agent (CTR values) show greater levels of cell death under hypoxia than under aerobic conditions for mitomycin C (MC) (CTR = 0.7 at 1 microM) and NBQ-91 (CTR = 0.4 at 200 microM) than for BQ-106 (CTR = 1.0 at 200 microM), which agreed with the previously reported data for MC and confirmed the importance of nitro-functionality for reactivity under hypoxic conditions. There was no correlation between noncovalent binding affinity constants and their cytotoxicity under hypoxic conditions. Adduct formation between the NBQ-91 and 2'-dG was also assessed by reacting 2'-dG or DNA with NBQ-91 and BQ-106 under N2-saturated conditions in the presence of hypoxanthine and xanthine oxidase (HX/XO). DNA covalent adduct formation was analyzed by two techniques: LC-ESI-MS and Sephadex size exclusion chromatography. LC-ESI-MS results clearly indicate the formation of a prominent molecular ion at masses of 266.0 and 530.58 Da, corresponding to the [M + H](+2) and [M](+) molecular ions of the monitored 2'-dG-NBQ-91 adduct. Results from the Sephadex size exclusion chromatography support these findings because the NBQ-91 elution percentage increases in the presence of HX/XO due to the reduction of the nitro-functionality, which results in covalent binding to DNA. This study reports evidence of the DNA binding capacity of this bioreductive drug. The preferential N2-saturated over aerobic conditions for DNA binding makes NBQ-91 a potential bioreductive compound for hypoxic cell killing.
In a randomized controlled clinical trial of hyperbaric oxygen in the radiotherapy of carcinoma of the bladder a total of 241 cases were contributed by four radiotherapy centres in the United Kingdom. In this trial where in each centre identical radiotherapy was employed for both oxygen and air cases, no benefit was shown with the use of hyperbaric oxygen.
The hypoxic cell radiosensitizer, Ro 07-0582, has now been given in multiple doses to 16 patients. They have received a total of 15-51 g in 3-20 doses. Immediate tolerance was good, and satisfactory plasma levels of the drug were consistently obtained. Neurotoxicity was, however, troublesome: convulsions occurred in the patient given the highest dose, and there was peripheral neuropathy in 11 cases. Tumour concentrations similar to those in plasma were obtained in human tumours, in contrast to the findings in mouse tumours where concentrations are usually below 40% of plasma levels. In the treatment of human tumours, a lower dose of Ro 07-0582 should give useful hypoxic cell sensitization. Although the total dose of Ro 07-0582 must be limited, there is a real prospect that it will give benefit in clinical radiotherapy.
Images
Fig. 4
3-Amino-1,2,4-benzotriazine-1,4-dioxide (SR 4233) is a bioreductive anticancer drug which has a high selective toxicity to hypoxic cells. We have characterized the DNA and chromosome damage in wild-type Chinese hamster ovary (CHO) cells and mutant XR-1 cells after exposure to SR 4233 under hypoxia and compared it to the damage produced by ionizing radiation (gamma-rays). Using the technique of pulsed field gel electrophoresis, we found that the kinetics of rejoining of DNA double-strand breaks in CHO cells after treatment with SR 4233 was concentration dependent, varying from 95% (less than 50 microM) to 10% (200 microM) by 24 h. This contrasted with the dose-independent kinetics exhibited in cells after gamma-ray exposure. XR-1 cells were deficient in rejoining double-strand breaks produced by either SR 4233 or gamma-rays. XR-1 cells were 2-fold more sensitive than wild-type CHO cells to SR 4233 but were 10-fold more sensitive than CHO to gamma-rays. These results suggested that DNA double-strand breaks are involved in hypoxic cell killing by SR 4233, but the specific type of lesion produced is not identical with that causing cell killing by gamma-rays. To further investigate this, we measured chromosome breaks in CHO cells by premature chromosome condensation after equitoxic doses of SR 4233 under hypoxia and gamma-rays. SR 4233 produced lower initial but similar final (after 6 h of repair) numbers of chromosome breaks compared to gamma-rays at equitoxic doses. These results suggest that, at low doses, chromosome breaks can entirely account for hypoxic cell killing by SR 4233 and that chromosome breaks produced by SR 4233 are more damaging and/or more difficult to repair than those produced by gamma-rays.
The drug SR 4233 (3-amino-1,2,4-benzotriazine 1,4-dioxide) is under pharmacological study as the lead compound in a new series of hypoxia-activated drugs, the benzotriazine N-oxides. However, the stable two- and four-electron-reduced metabolites of SR 4233, formed by the successive loss of the two oxygen atoms, are not pharmacologically active. In order to evaluate the possibility of an initial one-electron intermediate as the active species, we have used microsomal reduction and EPR spectroscopy to identify the first free radical reduction product. The unpaired electron is primarily centered on the 1-nitrogen, and the radical is best described as a nitroxide. Results with spin-trapping experiments show that reduction of SR 4233 to a free radical is followed by its air oxidation, resulting in the formation of the superoxide radical. Experiments with specific inhibitors suggest that the drug is being reduced by microsomal NADPH-cytochrome P-450 reductase.
The radiosensitizing properties of the highly electron-affinic nitroketone, para-nitroacetophenone (PNAP) have been investigated in resistant and sensitive bacteria, fern spores, mammalian cells in tissue culture and in suspensions of bacteriophage. Radiosensitization occurs in anoxic suspensions of Serratia marcescens Micrococcus radiodurans and in anoxic preparations of Chinese hamster cells line V79–379A. The sensitization of the mammalian cells (enhancement ratio 1·7 for 0·4 mM PNAP) is not inhibited in the presence of serum protein. No sensitization was observed for the spore of the fern Osmunda regalis.PNAP resembles oxygen in conferring some radioprotection on suspensions of bacteriophage T7 irradiated in broth.
