Phase I/pharmacokinetic/biochemical study of the nitroimadazole hypoxic cell sensitiser SR2508 (etanidazole) in combination with cyclophosphamide

Pj, O'Dwyer; LaCreta, FP; Walczak, Judy; Cox, Timothy; Litwin, Samuel; Hoffman, JP; Zimny, M.; Comis, R

doi:10.1038/bjc.1993.424

Cited by 6 publications

(2 citation statements)

References 34 publications

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“…Etanidazole1 is a hypoxic cell radiosensitizer, which are drugs that increase the lethal effect of radiation on cancer cells while possessing the least effect on normal tissues. Studies have shown that tumor with hypoxic cells2 required three times the radiation doses than well‐oxygenated cells 3. Etanidazole can mimic the effects of oxygen, forming toxic DNA radicals that damage cellular DNA and prevent DNA repair,3 thereby enhancing the radiosensitization effect.…”

Section: Introductionmentioning

confidence: 99%

Simulation of intratumoral release of etanidazole: Effects of the size of surgical opening

Tan

Lee

Wang

2003

Journal of Pharmaceutical Sciences

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Section: Introductionmentioning

confidence: 99%

Simulation of intratumoral release of etanidazole: Effects of the size of surgical opening

Tan

Lee

Wang

2003

Journal of Pharmaceutical Sciences

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“…Etanidazole is a 2-nitroimidazole compound postulated to inhibit glutathione S-transferase, rendering tissues more sensitive to the ionizing radiation and alkylating agents used in anti-cancer therapies (O'Dwyer et al, 1993). Etanidazole is structurally very similar to RB6145, whereby the terminal RB6145 Br halide functional group has been substituted with a hydroxy group.…”

Section: Discussionmentioning

confidence: 99%

Engineering Nitroreductase Enzymes for Improved Cancer Gene Therapy and Targeted Cellular Ablation

Sharrock¹

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Bacterial nitroreductases are members of a diverse family of oxidoreductase enzymes that can catalyse the bioreductive activation of nitroaromatic compounds, including anti-cancer prodrugs such as CB1954, SN36506 and nitro-CBI-DEI, and antibiotic prodrugs such as metronidazole. These enzymes have diverse applications in medicine and research, including the anti-cancer strategy gene-directed enzyme-prodrug therapy and targeted ablation of nitroreductase-expressing cells in transgenic zebrafish to model degenerative disease. However, research in these fields to date has focused almost exclusively on the canonical nitroreductase NfsB (from Escherichia coli), which is a relatively inefficient nitroreductase. This thesis presents work aiming to develop superior nitroreductases as tools for targeted cellular ablation and cancer gene therapy through enzyme engineering. For targeted cellular ablation, this research employed rational and random mutagenesis to engineer nitroreductase variants exhibiting substantially improved metronidazole reductase activity when expressed in both bacterial and human cell lines. One such variant was found capable of achieving robust ablation in a transgenic zebrafish model at a 100-fold reduced metronidazole concentration compared to NfsB. To expand the utility of this ablation system, this research additionally identified pairs of nitroreductases with non-overlapping prodrug specificity suitable for use in a ‘multiplex’ system of cellular ablation. It was shown that targeted expression of either nitroreductase ‘partner’ combined with selective administration of its preferred prodrug could enable specific ablation of either of two different cell populations within a mixed culture. Trialling of this system in zebrafish models is ongoing. For cancer gene therapy, directed evolution was carried out to develop a repertoire of candidate nitroreductases having improved abilities to activate a next generation nitroaromatic prodrug, for use in clostridia directed enzyme prodrug therapy (CDEPT). Generation and screening of a targeted site-saturation mutagenesis library identified several variants that displayed improved prodrug activity in vivo. Interestingly, these improvements were not reflected in in vitro purified protein kinetic analyses. Further investigation suggested that an inadvertent driving force behind the in vivo selection of directed evolution libraries in E. coli was the evolution of variants towards heightened specificity for the prodrug of interest over competing intracellular metabolites, rather than the expected improvements in catalytic efficiency. Ongoing evaluation of the top CDEPT candidate nitroreductases will involve assessment of their therapeutic effect in preclinical models when expressed by Clostridium sporogenes. In addition, this research sought to investigate an alternative, novel approach to gene therapy involving the use of CAR-T cells as gene therapy vectors. To achieve this, nitroreductases were engineered to extend the cytotoxic reach of the therapy through activation of high-bystander anticancer prodrugs, while also introducing a metronidazole-mediated kill-switch functionality that would enable targeted ablation of administered CAR-T cells within patients if required. Validation of lead nitroreductases was achieved in cultured human cell models. This research also explored the potential for a bacterial DNA glycosylase to defend nitroreductase-containing cells against the cytotoxic effects of reduced prodrug metabolites. Throughout this work, to complement biological assay data, crystallographic analysis of a selection of evolved nitroreductase variants was undertaken to elucidate the structural bases for the improved prodrug activities observed in vivo.

