Calcium signals inhibition sensitizes ovarian carcinoma cells to anti-Bcl-xL strategies through Mcl-1 down-regulation

Ovarian carcinoma is the leading cause of death from gynecologic cancer in the developed world and is characterized by acquired chemoresistance leading to an overall 5-year survival rate of about 30 %. We previously showed that Bcl-x(L) and Mcl-1 cooperatively protect platinum-resistant ovarian cancer cells from apoptosis. Despite BH3-mimetics represent promising drugs to target Bcl-x(L), anti-Mcl-1 strategies are still in pre-clinical studies and required new investigations. Calcium is a universal second messenger and dysregulation of calcium signal is often observed during carcinogenesis. As change in cytosolic free calcium concentration [Ca2+](i) is known to control the fate of the cell by regulating Bcl-2 family members, we wonder if calcium signal could impact on Mcl-1 expression and if its pharmacological inhibition could be useful to sensitize ovarian carcinoma cells to anti-Bcl-x(L) strategies. We therefore studied the effect of different calcium signals inhibitors in ovarian carcinoma cell lines SKOV3 and IGROV1-R10 and analysed their effects on proliferation and Mcl-1 expression. We also exposed these cells to these inhibitors in combination with anti-Bcl-x(L) strategies (siRNA or BH3-mimetic: ABT-737). We found that calcium signaling regulates Mcl-1 through translational events and a calmodulin-mediated pathway. BAPTA-AM and calmodulin inhibitor combination with ABT-737 leads to apoptosis, a process that is reversed by Mcl-1 enforced expression. As Mcl-1 represents a crucial hurdle to the success of chemotherapy, these results could open to new area of investigation using calcium modulators to directly or indirectly target Mcl-1 and thus efficiently sensitize ovarian carcinoma cells to anti-Bcl-x(L) strategies.