The alkylating activity of reduced diaziquone was studied by the nitrobenzylpyridine (NBP) assay and was compared to those of the parent compound and aziridine-containing (Thio-TEPA). Diaziquone (AZQ) was reduced enzymatically by 2e− using S9 cell fraction from MCF-7 cells which is rich in NAD(P)H:quinone-acceptor oxidoreductase (DT-diaphorase) (QAO) activity. One electron enzymatic reduction was performed with NADPH-cytochrome c reductase. The alkylating activity of AZQ increased 3-fold when reduced by 2e−. This increase was inhibited by dicumarol, an inhibitor of QAO. In contrast, the alkylating activity of AZQ did not increase beyond that of the parent compound when reduced by 1e− using purified NADPH-cytochrome c reductase. Similar results were obtained when AZQ was reduced chemically with borohydride (2e−) and with NADPH (1e−). Anaerobic incubations of AZQ with the S9 fraction of MCF-7 cells (2e− reduction) resulted in an increase in NBP alkylation over its aerobic counterpart (1.8-fold) while maintaining the near 3-fold increase in alkylation over untreated AZQ. In contrast, AZQ incubations with NADPH-cytochrome c reductase (1e− reduction) under the same conditions did not result in an NBP alkylation increase over untreated AZQ. These results indicate that AZQ hydroquinone is most likely the responsible species for the observed alkylation of this antitumor agent to DNA and other nucleophiles. The results also suggest that NAD(P)H:quinone-acceptor oxidoreductase is a very important enzyme in the bioactivation of AZQ.
PURPOSE: A phase III trial, Cisplatin and Tirapazamine in Subjects with Advanced Previously Untreated Non–Small-Cell Lung Tumors (CATAPULT I), was designed to determine the efficacy and safety of tirapazamine plus cisplatin for the treatment of non–small-cell lung cancer (NSCLC).
PATIENTS AND METHODS: Patients with previously untreated NSCLC were randomized to receive either tirapazamine (390 mg/m ² infused over 2 hours) followed 1 hour later by cisplatin (75 mg/m ² over 1 hour) or 75 mg/m ² of cisplatin alone, every 3 weeks for a maximum of eight cycles.
RESULTS: A total of 446 patients with NSCLC (17% with stage IIIB disease and pleural effusions; 83% with stage IV disease) were entered onto the study. Karnofsky performance status (KPS) was ≥ 60 for all patients (for 10%, KPS = 60; for 90%, KPS = 70 to 100). Sixty patients (14%) had clinically stable brain metastases. The median survival was significantly longer (34.6 v 27.7 weeks; P = .0078) and the response rate was significantly greater (27.5% v 13.7%; P < .001) for patients who received tirapazamine plus cisplatin (n = 218) than for those who received cisplatin alone (n = 219). The tirapazamine-plus-cisplatin regimen was associated with mild to moderate adverse events, including acute, reversible hearing loss, reversible, intermittent muscle cramping, diarrhea, skin rash, nausea, and vomiting. There were no incremental increases in myelosuppression, peripheral neuropathy, or renal, hepatic, or cardiac toxicity and no deaths related to tirapazamine.
CONCLUSION: The CATAPULT I study shows that tirapazamine enhances the activity of cisplatin in patients with advanced NSCLC and confirms that hypoxia is an exploitable therapeutic target in human malignancies.
Catalytic reduction (H2, PtO2-EtOH) of indoloquinones affords indoloquinones . Depending on their leaving group ability one or both substituents X and Y can be eliminated. Evidence is provided, on carrying out the reduction reactions in EtOD, for the intermediacy of quinone methides , and/or and iminium derivatives .
Antineoplastic activity of C. butyricum has been demonstrated in spontaneous adenocarcinoma of mice and in tumors of man. Improved survival of mice occurred among those undergoing clostridial oncolysis when treated supportively with antibiotics, corticosteroids, and electrolyte solutions. Five patients were treated with 1 × 1010 spores of C. butyricum. Blood cultures were positive for this microorganism for 4-9 days after injection. Oncolysis occurred in three patients in their largest tumors, but not in their smaller tumors. Spore treatment resulted in transient clinical benefit in one subject, oncolysis of a clinically occult tumor in another, and oncolysis in a third patient which was not clinically recognized. A sensitive and specific hemagglutination test was developed to measure the bacterial antibody response of the patients and other subjects. Antibodies in low titers were demonstrated in healthy blood donors and patients with cancer. The five patients treated with spores developed antibodies in substantial titers. These titers were higher in the three subjects with oncolysis than in the two patients whose tumors failed to lyse. Clostridial oncolysis appears to be related to the physiologic and biochemical characteristics of large tumor masses rather than to qualitative differences between normal and neoplastic cells or to immunologic cytolysis, and thus appears to be of limited, if any, clinical usefulness.
A series of novel bis(nitroimidazolyl)alkanecarboxamides has been prepared and evaluated for hypoxia-selective cytotoxicity and hypoxic cell radiosensitisation in vitro and in vivo. The compounds were prepared by direct coupling of preformed side chain acid and amine components, using diethyl phosphorocyanidate at room temperature. Although designed to be bis-bioreductive prodrugs of DNA cross-linking agents, none of the compounds showed evidence of DNA crosslinking activity, being equally potent against cell lines deficient and proficient in repair of crosslinks. However, one of these compounds, N-[2-(2-methyl-5-nitro-1H-imidazolyl) ethyl]-4-(2-nitro-1H-imidazolyl) butanamide (10; SN 24699), showed high hypoxic selectivity as a cytotoxin (rising to 200-fold after exposure to the drug for several hours) in the repair-proficient Chinese hamster cell line AA8. This selectivity was greater than-observed for the alkylating 2-nitroimidazole (4; RB 6145) (40-fold) or simple mononitroimidazoles (5-25-fold). Investigation of structure-activity relationships for hypoxic selectivity of bis(nitroimidazoles) was restricted by their low aqueous solubility, but a certain minimum separation of the two nitroimidazole units (by more than five atoms) appears desirable. All the compounds radiosensitized hypoxic cells in vitro but were little more potent as radiosensitizers than the corresponding monomeric nitroimidazoles. Compound 10 caused additional cell killing in the KHT tumor when multiple drug doses were administered in combination with a single dose of radiation. It is not yet clear whether this activity reflects hypoxic cell radiosensitization or cytotoxicity toward hypoxic cells, but this new class of bis-bioreductive agent clearly warrants further investigation.
