Some anticancer compounds are
pro-drugs which give rise to toxic species through enzymatic reduction. The
quinoxaline-di-N-oxide derivative
Q-85 HCl (7-chloro-3-[[(N,N-dimethylamino)propyl]amino]-2-quinoxalinecarbonitrile 1,4-di-N-
oxide hydrochloride) is a bioreductive compound selectively toxic in
hypoxia. Due to the possibility of secondary
tumors the study of the genotoxic capability of antitumoral drugs is very important. The aim of this study was to assess the ability of
Q-85 HCl to produce
reactive oxygen species (ROS) and oxidative DNA damage in Caco-2 cells, both in
hypoxia and in well-oxygenated conditions. Secondly, we attempted to evaluate the effect of
vitamins C and E under hypoxic and normoxic conditions, in order to determine if these
antioxidant substances modify
Q-85 HCl effect in hypoxic cells or possibly exert a protective action in normal cells. Caco-2 cells were treated with
Q-85 HCl for 2h, at high concentrations in normoxia (0.1-5 microM) and at low concentrations in
hypoxia (0.002-0.1 microM). In normoxia, a dose-related significant increase in intracellular ROS level was evident; in
hypoxia all the concentrations produced very high level of ROS. Just after the treatment and 24h later, oxidative DNA damage was evaluated by the modified comet assay after post-digestion of the cells with
formamidopyrimidine-DNA glycosylase (FPG) and
endonuclease III (Endo III).
Q-85 HCl treatment evoked a significant dose-dependent increase in the total comet score of the cells both in
hypoxia and normoxia, indicating that this compound or some metabolite is able to oxidize
purine and
pyrimidine bases. After 24h DNA damage caused by the compound was completely repaired with only one exception: cells treated with the highest concentration of
Q-85 HCl in
hypoxia and post-digested with FPG.
Vitamin C (5-100 microM) and
vitamin E (500-400 microM) did not have a
pro-oxidant effect in Caco-2 cells. Treatment of cells with
vitamin C (10 microM) or
vitamin E (100 microM) did not significantly reduce oxidative DNA damage in
hypoxia and normoxia. In conclusion, the use of these
vitamins would not hinder toxicity against hypoxic cells, but a protective effect in normoxic cells was not evident.