Evaluation of in vitro genotoxic activity of bleomycin and mitomycin C in human lymphocytes using the alkaline comet assay

Although chemotherapy targets cancer tissue, it also damages the DNA of non-cancer cells. The aim of this study was to evaluate the in vitro genotoxic potential of therapeutic concentrations of bleomycin and mitomycin C, added alone or in combination to cultures of human peripheral lymphocytes. The levels of DNA damage and repair were assessed using the alkaline comet assay immediately after cell treatment as well as 24 and 48 hours following treatment. The results indicate that individual drugs and their combination induce a significant DNA damage to peripheral blood lymphocytes. Bleomycin alone induced the highest levels of primary DNA damage immediately after cell treatment. Although mitomycin C alone induced massive cross-linking and retarded DNA migration in resting cells, active proliferation and repair processes significantly increased DNA damage. Combined, they showed a synergetic effect, inducing complex patterns of DNA damage in peripheral blood lymphocytes and producing different types of lesions and a number of DNA alterations that directly or indirectly increased DNA migration. Our study has confirmed the sensitivity of the alkaline comet assay for assessing bleomycin and/or mitomycin C genotoxicity to human lymphocytes at concentration levels used in clinic. It has also demonstrated the utility of the alkaline comet assay as one of the primary screening methods for in vitro studies of drug-DNA interactions, especially in studying mechanisms of action of new drugs.