Proteasome inhibitors represent effective anti-tumor drugs. ONX0912 is a novel oral proteasome inhibitor that selectively targets the chymotrypsin-like activity of 20S proteasome subunits β5 and LMP7 （Low molecular mass polypeptide-7）. It has been shown to be effective in hematologic malignancies. However, its anti-tumor effect in solid tumors remains unclear. Here, we discovered that ONX0912 suppressed the expansion of liver cancer cells. ONX0912 treatment led to an increased level of mitochondrial membrane potential collapse and mitochondrial ROS in tumor cells in a concentration- and exposure time-dependent manner, indicating ONX0912 triggers apoptosis through the intrinsic mitochondrial pathway. ONX0912 also induced mitophagy by activating Parkin/Pink pathway. Silencing mitophagy receptor protein, p62, aggravated the ONX0912-mediated apoptosis, which implied a new mechanism for the conversion between autophagy and apoptosis. Furthermore, we found that the ONX0912 target protein, LMP7 was overexpressed in liver cancer tissues compared to their adjacent tissues and increased level of LMP7 predicted worse clinical characteristics and poorer prognosis. In conclusion, we demonstrated that ONX0912 suppressed liver cancer cell expansion by inducing apoptosis and mitophagy. Our data also revealed ONX0912 as a potential clinical therapeutic drug for liver cancer therapy, and inhibition of mitophagy may sensitize the anti-tumor effect of ONX0912.
Keywords: LMP7; Liver cancer; Mitochondrial apoptosis; Mitophagy; ONX0912.
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