DNA Cleavage by the Antitumor Agent 3-Amino-1,2,4-benzotriazine 1,4-Dioxide (SR4233):  Evidence for Involvement of Hydroxyl Radical

Abstract

3-Amino-1,2,4-benzotriazine 1,4-dioxide (SR4233, WIN59075, tirapazamine, 1) is a clinically promising antitumor agent that requires bioreductive activation, selectively kills oxygen-deficient cells, and is believed to derive its biological activity from DNA cleavage. Using a xanthine−xanthine oxidase enzyme system as a one-electron reductant to activate 1 for DNA cleavage, it has been found that radical scavengers such as mannitol, dimethyl sulfoxide, ethanol, methanol, and tert-butyl alcohol significantly inhibit drug-dependent DNA cleavage. Compound 1, in concert with the xanthine−xanthine oxidase system, converts DMSO to methanesulfinic acid, a reaction characteristic of hydroxyl radical. In addition, treatment of a 32P-labeled restriction fragment with reductively-activated 1 results in cleavage at every base pair, with little sequence specificity, consistent with involvement of a highly reactive, nonselective agent such as hydroxyl radical. These results strongly support the involvement of radicals in the cleavage of DNA by 1 and are consistent with hydroxyl radical as the major DNA-cleaving species generated by reduction of 1.

A mass spectrometry study of tirapazamine and its metabolites: Insights into the mechanism of metabolic transformations and the characterization of reaction intermediates

“…A minor peak, corresponding to a loss of HO ⅐ , indicated a hydrogen atom migration between the amino group and the oxygen atom. There were some differences in the fragmentation of the ionized 4 and its isomers, 1-N-(3) and 2-N-oxides (6). A loss of N 2 was a unique feature of the ionized 4.…”

“…The exact mechanism by which DNA damage occurs remains uncertain. Recent studies have provided support for the idea that neutral radical 2 undergoes homolytic fragmentation to produce the well known DNA-damaging agent hydroxyl radical, OH ⅐ , and the observed mono-N-oxide metabolite 3 [6] (Scheme 1). Although this mechanism is widely accepted at this time, no direct experimental evidence exists to support the formation of the radical 2.…”

Prediction of Tumour Tissue Diffusion Coefficients of Hypoxia-Activated Prodrugs from Physicochemical Parameters

“…Under normal oxygenation, the resulting free radical is rapidly and spontaneously reoxidized to the initial prodrug by dioxygen, with formation of relatively non-toxic superoxide. The longer lifetime of the TPZ radical under hypoxic conditions allows its spontaneous decomposition to a cytotoxic oxidizing radical, considered to be either the hydroxyl [21,22] or benzotriazinyl radical [23,24] (Fig. 1).…”

Reactions of amidrazones with 1,4-quinones

“…[3][4][5] Known syntheses of this azaaromatic framework involve the reaction of 2-nitroaniline with cyanamide, 6 the base-induced cyclization of 2-nitrophenylurea followed by successive treatment with phosphoryl chloride and gaseous ammonia, 7 and the addition of diisocyanamide to benzofuroxan followed by acidic work-up. 8 Some time ago, a convenient synthesis of 3-amino-1,2,4-benzotriazine derivatives by the reaction of o-fluoronitro-benzenes with free guanidine base was developed.…”