Bcl-x inhibition enhances Dinaciclib-induced cell death in soft-tissue sarcomas.

Soft-tissue sarcomas (STS) are an uncommon and heterogeneous group of malignancies that result in high mortality. Metastatic STS have very bad prognosis due to the lack of effective treatments. Dinaciclib is a model drug for the family of CDK inhibitors. Its main targets are cell cycle regulator CDK1 and protein synthesis controller CDK9. We present data supporting Dinaciclib ability to inactivate in vitro different STS models at nanomolar concentrations. Moreover, the different rhythms of cell death induction allow us to further study into the mechanism of action of the drug. Cell death was found to respond to the mitochondrial pathway of apoptosis. Anti-apoptotic Bcl-x was identified as the key regulator of this process. Already natural low levels of pro-apoptotic proteins BIM and PUMA in tolerant cell lines were insufficient to inhibit Bcl-x as this anti-apoptotic protein showed a slow decay curve after Dinaciclib-induced protein synthesis disruption. Combination of Dinaciclib with BH3-mimetics led to quick and massive apoptosis induction in vitro, but in vivo assessment was prevented due to liver toxicity. Additionally, Bcl-x inhibitor A-1331852 also synergized with conventional chemotherapy drugs as Gemcitabine. Thus, Bcl-x targeted therapy arises as a major opportunity to the treatment of STS.