Liver cancer is the second-most frequent cause of
cancer death in the world and is highly treatment resistant. We reported previously that inhibition of neddylation pathway with specific NAE inhibitor
MLN4924, suppressed the malignant phenotypes of
liver cancer. However, during the process,
MLN4924 induces pro-survival autophagy as a mechanism of drug resistance. Here, we report that blockage of autophagy with clinically-available autophagy inhibitors (e.g.
chloroquine) significantly enhanced the efficacy of
MLN4924 on
liver cancer cells by triggering apoptosis. Mechanistically,
chloroquine enhanced MLN4924-induced up-regulation of
pro-apoptotic proteins (e.g. NOXA) and down-regulation of
anti-apoptotic proteins. Importantly, the down-regulation of NOXA expression via
siRNA silencing substantially attenuated apoptosis of
liver cancer cells. Further mechanistic studies revealed that blockage of autophagy augmented MLN4924-induced DNA damage and
reactive oxygen species (ROS) generation. The elimination of DNA damage or blockage of ROS production significantly reduced the expression of NOXA, and thereby attenuated apoptosis and reduced growth inhibition of
liver cancer cells. Moreover, blockage of autophagy enhanced the efficacy of
MLN4924 in an orthotopic model of human
liver cancer, with induction of NOXA and apoptosis in
tumor tissues. These findings provide important preclinical evidence for clinical investigation of synergistic inhibition of neddylation and autophagy in
liver cancer.