Activation of the mitogen-activated protein kinase kinase/extracellular signal-regulated kinase pathway overcomes cisplatin resistance in ovarian carcinoma cells

Objective: This study was aimed to elucidate the roles of the mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) and phosphatidylinositol 3'-kinase (PI3K)/Akt pathways in regulating cytotoxicity induced by cisplatin (CDDP) in ovarian carcinoma cells. Methods: We treated 7 ovarian cancer cell lines with CDDP alone or with CDDP and either a PI3K inhibitor (LY294002), a MEK inhibitor (PD98059), or a MEK/ERK activator (phorbol 12-myristate 13-acetate [PMA]) and assessed cell viability, expression of MEK/ERK and PI3K/Akt, cell cycle distribution, and apoptosis. We also investigated the effect of combination treatment on survival in a xenograft model. Results: The cell lines showed half-maximal inhibitory concentrations (IC ₅₀) of CDDP from 2.4 to 26.9 μmol/L. KFr, a CDDP-resistant cell line developed from KF cells, showed an IC ₅₀ of CDDP of 9.6 μmol/L. Five of the cell lines with IC ₅₀ values of 9.6 μmol/L or greater were defined as CDDP-resistant. Cisplatin and LY294002 had an additive effect on inhibiting cell growth, and CDDP and PD98059 had and antagonistic effect on cell growth in all cell lines. In CDDP-resistant cells, CDDP and PMA dramatically suppressed the cell growth, upregulated the expression of phosphorylated ERK and cleaved caspase-9, down-regulated the expression of checkpoint kinases, and increased the proportion of cells in the synthesisphase fraction and apoptotic cells. The treatment of nude mice with CDDP and PMA prolonged survival in an ovarian cancer xenograft model. Conclusions: The present study indicates that further study is warranted to determine the effectiveness of combination treatment with CDDP and PMA for platinum-resistant ovarian carcinoma.