title: 3-amino-1,2,4-benzotriazine 4-oxide: characterization of a new metabolite arising from bioreductive processing of the antitumor agent 3-amino-1,2,4-benzotriazine 1,4-dioxide (tirapazamine).
abstract: Tirapazamine (1) is a promising antitumor agent that selectively causes DNA damage in hypoxic tumor cells, following one-electron bioreductive activation. Surprisingly, after more than 10 years of study, the products arising from bioreductive metabolism of tirapazamine have not been completely characterized. The two previously characterized metabolites are 3-amino-1,2,4-benzotriazine 1-oxide (3) and 3-amino-1,2,4-benzotriazine (5). In this work, 3-amino-1,2,4-benzotriazine 4-oxide (4) is identified for the first time as a product resulting from one-electron activation of the antitumor agent tirapazamine by the enzymes xanthine/xanthine oxidase and NADPH:cytochrome P450 oxidoreductase. As part of this work, the novel N-oxide (4) was unambiguously synthesized and characterized using NMR spectroscopy, UV-vis spectroscopy, LC/MS, and X-ray crystallography. Under conditions where the parent drug tirapazamine is enzymatically activated, the metabolite 4 is produced but readily undergoes further reduction to the benzotriazine (5). Thus, under circumstances where extensive reductive metabolism occurs, the yield of the 4-oxide (4) decreases. In contrast, the isomeric two-electron reduction product 3-amino-1,2,4-benzotriazine 1-oxide (3) does not readily undergo enzymatic reduction and, therefore, is found as a major bioreductive metabolite under all conditions. Finally, the ability of the 4-oxide metabolite (4) to participate in tirapazamine-mediated DNA damage is considered.
authors: Departments of Chemistry and Biochemistry, University of Missouri-Columbia, Columbia, Missouri 65211, USA.
authors: T
authors: T
authors: Fuchs
authors: G
authors: G
authors: Chowdhury
authors: C L
authors: CL
authors: Barnes
authors: K S
authors: KS
authors: Gates
mesh_terms: D000970:Antineoplastic Agents / Q000737:chemistry / Q000493:pharmacokinetics*; D002851:Chromatography, High Pressure Liquid; D004249:DNA Damage / Q000187:drug effects; D007202:Indicators and Reagents; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D009251:NADPH-Ferrihemoprotein Reductase / Q000378:metabolism; D010084:Oxidation-Reduction; D000077704:Tirapazamine; D014227:Triazines / Q000138:chemical synthesis* / Q000737:chemistry / Q000493:pharmacokinetics*; D014969:Xanthine Oxidase / Q000378:metabolism
chemical_list: C431670:3-amino-1,2,4-benzotriazine 4-oxide; D000970:Antineoplastic Agents; D007202:Indicators and Reagents; D014227:Triazines; D000077704:Tirapazamine; D014969:Xanthine Oxidase; D009251:NADPH-Ferrihemoprotein Reductase