New insights into the antimicrobial action and protective therapeutic effect of tirapazamine towards Escherichia coli-infected mice

OBJECTIVES

Escherichia coli is an important pathogen responsible for numerous cases of diarrhoea worldwide. The bioreductive agent tirapazamine (TPZ), which was clinically used to treat various types of cancers, has obvious antibacterial activity against E. coli strains. In the present study, we aimed to evaluate the protective therapeutic effects of TPZ in E. coli-infected mice and provide insights into its antimicrobial action mechanism.

METHODS

The MIC and MBC tests, drug sensitivity test, crystal violet assay and proteomic analysis were used to detect the in vitro antibacterial activity of TPZ. The clinical symptoms of infected mice, tissue bacteria load, histopathological features and gut microbiota changes were regarded as indicators to evaluation the efficacy of TPZ in vivo.

RESULTS

Interestingly, TPZ-induced the reversal of drug resistance in E. coli by regulating the expression of resistance-related genes, which may have an auxiliary role in the clinical treatment of drug-resistant bacterial infections. More importantly, the proteomics analysis showed that TPZ upregulated 53 proteins and downregulated 47 proteins in E. coli. Among these, the bacterial defence response-related proteins colicin M and colicin B, SOS response-related proteins RecA, UvrABC system protein A, and Holliday junction ATP-dependent DNA helicase RuvB were all significantly upregulated. The quorum sensing-related protein glutamate decarboxylase, ABC transporter-related protein glycerol-3-phosphate transporter polar-binding protein, and ABC transporter polar-binding protein YtfQ were significantly downregulated. The oxidoreductase activity-related proteins pyridine nucleotide-disulfide oxidoreductase, glutaredoxin 2 (Grx2), NAD(+)-dependent aldehyde reductase, and acetaldehyde dehydrogenase, which participate in the elimination of harmful oxygen free radicals in the oxidation-reduction process pathway, were also significantly downregulated. Moreover, TPZ improved the survival rate of infected mice; significantly reduced the bacteria load in the liver, spleen, and colon; and alleviated E. coli-associated pathological damages. The gut microbiota also changed in TPZ-treated mice, and these genera were considerably differentiated: Candidatus Arthromitus, Eubacterium coprostanoligenes group, Prevotellaceae UCG-001, Actinospica, and Bifidobacterium.

CONCLUSIONS

TPZ may represent an effective and promising lead molecule for the development of antimicrobial agents for the treatment of E. coli infections.

Compartmentalized Nano-MOFs as Co-delivery Systems for Enhanced Antitumor Therapy

Therapeutic bioactive macromolecules hold great promise in cancer therapy, but challenges such as low encapsulation efficiency and susceptibility to inactivation during the targeted co-delivery hinder their widespread applications. Compartmentalized nano-metal-organic frameworks (nMOFs) can easily load macromolecules in the innermost layer, protect them from the outside environment, and selectively release them in the target location after stimulation, showing great potential in the co-delivery of biomacromolecules. Herein, the rationally designed (GOx + CAT)/ZIF-8@BSATPZ/ZIF-8 (named GCZ@BTZ) nMOFs with compartmentalized structures are employed to deliver cascaded enzymes and the chemotherapeutic drug tirapazamine (TPZ)-conjugated bovine serum albumin (BSATPZ). Benefiting from the compartmentalized structure and protective shell, the GCZ@BTZ system is stable during blood circulation and preferentially accumulates in the tumor. Furthermore, in response to the acidic tumor environment, GCZ@BTZ effectively released the loading enzymes and BSATPZ. Along with the tumor starvation caused by depletion of glucose, cascaded reactions could also contribute to the enhancement of tumor hypoxia, which further activated BSATPZ-based chemotherapy. Notably, in the mouse tumor models, GCZ@BTZ treatment significantly inhibits tumor survival and metastasis. Such a compartmentalized nMOF delivery system presents a promising avenue for the efficient delivery of bioactive macromolecules.

Engineered biomimetic nanoreactor for synergistic photodynamic-chemotherapy against hypoxic tumor

Photodynamic therapy (PDT) can produce a large amount of reactive oxygen species (ROS) in the radiation field to kill tumor cells. However, the sustainable anti-tumor efficacy of PDT is limited due to the hypoxic microenvironment of tumor. In this study, classic PDT agent indocyanine green (ICG) and hypoxia-activated chemotherapeutic drug tirapazamine (TPZ) were loaded on mesoporous polydopamine (PDA) to construct PDA@ICG-TPZ nanoparticles (PIT). Then, PIT was camouflaged with cyclic arginine-glycine-aspartate (cRGD) modified tumor cell membranes to obtain the engineered membrane-coated nanoreactor (cRGD-mPIT). The nanoreactor cRGD-mPIT could achieve the dual-targeting ability via tumor cell membrane mediated homologous targeting and cRGD mediated active targeting. With the enhanced tumor-targeting and penetrating delivery system, PIT could efficiently accumulate in hypoxic tumor cells and the loaded drugs were quickly released in response to near-infrared (NIR) laser. The nanoreactor might produce cytotoxic ROS under NIR and further enhance hypoxia within tumor to activate TPZ, which efficiently inhibited hypoxic tumor by synergistic photodynamic-chemotherapy. Mechanically, hypoxia-inhibitory factor-1α (HIF-1α) was down-regulated by the synergistic therapy. Accordingly, the cRGD-mPIT nanoreactor with sustainable and cascade anti-tumor effects and satisfied biosafety might be a promising strategy in hypoxic tumor therapy.

Hypoxia-targeted cupric-tirapazamine liposomes potentiate radiotherapy in prostate cancer spheroids

In this study, novel cupric-tirapazamine [Cu(TPZ)₂]-liposomes were developed as an effective hypoxia-targeted therapeutic, which potentiated radiotherapy in a three dimensional (3D) prostate cancer (PCa) model. To overcome the low water solubility of the Cu(TPZ)₂, a remote loading method was developed to efficiently load the lipophilic complex into different liposomal formulations. The effect of pH, temperature, PEGylation, lipid composition, liposome size, lipid: complex ratio on the liposome properties, and drug loading was evaluated. The highest loading efficiency was obtained at neutral pH, which was independent of lipid composition and incubation time. In addition, enhanced drug loading was achieved upon decreasing the lipid:complex molar ratio with minimal effects on liposomes' morphology. Interestingly, the in vitro potency of the developed liposomes was easily manipulated by changing the lipid composition. The hydrophilic nature of our liposomal formulations improved the complex's solubility, leading to enhanced cellular uptake and toxicity, both in PCa monolayers and tumour spheroids. Moreover, Cu(TPZ)₂-loaded liposomes combined with radiation, showed a significant reduction in PCa spheroids growth rate, compared to the free complex or radiation alone, which could potentiate radiotherapy in patients with localised advanced PCa.

Photodynamic Therapy with Liposomal Zinc Phthalocyanine and Tirapazamine Increases Tumor Cell Death via DNA Damage

The efficacy of photodynamic therapy (PDT) in some solid tumors is limited by the poor biodistributive properties of conventional photosensitizers and a natural predisposition of tumor cells to survive hypoxia and oxidative stress. This study investigated the therapeutic potential of a third-generation photosensitizer, liposomal zinc phthalocyanine (ZnPC), in combination with the hypoxic cytotoxin tirapazamine (TPZ). TPZ induces DNA double strand breaks (DSBs) under hypoxic conditions and subsequent apoptosis via p53 signaling. Experiments were performed in tumor cells with functional p53 (Sk-Cha1) and dysfunctional p53 (A431). The combination therapy of TPZ and PDT induced DNA DSBs and cell cycle stalling and enhanced the cytotoxicity of PDT by exacerbating apopotic and non-apoptotic tumor cell death. These phenomena occurred regardless of oxygen tension and the mechanism of cell death differed per cell line. Liposomes containing both ZnPC and TPZ exhibited no dark toxicity but were more lethal to both cell types after PDT compared to ZnPC-liposomes lacking TPZ—an effect that was more pronounced under hypoxic conditions. In conclusion, TPZ is a suitable pharmaceutical compound to increase PDT efficacy by exploiting the post-PDT tumor hypoxia. The inclusion of TPZ and ZnPC into a single liposomal delivery system was feasible. The PDT strategy described in this study may be valuable for the treatment of PDT-recalcitrant tumors.

