Small-molecule High-throughput Screening Identifies an MEK Inhibitor PD198306 that Enhances Sorafenib Efficacy via MCL-1 and BIM in Hepatocellular Carcinoma Cells

Background: Sorafenib is the most widely used systematic therapy drug for treating unresectable Hepatocellular Carcinoma (HCC) but showed dissatisfactory efficacy in clinical applications. Objective: We conducted a combinational quantitative small-molecule high-throughput screening (qHTS) to identify potential candidates to enhance the treatment effectiveness of sorafenib. Methods: First, using a Hep3B human HCC cell line, 7051 approved drugs and bioactive compounds were screened, then the primary hits were tested with/without 0.5 μM sorafenib respectively, the compound has the half maximal Inhibitory Concentration (IC50) shift value greater than 1.5 was thought to have the synergistic effect with sorafenib. Furthermore, the MEK inhibitor PD198306 was selected for the further mechanistic study. Results: 12 effective compounds were identified, including kinase inhibitors targeting MEK, AURKB, CAMK, ROCK2, BRAF, PI3K, AKT and EGFR, and a μ-opioid receptor agonist and a Ltype calcium channel blocker. The mechanistic research of the combination of sorafenib plus PD198306 showed that the two compounds synergistically inhibited MEK-ERK and mTORC1- 4EBP1 and induced apoptosis in HCC cells, which can be attributed to the transcriptional and posttranslational regulation of MCL-1 and BIM. Conclusion: Small-molecule qHTS identifies MEK inhibitor PD1938306 as a potent sorafenib enhancer, together with several novel combination strategies that are valuable for further studies.