alpha-((1-Aziridinyl)methyl)-2-nitro-1H-imidazole-1-ethanols, of general formula ImCH2CH(OH)CH2NCR1R2CR3R4, where Im = 2-nitroimidazole and R1, R2, R3, R4 = H, Me, are radiosensitizers and selective bioreductively activated cytotoxins toward hypoxic tumor cells in vitro and in vivo. Treatment of the aziridines with hydrogen halide in acetone or aqueous acetone gave the corresponding 2-haloethylamines of general formula ImCH2CH(OH)CH2(+)-NH2CR1R2CR3R4X X-, where R1, R2, R3, R4 = H, Me, and X = F, Cl, Br, I. These 2-haloethylamines were evaluated as prodrugs of the parent aziridines. The rates of ring closure in aqueous solution at pH approximately 6 were found to increase with increasing methyl substitution and to depend on the nature of the leaving group (I approximately Br greater than Cl much greater than F). A competing reaction of ImCH2CH(OH)CH2+NH2CH2CH2X X- (X = Cl, Br) with aqueous HCO3- ions gives 3-(2-hyroxy-3-(2-nitro-1H-imidazol-1-yl)propyl)-2-oxazolidinone. The activities of these prodrugs as radiosensitizers or as bioreductively activated cytotoxins were consistent with the proportion converted to the parent aziridine during the course of the experiment. alpha-(((2-Bromoethyl)amino)methyl)-2-nitro-1H-imidazole-1- ethanol (RB 6145, 10), the prodrug of alpha-((1-aziridinyl)methyl)-2-nitro-1H-imidazole-1-ethanol (RSU-1069, 3), is identified as the most useful compound in terms of biological activity and rate of ring closure under physiological conditions.
The radical species formed on the reaction of eaq- with a series of aryl compounds, all containing a N,N-bis(2-chloroethyl)-N-methylammoniomethyl substituent, have been studied in neutral aqueous solutions by pulse radiolysis using optical absorption spectrophotometry. The benzene, 1, and 4-methylsulfonylbenzene, 2, derivatives fragmented immediately to yield different amounts of benzyl radicals, but the 2-nitrobenzene, 3, and 4-nitrobenzene, 4, derivatives were reduced to long-lived radical anions which decayed by bimolecular processes. These nitrobenzene derivatives differed from the corresponding benzyl halides in that they did not fragment to benzyl radicals. Similarly, no evidence was found for the formation of a benzyl-type radical from the radical anion of the 8-nitronaphthalene derivative, 5. However, benzyl-type radicals were produced upon intramolecular electron transfer from the initially formed radical anions of the 4-nitro-5-imidazole, 6, and the 5-nitro-2-pyrrole, 7, derivatives at rate constants of (8.0 ± 1.0) × 103 and (1.0 ± 0.1) × 104 s-1, respectively. The latter heterocyclic analogues provide an approach for release of cytotoxic tertiary amines via enzymatic or radiolytic reduction in hypoxic regions of tumors.
We have been developing prodrugs of anticancer agents such as 5-fluorouracil (5-FU) that are activated by irradiation under hypoxic conditions via one-electron reduction. Among them, OFU001 [1-(2′-oxopropyl)-5-fluorouracil] is a prototype radiation-activated prodrug. In this study, we investigated the radiation chemical reactivity and the biological effects of OFU001. This prodrug is presumed to release 5-FU through incorporation of hydrated electrons into the antibonding σ* orbital of the C(1′)-N(1) bond. Hydrated electrons are active species derived from radiolysis of water, but are readily deactivated by O2 into superoxide anion radicals () under conditions of aerobic irradiation. Therefore, 5-FU release occurs highly specifically upon irradiation under hypoxic conditions. OFU001 dissolved in phosphate buffer released 5-FU with a G-value (mol number of molecules that are decomposed or produced by 1 J of absorbed radiation energy) of 1.9×10−7 mol/ J following hypoxic irradiation, while the G-value for 5-FU release was 1.0×10−8 mol/J following aerobic irradiation. However, the G-values for decomposition of OFU001 were almost the same, i.e., 3.4×10−7 mol/J following hypoxic irradiation and 2.5×10−7 mol/J following aerobic irradiation. When hypoxically irradiated (7.5–30 Gy) OFU001 was added to murine SCCVII cells for 1–24 h, a significant cell-killing effect was observed. The degree of this cytotoxicity was consistent with that of authentic 5-FU at the corresponding concentrations. On the other hand, cytotoxicity was minimal when the cells were treated with aerobically irradiated or unirradiated OFU001. This compound had no radiosensitizing effect against SCCVII cells under either aerobic or hypoxic conditions when the drug was removed immediately after irradiation. Since hypoxia is generally most marked in tumors and irradiation is applied at the tumor site, this concept of prodrug design appears to be potentially useful for selective tumor treatment with minimal adverse effects of anticancer agents.
We studied the role of DNA topoisomerase II in the biological actions of a series of novel alkylaminoanthraquinones, including
N-oxide derivatives designed as prodrugs liable to bioreductive activation in hypoxic tumour cells. Drug structures were based
upon the DNA-binding anticancer topoisomerase II poison mitoxantrone with modifications to the alkylamino side chains. The
agents included AQ4, 1,4-bis{[2-(dimethylamino)ethyl]amino}5,8-dihydroxy-anthracene-9,10-dione, and AQ6, 1{[2-dimethylamino)-ethyl]amino}4-{[2[(hydroxyethyl)amino]ethyl]-amino}5,8-dihydroxy-anthracene-9,10-dione,
together with the corresponding mono-N-oxide (AQ6NO) and di-N-oxide (AQ4NO). The R3N+-O- modification renders the terminal nitrogen group electrically neutral and was found to reduce AQ6NO or effectively abolish
AQ4NO-DNA binding. Comparative studies were carried out using two SV40-transformed fibroblast cell lines, MRC5-V1 and AT5BIVA,
the latter being a relative overproducer of DNA topoisomerase IIα. The inhibition of DNA topoisomerase II decatenation activity
ranked according to DNA-binding capacity. A similar ranking was found for drug-induced DNA-protein cross-linking in intact
cells, depending upon topoisomerase II availability. Inhibition of DNA synthesis in S-phase synchronized cultures ranked in
the order of AQ6>mitoxantrone≫AQ6NO and was independent of topoisomerase II availability. Cytotoxicity of acute 1-h exposures
for all agents except the inactive AQ4NO was enhanced in the topoisomerase II-overproducing cell line. The results indicate
an important role for enzyme targeting in anthraquinone action. However, DNA synthesis inhibition and cytotoxicity were greater
than expected for AQ6, given its topoisomerase- and DNA-interaction properties, and parallel studies have provided evidence
of an additional role for enhanced subcellular accumulation and nuclear targeting. The inactivity of AQ4NO and the retention
of only partial activity of AQ6NO, allied with the effective topoisomerase II-targeting and high cytotoxic potential of their
presumed metabolites, favour their use as prodrugs in tumour cells with enhanced bioreductive potential.