Mini-pillar array for hydrogel-supported 3D culture and high-content histologic analysis of human tumor spheroids

Three-dimensional (3D) cancer cell culture models mimic the complex 3D organization and microenvironment of human solid tumor tissue and are thus considered as highly predictive models representing avascular tumor regions. Confocal laser scanning microscopy is useful for monitoring drug penetration and therapeutic responses in 3D tumor models; however, photonic attenuation at increasing imaging depths and limited penetration of common fluorescence tracers are significant technical challenges to imaging. Immunohistological staining would be a good alternative, but the preparation of tissue sections from rather fragile spheroids through fixing and embedding procedures is challenging. Here we introduce a novel 3 × 3 mini-pillar array chip that can be utilized for 3D cell culturing and sectioning for high-content histologic analysis. The mini-pillar array chip facilitated the generation of 3D spheroids of human cancer cells within hydrogels such as alginate, collagen, and Matrigel. As expected, visualization of the 3D distribution of calcein AM and doxorubicin by optical sectioning was limited by photonic attenuation and dye penetration. The integrity of the 3D microtissue section was confirmed by immunostaining on paraffin sections and cryo-sections. The applicability of the mini-pillar array for drug activity evaluation was tested by measuring viability changes in spheroids exposed to anti-cancer agents, 5-fluorouracil and tirapazamine. Thus, our novel mini-pillar array platform can potentially promote high-content histologic analysis of 3D cultures and can be further optimized for field-specific needs.

Systematic and Molecular Basis of the Antibacterial Action of Quinoxaline 1,4-Di-N-Oxides against Escherichia coli

Quinoxaline 1,4-di-N-oxides (QdNOs) are widely known as potent antibacterial agents, but their antibacterial mechanisms are incompletely understood. In this study, the transcriptomic and proteomic profiles of Escherichia coli exposed to QdNOs were integratively investigated, and the results demonstrated that QdNOs mainly induced an SOS response and oxidative stress. Moreover, genes and proteins involved in the bacterial metabolism, cellular structure maintenance, resistance and virulence were also found to be changed, conferring bacterial survival strategies. Biochemical assays showed that reactive oxygen species were induced in the QdNO-treated bacteria and that free radical scavengers attenuated the antibacterial action of QdNOs and DNA damage, suggesting an oxidative-DNA-damage action of QdNOs. The QdNO radical intermediates, likely carbon-centered and aryl-type radicals, as identified by electron paramagnetic resonance, were the major radicals induced by QdNOs, and xanthine oxidase was one of the QdNO-activating enzymes. This study provides new insights into the action of QdNOs in a systematic manner and increases the current knowledge of bacterial physiology under antibiotic stresses, which may be of great value in the development of new antibiotic-potentiating strategies.

A computational model of drug delivery through microcirculation to compare different tumor treatments

Starting from the fundamental laws of filtration and transport in biological tissues, we develop a computational model to capture the interplay between blood perfusion, fluid exchange with the interstitial volume, mass transport in the capillary bed, through the capillary walls and into the surrounding tissue. These phenomena are accounted at the microscale level, where capillaries and interstitial volume are viewed as two separate regions. The capillaries are described as a network of vessels carrying blood flow. We apply the model to study drug delivery to tumors. The model can be adapted to compare various treatment options. In particular, we consider delivery using drug bolus injection and nanoparticle injection into the blood stream. The computational approach is suitable for a systematic quantification of the treatment performance, enabling the analysis of interstitial drug concentration levels, metabolization rates and cell surviving fractions. Our study suggests that for the treatment based on bolus injection, the drug dose is not optimally delivered to the tumor interstitial volume. Using nanoparticles as intermediate drug carriers overrides the shortcomings of the previous delivery approach. This work shows that the proposed theoretical and computational framework represents a promising tool to compare the efficacy of different cancer treatments.

Toward hypoxia-selective DNA-alkylating agents built by grafting nitrogen mustards onto the bioreductively activated, hypoxia-selective DNA-oxidizing agent 3-amino-1,2,4-benzotriazine 1,4-dioxide (tirapazamine)

Tirapazamine (3-amino-1,2,4-benzotriazine 1,4-dioxide) is a heterocyclic di-N-oxide that undergoes enzymatic deoxygenation selectively in the oxygen-poor (hypoxic) cells found in solid tumors to generate a mono-N-oxide metabolite. This work explored the idea that the electronic changes resulting from the metabolic deoxygenation of tirapazamine analogues might be exploited to activate a DNA-alkylating species selectively in hypoxic tissue. Toward this end, tirapazamine analogues bearing nitrogen mustard units were prepared. In the case of the tirapazamine analogue 18a bearing a nitrogen mustard unit at the 6-position, it was found that removal of the 4-oxide from the parent di-N-oxide to generate the mono-N-oxide analogue 17a did indeed cause a substantial increase in reactivity of the mustard unit, as measured by hydrolysis rates and DNA-alkylation yields. Hammett sigma values were measured to quantitatively assess the magnitude of the electronic changes induced by metabolic deoxygenation of the 3-amino-1,2,4-benzotriazine 1,4-dioxide heterocycle. The results provide evidence that the 1,2,4-benzotiazine 1,4-dioxide unit can serve as an oxygen-sensing prodrug platform for the selective unmasking of bioactive agents in hypoxic cells.

Bioreductive prodrugs as cancer therapeutics: targeting tumor hypoxia

Hypoxia, a state of low oxygen, is a common feature of solid tumors and is associated with disease progression as well as resistance to radiotherapy and certain chemotherapeutic drugs. Hypoxic regions in tumors, therefore, represent attractive targets for cancer therapy. To date, five distinct classes of bioreactive prodrugs have been developed to target hypoxic cells in solid tumors. These hypoxia-activated prodrugs, including nitro compounds, N-oxides, quinones, and metal complexes, generally share a common mechanism of activation whereby they are reduced by intracellular oxidoreductases in an oxygen-sensitive manner to form cytotoxins. Several examples including PR-104, TH-302, and EO9 are currently undergoing phase II and phase III clinical evaluation. In this review, we discuss the nature of tumor hypoxia as a therapeutic target, focusing on the development of bioreductive prodrugs. We also describe the current knowledge of how each prodrug class is activated and detail the clinical progress of leading examples.

A hybrid cellular automaton model of solid tumor growth and bioreductive drug transport

Bioreductive drugs are a class of hypoxia selective drugs that are designed to eradicate the hypoxic fraction of solid tumors. Their activity depends upon a number of biological and pharmacological factors and we used a mathematical modeling approach to explore the dynamics of tumor growth, infusion, and penetration of the bioreductive drug Tirapazamine (TPZ). An in-silico model is implemented to calculate the tumor mass considering oxygen and glucose as key microenvironmental parameters. The next stage of the model integrated extra cellular matrix (ECM), cell-cell adhesion, and cell movement parameters as growth constraints. The tumor microenvironments strongly influenced tumor morphology and growth rates. Once the growth model was established, a hybrid model was developed to study drug dynamics inside the hypoxic regions of tumors. The model used 10, 50 and 100 \mu {\rm M} as TPZ initial concentrations and determined TPZ pharmacokinetic (PK) (transport) and pharmacodynamics (cytotoxicity) properties inside hypoxic regions of solid tumor. The model results showed that diminished drug transport is a reason for TPZ failure and recommend the optimization of the drug transport properties in the emerging TPZ generations. The modeling approach used in this study is novel and can be a step to explore the behavioral dynamics of TPZ.

Generation of oxygen gradients in microfluidic devices for cell culture using spatially confined chemical reactions

This paper reports a microfluidic device capable of generating oxygen gradients for cell culture using spatially confined chemical reactions with minimal chemical consumption. The microfluidic cell culture device is constructed by single-layer polydimethylsiloxane (PDMS) microfluidic channels, in which the cells can be easily observed by microscopes. The device can control the oxygen gradients without the utilization of bulky pressurized gas cylinders, direct addition of oxygen scavenging agents, or tedious gas interconnections and sophisticated flow control. In addition, due to the efficient transportation of oxygen within the device using the spatially confined chemical reactions, the microfluidic cell culture device can be directly used in conventional cell incubators without altering their gaseous compositions. The oxygen gradients generated in the device are numerically simulated and experimentally characterized using an oxygen-sensitive fluorescence dye. In this paper, carcinomic human alveolar basal epithelial (A549) cells have been cultured in the microfluidic device with a growth medium and an anti-cancer drug (Tirapazamine, TPZ) under various oxygen gradients. The cell experiment results successfully demonstrate the hyperoxia-induced cell death and hypoxia-induced cytotoxicity of TPZ. In addition, the results confirm the great cell compatibility and stable oxygen gradient generation of the developed device. Consequently, the microfluidic cell culture device developed in this paper is promising to be exploited in biological labs with minimal instrumentation to study cellular responses under various oxygen gradients.

