Downregulation of PD-L1 expression by Wnt pathway inhibition to enhance PD-1 blockade efficacy in hepatocellular carcinoma

BACKGROUND: Immunotherapy targeting the programmed death-ligand 1 (PD-L1) pathway is a standard treatment for advanced hepatocellular carcinoma (HCC). The Wnt signaling pathway, often upregulated in HCC, contributes to an immunosuppressive tumor microenvironment. This study investigated the impact of Wnt pathway inhibition on PD-L1 expression in HCC and evaluated the potential therapeutic benefit of combining Wnt pathway inhibition with PD-L1 blockade. METHODS: The effects of Wnt pathway inhibitors XAV939 and IWR-1 on PD-L1 expression were examined in human HCC cell lines HuH7 and Hep3B. Beta-catenin overexpression and knockdown experiments confirmed these findings. For in vivo efficacy, the BNL 1ME A.7R.1 mouse HCC cell line was orthotopically implanted in mice, which were subsequently treated with XAV939, anti-PD-L1 antibodies, or both. RESULTS: Wnt pathway inhibitors XAV939 and IWR-1 significantly reduced PD-L1 protein expression in a dose-dependent manner in HuH7 and Hep3B cells, without affecting mRNA levels. CTNNB1 knockdown produced similar results, and beta-catenin overexpression reversed the effects of Wnt pathway inhibitors on PD-L1 expression. Wnt pathway inhibition did not promote PD-L1 protein degradation but instead increased the level of unphosphorylated 4EBP1, which could prevent the translation function of eIF-4E. In vivo, mice treated with a combination of XAV939 and an anti-PD-L1 antibody had significantly smaller tumors compared to those treated with either agent alone. The combination treatment also enhanced multiple immune-related pathways in harvested tumors. CONCLUSION: Inhibition of the Wnt pathway reduced PD-L1 expression in HCC cells and enhanced the efficacy of PD-L1 blockade, supporting its potential as HCC treatment.