: Tumor hypoxia adversely affects short term clinical radiation response of head and neck cancer lymph node metastases and long term disease-free survival (DFS) in cervix carcinoma. This study was performed to evalaute the relationship between tumor hypoxia and DFS in patients with squamous carcinoma of th ehead and neck (SCCHN).: Pretreatment tumor pO2 was assessed polagographically in SCCHN patients. All patients were AJCC Stage IV and had pretreatment oxygen measureemnt taken from locally advanced primaries (T3 or T4) or neck nodes ≥ 1.5 cm diameter. Treatment consisted of once daily (2 Gy/day to 66–70 Gy) or twice daily irradiation 91.25 Gy B.I.D. to 70–75 Gy) +/- planned neck dissection (for ≥N2A disease) according to institutiional treatment protocols.: Twenty-eight patients underwent tumor pO2 measurement. The average pre-treatment median pO2 was 11.2 mm Hg (range 0.4–60 mm Hg). The DFS at 12 months was 42%. The DFS was 78% for patients with median tmor pO2 > 10 mm Hg but only 22% for median pO2 < 10 mm Hg (p = 0.009). The average tumor median pO2 for relapsing patients was 4.1 mm Hg and 17.1 mm Hg in non-relapsing (NED) patients (p = 0.07).: Tumor hypoxia adversely affected the prognosis of patients in this study. Understanding of the mechanistic relatiosnhip between hypoxia and treatment outcome will allow for the development of new and rational treatment programs in the future.
The mitochondrial NADH dehydrogenase catalyzes a one-electron reduction of quinones. Semiquinones thus formed have the hyperfine structures of their free anion radicals and are suggested to be detached from the enzyme. In the presence of suitable electron acceptors electron transfer occurs from the semiquinone to the acceptor. The mechanism of quinone reduction by spinach ferredoxin-NADP reductase is the same as that by the NADH dehydrogenase.On the other hand, the NAD(P)H dehydrogenase (DT-diaphorase) prepared from liver soluble fraction catalyzes a typical two-electron reduction of quinones such as p-benzoquinone and 2-methyl-1,4-naphthoquinone. The mechanisms of one-electron and two-electron reduction of quinones are readily distinguishable by the use of an electron spin resonance spectrometer equipped with a flow apparatus and also by the use of an appropriate set of electron acceptors.It is concluded that the reduction of quinones and oxygen by flavoproteins falls into three mechanistic categories: one-electron, two-electron and mixed-type reactions.
There are three models of parasite-mediated sexual selection by female choice. Females may get (1) indirect, genetic gains; (2) direct, parental care gains and (3) direct contagion avoidance gains. Little is known about frequency and mechanisms of parasite transfer during mating. In an experiment, 20 male pheasants had lice removed. One week later sticky tape was placed on their legs and they were then allowed to mate with Mallophaga-infested females. A significant number of males were infested with lice within two seconds. These results support the contagion avoidance hypothesis, while not discounting other models.
The anti-cancer compound CI-1010, designated as (R)-alpha-([(2-bromoethyl)amino]methyl)-2-nitro-1H-imidazole-1-ethanol monohydrobromide, has a proposed dual mechanism of action due to alkylating and radiosensitizing activities. To assess potential toxicity, adult Wistar rats were treated with a single intravenous injection (0, 50, 100, 150, 225, or 350 mg/kg) and necropsied at 4 or 29 days following treatment. In a repeated dose experiment, rats were injected daily (0, 10, 40, or 80 mg/kg; 5 doses/wk) for 3 wk and necropsied at the end of week 3 or 7. CI-1010 induced retinal degeneration by 4 days after a single injection of > or = 225 mg/kg or by 3 wk of repeated injections of > or = 40 mg/kg. The locally extensive to diffuse retinal degeneration involved the photoreceptor and outer nuclear layer. The photoreceptor layer was vacuolated and compressed corresponding to ultrastructural evidence of inner segment swelling and outer segment fragmentation. The outer nuclear layer was thinned due to loss of nuclei and contained numerous pyknotic or karyorrhectic nuclei. These nuclear changes were morphologically consistent with apoptosis and many outer nuclear layer nuclei labeled with in situ TdT-mediated dUTP-digoxigenin nick end labeling (Apoptag). The retinal degeneration was nonreversible, evidenced by increased lesion severity and incidence after CI-1010 was withdrawn for either 25 or 28 days.
The physiology of solid tumors differs from that of normal tissues in a number of important aspects, the majority of which stem from differences between the two vasculatures. Compared with the regular, ordered vasculature of normal tissues, blood vessels in tumors are often highly abnormal, distended capillaries with leaky walls and sluggish flow. Tumor growth also requires continuous new vessel growth, or angiogenesis. These physiological differences can be problems for cancer treatment; for example, hypoxia in solid tumors leads to resistance to radiotherapy and to some anticancer drugs. However, these differences can also be exploited for selective cancer treatment. Here we review four such areas that are under active investigation: (a) hypoxia-selective cytotoxins take advantage of the unique low oxygen tension in the majority of human solid tumors. Tirapazamine, a drug in the final stages of clinical trials, is one of the more promising of these agents; (b) leaky tumor blood vessels can be exploited using liposomes that have been sterically stabilized to have a long intravascular half-life, allowing them to selectively accumulate in solid tumors; (c) the tumor microenvironment is a stimulus to angiogenenesis, and inhibition of angiogenesis can be a powerful anticancer therapy not susceptible to acquired drug resistance; and (d) we discuss attempts to use gene therapy activated either by the low oxygen environment or by necrotic regions of tumors.
A multicenter randomized and balanced double-blind trial with the objective of assessing the efficacy and tolerance of nimorazole given as a hypoxic radiosensitizer in conjunction with primary radiotherapy of invasive carcinoma of the supraglottic larynx and pharynx.
Between January 1986 and September 1990, 422 patients (414 eligible) with pharynx and supraglottic larynx carcinoma were double-blind randomized to receive the hypoxic cell radiosensitizer nimorazole, or placebo, in association with conventional primary radiotherapy (62-68 Gy, 2 Gy per fraction, five fractions per week). The median observation time was 112 months.