Suppression of hypoxia-inducible factor 1α (HIF-1α) by tirapazamine is dependent on eIF2α phosphorylation rather than the mTORC1/4E-BP1 pathway

Hypoxia-inducible factor 1 (HIF-1), a heterodimeric transcription factor that mediates the adaptation of tumor cells and tissues to the hypoxic microenvironment, has attracted considerable interest as a potential therapeutic target. Tirapazamine (TPZ), a well-characterized bioreductive anticancer agent, is currently in Phase II and III clinical trials. A major aspect of the anticancer activity of TPZ is its identity as a tumor-specific topoisomerase IIα inhibitor. In the study, for the first time, we found that TPZ acts in a novel manner to inhibit HIF-1α accumulation driven by hypoxia or growth factors in human cancer cells and in HepG2 cell-derived tumors in athymic nude mice. We investigated the mechanism of TPZ on HIF-1α in HeLa human cervical cancer cells by western blot analysis, reverse transcription-PCR assay, luciferase reporter assay and small interfering RNA (siRNA) assay. Mechanistic studies demonstrated that neither HIF-1α mRNA levels nor HIF-1α protein degradation are affected by TPZ. However, TPZ was found to be involved in HIF-1α translational regulation. Further studies revealed that the inhibitory effect of TPZ on HIF-1α protein synthesis is dependent on the phosphorylation of translation initiation factor 2α (eIF2α) rather than the mTOR complex 1/eukaryotic initiation factor 4E-binding protein-1 (mTORC1/4E-BP1) pathway. Immunofluorescence analysis of tumor sections provide the in vivo evidences to support our hypothesis. Additionally, siRNA specifically targeting topoisomerase IIα did not reverse the ability of TPZ to inhibit HIF-1α expression, suggesting that the HIF-1α inhibitory activity of TPZ is independent of its topoisomerase IIα inhibition. In conclusion, our findings suggest that TPZ is a potent regulator of HIF-1α and provide new insight into the potential molecular mechanism whereby TPZ serves to reduce HIF-1α expression.

DNA strand cleaving properties and hypoxia-selective cytotoxicity of 7-chloro-2-thienylcarbonyl-3-trifluoromethylquinoxaline 1,4-dioxide

The heterocyclic N-oxide, 3-amino-1,2,4-benzotriazine 1,4-dioxide (tirapazamine, 1), shows promising antitumor activity in preclinical studies, but there is a continuing need to explore new compounds in this general structural category. In the work described here, we examined the properties of 7-chloro-2-thienylcarbonyl-3-trifluoromethylquinoxaline 1,4-dioxide (9h). We find that 9h causes redox-activated, hypoxia-selective DNA cleavage that mirrors the lead compound, tirapazamine, in both mechanism and potency. Furthermore, we find that 9h displays hypoxia-selective cytotoxicity against human cancer cell lines.

Effectiveness of combined modality radiotherapy of orthotopic human squamous cell carcinomas in Nu/Nu mice using cetuximab, tirapazamine and MnSOD-plasmid liposome gene therapy

Hypoxic regions limit the radiocontrollability of head and neck carcinomas. Whether or not combinations of plasmid/liposome mediated overexpression of normal tissue protective manganese superoxide dismutase (MnSOD), cetuximab (C225), and the hypoxic cytotoxin tirapazamine (TPZ) enhanced radiotherapeutic effects was tested in a CAL-33 orthotopic mouse cheek tumor model. The tumor volume continued to increase in the control (untreated) mice, with a ninefold increase by 10 days when the tumors exceeded 2 cm(3). The mice receiving 14 Gy only showed reduced tumor growth to 3.1+/-0.1 fold at day 10. The mice receiving MnSOD-PL, C225, TPZ plus 14 Gy had the best outcome with 0.7+/-0.1 fold increase in tumor volume by 10 days (p=0.015) compared to irradiation only. The addition of MnSOD-PL, TPZ, and C225 to irradiation optimized the therapeutic ratio for the local control of hypoxic region-containing CAL-33 orthotopic tumors.

The usefulness of continuous administration of hypoxic cytotoxin combined with mild temperature hyperthermia, with reference to effects on quiescent tumour cell populations

To evaluate the usefulness of continuous administration of hypoxic cytotoxins in terms of targeting acute hypoxia in solid tumours and the significance of combination with mild temperature hyperthermia (MTH) (40 degrees C, 60 min), the cytotoxic effects of singly or continuously administered tirapazamine (TPZ) and TX-402 were examined in combination with or without MTH in vivo. Further, the effects were also analysed on total (=proliferating (P)+quiescent (Q)) and Q cell populations in solid tumours with the method for selectively detecting the Q cell response. C3H/He mice bearing SCC VII tumours received a continuous administration of 5-bromo-2'-deoxyuridine (BrdU) for 5 days to label all P cells. The tumour-bearing mice then received a single intra-peritoneal injection or 24 h continuous subcutaneous infusion of hypoxic cytotoxin, TPZ or TX-402, with or without MTH. On the other hand, to detect the changes in the hypoxic fraction (HF) in the tumours by MTH, another group of mice with or without MTH received a series of test doses of gamma-rays while alive or after tumour clamping. After each treatment, the tumour cells were isolated and incubated with a cytokinesis blocker (=cytochalasin-B) and the micronucleus (MN) frequency in cells without BrdU labelling (=Q cells) was determined using immunofluorescence staining for BrdU. The MN frequency in total tumour cells was determined from the tumours that were not pre-treated with BrdU. The sensitivity to TX-402 was slightly higher than that to TPZ in both total and Q tumour cells. Continuous administration elevated the sensitivity of both total and Q cells, especially total cells. MTH raised the sensitivity of Q cells more remarkably than that of total cells in both single and continuous administrations. It was thought to be probably because of the higher dose distribution of hypoxic cytotoxin in intermediately hypoxic areas derived mainly from chronic hypoxia through MTH. From the viewpoint of tumour control as a whole including both total and Q tumour cells, the continuous administration of hypoxic cytotoxin combined with MTH may be useful for sensitizing tumour cells in vivo.

Phase II study of tirapazamine, cisplatin, and etoposide and concurrent thoracic radiotherapy for limited-stage small-cell lung cancer: SWOG 0222

PURPOSE

A SWOG pilot study (S0004) showed that tirapazamine (TPZ) when combined with concurrent chemoradiotherapy yielded a promising median survival of 22 months in limited-stage small-cell lung cancer (LSCLC). We report results of the phase II study designed to confirm this result.

PATIENTS AND METHODS

The concurrent phase consisted of two cycles of cisplatin, etoposide, and once-daily radiation to 61 Gy. TPZ was given at 260 mg/m(2) on days 1, 29, and at 160 mg/m(2) on days 8, 10, 12, 36, 38, and 40. Consolidation consisted of two cycles of cisplatin and etoposide. Complete responders received prophylactic cranial irradiation. Results were considered promising if the median survival time was at least 21 months and of no further interest if < or = 14 months.

RESULTS

S0222 was closed early due to a report of excess toxicity for TPZ in a head and neck cancer trial elsewhere. Of planned 85 patients, 69 were accrued. In 68 assessable patients, 17 (25%) had grade 3 to 4 esophagitis and eight (12%) had grade 3 febrile neutropenia during the concurrent phase. There were three possible treatment-related deaths, two in concurrent phase (one progressive disease not otherwise specified within 30 days, one pericardial effusion) and one in consolidation phase (esophageal hemorrhage). At a median follow-up of 35 months, median progression-free survival was 11 months (95% CI, 10 to 13 months) and median overall survival was 21 months (95% CI, 17 to 33 months).

CONCLUSION

S0222 showed acceptable levels of toxicity and similar promising median survival as S0004. Further study of hypoxia-targeted therapy is warranted in LSCLC.

Initiation of DNA strand cleavage by 1,2,4-benzotriazine 1,4-dioxide antitumor agents: mechanistic insight from studies of 3-methyl-1,2,4-benzotriazine 1,4-dioxide

The antitumor agent 3-amino-1,2,4-benzotriazine 1,4-dioxide (tirapazamine, TPZ, 1) gains medicinal activity through its ability to selectively damage DNA in the hypoxic cells found inside solid tumors. This occurs via one-electron enzymatic reduction of TPZ to yield an oxygen-sensitive drug radical (2) that leads to oxidatively generated DNA damage under hypoxic conditions. Two possible mechanisms have been considered to account for oxidatively generated DNA damage by TPZ. First, homolysis of the N-OH bond in 2 may yield the well-known DNA-damaging agent, hydroxyl radical. Alternatively, it has been suggested that elimination of water from 2 generates a benzotriazinyl radical (4) as the ultimate DNA-damaging species. In the studies described here, the TPZ analogue 3-methyl-1,2,4-benzotriazine 1,4-dioxide (5) was employed as a tool to probe the mechanism of DNA damage within this new class of antitumor drugs. Initially, it was demonstrated that 5 causes redox-activated, hypoxia-selective oxidation of DNA and small organic substrates in a manner that is completely analogous to TPZ. This suggests that 5 and TPZ damage DNA by the same chemical mechanism. Importantly, the methyl substituent in 5 provides a means for assessing whether the putative benzotriazinyl intermediate 7 is generated following one-electron reduction. Two complementary isotopic labeling experiments provide evidence against the formation of the benzotriazinyl radical intermediate. Rather, a mechanism involving the release of hydroxyl radical from the activated drug radical intermediates can explain the DNA-cleaving properties of this class of antitumor drug candidates.

