The role of cytochrome P450 and cytochrome P450 reductase in the reductive bioactivation of the novel benzotriazine di-N-oxide hypoxic cytotoxin 3-amino-l,2,4-benzotriazine-l ,4-dioxide (SR 4233, WIN 59075) by mouse liver

doi:10.1016/0006-2952(92)90007-6

Biochemical Pharmacology

Volume 44, Issue 2, 22 July 1992, Pages 251-259

https://doi.org/10.1016/0006-2952(92)90007-6 Get rights and content

Abstract

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-l-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: β- 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-a-carbonitrile and β-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.

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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.
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Nilutamide is a non-steroidal anti-androgen drug proposed in the treatment of metastatic prostatic carcinoma. Its therapeutic effects are overshadowed by the occurrence of adverse reactions, mediated by mechanisms that remain elusive. To elucidate possible mechanisms for nilutamide toxicity, we investigated the metabolism of nilutamide in rat lung homogenates, in subcellular fractions and in freshly isolated cells.
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^†: Present address: The Institute of Cancer Research, Royal Cancer Hospital, Drug Development Section, 15 Cotswold Road, Belmont, Sutton, Surrey SM2 5NG, U.K.

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The role of cytochrome P450 and cytochrome P450 reductase in the reductive bioactivation of the novel benzotriazine di-N-oxide hypoxic cytotoxin 3-amino-l,2,4-benzotriazine-l ,4-dioxide (SR 4233, WIN 59075) by mouse liver

Abstract

Int J Radiat Oncol Biol Phys

Radiother Oncol

Int J Radial Oncol Biol Phys

Int J Radiat Oncol Biol Phys

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