We previously showed that Bcl-xL and Mcl-1 cooperatively protect platinum-resistant ovarian cancer cells from apoptosis. Here we assessed the anticancer potential of combining ABT-737-induced inhibition of Bcl-xL with Mcl-1 inhibition via PI3K/Akt/mTOR pathway disruption using NVP-BEZ235. NVP-BEZ235 inhibited cell proliferation without inducing apoptosis. It strongly repressed Mcl-1 expression and induced Puma expression in both cell lines tested while differentially modulating Bim between the two. Interestingly, NVP-BEZ235 efficiently sensitized ovarian carcinoma cells to ABT-737, provided that Bim expression was induced. Moreover, inhibiting the ERK1/2 pathway restored Bim expression and sensitized low Bim-expressing cancer cells to the BEZ235/ABT-737 treatment.

The identification of novel therapeutic strategies is an important urgent requirement for the clinical management of ovarian cancer, which remains the leading cause of death from gynecologic cancer. Several studies have shown that the antiapoptotic proteins Bcl-x L and Mcl-1, as well as the proapoptotic protein Bim, are key elements to be modulated to kill ovarian cancer cells. Pharmacologic inhibition of Bcl-x L is possible by using BH3-mimetic molecules like ABT-737. However, inhibition of Mcl-1 and/or promotion of its BH3-only partners (including Bim, Puma, and Noxa) remains a challenge that may be achieved by modulating the signaling pathways upstream. This study sought whether AZD8055-induced mTOR inhibition and/or trametinibinduced MEK inhibition could modulate Mcl-1 and its partners to decrease the Mcl-1/BH3-only ratio and thus sensitize various ovarian cancer cell lines to ABT-737. AZD8055 treatment inhibited Mcl-1 and increased Puma expression but did not induce massive apoptosis in combination with ABT-737. In contrast, trametinib, which decreased the Mcl-1/BH3-only protein ratio by upregulating Puma and dephosphorylated active Bim, sensitized IGROV1-R10 and OVCAR3 cells to ABT-737. Adding AZD8055 to trametinib further reduced the Mcl-1/BH3-only protein ratio and triggered apoptosis without ABT-737 in IGROV1-R10 cells. Moreover, the AZD8055/trametinib association highly sensitized all cell lines including SKOV3 to ABT-737, the induced dephosphorylated Bim being crucial in this sensitization. Finally, the three-drug combination was also very efficient when replacing AZD8055 by the pan-Akt inhibitor MK-2206. This study thus proposes original multitargeted strategies and may have important implications for the design of novel approaches for ovarian cancer treatment. Mol Cancer Ther; 16(1); 102-15. Ó2016 AACR.

Apoptosis control defects such as the deregulation of Bcl-2 family member expression are frequently involved in chemoresistance. In ovarian carcinoma, we previously demonstrated that Bcl-xL and Mcl-1 cooperate to protect cancer cells against apoptosis and their concomitant inhibition leads to massive apoptosis even in the absence of chemotherapy. Whereas Bcl-xL inhibitors are now available, Mcl-1 inhibition, required to sensitize cells to Bcl-xL-targeting strategies, remains problematic. In this context, we designed and synthesized oligopyridines potentially targeting the Mcl-1 hydrophobic pocket, evaluated their capacity to inhibit Mcl-1 in live cells, and implemented a functional screening assay to evaluate their ability to sensitize ovarian carcinoma cells to Bcl-xL-targeting strategies. We established structure-activity relationships and focused our attention on MR29072, named Pyridoclax. Surface plasmon resonance assay demonstrated that pyridoclax directly binds to Mcl-1. Without cytotoxic activity when administered as a single agent, pyridoclax induced apoptosis in combination with Bcl-xL-targeting siRNA or with ABT-737 in ovarian, lung, and mesothelioma cancer cells.