Lower osteopontin plasma levels are associated with superior outcomes in advanced non-small-cell lung cancer patients receiving platinum-based chemotherapy: SWOG Study S0003

PURPOSE

S0003 was a phase III trial of carboplatin/paclitaxel with or without the hypoxic cytotoxin tirapazamine in patients with advanced or metastatic non-small-cell lung cancer (NSCLC). We investigated the relationship between clinical outcomes and plasma levels of the hypoxia-associated protein osteopontin (OPN) in patients on this protocol.

PATIENTS AND METHODS

Baseline plasma was obtained from 172 patients. In 56 patients, sequential plasma was obtained after one or two cycles. Concentrations of OPN, as well as plasminogen activator inhibitor-1 (PAI-1) and vascular endothelial growth factor (VEGF), were measured using enzyme-linked immunosorbent assay. Tumor expression of OPN was assessed by immunohistochemistry in 61 matched archival specimens.

RESULTS

Patients with lower OPN levels (below the median) had a significantly superior overall survival compared with patients with higher levels, regardless of treatment arm (hazard ratio [HR] = 0.60, P = .002). A similar correlation was observed for progression-free survival (HR = 0.69, P = .02). When examined as a continuous variable, OPN maintained its significant association with both progression-free (HR = 1.05, P = .01) and overall survival (HR = 1.09, P < .0001). Patients with lower plasma OPN levels were significantly more likely to have tumor response (P = .03). No differences were observed between treatment arms. Tumor OPN levels did not correlate with patient outcomes or with plasma levels. No associations were observed between patient outcomes and VEGF or PAI-1 levels; however, plasma concentrations of these markers were significantly interrelated (P < .0001) and significantly decreased after treatment (P = .0002 and P = .03, respectively).

CONCLUSION

Pretreatment plasma levels of OPN are significantly associated with patient response, progression-free survival, and overall survival in chemotherapy-treated patients with advanced NSCLC.

Quantitative measure of cytotoxicity of anticancer drugs and other agents

Many anticancer drugs act on cancer cells to promote apoptosis, which includes impairment of cellular respiration (mitochondrial O(2) consumption). Other agents also inhibit cellular respiration, sometimes irreversibly. To investigate the sensitivity of cancer cells to cytotoxins, including anticancer drugs, we compare the profiles of cellular O(2) consumption in the absence and presence of these agents. Oxygen measurements are made at 37 degrees C, using glucose as a substrate, with [O(2)] obtained from the phosphorescence decay rate of a palladium phosphor. The rate of respiration k is defined as -d[O(2)]/dt in a sealed container. Different toxins produce different profiles of impaired respiration, implying different mechanisms for the drug-induced mitochondrial dysfunction. The decrease in the average value of k over a fixed time period, I, is proposed as a characteristic value to assess mitochondrial injury. The value of I depends on the nature of the toxin, its concentration, and the exposure time as well as on the cell type. Results for several cell types and 10 cytotoxins are presented here.

Homologous recombination is the principal pathway for the repair of DNA damage induced by tirapazamine in mammalian cells

Tirapazamine (3-amino-1,2,4-benzotriazine-1,4-dioxide) is a promising hypoxia-selective cytotoxin that has shown significant activity in advanced clinical trials in combination with radiotherapy and cisplatin. The current study aimed to advance our understanding of tirapazamine-induced lesions and the pathways involved in their repair. We show that homologous recombination plays a critical role in repair of tirapazamine-induced damage because cells defective in homologous recombination proteins XRCC2, XRCC3, Rad51D, BRCA1, or BRCA2 are particularly sensitive to tirapazamine. Consistent with the involvement of homologous recombination repair, we observed extensive sister chromatid exchanges after treatment with tirapazamine. We also show that the nonhomologous end-joining pathway, which predominantly deals with frank double-strand breaks (DSB), is not involved in the repair of tirapazamine-induced DSBs. In addition, we show that tirapazamine preferentially kills mutants both with defects in XPF/ERCC1 (but not in other nucleotide excision repair factors) and with defects in base excision repair. Tirapazamine also induces DNA-protein cross-links, which include stable DNA-topoisomerase I cleavable complexes. We further show that gamma H2AX, an indicator of DNA DSBs, is induced preferentially in cells in the S phase of the cell cycle. These observations lead us to an overall model of tirapazamine damage in which DNA single-strand breaks, base damage, and DNA-protein cross-links (including topoisomerase I and II cleavable complexes) produce stalling and collapse of replication forks, the resolution of which results in DSB intermediates, requiring homologous recombination and XPF/ERCC1 for their repair.

Oxygen Dependence and Extravascular Transport of Hypoxia-Activated Prodrugs: Comparison of the Dinitrobenzamide Mustard PR-104A and Tirapazamine

PURPOSE

To compare oxygen dependence and tissue transport properties of a new hypoxia-activated prodrug, PR-104A, with tirapazamine, and to evaluate the implications for antitumor activity when combined with radiotherapy.

METHODS AND MATERIALS

Oxygen dependence of cytotoxicity was measured by clonogenic assay in SiHa cell suspensions. Tissue transport parameters were determined using SiHa multicellular layers. Spatially resolved pharmacokinetic (PK) and pharmacodynamic (PD) models were developed to predict cell killing in SiHa tumors and tested by clonogenic assay 18 h after treatment with the corresponding phosphate ester, PR-104.

RESULTS

The K-value (oxygen concentration to halve cytotoxic potency) of PR-104A was 0.126 +/- 0.021 microM (10-fold lower than tirapazamine at 1.30 +/- 0.28 microM). The diffusion coefficient of PR-104A in multicellular layers (4.42 +/- 0.15 x 10(-7) cm2 s(-1)) was lower than that of tirapazamine (1.30 +/- 0.05 x 10(-6) cm2 s(-1)) but PK modeling predicted better penetration to hypoxic cells in tumors because of its slower metabolism. The tirapazamine PK/PD model successfully predicted the measured activity in combination with single-dose radiation against SiHa tumors, and the PR-104A model underpredicted the activity, which was greater for PR-104 than for tirapazamine (at equivalent host toxicity) both with radiation and as a single agent.

CONCLUSION

PR-104/PR-104A has different PK/PD properties from tirapazamine and superior activity with single-dose radiotherapy against SiHa xenografts. We have inferred that PR-104A is better able to kill cells at intermediate partial pressure of oxygen in tumors than implied by the PK/PD model, most likely because of a bystander effect resulting from diffusion of its activated metabolites from severely hypoxic zones.

DNA strand damage product analysis provides evidence that the tumor cell-specific cytotoxin tirapazamine produces hydroxyl radical and acts as a surrogate for O(2)

The compound 3-amino-1,2,4-benzotriazine 1,4-dioxide (tirapazamine, TPZ) is a clinically promising anticancer agent that selectively kills the oxygen-poor (hypoxic) cells found in solid tumors. It has long been known that, under hypoxic conditions, TPZ causes DNA strand damage that is initiated by the abstraction of hydrogen atoms from the deoxyribose phosphate backbone of duplex DNA, but exact chemical mechanisms underlying this process remain unclear. Here we describe detailed characterization of sugar-derived products arising from TPZ-mediated strand damage. We find that the action of TPZ on duplex DNA under hypoxic conditions generates 5-methylene-2-furanone (6), oligonucleotide 3'-phosphoglycolates (7), malondialdehyde equivalents (8 or 9), and furfural (10). These results provide evidence that TPZ-mediated strand damage arises via hydrogen atom abstraction from both the most hindered (C1') and least hindered (C4' and C5') positions of the deoxyribose sugars in the double helix. The products observed are identical to those produced by hydroxyl radical. Additional experiments were conducted to better understand the chemical pathways by which TPZ generates the observed DNA-damage products. Consistent with previous work showing that TPZ can substitute for molecular oxygen in DNA damage reactions, it is found that, under anaerobic conditions, reaction of TPZ with a discrete, photogenerated C1'-radical in a DNA 2'-oligodeoxynucleotide cleanly generates the 2-deoxyribonolactone lesion (5) that serves as the precursor to 5-methylene-2-furanone (6). Overall, the results provide insight regarding the chemical structure of the DNA lesions that confront cellular repair, transcription, and replication machinery following exposure to TPZ and offer new information relevant to the chemical mechanisms underlying TPZ-mediated strand cleavage.

