Resveratrol sensitizes breast cancer to PARP inhibitor, talazoparib through dual inhibition of AKT and autophagy flux.

The efficacy of poly (ADP-ribose) polymerase inhibitors (PARPi) is largely limited to the homologous recombination (HR) deficient cancers. Therefore, there is a necessity to explore novel drug combinations with PARPi to enhance its anti-cancer activity in HR-proficient cancers. By analysing the patient data in cBioPortal, we found copy number amplification of PARP1 in ∼ 22.8% of breast cancers. PARP1 upregulation has been correlated with unfavourable outcome with PARPi treatment. To overcome this adversity, we explored the effect of resveratrol, a natural molecule chemosensitizer, in enhancing the effects of the third generation PARPi, talazoparib (BMN673), against breast adenocarcinoma. Our results show that resveratrol effectively sensitized talazoparib induced cell death in HR proficient and BRCA wild-type breast cancer cells in vitro. Mechanistically, resveratrol caused dysregulation of cell cycle and enhanced talazoparib-induced double strand breaks (DSBs), leading to abnormal mitotic progression culminating in mitotic catastrophe. Intriguingly, our results showed potential of resveratrol in dual-inhibition of AKT-signalling and autophagy flux to impair HR-mediated DSB-repair in breast cancer cells. By using EGFP-LC3 and tf-LC3 (mRFP-EGFP-LC3) expressing breast cancer cells, we found that resveratrol attenuates fusion of autophagosome and lysosome though induction of lysosomal-membrane-permeabilization (LMP). The combination of resveratrol and talazoparib effectively reduced cell proliferation in the high-density cell proliferation assay and also led to tumour volume reduction in vivo pre-clinical SCID-mice model. The combination caused no or minimal cytotoxicity in three different normal cell lines in vitro. Taken together, our work proposes the usage of resveratrol as a chemosensitizer along with talazoparib for targeting HR-proficient breast cancers in clinical settings.