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Background: Pyridoclax is an original lead, recently identified as very promising in treatment of chemoresistant ovarian cancers. To correct the unfavorable intrinsic physico-chemical properties of this BCS II drug, a formulation strategy was implied in the drug discovery step. Pyridoclax-loaded nanoemulsions (NEs) were developed to permit its preclinical evaluation., Results: The resulting nanoemulsions displayed a mean size of about 100 nm and a high encapsulation efficiency (>95%) at a drug loading of 2 wt%, enabling a 1,000-fold increase of the Pyridoclax apparent solubility. NEs have enabled a sustained release of the drug as assayed by a dialysis bag method. In addition, anti-tumor effects of the Pyridoclax-loaded nanoemulsions (PNEs) showed a 2.5-fold higher activity on chemoresistant ovarian cancer cells than free Pyridoclax. This effect was confirmed by a drastic increase of caspase 3/7 activation from 10 µM PNEs, as newly objectified by real time apoptose imaging. The Pyridoclax bioavailability was kept unchanged after encapsulation in nanoemulsions as determined in a mice model after oral administration., Conclusion: Thus, NEs should permit valuable Pyridoclax oral administration, and valorization of this promising anticancer drug by maintaining its original anticancer activity, and by reducing the Pyridoclax therapeutic concentration., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

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.

Chemoresistance of ovarian carcinoma has been associated previously to the absence of Bcl-x(L) expression downregulation in response to cisplatin. Among BH3-mimetic molecules constituting promising anticancer agents able to inhibit the activity of antiapoptotic Bcl-2 family proteins, we evaluated the effect of one of them, HA14-1, on various ovarian carcinoma cell lines. In response to HA14-1, the cisplatin-resistant IGROV1-R10 cell line underwent massive cell death, whereas other cell lines presented a partial response (IGROV1, SKOV3, and A2780) or did not respond to this molecule (OAW42 and OAW42-R). However, the expression of HA14-1 targets (Bcl-2 and Bcl-x(L)) did not correlate to these different responses. In contrast, cell death was associated with the disappearance of Mcl-1 after exposure to HA14-1. We showed that, in the HA14-1 nonresponsive cell lines (SKOV3 and OAW42), small interfering RNA-mediated Mcl-1 downregulation allowed HA14-1-induced massive apoptosis in the absence of chemotherapy. Furthermore, cisplatin-induced Mcl-1 downregulation was also able to sensitize highly chemoresistant SKOV3 cells to HA14-1. Taken together, these results show that Bcl-x(L) and Mcl-1 are able to cooperate to protect ovarian carcinoma cells against oncogenic stress or chemotherapy-induced apoptosis and suggest that the development of multitargeted strategies directed against these two antiapoptotic proteins may constitute a major challenge for the therapeutic care of chemoresistant ovarian carcinomas. BH3-mimetic compounds represent promising tools for this purpose either on their own (direct or indirect pan-inhibitors) or in combination with new drugs aiming to inactivate Mcl-1.