Different effectiveness of 4-nitroquinoline-1-oxide, mitomycin C and ethyl methanesulfonate to induce lesions in DNA leading to sister chromatid exchange throughout successive cell cycles in Chinese hamster ovary cells

The present study was carried out in Chinese hamster ovary cells in order to determine whether lesions induced by three different mutagens, namely 4-nitroquinoline-1-oxide (4-NQO), Mitomycin C (MMC) and Ethyl methanesulfonate (EMS), can persist for more than one cell generation leading to sister chromatid exchanges (SCE) or, alternatively, they are efficiently repaired during the next replicative period after treatment. In order to accurately score the number of SCEs arising during the first (S1), second (S2) and third (S3) DNA synthetic periods, third-cycle (M3) metaphases showing three-way differential (TWD) staining were analyzed. Our results show that, even though the three compounds tested were efficient in increasing the yield of SCE, the frequency of SCE was more dramatically increased after MMC treatment. Differences were also observed among the three mutagens with regard to the persistence of the lesions leading to SCE throughout successive cell generations. EMS-induced lesions appeared as more persistent than those induced by MMC. However, most of the damage induced by the UV mimetic agent 4-NQO seems to be efficiently repaired after the first round of DNA replication following treatment with the drug.