Metabolism of tirapazamine by multiple reductases in the nucleus

Citation
Ym. Delahoussaye et al., Metabolism of tirapazamine by multiple reductases in the nucleus, BIOCH PHARM, 62(9), 2001, pp. 1201-1209
Citations number
33
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Pharmacology & Toxicology
Journal title
BIOCHEMICAL PHARMACOLOGY
ISSN journal
0006-2952 → ACNP
Volume
62
Issue
9
Year of publication
2001
Pages
1201 - 1209
Database
ISI
SICI code
0006-2952(20011101)62:9<1201:MOTBMR>2.0.ZU;2-Y
Abstract
Tirapazamine (TPZ, 3-amino-1,2,4-benzotriazine 1,4-di-N-oxide, SR4233, Tira zone), a bioreductive drug currently in clinical trials, is selectively tox ic to hypoxic cells commonly found in solid tumors. The toxicity results fr om the intracellular metabolism of TPZ to a highly toxic radical. When oxyg en levels are low, the TPZ radical reacts with cellular molecules, producin g DNA damage and cell death. The much lower toxicity towards aerobic cells results from the back-oxidation of the TPZ radical by oxygen. A major unres olved aspect of the mechanism of TPZ is the identity of the reductase(s) in the cell responsible for activating the drug to its toxic form. We have st udied both the metabolism of the drug using HPLC and the formation of the T PZ radical with a fluorescence assay using dihydrorhodamine 123. We also me asured DNA double- and single-strand breaks produced by TPZ, using the come t assay. We demonstrated that multiple reductases in the nucleus metabolize TPZ under hypoxia. Using the cofactor dependence of the reductases for met abolizing TPZ and of the DNA damage caused by TPZ, we show that DNA single- strand breaks after TPZ metabolism are probably caused by the most abundant source of reductase in the nucleus. DNA double-strand breaks, on the other hand, are formed by TPZ metabolism by an unknown nuclear reductase that re quires only NADPH for its activity. This study is the first to characterize multiple nuclear reductases capable of activating TPZ. (C) 2001 Elsevier S cience Inc. All rights reserved.