Carbonic anhydrase 9 (CA9) expression in tumor cells enhances sensitivity to tirapazamine

PURPOSE

Carbonic anhydrase 9 (CA9) is over-expressed in many human solid tumors under conditions of low oxygen concentration and can be associated with a low probability of survival. In this study, stable CA9-expressing cell lines were established using the CA9 gene-defective human C33a cell line and the HeLa cell line to investigate the role of CA9 in response to ionizing radiation and hypoxia-selective cytotoxin, Tirapazamine (TPZ).

METHODS AND MATERIALS

Human CA9 cDNA or an empty vector was transfected into the C33a and HeLa cell lines and C33a-vector, C33a-CA9, HeLa-vector, and HeLa-CA9 cell lines were produced accordingly. Sensitivity of the C33a-vector/C33a-CA9 cells to ionizing radiation and TPZ was measured using clonogenic assays. The alkaline comet assay was used to measure single strand DNA breaks caused by TPZ in the C33a-vector, C33a-CA9, HeLa-vector, and HeLa-CA9 cell lines.

RESULTS

Radiation sensitivity, as determined with clonogenic survival assays, of C33a-vector/C33a-CA9 cells did not differ under either normoxic or hypoxic conditions. However, increased clonogenic sensitivity to TPZ was observed in C33a-CA9 cells under the hypoxic condition by 26% (95% CI 14-39%, P = 0.02 in comparison to the C33a-vector cells). The comet assay showed significantly greater DNA damage in the C33a-CA9 cells compared with that of the C33a-vector cells with the same treatment under hypoxic conditions, supporting the results of the clonogenic survival data. Because this difference in the amount of DNA damage was not observed for the hypoxic HeLa-CA9/HeLa-vector cell lines, both of which have induced CA9 expression by hypoxia, the enhanced sensitivity of C33a-CA9 cells to TPZ is considered to be due to the specific condition of CA9 over-expression.

CONCLUSION

Our results suggest the possibility that CA9 over-expression in tumors might be exploited to increase the treatment effects of TPZ.

The usefulness of mild temperature hyperthermia combined with continuous tirapazamine administration under reduced dose-rate irradiation with gamma-rays

PURPOSE

We clarified the usefulness of mild temperature hyperthermia (MTH) in combination with the continuous administration of tirapazamine (TPZ) under reduced dose-rate irradiation (RDRI) using gamma-rays.

MATERIALS AND METHODS

SCC VII tumour-bearing mice received a continuous administration of 5-bromo-2'-deoxyuridine (BrdU) to label all proliferating (P) cells. Then, they received a 24 h continuous subcutaneous infusion of TPZ either with or without MTH under high dose-rate irradiation (HDRI) or RDRI using gamma-rays. After the irradiation, the tumour cells were isolated and incubated with a cytokinesis blocker, and the micronucleus (MN) frequency in non-proliferating tumour cells without BrdU labeling (= quiescent (Q) cells) was determined using immunofluorescence staining for BrdU. The MN frequency in the total tumour cell populations was determined using tumours that were not pretreated with BrdU.

RESULTS

The sensitivity of both the total and Q cell populations, especially the latter, was significantly reduced with RDRI compared with HDRI. TPZ increased the sensitivity of both populations, with a slightly more remarkable increase in Q cells. Further, MTH combined with TPZ raised the sensitivity of both the total and Q cell populations, especially the latter, under RDRI more markedly than under HDRI.

CONCLUSION

From the viewpoint of solid tumour control as a whole, including intratumour Q-cell control, the use of TPZ, especially in combination with MTH, is useful for suppressing the reduction in the sensitivity of tumour cells caused by the decrease in irradiation dose rate in vivo.

Tirapazamine plus cisplatin and irradiation in a mouse model: improved tumor control at the cost of increased toxicity

PURPOSE

Tirapazamine (TPZ) reportedly enhances the tumor cell killing effect of cisplatin up to fivefold and it is an attractive drug for combination with radiotherapy. We evaluated the toxicity of a fractionated combined treatment.

METHODS

Murine RIF-1 fibrosarcomas growing on the right hind foot of C3-H mice were used. Within 2 weeks, animals were treated with six i.p. injections of TPZ (43.2-172.8 mg/kg total), and/or cisplatin (24 mg/kg total) and ten fractions of 2 Gy to the tumor. All treatments were carried out under anesthesia. Maximum follow-up was 35 days. The local tumor control was determined by calculating the tumor doubling time t (2vo). In addition to standard toxicity assessment, the major inner organs were examined histologically.

RESULTS

The administration of low TPZ doses to the cisplatin/radiotherapy treatment caused only little changes in tumor doubling time (t (2vo)) and led to a lethality rate of 15-30%. Higher TPZ doses caused an increase in t (2vo), but also a further increase in lethality and toxicity in particular to the heart, liver, kidney and stomach. Cisplatin/radiotherapy treatment without TPZ produced no severe toxicity.

CONCLUSIONS

This is a detailed study of both the acute and delayed toxicities of combined TPZ treatment in a mouse model. In our study the addition of TPZ to the cisplatin/radiotherapy treatment caused a significant increase in toxicity with only moderate effect on the tumor.

Synthesis, structure and hypoxic cytotoxicity of 3-amino-1,2,4-benzotriazine-1,4-dioxide derivatives

A series of novel 3-amino-1,2,4-benzotriazine-1,4-dioxide derivatives were synthesized and screened for their in vitro cytotoxicity against promyelocytic leukemia HL-60, androgen-independent prostate tumor PC3, hepatocellular carcinoma Bel-7402, human esophagus tumor ECA-109, and human breast tumor MCF-7 cell lines in hypoxia and in normoxia. Most compounds showed higher cytotoxic activity both in hypoxia and in normoxia. Among them, compounds 61 and 62 showed more potent cytotoxic activity and hypoxic selectivity when compared to tirapazamine.

Pretreatment 18F-FAZA PET Predicts Success of Hypoxia-Directed Radiochemotherapy Using Tirapazamine

We evaluated the predictive value of PET using the hypoxia tracer (18)F-fluoroazomycin arabinoside ((18)F-FAZA) for success of radiotherapy in combination with tirapazamine, a specific cytotoxin for hypoxic cells.

METHODS

Imaging was performed on EMT6 tumor-bearing nude mice before allocating mice into 4 groups: radiochemotherapy (RCT: 8 fractions of 4.5 Gy within 4 d combined with tirapazamine, 14 mg/kg), radiotherapy alone (RT), chemotherapy alone (tirapazamine) (CHT), or control. Treatment success was assessed by several tumor growth assays, including tumor growth time from 70 to 500 microL and absolute growth delay (aGD). The median pretreatment (18)F-FAZA tumor-to-background ratio served as a discriminator between "hypoxic" and "normoxic" tumors.

RESULTS

The mean tumor growth was significantly accelerated in hypoxic control tumors (growth time from 70 to 500 microL, 11.0 d) compared with normoxic control tumors (growth time from 70 to 500 microL, 15.6 d). Whereas RT delayed tumor growth regardless of the level of hypoxia, an additive beneficial therapeutic effect of tirapazamine to RT was observed only in hypoxic tumors (aGD, 12.9 d) but not in normoxic tumors (aGD, 6.0 d).

CONCLUSION

This study provides compelling evidence that hypoxia imaging using (18)F-FAZA PET is able to predict the success of RCT of tumor-bearing mice using the hypoxia-activated chemotherapeutic agent tirapazamine. Pretreatment (18)F-FAZA PET, therefore, offers a way for the individualization of tumor treatment involving radiation. The data suggest that by reserving hypoxia-directed therapy to tumors with high (18)F-FAZA uptake, improvement of the therapeutic ratio is possible, as the therapeutic effect of tirapazamine seems to be restricted to hypoxic tumors.

[Inhibitory effect of tirapazamine combined with phosphatidylinositol 3-kinase inhibitor LY294002 to ovarian cancer cells]

OBJECTIVE

To study the inhibitory effect of tirapazamine (TPZ) combined with LY294002, an inhibitor of phosphatidylinositol 3-kinase (PI3K), on the growth of human ovarian carcinoma cells.

