Comparison of two human ovarian carcinoma cell lines (A2780/CP70 and MCAS) that are equally resistant to platinum, but differ at codon 118 of the ERCC1 gene

ERCC1 is an essential gene within the nucleotide excision repair process. We studied two human ovarian carcinoma cell lines for cisplatin resistance, which differed with respect to ERCC1. The A2780/CP70 cell line has been extensively studied previously, and has the wild-type ERCC1 sequence. The MCAS cell line has a recently described ERCC1 polymorphism at codon 118, which is associated with an approximate 50% reduction in codon usage. These cells did not differ with respect to p53 sequence nor p53 mRNA induction following cisplatin exposure. The induction of ERCC1 mRNA was markedly reduced in MCAS cells as compared to A2780/CP70 cells. At the IC50 cisplatin dose for each cell line, MCAS cells were less proficient at cisplatin-DNA adduct repair than A2780/CP70 cells. In absolute terms, A2780/CP70 cells repaired 3-fold as much adduct (2.7 pg/mu g DNA over 6 h vs 0.86 pg/mu g DNA); and when expressed in terms of the maximal DNA adduct load, A2780/CP70 cells repaired 50% more adduct than MCAS cells. MCAS cells had increased cytosolic inactivation of drug at the IC50 dose level, which has been previously suggested to be a compensatory cellular response for reduced DNA repair capacity. These data suggest the possibility that this specific ERCC1 polymorphism, may be associated with reduced DNA repair capacity in human ovarian cancer cells. This association may be effected through a reduction in peak production of ERCC1 mRNA, and a consequent reduction in the translation of ERCC1 mRNA into protein.