Univariate analysis showed that the outcome (5-year actuarial loco-regional tumor control) was significantly related to T-classification (T1-T2 48% versus T3-T4 36%, P = 0.0008), neck-nodes (N- 53% versus N+ 33%), pre-irradiation hemoglobin (Hb) concentration (high 46% versus low 37%, P = 0.02) and sex (females 51% versus males 38%, P = 0.03). Overall the nimorazole group showed a significantly better loco-regional control rate than the placebo group (49 versus 33%, P = 0.002). A similar significant benefit of nimorazole was observed for the end-points of final loco-regional control (including surgical salvage) and cancer-related deaths (52 versus 41%, P = 0.002). This trend was also found in the overall survival but to a lesser, non-significant extent (26 versus 16%, 10-year actuarial values, P = 0.32). Cox multivariate regression analysis showed the most important prognostic parameters for loco-regional control to be positive neck nodes (relative risk 1.84 (1.38-2.45)), T3-T4 tumor (relative risk 1.65 (1.25-2.17)) and nimorazole (relative risk 0.69 (0.52-0.90)). The same parameters were also significantly related to the probability of dying from cancer. The compliance to radiotherapy was good and 98% of the patients received the planned dose. Late radiation-related morbidity was observed in 10% of the patients, irrespective of nimorazole treatment. Drug-related side-effects were minor and tolerable with transient nausea and vomiting being the most frequent complications.
Nimorazole significantly improves the effect of radiotherapeutic management of supraglottic and pharynx tumors and can be given without major side-effects.
The radiosensitizing ability of the 1-nitroacridine nitracrine (NC) is of interest since it is an example of a DNA intercalating agent with an electron-affinic nitro group. NC radiosensitization was evaluated in Chinese hamster ovary cell (AA8) cultures at 4 degrees C in order to suppress the rapid metabolism and potent cytotoxicity of the drug. Under hypoxic conditions, submicromolar concentrations of NC resulted in sensitization (SER = 1.6 at 1 mumol dm-3). Sensitization was also seen under aerobic conditions but a concentration more than 10-fold higher was required. In aerobic cultures NC radiosensitization was independent of whether cells were exposed before and during, or after, irradiation. Postirradiation sensitization was not observed under hypoxic conditions. The time dependence of NC uptake and the development of radiosensitization were similar (maximal at 30 min at 4 degrees C under hypoxia) suggesting that sensitization, unlike cytotoxicity, is due to unmetabolized drug. NC is about 1700 times more potent as a radiosensitizer than misonidazole. This high potency is adequately accounted for by the electron affinity of NC (E(1) value at pH7 of -275 mV versus NHE) and by its accumulation in cells to give intracellular concentrations approximately 30 times greater than in the medium. However, concentrations of free NC appear to be low in AA8 cells, presumably because of DNA binding. If radiosensitization by NC is due to bound rather than free drug, it suggests that intercalated NC can interact very efficiently with DNA target radicals. This is despite a binding ratio in the cell estimated as less than 1 NC molecule/400 base pairs under conditions providing efficient sensitization. This work suggests a new approach in the search for more effective clinical radiosensitizers, and poses questions on the means by which intercalated drugs can interact with DNA damage.
Thesis (PhD--Pathology)--University of Auckland, 2003.
Background:
A novel bioreductive alkylating indoloquinone compound, E09 [3-hydroxy-5-aziridinyl-1-methyl-2-(1H-indole-4,7-indione)- prop-F128b-en-alpha-ol], has been shown to have distinct antitumor activity against solid tumors, excellent activity under hypoxic conditions, but no notable bone marrow toxicity in preclinical models.
Purpose:
A phase I study was carried out to determine the toxicity, maximum tolerated dose (MTD), pharmacology, and antitumor response of E09.
Methods:
E09 was administered as a 5-minute intravenous infusion once every 3 weeks to 32 patients with solid tumors. The starting dose of 2.7 mg/m2 was one tenth of the mouse equivalent of lethal dose to 10% of animals (MELD10). Dose was escalated by 100% until the area under the curve (AUC) at the MELD10 was reached, following a Fibonacci-like schedule. The pharmacokinetics of E09 and its metabolite E05A with an open aziridine ring was determined using a new high-pressure liquid chromatographic method and noncompartmental calculation of kinetic parameters. The sigmoid Emax model was used to fit pharmacokinetic parameters to toxicity. The renal function and proteinuria were quantitated and were further evaluated by determining renal clearance ratios of immunoglobulin G (IgG) to albumin and pancreatic amylase to salivary amylase.
Results:
The 32 patients were treated with a total of 85 assessable courses of E09. The dose-limiting toxicity was proteinuria, which was accompanied by sodium and water retention. All symptoms were reversible on day 15 except in two patients, who developed acute renal failure. The ratios of IgG to albumin and pancreatic amylase to salivary amylase suggested a loss of glomerular negative charge consistent with a minimal change glomerulopathy. The pharmacokinetics of E09 showed its rapid elimination from the central compartment but with wide interpatient variation in the overall disposition of the drug. Total plasma clearance of E09 ranged from 3.2 to 24 L/min. The AUC of E09 was linearly related to the administered dose. The relationship between the AUC and proteinuria was best fitted by the sigmoid Emax model (r = .98). In two patients with adenocarcinoma of unknown primary site and in a third patient with bile duct cancer, a partial response was observed.
Conclusions:
The MTD of E09 was determined to be 27 mg/m2. The standard approach of drug administration is considered unsuitable because of potential renal toxicity and wide variability in the pharmacokinetics of E09. Individual dose adjustments based on plasma concentration measurements are recommended to combine maximally achievable exposure with tolerable toxicity.
The inhibition of many nitroreductases by oxygen has been explained by Mason and Holtzman in terms of electron transfer to oxygen from the nitro radical-anions, which have been identified as the first intermediate in some reductase systems. We have used the pulse radiolysis technique to measure the bimolecular rate constants of this electron-transfer reaction for over 20 nitro compounds, including substituted 2- and 5-nitroimidazoles of interest as antiprotozoal drugs and radiosensitizers, nitrofurans in use as antibacterial agents, and substituted nitrobenzenes previously used as model substrates for nitroreductases. The logarithm of the rate constant for the reaction of the nitro radical-anion with oxygen is linearly related to the one-electron reduction potential of the nitro compound.
