Abstract
Using the alkaline comet assay (single cell gel electrophoresis), we studied the induction and persistence of DNA damage induced by methyl methanesulfonate (MMS) and neocarzinostatin (NCS) in the repair-deficient Chinese hamster cell lines V-E5 and XR-V15B. Effects in the comet assay were analyzed directly after treatment as well as after a postincubation period in mutagen-free medium to gain insight into the DNA repair capacities of the mutant cell lines in relation to different primary DNA lesions. Both mutagens caused a concentration-related increase in DNA strand breakage in both mutant cell lines and in the normal parental cell lines. Repair of MMS-induced DNA damage during postincubation was similar in normal and mutant cell lines, while diminished repair was seen after NCS treatment in XR-V15B cells. Our data show that XR-V15B cells only repaired about 30% of NCS-induced DNA damage within 1 h, while the parental V79 cell line repaired about 70%. Since this cell line is defective in the repair of DNA double-strand breaks (DSB), the results indicate that NCS-induced DSB significantly contribute to the genotoxic effects seen in the comet assay. However, compared to previously studied induction of gene mutations and chromosome aberrations, detection of NCS-induced DNA effects with the comet assay was less sensitive and increased DNA migration only occurred under strong cytotoxic conditions.
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