DNA damage induced in HT-29 colon cancer cells by exposure to 1-methyl-2-nitrosoimidazole, a reductive metabolite of 1-methyl-2-nitroimidazole

Abstract

Exposure of HT-29 colon carcinoma cells to 1-methyl-2-nitrosoimidazole (INO), a reductive metabolite of a model 2-nitroimidazole, induced concentration-dependent DNA damage detectable by conventional alkaline (single-strand breaks) and neutral (double-strand breaks) filter elution techniques. Elution of DNA from the filters under alkaline conditions was distinctly biphasic. No evidence of DNA damage was detected when cellular DNA was incubated directly with INO prior to filter elution. DNA damage was enhanced markedly in HT-29 cells incubated with buthionine sulfoximine to deplete intracellular glutathione levels prior to INO treatment. The biphasic shape of the elution profiles was not attributable to loss of labeled thymidine mononucleotides or to the formation of DNA-protein crosslinks. Rather, the data suggest the existence of two subpopulations of cells differing in sensitivity to the DNA-damaging effects of INO exposure. Based upon differential adherence, two populations of cells, differing with respect to the rate and extent of elution from the filters during alkaline elution assays, were detected, although they could not be purified sufficiently by this technique to permit biochemical characterization. The results suggest that the nitroso intermediate is either an active metabolite, or a proximate form of the ultimate DNA-reactive species, responsible for DNA damage in cells exposed to 2-nitroimidazoles under reducing conditions.