Genotoxic effects of 3-amino-1,2,4-benzotriazine-1,4-dioxide (SR 4233) and nitrogen mustard-N-oxide (nitromin) in Walker carcinoma cells under aerobic and hypoxic conditions.

As judged by alkaline elution, exposure of Walker cells to either 3-amino-1,2,4-benzotriazine-1,4-dioxide (SR 4233) or nitromin results in a dose-dependent increase in DNA damage due to single-strand breaks. With nitromin or SR 4233 there was little difference in the extent of DNA single-strand breaks between Walker cells incubated either hypoxically or aerobically. In contrast, there was a 24-fold enhancement in the differential hypoxic/aerobic response to SR 4233 in clonogenic studies. Following incubation of cells with nitrogen mustard, DNA cross-linking is observed. Bioreduction of nitromin would be expected to yield nitrogen mustard as the putative reactive metabolite. However, only DNA strand-breaks could be detected in Walker cells incubated with nitromin, suggesting that reduction of this pro-drug to nitrogen mustard was not a major activation pathway. In cells incubated under aerobic conditions, SR 4233 induces oxidative DNA damage, as indicated by the formation of 8-hydroxydeoxyguanosine, suggesting the involvement of futile redox cycling. In rats dosed with SR 4233 in vivo, significantly higher levels of 8-hydroxydeoxyguanosine could be detected in liver, compared to vehicle-dosed controls.