PO-477 BCL-Xl inhibition enhances dinaciclib-induced cell death in soft-tissue sarcoma cell lines

Abstract

IntroductionMetastatic disease in soft-tissue sarcomas (STSs) lack successful treatments. Mortality rates are indeed quite high. Dinaciclib is a representative of the new CDK inhibitor class of drugs. It preferentially targets CDK1 and CDK9, involved respectively in cell cycle and transcription regulation. Data in literature shows that Dinaciclib is a good candidate for combinatorial therapies.Material and methodsWe analysed Dinaciclib apoptotic induction (visualised by Flow Cytometry) in a series of different STSs established cell lines. Cell lines were thus categorised as Dinaciclib-sensitive or Dinaciclib-tolerant. Differences in relevant protein expression behaviour during treatment led to hypothesis proposal for key regulators. Validation of targets was performed by siRNA technology prior to engage in drug combination testing. Drugs safety and efficiency was finally addressed by in vivo experiments.Results and discussionsRelevant differences in apoptotic extent and timing among cell lines were found. Responses varied from more that 75% of cell death (72 hour treatment) in liposarcoma 402–91 to a mere 25% in leiomyosarcoma SK-LMS-1. The inhibition status of anti-apoptotic protein Bcl-xL was identified as the main determinant of the rhythm and extent of apoptotic demise. Dinaciclib-tolerant cells kept Bcl-xL active for longer times and get rid of BIM faster than sensitive cells. Both Bcl-xL knock-down and chemical Bcl-xL inhibitors (BH3-mimetics) overcame Dinaciclib tolerance and triggered complete annihilation of cell cultures (95% of cell death after 24 hour). Once safely escalated, drug combination effectiveness was tested on mice engrafted tumours.ConclusionThe group of CDK inhibitors can be employed as therapeutic agents for STSs. Levels of the Bcl-2 family of proteins inform about cell proneness to trigger apoptotic cell death. This information can be used to design combination approaches involving BH3-mimetics that enhance efficiency and reduce treatment resistance.