MULTIPLE MECHANISMS OF RESISTANCE TO CISPLATIN TOXICITY IN AN ESCHERICHIA-COLI K12 MUTANT

The mechanisms underlying cellular resistance to the antitumor drug ci s-diamminedichloroplatinum(II) (CDDP)were studied in Escherichia coli K12. A bacterial strain (MC4100/DDP) was selected from the MC4100 wild -type strain after growth for four cycles in CDDP. MC4100/DDP bacteria showed a high level of resistance and exhibited various modifications including (1) a decrease in drug uptake and platinum/DNA binding whic h only partly contributed to resistance, (2) an increase in glutathion e content not involved in the resistant phenotype, (3) an increase in DNA repair capacity. Resistance was unmodified by introducing a uvrA m utation which neutralizes the excision-repair pathway. In contrast, it was abolished by deletion of the recA gene which abolishes recombinat ion and SOS repair but also by a mutation in the recA gene leading to RecA co-protease minus (no SOS induction). RecA protein was unchanged in MC4100/DDP but the expression of RecA-dependent gene(s) was require d for CDDP resistance. The regulation of genes belonging to the SOS re gulon was analysed in MC4100/DDP by monitoring the expression of sfiA and recA::lacZ gene fusions after UV irradiation. These gene fusions w ere derepressed faster and the optimal expression was obtained for a l ower number of UV lesions in MC4100/DDP, suggesting a role of RecA co- protease activity in the mechanism of resistance to CDDP in this E. co li strain.