Britannin Inhibits PD-L1 Expression By Eliminating The Crosstalk Between Myc And HIF-1α In Tumor

Background: Programmed cell death-ligand 1(PD-L1)is overexpressed in tumor cells,which causes tumor cells to escape T cell killing,and promotes tumor cell survival,cell proliferation,migration,invasion,and angiogenesis.Britannin is a natural product with anticancer pharmacological effects.However,britannin inhibits tumor growth molecular mechanisms remain unknown.Purpose: In this work,we studied the anticancer potential of britannin and explored whether britannin mediated its effect by inhibiting the expression of PD-L1 in tumor cells.Methods: 1.MTT assay,homology modeling and molecular docking,RT-PCR and western blotting were used to investigate the effect of britannin on the expression of PD-L1 in vitro.2.The effect of britannin on HIF-1α and Myc and its molecular mechanism were studied by homology modeling,molecular docking,western blot and immunofluorescence.3.The role of HIF-1α and Myc in the effect of britannin on PD-L1 expression was detected by western blotting,immunofluorescence and immunoprecipitation.4.T cell killing assays,Ed U labeling,colony formation,flow cytometry and other methods were used to analyze the effects of britannin on tumor killing activity,cell proliferation and cell cycle.5.The effects of britannin on migration,invasion and angiogenesis were detected by wound healing,matrigel transwell invasion,and tube formation.6.The antitumor activity of britannin was evaluated in HCT116 xenograft tumor model in vivo.Results:1.Britannin reduced the expression of PD-L1 in tumor cells by inhibiting the synthesis of the PD-L1 protein but did not affect the degradation of the PD-L1 protein.2.Britannin also inhibited HIF-1α expression through the mTOR/P70S6K/e IF4E pathway and Myc activation through the Ras/RAF/MEK/ERK pathway.3.Britannin inhibited the expression of PD-L1 by blocking the interaction between HIF-1α and Myc.4.Britannin could enhance the activity of cytotoxic T lymphocytes and inhibit tumor cell proliferation and angiogenesis by inhibiting PD-L1.5.Britannin inhibits angiogenesis by inhibiting PD-L1.6.In vivo observations were confirmed by demonstrating the antitumor activity of britannin in a murine xenograft model.Conclusion: Britannin inhibits the expression of PD-L1 by blocking the interaction between HIF-1α and Myc.Moreover,britannin stabilizes T cell activity and inhibits proliferation and angiogenesis by inhibiting PD-L1 in cancer.The current work highlights the anti-tumor effect of britannin,providing insights into the development of cancer therapeutics via PD-L1 inhibition.