RESUMO
The anti-apoptotic proteins Bcl-xL and Mcl-1 have been identified to play a pivotal role in apoptosis resistance in ovarian cancer and constitute key targets for innovative therapeutic strategies. Although BH3-mimetics (i.e. ABT-737) potently inhibit Bcl-xL activity, targeting Mcl-1 remains a hurdle to the success of these strategies. Calcium signaling is profoundly remodeled during carcinogenesis and was reported to activate the signaling pathway controlling Mcl-1 expression. In this context, we investigated the effect of carboxyamidotriazole (CAI), a calcium channel inhibitor used in clinical trials, on Mcl-1 expression. CAI had an anti-proliferative effect on ovarian carcinoma cell lines and strongly down-regulated Mcl-1 expression. It inhibited store-operated calcium entry (SOCE) and Mcl-1 translation through mTORC1 deactivation. Moreover, it sensitized ovarian carcinoma cells to anti-Bcl-xL strategies as their combination elicited massive apoptosis. Its effect on mTORC1 and Mcl-1 was mimicked by the potent SOCE inhibitor, YM58483, which also triggered apoptosis when combined with ABT-737. As a whole, this study suggests that CAI sensitizes to anti-Bcl-xL strategies via its action on Mcl-1 translation and that modulation of SOCE could extend the therapeutic arsenal for treatment of ovarian carcinoma.
RESUMO
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-xL and Mcl-1 cooperatively protect platinum-resistant ovarian cancer cells from apoptosis. Despite BH3-mimetics represent promising drugs to target Bcl-xL, 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 [Ca(2+)]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-xL 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-xL 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-xL strategies.