The role of the key autophagy kinase ULK1 in hepatocellular carcinoma and its validation as a treatment target.

Although macroautophagy/autophagy is involved in hepatocellular carcinoma (HCC) initiation and development and has been identified as a mechanism of HCC therapy resistance, the role of ULK1 (unc-51 like autophagy activating kinase 1) in HCC remains unclear. Here, we report that both knockdown and knockout of ULK1 inhibited human HCC cell proliferation and invasion, and Ulk1 deletion abrogated tumor growth in a xenograft mouse model. Furthermore, ULK1 ablation in combination with sorafenib significantly inhibited HCC progression compared with sorafenib treatment alone or vehicle control. To identify candidate ULK1 inhibitors, we used a structure-based virtual docking approach to screen 3428 compounds. Among these compounds, XST-14 showed the highest affinity for the ULK1 protein and specifically blocked ULK1 kinase activity. Moreover, the Lys46, Tyr94 and Asp165 amino acid residues of ULK1 were required for its binding to XST-14 according to molecular docking and mutagenesis experiments. Functional assays revealed that XST-14 blocked autophagy and subsequently induced apoptosis and inhibited growth in HCC cells. More importantly, XST-14 acted synergistically with sorafenib to attenuate HCC progression by inhibiting sorafenib-induced autophagy activation both in vitro and in vivo. In addition, XST-14 was well tolerated and exhibited favorable drug metabolism and pharmacokinetic properties and low toxicity in mice. In summary, our study determined that ULK1 may represent a new therapeutic target for HCC and that targeting ULK1 in combination with sorafenib treatment may serve as a promising interventional strategy for treating HCC. Abbreviations: 3MA: 3-methyladenine; ADV: AutoDock Vina; ATP: adenosine triphosphate; EdU: 5-ethynyl-2'-deoxyuridine; ESI: electrospray ionization; HCC: hepatocellular carcinoma; IC50: half maximal inhibitory concentration; KD: kinase domain; q.o.d., every other day; SDS-PAGE, sodium dodecyl sulfate-polyacrylamide gel electrophoresis; SPR, surface plasmon resonance.