The highlyactive, quinone-containinganticancer drugs, Adriamycin, daunorubicin,carminomycin,rubidazone, no- galamycin, aclacinomycin A, and steffimycin (benzan- thraquinones); mitomycin C and streptonigrin (/V-hetero- cyclic quiñones); and lapacho! (naphthoquinone)interact with mammalian microsomes and function as free radical carriers. These quinone drugs augment the flow of elec trons from reduced nicotinamide adenine dinucleotide phosphate to molecular oxygen as measured by en hanced reduced nicotinamide adenine dinucleotide phos phate oxidation and oxygen consumption.This reaction is catalyzed by microsomal protein and produces a free radical intermediate form of the drugs as determined by electron paramagnetic resonance spectroscopy. Micro- somes from mouse and rat liver, heart, lung, and spleen and mouse L1210 and P388 tumors all catalyze the aug mented oxygen consumption. Apparent Kmvalues deter mined with normal rat liver microsomes range from 0.49 x 10~"Mfor steffimycinto 13.4 x 10~"Mfor lapacho!. Since SKF 525A and carbon monoxide have little effect on this reaction, cytochrome P-450 is probably not involved. Sev eral nonquinoneanticancer agents were tested and were found inactive in the system. Since quinone anticancer drugs are associated with chromosomal damage that appears to be dependent on metabolic activation of these drugs, we propose that the intracellular activation of these drugs to a free radical state may be primary to their cytotoxic activity. As free radicals, these drugs, because of their high affinity and selective bindingto nucleic acids, have the potential to be "site-specific free radicals" that bind to DMA or RNA and either react directly or generate oxygen-dependent free radicals such as Superoxideradi cal or hydroxyl radical to cause the damage associated with their cytotoxic actions.
With NADPH as the electron donor, rat liver NADPH cytochrome P-450 reductase (NADPH:ferricytochrome oxidoreductase, EC 1.6.2.4) catalyzes the single-electron reduction of several quinone antibiotics to a semiquinone or free radical state. The benzanthraquinones adriamycin, daunorubicin, carminomycin, 7-O-methylnogalarol, and aclacinomycin A and the N-heterocyclic quinones streptonigrin and mitomycin C are activated to free radical intermediates which can transfer their single electron to molecular oxygen to form superoxide. The overall Km range for this electron transfer is 0.4 to 42.1 X 10(-4) M. We postulate that the formation of the "site-specific free radical/ intermediate is central to the cytotoxic action of these antibiotics.
Electron spin resonance spectra are observed during the enzymatic reduction of many nitrophenyl derivatives by rat hepatic microsomes or mitochondria. The spectra indicate that nitroaromatic anion radicals are present and are freely rotating in aqueous solution at a steady-state concentration of 0.1-6 muM. The rate of formation of p-nitrobenzoate (NBZO) dianion radical in microsomal incubates is consistent with the radical being an obligate intermediate in the reduction of NBZO to p-aminobenzoic acid. A model system consisting of NBZO, NADPH, and FMN, but no heme-containing compounds, also reduced NBZO to the NBZO dianion free radical. The steady-state concentration of the anion radicals in microsomal systems is not altered by CO. This observation, together with the results from the model system, suggests that the formation of nitroaromatic anion radicals is mediated through a flavine and not cytochrome P-450. The oxidation of the anion radical intermediate by O2 to the parent nitro compound is proposed to account for the well-known O2 inhibition of microsomal nitroreductase.
We used "high-dose" metronidazole, an "in vitro" and "in vivo" specific radiosensitizer of hypoxic cells, in a controlled trial to evaluate possible enhancement of radiation effect in patients with supratentorial glioblastomas. Thirty-six patients were stratified according to functional level and randomly allocated within two weeks of operation to one of two therapeutic groups: Group 1, radiation alone; and Group 2, radiation as in Group 1 but with high-dose metronidazole. We examined survival with the Kaplan-Meier probability plot and non-parametric tests. Patients in Group 2 had a 4 1/2-month delay between relapse and subsequent death (P = 0.02). This shift of the survival curves suggests a delay in the time of tumor regrowth consistent with the ability of metronidazole to make the hypoxic tumor cells less radioresistant. Nitroimidazole derivatives may be useful radiosensitizers in human solid tumors.
The response of 3 different tumours to single doses and fractionated irradiation with and without misonidazole was compared. The osteosarcoma BS2 showed no significant drop in sensitization for 2 fractions compared with a single dose. The rapidly shrinking carcinoma NT and the non-shrinking fibrosarcoma showed a significant drop in the SER as the radiation dose was fractionated. This is consistent with effective reoxygenation occurring in both tumours. No sensitizing effect was observed in the fibrosarcoma for 5 fractions each given with metronidazole. When only 2 out of 5 fractions were given with the drug misonidazole, they were slightly more effective with the first 2 than with the last 2 fractions.
Single doses or multiple fractions of 2, 3, 5 or 10 Gy were given daily to KHT Sarcomas, growing in C3H mice, in combination with a misonidazole dose of 0.5 mg/g body weight administered 30--40 min before each radiation dose. Cell survival assays were performed on groups of tumours after different total doses to determine tumour cell survival curves for each fractionation schedule. The results indicate that misonidazole is effective in sensitizing the tumours to single doses and to large dose fractions, but that the degree of sensitization declines with fraction size such that there is no difference between the survival curves obtained for 2 Gy fractions given with or without prior drug treatment. Comparison of iso-effect curves, derived from the data, with those for normal skin suggests that, even though misonidazole increases the effect of the radiation on the tumour when large dose fractions are used, the small dose fractions probably still give a better "therapeutic ratio".
1. The metabolism of the radiosensitizing 2-nitroimidazole, misonidazole, has been investigated in mice, rats, baboons, human volunteers, and in patients receiving radiotherapy for advanced malignant disease. 2. Plasma levels of unchanged drug and its desmethylated metabolite have been measured, and in humans there is good correlation of peak plasma concn. with drug dose. All drug-related material in plasma was accounted for as unchanged misonidazole or its desmethylated metabolite, both compounds being radiosensitizers in vitro. 3. Extensive faecal excretion of material not containing any nitro group occurred in mice, rats, and baboons dosed with radiolabelled drug. 4. Renal excretion is the preferred route of elimination in man, baboon and mouse. Nitroimidazole metabolites accounting for over half the urinary excretion in all species were identified. 5. The compound penetrates solid murine tumours in concentrations sufficient to achieve radiosensitization.
