Regorafenib, a multiple kinase inhibitor, is recently approved for treatment of patients with advanced hepatocellular carcinoma (HCC). Previous studies demonstrated that regorafenib was a mitochondrial toxicant, which associated with the impairment of mitochondria. Sirt3 is involved in the regulation of mitochondrial function in cancers. This study aimed to investigate the mechanism of Sirt3 involved in the mitochondrial dysfunction which associated with regorafenib treatment in liver cancer cells. We found regorafenib inhibited Sirt3 and p-ERK expression in HCC cells in a dose-dependent manner. Bioinformatics analysis showed that Sirt3 expression was down-regulated in liver cancer tissues and its low expression was correlated with worse overall survival (OS) in liver cancer patients. After transfected with Sirt3 overexpression plasmid, we found that Sirt3 sensitized liver cancer cells to regorafenib and resulted in much more apoptosis with a significant increase of ROS level. However, exogenous antioxidant could not weaken the apoptosis. Mitochondrial membrane potential assay indicated that Sirt3 overexpression accelerated the mitochondrial depolarization process induced by regorafenib and aggravated mitochondrial injury. Cellular oxygen consumption assay showed that mitochondrial dysfunction was caused by the damage of the electron transport chain. The results demonstrated that Sirt3 overexpression promoted the increase of ROS and apoptosis induced by regorafenib through the acceleration of mitochondrial dysfunction by impairing function of the electron transport chain in liver cancer cells. Our studies verified the functional role of Sirt3 in regorafenib treatment and suggested that regorafenib accompanied with Sirt3 activator as a novel treatment strategy for HCC.