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Antitumor efficacy and pharmacokinetic analysis of 4-hydroperoxycyclophosphamide in comparison with cyclophosphamide±hepatic enzyme effectors

Teicher

Holden

Goff

et al. 1996

Cancer Chemotherapy and Pharmacology

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4-Hydroperoxycyclophosphamide is an oxazaphosphorine which is readily converted without enzymatic involvement to 4-hydroxycyclophosphamide-a key intermediate in the antitumor activity of this class of drugs. The efficacy of 4-hydroperoxycyclophosphamide as a systemically administered antitumor drug was examined in mice bearing EMT-6 mammary carcinoma and in rats bearing 13762 mammary carcinoma in comparison with other oxazaphosphorines. 4-Hydroperoxycyclophosphamide was a more potent tumor cell killing agent than cyclophosphamide or ifosfamide in animals bearing the EMT-6 tumor. There were no significant differences in the toxicity to bone marrow amongst the three oxazaphosphorines. 4-Hydroperoxycyclophosphamide (90 mg/kg) on days 7, 9 and 11 produced 11.5 days of tumor growth delay compared with 10.4 days and 7.1 days for cyclophosphamide (150 mg/kg) and ifosfamide (150 mg/kg) administered on the same schedule, respectively. 4-Hydroperoxycyclophosphamide was tolerated at 90 mg/kg daily for 5 days and at 75 mg/kg twice daily for 4 days producing tumor growth delays of 14.4 days and 16.6 days, respectively. In rats bearing 13762 tumors, 4-hydroperoxycyclophosphamide (90 mg/kg) on days 8, 10 and 12 produced a tumor growth delay of 14.5 days compared with 8.9 days for cyclophosphamide (100 mg/kg) administered on the same schedule. Treatment of 13762 tumor-bearing rats with phenobarbital, pentobarbital or etanidazole increased the tumor growth delay produced by cyclophosphamide while treatment with cimetidine decreased the tumor growth delay produced by cyclophosphamide but not significantly. Administration of 4-hydroperoxycyclophosphamide (90 mg/kg) produced blood concentrations of 4-hydroxycyclophosphamide three-fold higher than those produced by administration of cyclophosphamide (100 mg/kg) at 15 min after drug injection. Treatment with phenobarbital or pentobarbital increased 4-hydroxycyclophosphamide blood concentration while pretreatment with cimetidine decreased 4-hydroxycyclophosphamide blood concentration from cyclophosphamide. 4-Hydroperoxycyclophosphamide is an effective antitumor agent worthy of further investigation.

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Phase I/pharmacokinetic/biochemical study of the nitroimadazole hypoxic cell sensitiser SR2508 (etanidazole) in combination with cyclophosphamide

Cited by 6 publications

References 34 publications

Simulation of intratumoral release of etanidazole: Effects of the size of surgical opening

Simulation of intratumoral release of etanidazole: Effects of the size of surgical opening

Engineering Nitroreductase Enzymes for Improved Cancer Gene Therapy and Targeted Cellular Ablation

Antitumor efficacy and pharmacokinetic analysis of 4-hydroperoxycyclophosphamide in comparison with cyclophosphamide±hepatic enzyme effectors

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