First evidence that oligopyridines, α-helix foldamers, inhibit Mcl-1 and sensitize ovarian carcinoma cells to Bcl-xL-targeting strategies

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.

PI3K/mTOR dual inhibitor NVP-BEZ235 decreases Mcl-1 expression and sensitizes ovarian carcinoma cells to Bcl-xL-targeting strategies, provided that Bim expression is induced

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.