An ATG4B inhibitor blocks autophagy and sensitizes Sorafenib inhibition activities in HCC tumor cells

Autophagy related 4B (ATG4B) which regulates autophagy by promoting the formation of autophagosome through reversible modification of LC3, is closely related to cancer cell growth and drug resistance, and therefore is an attractive therapeutic target. Recently, ATG4B inhibitors have been reported, yet with drawbacks including weak potency. To discover more promising ATG4B inhibitors, we developed a high-throughput screening (HTS) assay and identified a new ATG4B inhibitor named DC-ATG4in. DC-ATG4in directly binds to ATG4B and inhibits its enzyme activity with an IC50 of 3.08 +/- 0.47 mu M. We further confirmed that DC-ATG4in is an autophagy inhibitor and blocks autophagy induced by Sorafenib in Hepatocellular Carcinoma (HCC) cells. More impor-tantly, combination of DC-ATG4in with Sorafenib synergized the cancer cell killing effect and proliferation in-hibition activities on HCC cells. Our data suggested that inactivation of autophagy via ATG4B inhibition may be a viable strategy to sensitize existing targeted therapy such as Sorafenib in the future.