Analysis of DNA damage and cellular responses to platinum-based chemotherapeutic agents in 'in vitro' models of non-small cell lung cancer
Response to cisplatin was investigated in a panel of NSCLC cell lines in terms of sensitivity/resistance to this agent, DNA crosslink formation and repair, cell cycle effects, apoptosis and gene expression changes. Measures of survival revealed a differential response between cell lines. The level of maximal DNA crosslink formation and efficiency of repair was also variable, with the most cisplatin-resistant cell lines being the ones with higher levels of crosslinks and poorer repair. Cisplatin induced a transient cell cycle arrest at S and G2/M phases in cell lines; however, only the most cisplatin-resistant ones were able to overcome this arrest. The degree of cisplatin-induced apoptosis was variable, but no direct correlation was found between cell sensitivity and apoptotic index. Cisplatin induced the expression of several apoptotic, cell cycle regulator and DNA repair genes. The fact that cisplatin-resistant cells exhibited higher crosslink formation and reduced repair was somehow unanticipated and could be attributed to increased lesion tolerance, i.e. an ability of the most resistant cells to progress through the cell cycle without completely repairing cisplatin-induced damage. Lesion tolerance may, therefore, be an important route for cisplatin resistance in the NSCLC panel. Finally, the alkaline Comet assay was used, for the first time, to detect the formation and repair of oxaliplatin-induced DNA crosslinks in cultured cells and in peripheral blood lymphocytes of patients undergoing chemotherapy. An inter-individual variability in crosslink formation and repair efficiency was observed. The Comet assay could therefore be a useful tool in future oxaliplatin-related clinical studies.