METHODS

Human ovarian carcinoma cells of the line HO8910PM were cultured and treated with tirapazamine alone and treated with TPZ of different concentrations combined with LY294002 of the concentration of 50 micromol/L respectively under aerobic and hypoxic conditions. And human ovarian carcinoma cells of the line OVCAR-3 were cultured and treated with YPZ alone and treated with TPZ of different concentrations combined with LY294002 of the concentration of 25 micromol/L respectively under aerobic and hypoxic conditions. MTT method was used to detect the surviving fractions of these carcinoma cells.

RESULTS

The IC(50) values of TPZ on the HO8910PM cells under hypoxic condition was 40.6 micromol/L, significantly lower than that under aerobic condition (53.0 micromol/L, P < 0.01). The IC(50) values of TPZ on the OVCAR-3 cells under hypoxic condition was 65.9 micromol/L, significantly lower than that under aerobic condition (97.4 micromol/L, P < 0.01). The IC(50) value of TPZ combined with LY294002 on the HP8910PM cells under hypoxic condition was 22.7 micromol/L, significantly lower than that under aerobic condition (31.5 micromol/L, P < 0.01). The IC(50) value of TPZ combined with LY294002 on the OVCAR-3 cells under hypoxic condition was 49.1 micromol/L, not significantly different from that under aerobic condition (51.0 micromol/L, P > 0.05).

CONCLUSION

TPZ inhibits the growth of human ovarian carcinoma cells. The inhibitory effects of TPZ on the growth of human ovarian carcinoma cell of the lines HO8910PM and OVCAR-3 under hypoxic conditions are significantly higher than those under aerobic condition1. LY294002 increases the inhibitory effect of TPZ on the ovarian cancer cells, compared with TPZ treatment alone, TPZ combined with LY294002 decreases the IC(50) of HO8910PM and OVCAR-3 cells significantly.

Bioreductive drugs: from concept to clinic

One of the key issues for radiobiologists is the importance of hypoxia to the radiotherapy response. This review addresses the reasons for this and primarily focuses on one aspect, the development of bioreductive drugs that are specifically designed to target hypoxic tumour cells. Four classes of compound have been developed since this concept was first proposed: quinones, nitroaromatics, aliphatic and heteroaromatic N-oxides. All share two characteristics: (1) they require hypoxia for activation and (2) this activation is dependent on the presence of specific reductases. The most effective compounds have shown the ability to enhance the anti-tumour efficacy of agents that kill better-oxygenated cells, i.e. radiation and standard cytotoxic chemotherapy agents such as cisplatin and cyclophosphamide. Tirapazamine (TPZ) is the most widely studied of the lead compounds. After successful pre-clinical in vivo combination studies it entered clinical trial; over 20 trials have now been reported. Although TPZ has enhanced some standard regimens, the results are variable and in some combinations toxicity was enhanced. Banoxantrone (AQ4N) is another agent that is showing promise in early phase I/II clinical trials; the drug is well tolerated, is known to locate in the tumour and can be given in high doses without major toxicities. Mitomycin C (MMC), which shows some bioreductive activation in vitro, has been tested in combination trials. However, it is difficult to assign the enhancement of its effects to targeting of the hypoxic cells because of the significant level of its hypoxia-independent toxicity. More specific analogues of MMC, e.g. porfiromycin and apaziquone (EO9), have had variable success in the clinic. Other new drugs that have good pre-clinical profiles are PR 104 and NLCQ-1; data on their clinical safety/efficacy are not yet available. This paper reviews the pre-clinical data and discusses the clinical studies that have been reported.

Assessment of DNA damage at the dimer level: measurement of the formamide lesion

UVC-radiation-induced DNA damage was measured in mouse fibroblast cells using liquid chromatography-tandem mass spectrometry (LC-MS/MS) in conjunction with isotopically labeled internal standards. The thymine glycol and formamide lesions were assayed in the form of modified dinucleoside monophosphates. The 8-oxo-7,8-dihydroguanine lesion was measured as the modified nucleoside. DNA damage in cells treated with tirapazamine was also measured. Tirapazamine is a chemotherapeutic agent that acts via a free radical mechanism. The two agents, UVC radiation and tirapazamine, produce markedly different profiles of DNA damage, reflecting their respective mechanisms of action. Both agents produce significant amounts of thymine glycol and formamide damage, but only the former produced a measurable amount of the 8-oxo-7,8-dihydroguanine lesion. The merits of measuring DNA damage at the dimer level are discussed.

On the mechanism of reaction of radicals with tirapazamine

Ketyl radicals produced by photolysis of ketones or di-tert-butyl peroxide (DTBP) in alcohol solvents react rapidly with tirapazamine (TPZ). The acetone ketyl radical (ACOH) reacts with TPZ with an absolute second-order rate constant of (9.7 +/- 0.4) x 108 M-1 s-1. The reaction kinetics can be followed by monitoring the bleaching of TPZ absorption at 475 nm or the formation of a reaction product which absorbs at 320 and 410 nm. The ACOD radical reacts with TPZ in 2-propanol-OD with an absolute rate constant of (6.7 +/- 0.5) x 108 M-1 s-1, corresponding to a kinetic isotope effect (KIE) of 1.4. Deuteration of the radical on carbon (ACOH-d6) retards the reaction of the radical with TPZ even further (absolute rate constant = (4.8 +/- 0.04) x 108 M-1 s-1). This result corresponds to a KIE of 2.0. Radicals derived from dioxane and diisopropyl ether by flash photolysis of DTBP in ethereal solvent react with TPZ more slowly than do ketyl radicals. It is concluded that ketyl radicals react, in part, with TPZ in organic solvents by transfer of a hydrogen atom from the OH and CH3 groups of the ketyl radical to the oxygen atom at the N4 position of TPZ to form acetone or acetone enol and a radical derivative of TPZ (TPZH). The latter species absorbs at 320 and 405 nm, has a lifetime of hundreds of microseconds in alcohol solvents, and decays by disproportionation to form TPZ and a reduced heterocycle. The reduced heterocycle eventually forms a desoxytirapazamine by a polar mechanism. The results are supported by density functional theory calculations. It is proposed that dioxanyl radical will also react, in part, with TPZ by transfer of a hydrogen atom from the carbon adjacent to the radical center to the oxygen atom at the N4 position of TPZ. This produces the enol ether and the previously mentioned TPZH radical. It is further posited that ether radicals react a bit more slowly than ketyl radicals because they lack the second mode of hydrogen transfer (from the OH group) that is present in the ACOH radical. Our data are permissive of the possibility that ether radicals add to TPZ at a rate that is competitive with beta-hydrogen atom transfer.

Distribution of hematopoietic stem cells in the bone marrow according to regional hypoxia

The interaction of stem cells with their bone marrow microenvironment is a critical process in maintaining normal hematopoiesis. We applied an approach to resolve the spatial organization that underlies these interactions by evaluating the distribution of hematopoietic cell subsets along an in vivo Hoechst 33342 (Ho) dye perfusion gradient. Cells isolated from different bone marrow regions according to Ho fluorescence intensity contained the highest concentration of hematopoietic stem cell (HSC) activity in the lowest end of the Ho gradient (i.e., in the regions reflecting diminished perfusion). Consistent with the ability of Ho perfusion to simulate the level of oxygenation, bone marrow fractions separately enriched for HSCs were found to be the most positive for the binding of the hypoxic marker pimonidazole. Moreover, the in vivo administration of the hypoxic cytotoxic agent tirapazamine exhibited selective toxicity to the primitive stem cell subset. These data collectively indicate that HSCs and the supporting cells of the stem cell niche are predominantly located at the lowest end of an oxygen gradient in the bone marrow with the implication that regionally defined hypoxia plays a fundamental role in regulating stem cell function.

Phase I trial of tirapazamine, cisplatin, and concurrent accelerated boost reirradiation in patients with recurrent head and neck cancer

PURPOSE

Reirradiation (re-RT) with concurrent chemotherapy offers a therapeutic option in patients who have locoregional recurrence of head and neck cancer (HNC). The hypoxic cell sensitizer, tirapazamine (TPZ), has demonstrated promising results in first-line therapy for HNC. This phase I trial was designed to test the feasibility of giving TPZ in the re-RT setting.

METHODS AND MATERIALS

Patients with recurrent HNC who received prior radiotherapy (RT) were enrolled and received TPZ (260 mg/m2) and cisplatin (50 mg/m2) Weeks 1, 3, and 5 concurrently with RT (72 Gy, 42 fractions over 6 weeks). TPZ (160 mg/m2) alone was added on Days 1, 3, and 5 of Week 2 (cohort 1) or Weeks 2 and 4 (cohort 2).

