Regorafenib enhances anti-tumor efficacy of immune checkpoint inhibitor by regulating IFN-γ/NSDHL/SREBP1/TGF-β1 axis in hepatocellular carcinoma.

Immune checkpoint inhibitor (ICI) shows low response rate in hepatocellular carcinoma (HCC) but the mechanisms underlying ICI resistance remains unclear. Interferon-γ (IFN-γ) has been widely determined as a prototypical antitumor cytokine. However, growing studies suggest that IFN-γ also mediates immunosuppression to promote tumor progression. Herein, we explored whether ICI-induced IFN-γ could activate immunosuppressive TGF-β1 to mediate ICI resistance. We demonstrated that cholesterol biosynthetic enzyme, NSDHL, was decreased in HCC tissues and associated with poor clinical prognosis. ICI-induced IFN-γ decreased NSDHL to activate SREBP1, which promoted TGF-β1 production, reduced T cell toxicity and enhanced Tregs infiltration, leading to ICI resistance. We also found that novel tyrosine kinase inhibitor, regorafenib, significantly reverse the above immunosuppressive effects by regulating NSDHL/SREBP1/TGF-β1 axis, which strengthened the effects of regorafenib plus ICI therapy against HCC. Noteworthily, regorafenib plus ICI therapy was more effective in HCC patients with higher serum TGF-β1. In conclusion, IFN-γ induced TGF-β1 to mediate ICI resistance. Regorafenib promotes anti-tumor immune response of ICI by regulating IFN-γ/NSDHL/SREBP1/TGF-β1 axis. Serum TGF-β1 may serve as a biomarker for predicting efficacy of regorafenib plus ICI therapy in HCC.