The proportion of viable hypoxic cells in EMT6/St/lu tumours assayed 18 and 24 hours after a dose of misonidazole (1.2 mg/g), which killed 8-90% of the tumour cells, was reduced from 20% in the controls to 7% in the misonidazole treated mice. In other experiments, the radiation cell-survival curve of the RIF-1 tumour was assayed in both intradermal and intramuscular sites under both air-breathing and acutely hypoxic conditions. The slope of the survival curve of the intramuscular tumours irradiated under air-breathing conditions was significantly steeper than that of the same tumours growing intradermally (D 0 values of 187 rad vs. 357 rad), or when the tumours were irradiated in either site under acutely hypoxic conditions (D 0 = 375 rad). Both of these experimental observations are examined in the light of data from other sources, notably from the radiation response of hypoxic cells in spheroids and from observations made from tumours implanted between close, parallel mica sheets ('sandwich' tumours). It is concluded that these results taken together with the other data, suggest that rodent tumours contain acutely hypoxic cells, as well as the classically described chronically hypoxic cells. It is argued further that, if (as appears to be the case), acutely hypoxic cells are produced by intermittent opening and closing of tumour blood vessels, then this process would provide a simple explanation for the rapid reoxygenation seen in several mouse tumours. Finally, it is pointed out that a consequence of the presence of acutely hypoxic cells in tumours is that they would largely frustrate attempts to radiosensitize tumours using either respiratory inhibitors or high pressure oxygen, or agents designed to selectively kill hypoxic tumour cells, since both of these methods would deal only with the chronically hypoxic cells.
EMT6 tumor cells in vitro and in vivo were used to examine the cytotoxicity and metabolism of mitomycin C, a bioreductive alkylating agent, and to study the use of this drug in combination with radiation. Mitomycin C was active against both aerobic and hypoxic cells in vitro. The drug did not alter the Do's of the radiation dose-response curves of aerated or hypoxic cells when present during irradiation in vitro or in vivo. Preliminary experiments suggested that mitomycin C may be preferentially metabolized by and toxic to chronically hypoxic cells in vitro. In vivo, mitomycin C reached and was toxic to the cells of solid tumors, including some hypoxic tumor cells.
Vascular glioblastomas become liquefied when contaminated with spores of the non-pathogenic Clostridium butyricum M 55. The spores are administered by intracarotid injection. The oncolysis is complete one week after injection. The glioblastoma is converted into a brain abscess which is then operated on appropriately. Forty nine patients have been treated in this manner. The rate of recurrence, however, remained uninfluenced.
Incubation of Chinese hamster ovary cells and KHT murine fibrosarcoma tumor cells in the absence of oxygen with 1-[2-14C]nitro-1-imidazolyl)-3-methoxy-2-propanol, one of the most effective radiation sensitizers of hypoxic cells, results in the preferential reduction of 1-[2-14C]nitro-1-imidazolyl)-3-methoxy-2-propanol. The radioactivity associated with the acid-insoluble precipitate from cells incubated in nitrogen is about four times higher than that of cells incubated in air. When aqueous extracts of tissues of a C3H mouse bearing the KHT tumor, after i.p. injection with 1-[2-14C]nitro-1-imidazolyl)-3-methoxy-2-propanol, are analyzed, a reduction product is found in relatively higher yields in the tumor than in normal tissues. The relative radioactivity in the pellet from the tumor homogenate is also high in comparison with those of most normal tissues. These results provide suggestive evidence for a higher degree of hypoxic in the tumor than in most normal tissues. The formation of reduction products and their subsequent binding to macromolecules may explain the preferential toxicity of nitro compounds to mammalian cells under hypoxia conditions. These results suggest that some nitro compounds may be useful for the treatment of tumors having a high fraction of hypoxic cells even in the absence of radiation.
The nitroimidazoles have been found to selectively sensitize hypoxic cells to the effects of irradiation. The latest in this family of drugs is RO-07-0582, which is able to mimic 80% of the oxygen effect at a concentration of 5 mM by modifying the sensitivity of hypoxic cells to single doses of gamma rays; however, it is not a substitution for oxygen in promoting the repair of sublethal radiation damage between split doses. Studies show that it is a powerful cytotoxic agent as well and selectively operates against hypoxic cells.
We have identified a 50-nucleotide enhancer from the human erythropoietin gene 3'-flanking sequence which can mediate a sevenfold transcriptional induction in response to hypoxia when cloned 3' to a simian virus 40 promoter-chloramphenicol acetyltransferase reporter gene and transiently expressed in Hep3B cells. Nucleotides (nt) 1 to 33 of this sequence mediate sevenfold induction of reporter gene expression when present in two tandem copies compared with threefold induction when present in a single copy, suggesting that nt 34 to 50 bind a factor which amplifies the induction signal. DNase I footprinting demonstrated binding of a constitutive nuclear factor to nt 26 to 48. Mutagenesis studies revealed that nt 4 to 12 and 19 to 23 are essential for induction, as substitutions at either site eliminated hypoxia-induced expression. Electrophoretic mobility shift assays identified a nuclear factor which bound to a probe spanning nt 1 to 18 but not to a probe containing a mutation which eliminated enhancer function. Factor binding was induced by hypoxia, and its induction was sensitive to cycloheximide treatment. We have thus defined a functionally tripartite, 50-nt hypoxia-inducible enhancer which binds several nuclear factors, one of which is induced by hypoxia via de novo protein synthesis.
Two new bioreductive compounds, 9-[3-(2-nitro-1-imidazolyl)propylamino]acridine hydrochloride (NLA-1) and 9-[2-(2-nitro-1-imidazolyl)ethylamino]acridine hydrochloride (NLA-2), have been prepared. They feature an acridine ring to intercalate with DNA, a 2-nitroimidazole ring as the radiosensitizing moiety and an amino functionality for increased DNA-binding and hydrophilicity. Time and concentration dependent cytotoxicity as well as radiosensitization efficacy of the two compounds under hypoxic or aerobic conditions were determined in vitro using V-79 cells and an MTT colorimetric or clonogenic assay. The isosensitization point (ISP), defined as that drug concentration which results in the same survival decrement upon exposure of hypoxic or oxygenated cells to a given radiation dose, has been determined for both compounds at 7.5 Gy and the values are significantly lower than the ISPs of 5-[3-(2-nitro-1-imidazolyl)propyl]phenanthridinium bromide, 2-(2-nitro-1-imidazolyl)ethylamine or misonidazole (MISO). NLA-1 and NLA-2 are potent hypoxic cytotoxins and on a concentration basis, more potent than MISO as radiosensitizers in vitro. The sensitization enhancement ratios were significantly increased when 1 h drug preincubation under hypoxia at 37 degrees C was applied, before irradiation at room temperature.