RESULTS

Twenty-five subjects were enrolled, 7 and 18 on cohorts 1 and 2, respectively. Significant toxicities included Grade 3 dermatitis (20%) and Grade 3 mucositis (40%). Dose-limiting toxicity was observed on cohort 2 (1 patient with aspiration pneumonia). Four deaths occurred during treatment. Two fatalities occurred after completing therapy as a result of carotid artery rupture. With a minimum and median follow-up of 14 and 24 months, respectively, median overall survival was 14 months with actuarial 1-year and 2-year survival of 56% and 27%, respectively.

CONCLUSION

Reirradiation with concomitant chemotherapy including TPZ in patients with unresectable recurrent HNC is feasible and results in long-term survival in a significant proportion of patients.

DNA repair mechanisms are involved in the hypoxia-dependent toxicity of NLCQ-1 (NSC 709257) and its synergistic interaction with alkylating agents

BACKGROUND

The hypoxia selective cytotoxin NLCQ-1 significantly potentiates the antitumor effect of several alkylating agents in vitro and in vivo. Synergy in mice requires administration of NLCQ-1 ca. 1 h before the alkylating agent, a fact that may be related to an in vitro hypoxic pretreatment effect. Since NLCQ-1 targets DNA through weak intercalation, the induction of DNA lesions upon reductive metabolism may be a reasonable mechanism that predisposes cells to further damage by a subsequent alkylating agent.

MATERIALS AND METHODS

To indirectly identify such lesions, cell lines defective in specific DNA repair genes (EM9 and UV41) and their repair-proficient parental AA8, were exposed to NLCQ-1 +/-L-PAM/cisDDP under hypoxic/aerobic conditions and appropriate administration routes, and assessed for clonogenicity. Selected comparisons with tirapazamine (TPZ) were also performed.

RESULTS

EM9 cells, which lack the functional XRCC1 gene involved in base excision repair, and thus are unable to efficiently repair DNA single-strand breaks (ssbs), were 3.7-fold and 4.5-fold more sensitive to NLCQ-1 and TPZ, respectively, than the parental AA8 cells, under hypoxic conditions. UV41 cells, which are defective in repairing DNA interstrand cross-links (ERCC4/XPF), were 4.5-fold more sensitive than AA8 cells to NLCQ-1. In potentiation studies with melphalan or cisplatin, synergy was observed in AA8 cells but not in EM9 or UV41 cells, with either NLCQ-I or TPZ.

CONCLUSION

These results suggest that NLCQ-1 is involved in the formation of DNA ssbs and interstrand crosslinks under hypoxic conditions. The synergistic interaction of NLCQ-1 with L-PAM or cisDDP is probably due to an enhancement in the L-PAM/cisDDP-induced DNA interstrand cross-links, possibly as a result of an inhibited repair mechanism of these lesions.

Phase II study of tirapazamine plus cisplatin in patients with advanced or recurrent cervical cancer

The aim of this study was to evaluate the activity and toxicity of a tirapazamine (TPZ)/cisplatin drug combination in patients with stage IV or recurrent cervical cancer. The chemotherapy was administered for a maximum of eight cycles every 21 days. TPZ was administered intravenously at 330 mg/m(2) over a 2-h infusion, followed 1 h later by cisplatin intravenously at 75 mg/m(2) over 1 h on day 1. All patients received antiemetics including dexamethasone, ondansetron, and lorazepam. Subsequent doses were unchanged, reduced, or omitted according to observed toxicity and protocol guidelines. Response evaluation was performed every two cycles. Thirty-six patients with stage IV or recurrent cervical cancer were treated. Ninety-four percent of patients had prior radiotherapy. Two patients had prior chemotherapy. There were two complete responses and eight partial responses (27.8%). An additional 11 patients (30.6%) had stable disease as their best response. Response rate was greater in tumors outside of the previously radiated field (44.4% vs 11.1%). The median time to progression was 32.7 weeks. The most frequent grade 3 or 4 adverse events were nausea, vomiting, and fatigue, which occurred in 30.6%, 25%, and 22% of subjects, respectively. Anemia was the most frequent grade 3 or 4 hematologic toxicity at 8.3%. We conclude that the combination of cisplatin and TPZ was reasonably well tolerated in patients with recurrent or advanced cervical cancer. Further evaluation of this drug combination may be warranted.

Effects of fluctuating oxygenation on tirapazamine efficacy: Theoretical predictions

PURPOSE

To examine the effects of fluctuating oxygen levels on the hypoxic cytotoxin tirapazamine (TPZ) using theoretical predictions.

METHODS AND MATERIALS

Tirapazamine's pharmacokinetic and pharmacodynamic oxygen dependence has previously been characterized in vitro. Here, a one-dimensional theoretical model was used to examine the effects of fluctuating hypoxia on metabolized TPZ concentration, assuming sinusoidally fluctuating oxygen levels. TPZ concentration is changing according to published experimental data. Simulations of experimentally observed time-courses of perivascular pO2 were also conducted.

RESULTS

The predicted pharmacodynamic effect of TPZ was increased with fluctuating (vs. constant) hypoxia at all frequencies (1-30 min period) and all amplitudes (1-15 mm Hg). Additionally, fluctuating oxygen resulted in more metabolized TPZ near the oxygen source as compared with the steady-state condition of the same overall average pO2.

CONCLUSIONS

Fluctuating pO2 reduced the concentration of metabolized TPZ at distances farther from the source, thereby limiting its ability to reach and kill the most hypoxic cells. These results suggest that the kinetics of fluctuating oxygenation should be taken into account when considering drug designs that involve oxygen-sensitive agents.

Complete 1H, 13C and 15N NMR assignment of tirapazamine and related 1,2,4-benzotriazine N-oxides

1H, 13C and 15N NMR measurements (1D and 2D including 1H--15N gs-HMBC) have been carried out on 3-amino-1, 2,4-benzotriazine and a series of N-oxides and complete assignments established. N-Oxidation at any position resulted in large upfield shifts of the corresponding N-1 and N-2 resonances and downfield shifts for N-4 with the exception of the 3-amino-1,2,4-benzotriazine 1-oxide in which a small upfield shift of N-4 was observed. Density functional GIAO calculations of the 15N and 13C chemical shifts [B3LYP/6-31G(d)//B3LYP/6-311+G(2d,p)] gave good agreement with experimental values confirming the assignments. The combination of 13C and 15N NMR provides an unambiguous method for assigning the 1H and 13C resonances of N-oxides of 1,2,4-benzotriazines.

Use of three-dimensional tissue cultures to model extravascular transport and predict in vivo activity of hypoxia-targeted anticancer drugs

BACKGROUND

Because of the inefficient vasculature of solid tumors, anticancer drugs must penetrate relatively long distances through the extravascular compartment. The requirement for such diffusion may limit their activity, especially that of hypoxia-targeted drugs. We tested whether a three-dimensional pharmacokinetic/pharmacodynamic (PK/PD) model based on a representative mapped tumor microvascular network could predict the therapeutic activity of anticancer drugs in mouse xenograft tumors.

METHODS

Diffusion coefficients of the hypoxia-activated anticancer drug tirapazamine (TPZ) and of 15 TPZ analogs were estimated by measuring their transport through HT29 colon cancer multicellular layers (MCLs). Anoxic cytotoxic potency (by clonogenic assay) and metabolism of the TPZ analogs were measured in HT29 cell suspensions, and their plasma pharmacokinetics was measured in CD-1 nude mice. This information was used to create a spatially resolved PK/PD model for the tumor microvascular network. Model predictions were compared with actual hypoxic cell kill as measured by clonogenic assays on HT29 xenograft tumors 18 hours after treatment with each TPZ analog.

RESULTS

Modeling TPZ transport in the tumor microvascular network showed substantial drug depletion in the most hypoxic regions, with predicted maximum cell kill of only 3 logs, compared with more than 10 logs if there were no transport impediment. A large range of tissue diffusion coefficients (0.027 x 10(-6)-1.87 x 10(-6) cm2/s) was observed for the TPZ analogs. There was a strong correlation between model-predicted and measured hypoxic cell kill (R2 = 0.89) but a poor correlation when the model did not include extravascular transport (R2 = 0.32).

CONCLUSIONS

Extravascular transport in tumors, and its consequences for tumor cell killing, can be predicted by measuring drug penetration through MCLs in vitro and modeling pharmacokinetics at each position in three-dimensional microvascular networks.

Dependency of the effect of a vascular disrupting agent on sensitivity to tirapazamine and gamma-ray irradiation upon the timing of its administration and tumor size, with reference to the effect on intratumor quiescent cells

PURPOSE

The effect of vascular disrupting agent ZD6126 with time on the sensitivity to the hypoxic cytotoxin tirapazamine (TPZ) and gamma-rays was examined in large and small solid tumors.

