Compromised autophagy sensitizes hepatocellular carcinoma to PARP inhibition

Abstract Background Hepatocellular carcinoma (HCC), one of the most lethal malignancies worldwide, has limited efficient therapeutic options. Here we demonstrated that simultaneously targeting PARP and autophagy could evoke striking synergistic lethality in HCC. Methods: The synergistic antitumor effects of PARP inhibitor Niraparib combined with chloroquine (CQ) were evaluated in HCC cells and in xenograft mouse models. The formation of autophagy was determined via western blot, confocal and transmission electron microscopy analysis. Akt/mTOR and Erk1/2 signaling pathways were determined by western blot analysis and relative oxygen species (ROS) were observed by confocal microscopy. Then, cell cycle and EdU incorporation analysis were applied to exam the activation of DNA damage checkpoint. Finally, immunofluorescence staining was applied to detect the function of homologous recombinant (HR) repair proteins. Results: Specifically, we found that the PARP inhibitor Niraparib induced cytotoxicity and autophagic flux in HCC cells. Further experiments showed that Niraparib induced suppression of Akt/mTOR pathway and activation of Erk1/2 cascade, and induced the accumulation of ROS. Blocking autophagy by CQ in combination with Niraparib further enhanced cytotoxicity, induced apoptosis in HCC cells and enhanced antitumor effects in Huh7 xenografts. Mechanistically, we showed that autophagy inhibition abrogated Niraparib-induced cell cycle arrest and checkpoint activation, thus triggering abnormal cellular proliferation and mitosis. Cotreatment with CQ and Niraparib promoted the formation of gama-H2AX foci while reduced the recruitment of HR repair protein RAD51 to double-strand break sites. Conclusion: The present study demonstrated that simultaneously targeting PARP and autophagy induced synergistic lethality in HCC, exemplifing a novel promising strategy for the management of HCC in the clinic and highlighting a potential approach to expand the application of PARP inhibitors.