Drugs with two reducible centers, both of which must be metabolized by oxygen-inhibitable processes for full activation ("bis-bioreductive agents"), offer potential for the development of hypoxia-selective cytotoxins with improved oxygen sensitivity. The sidechain N-oxide (1-NCO) of the (mono)bioreductive agent nitracrine (1-NC) has been synthesized and evaluated as a potential example of such an approach. The association constant for reversible DNA binding of 1-NCO was 15-fold lower than that of 1-NC, as measured by equilibrium dialysis in a low ionic strength buffer, indicating that the N-oxide has the potential to act as a less toxic pro-drug of 1-NC. Cell uptake and aerobic cytotoxicity of 1-NCO were much lower than for 1-NC whereas its hypoxic selectivity as a cytotoxin was greatly increased. In stirred suspension cultures of AA8 cells, pure (less than 0.02% 1-NC) 1-NCO was 1000-1500 times more potent under hypoxia than in 20% O2. For 1-NC the corresponding ratio was 10 +/- 1. 1-NCO had greater hypoxic selectivity in this system than misonidazole (ratio 11), RSU 1069 (ratio 25), 8Me-5NQ (ratio 60), or SR 4233 (ratio 80). Studies of 1-NCO metabolism indicate rapid, O2-inhibited reduction to 1-NC. The data are consistent with a two-step bioactivation mechanism, with reduction of the N-oxide generating a DNA intercalator of increased binding affinity, followed by reduction of the nitro group of this DNA-targeted cytotoxin to form reactive cytotoxic metabolites.
SR 4233 or WIN 59075 (3-amino-1,2,4-benzotriazine-1,4-dioxide) is a novel and highly selective hypoxic cell cytotoxin requiring reductive bioactivation for its impressive antitumour effects. Expression of appropriate reductases will contribute to therapeutic selectivity. Here we provide more detailed information on the role of cytochrome P450 and cytochrome P450 reductase in SR 4233 reduction by mouse liver microsomes. Reduction of SR 4233 to the mono-N-oxide SR 4317 (3-amino-1,2,4-benzotriazine-1-oxide) is NADPH, enzyme and hypoxia dependent. An inhibitory antibody to cytochrome P450 reductase decreased the microsomal SR 4233 reduction rate by around 20%. Moreover, studies with purified rat cytochrome P450 reductase showed unequivocally that this enzyme was able to catalyse SR 4233 reduction at a rate of 20-30% of that for microsomes with equivalent P450 reductase activity. Exposure to the specific cytochrome P450 inhibitor carbon monoxide (CO) inhibited microsomal reduction by around 70% and CO plus reductase antibody blocked essentially all activity. Additional confirmation of cytochrome P450 involvement was provided by the use of other P450 ligands: beta-diethylaminoethyl diphenylpropylacetate hydrochloride gave a slight stimulation while aminopyrine, n-octylamine and 2,4-dichloro-6-phenylphenoxyethylamine were inhibitory. Induction of SR 4233 reduction was seen with phenobarbitone, pregnenalone-16-alpha-carbonitrile and beta-napthoflavone, suggesting that cytochrome P450 subfamilies IIB, IIC and IIIA may be involved. Since cytochrome P450 and P450 reductase catalyse roughly 70 and 30%, of mouse liver microsomal SR 4233 reduction respectively, we propose that expression of these and other reductases in normal and tumour tissue is likely to be a major factor governing the toxicity and antitumour activity of the drug.
Targeting of electron affinic radiosensitizers to DNA via reversible non-covalent intercalative binding has potential for increasing sensitizer concentrations locally at the DNA target while decreasing accessibility to reductases responsible for bioactivation and cytotoxicity. We have prepared an DNA-targeted acridine-linked 2-nitroimidazole (NLA-1) as an example of such a compound. NLA-1 binds reversibly to DNA with an affinity similar to 9-aminoacridine, and is approximately 1000 times more potent than MISO as a cytotoxin, despite a similar reduction potential. It shows less enhancement of cytotoxicity under hypoxia (5- to 6-fold) than does MISO (approximately 11-fold), but is a potent hypoxia-selective radiosensitizer in AA8 cells with a concentration for an enhancement ratio of 1.6 (C1.6) of 9 microM. The mean intracellular concentration at the C1.6 is 400 microM, on which basis its potency is about twice that of MISO. The in vitro therapeutic index (aerobic cytotoxic potency/hypoxic C1.6) of NLA-1 is approximately 6-fold lower than that for MISO. NLA-1 lacks radiosensitizing activity against SCCVII or EMT6 tumors in vivo at the maximum tolerated dose (MTD) of 100 mumol.kg-1.
3-Amino-1,2,4-benzotriazine-1,4-dioxide (SR 4233; WIN 59075) is a highly selective hypoxic cell cytotoxin soon to enter phase I clinical trial. The compound is thought to exert its action through a toxic one-electron reduced free radical intermediate. Preliminary data have suggested that SR 4233 may be metabolized by DT-diaphorase [NAD(P)H: (quinone acceptor) oxidoreductase (EC 1.6.99.2)] to both two- and four-electron reduced products and that this route of biotransformation may represent a bioprotection pathway. In this study, a highly purified enzyme preparation was employed in order to investigate further the metabolism of SR 4233 by DT-diaphorase and to examine the mechanism of reduction in more detail. Spectrophotometric analysis showed that SR 4233 underwent reduction by DT-diaphorase with an apparent Km of 1.23 +/- 0.27 mM and Vmax of 8.55 +/- 1.67 nmol/min/microgram protein. This reaction was inhibited completely by dicoumarol (100 microM) and partially by an antiserum raised against the purified enzyme. Characterization of the products of SR 4233 reduction by reverse-phase HPLC confirmed that both two- (SR 4317) and four- (SR 4330) electron reduction products were generated, the latter being the predominant metabolite, particularly in prolonged incubations. Further experiments showed that the four-electron reduction product, but not the two-electron reduction product, was also a substrate for DT-diaphorase with an apparent Km of 1.14 mM and a Vmax of 57.12 nmol/min/micrograms protein. The results presented confirm that SR 4233 is indeed a substrate for DT-diaphorase and that a mixture of two-, four- and six-electron reduced products may be formed. The possible toxicological and pharmacodynamic significance of this metabolism is discussed.