METHODS

Mice bearing SCC VII tumors 1 or 1.5 cm in diameter received 5-bromo-2'-deoxyuridine (BrdU) continuously to label all proliferating (P) cells, followed by injection with or without ZD6126. In the absence of ZD6126, or 1 or 24 h following ZD6126 injection, the response to TPZ or gamma-ray irradiation in quiescent (Q) cells was assessed in terms of induced micronucleus (MN) frequency using immunofluorescence staining for BrdU. The MN frequency in the total cell population was determined from the tumors not pretreated with BrdU. Another group of tumor-bearing mice received a series of test doses of gamma-rays while alive or after tumor clamping to obtain hypoxic fractions (HFs) in the tumors.

RESULTS

One hour after ZD6126 injection, both small and large tumors showed lower and higher sensitivity, and 24 h after, higher and lower sensitivity, to gamma-rays and TPZ, respectively, than the tumors not treated with ZD6126. Further, they showed larger and smaller HFs 1 and 24 h after ZD6126 injection, respectively. Without ZD6126 and 1 h after injection, small tumors were more sensitive to gamma-rays and less sensitive to TPZ than large tumors, probably due to the smaller HFs than large tumors. In contrast, 24 h after the injection, these differences in sensitivity and the HF between small and large tumors were reversed. The changes in sensitivity and the size of the HF were more marked in the total cell population than in Q cells.

CONCLUSIONS

Following ZD6126 treatment, in terms of tumor control, especially large tumors and total tumor cell population, administering TPZ 1 h later and gamma-ray irradiation 24 h later were effective. Intratumor physiologic factors such as the size of the HF, depending on the time after ZD6126 injection, have to be taken into account when combining another treatment with ZD6126.

The usefulness of a continuous administration of tirapazamine combined with reduced dose-rate irradiation using {gamma}-rays or reactor thermal neutrons

We clarified the usefulness of the continuous administration of tirapazamine (TPZ) in combination with reduced dose-rate irradiation (RDRI) using gamma-rays or reactor thermal neutrons. Squamous cell carcinoma (SCC) VII tumour-bearing mice received a continuous administration of 5-bromo-2'-deoxyuridine (BrdU) to label all proliferating (P) cells. Then, they received a single intraperitoneal injection or 24 h continuous subcutaneous infusion of TPZ in combination with conventional dose-rate irradiation (CDRI) or RDRI using gamma-rays or thermal neutrons. After irradiation, the tumour cells were isolated and incubated with a cytokinesis blocker, and the micronucleus (MN) frequency in cells without BrdU labelling ( = quiescent (Q) cells) was determined using immunofluorescence staining for BrdU. The MN frequency in the total tumour cells was determined using tumours that were not pre-treated with BrdU. The sensitivity of both total and Q cells, especially of Q cells, was significantly reduced with RDRI compared with CDRI. Combination of TPZ increased the sensitivity of both populations, with a slightly more remarkable increase in Q cells. Furthermore, the continuous administration of TPZ raised the sensitivity of both total and Q cell populations, especially the former, more markedly than the single administration, whether combined with CDRI or RDRI using gamma-rays or thermal neutrons. From the viewpoint of solid tumour control as a whole, including intratumour Q-cell control, the use of TPZ, especially when administered continuously, combined with RDRI, is useful for suppressing the reduction in the sensitivity of tumour cells caused by the decrease in irradiation dose rate in vivo.

Hypoxia: Targeting the Tumour

Solid tumours contain regions of very low oxygen concentrations that are said to be hypoxic. Hypoxia is a natural phenotype of solid tumours resulting from an imperfect vascular network. There are a number of consequences associated with tumour hypoxia including: resistance to ionising radiation, resistance to chemotherapy and the magnification of mutated p53. In addition tissue hypoxia has been regarded as a key factor for tumour aggressiveness and metastasis by activation of signal transduction pathways and gene regulatory mechanisms. It is clear that hypoxia in solid tumours promotes a strong oncogenic phenotype and is a phenomenon that occurs in all solid tumours. As such this provides a significant target for drug discovery particularly for tumour-targeting agents. A range of chemical classes (N-oxides, quinones, nitro-aromatics) have been explored as bioreductive agents that target tumour hypoxia. The most advanced agent, tirapazamine, is in phase III clinical trials in combination with cis-platin. The aim of this review is to give a brief overview of the current molecules and strategies being explored for targeting tumour hypoxia.

Synthesis and hypoxic-cytotoxic activity of some 3-amino-1,2,4-benzotriazine-1,4-dioxide derivatives

A series of 3-amino-1,2,4-benzotriazine-1,4-dioxide derivatives 1 have been synthesized and evaluated for their cytotoxic activity in vitro against human leukemia cell lines: Molt-4, K562, HL60, human liver cancer cell Hep-G2, human prostate cancer cell PC-3 in hypoxia. Most of the compounds showed more potent activity than TPZ. Compounds 1i and 1m displayed encouraging superior activity against Molt-4 and HL-60 cell lines. Three potential derivatives received the test of the activity in hypoxia and in normoxia against Molt-4 and HL-60 cell lines and showed obvious hypoxia selectivity. Further mechanism study revealed that the cytotoxic activities of compounds 1i and 1k in Molt-4 cells might be mediated by modulation of p53 protein expression and mitochondrial membrane potential (DeltaPsi(m)).

Concurrent Chemoradiotherapy for Locally Advanced, Nonmetastatic, Squamous Carcinoma of the Head and Neck: Consensus, Controversy, and Conundrum

Radiotherapy and concurrent chemotherapy (CRT) is superior to radiotherapy alone for the treatment of locally advanced, nonmetastatic squamous carcinoma of the head and neck (HNC). Three issues affect the use of CRT as primary treatment for advanced HNC. The first issue is the definition of advanced stage and the initial therapeutic choice of surgery or CRT and the role of post-CRT neck dissection. Function preservation considerations should guide the choice between surgery and CRT for patients with resectable disease. Fluorodeoxyglucose–positron emission tomography scanning may identify patients who require adjuvant neck dissection. The second issue is optimization of radiotherapy and chemotherapy schedules. Ideally, concurrent chemotherapy should be incorporated into radiotherapy (RT) regimens that would constitute optimal therapy were RT to be administered as single-modality treatment. Modified fractionation schemes constitute optimal single-modality RT. Platinum schedules other than bolus dosing every 3 to 4 weeks are effective and may be less toxic. The third issue is integration of biologically targeted therapy into CRT treatment programs. Epidermal growth factor receptor blockade enhances the effectiveness of RT alone. Its role and that of angiogenic blockade in CRT are under investigation.

Prognostic significance of [18F]-misonidazole positron emission tomography-detected tumor hypoxia in patients with advanced head and neck cancer randomly assigned to chemoradiation with or without tirapazamine: a substudy of Trans-Tasman Radiation Oncology Group Study 98.02

PURPOSE

To determine the association between tumor hypoxia, treatment regimen, and locoregional failure (LRF) in patients with stage III or IV squamous cell carcinoma of the head and neck randomly assigned to radiotherapy (70 Gy in 35 fractions over 7 weeks) plus either tirapazamine and cisplatin in weeks 1, 4, and 7 and tirapazamine alone in weeks 2 and 3 (TPZ/CIS) or cisplatin and infusional fluorouracil during weeks 6 and 7 (chemoboost).

PATIENTS AND METHODS

Forty-five patients were enrolled onto a hypoxic imaging substudy of a larger randomized trial. Pretreatment and midtreatment [18F]-fluoromisonidazole positron emission tomography scans (FMISO-PET) were performed 2 hours after tracer administration, with qualitative scoring of uptake in both primary tumors and nodes.

RESULTS

Thirty-two patients (71%) had detectable hypoxia in either or both primary and nodal disease. In patients who received chemoboost, one of 10 patients without hypoxia had LRF compared with eight of 13 patients with hypoxia; the risk of LRF was significantly higher in hypoxic patients (exact log-rank, P = .038; hazard ratio [HR] = 7.1). By contrast, in patients who received the TPZ/CIS regimen, only one of 19 patients with hypoxic tumors had LRF; risk of LRF was significantly higher in chemoboost patients (P = .001; HR = 15). Similarly, looking at the primary site alone, in patients with hypoxic primaries, zero of eight patients treated with TPZ/CIS experienced failure locally compared with six of nine patients treated with chemoboost (P = .011; HR = 0).

CONCLUSION

Hypoxia on FMISO-PET imaging, in patients receiving a nontirapazamine-containing chemoradiotherapy regimen, is associated with a high risk of LRF. Our data provide the first clinical evidence to support the experimental observation that tirapazamine acts by specifically targeting hypoxic tumor cells.