Anti-Cancer Effects of YAP Inhibitor (CA3) in Combination with Sorafenib against Hepatocellular Carcinoma (HCC) in Patient-Derived Multicellular Tumor Spheroid Models (MCTS)

SIMPLE SUMMARY: Activation of YAP/TAZ (mediators of Hippo signaling) is associated with the development of liver cancer. The expression level of YAP is known to relate to chemoresistance. However, the therapeutic effect of YAP/TAZ inhibition when combined with sorafenib and conventional chemotherapy in HCC is not known. Recent studies have highlighted the importance of the tumor microenvironment (TME) in chemoresistance. The multicellular tumor spheroid (MCTS) model has emerged as a promising tool for studying cancer drugs as it mimics actual TME. Here, we aimed at assessing the YAP/TAZ expression level of HCCs and identifying the therapeutic effects of CA3 (novel YAP inhibitor) when combined with sorafenib using a patient-derived MCTS model. We established patient-derived MCTS and confirmed that patient-derived MCTS with high YAP/TAZ expression responded more sensitively to the combination therapy (sorafenib with CA3) than MCTS with low or medium YAP/TAZ expression. These findings suggest that the YAP/TAZ inhibitor may serve as a potential therapeutic strategy to enhance sensitivity to sorafenib in HCCs with high YAP/TAZ expression. ABSTRACT: Purpose: To assess the expression levels of YAP and TAZ in patient-derived HCC tissue and identify the effects of YAP/TAZ inhibition depending on the baseline YAP/TAZ expression when combined with sorafenib using a patient-derived multicellular tumor spheroid (MCTS) model. Methods: Primary HCC cell lines were established from patient-derived tissue. Six patient-derived HCC cell lines were selected according to YAP/TAZ expression on Western blot: high, medium, low. Then, MCTS was generated by mixing patient-derived HCC cells and stroma cells (LX2, WI38, and HUVECs) and YAP/TAZ expression was assessed using Western blot. Cell viability of MCTS upon 48 h of drug treatment (sorafenib, sorafenib with CA3 0.1 µM, and CA3 (novel YAP1 inhibitor)) was analyzed. Results: Out of six patient-derived HCC cell lines, cell lines with high YAP/TAZ expression at the MCTS level responded more sensitively to the combination therapy (Sorafenib + CA3 0.1 μM) despite the potent cytotoxic effect of CA3 exhibited in all of the patient-derived HCCs. Conclusion: Targeting YAP/TAZ inhibition using the novel YAP1 inhibitor CA3 could be a promising therapeutic strategy to enhance sensitivity to sorafenib especially in HCCs with high YAP/TAZ expression in MCTS.