Erianin Regulates Programmed Cell Death Ligand1 Expression And Enhances Cytotoxic T Lymphocyte Activity

Background: As early as the 28 th century BC,the traditional Chinese medicine Dendrobium chrysotoxum Lindl had a wide range of clinical applications,including tonic,astringent,pain and anti-inflammatory effects.Erianin,a natural product,is a bibenzyl compound extracted from the whole plant of D.chrysotoxum Lindl in the Orchidaceae family.It is stipulated in the 2020 version of the Pharmacopoeia of the People’s Republic of China as a chemical marker for the quality control of D.chrysotoxum Lindl.It has been reported that erianin has an inhibitory effect on the proliferation of human lung cancer cells and breast cancer cells,and also has the property of promoting tumor cell apoptosis.In summary,erianin can exert its anti-tumor activity under various mechanisms,and has great potential for the development of clinical anti-tumor drugs.Materials and methods: The in vitro He La cell model and the in vivo cervical cancer xenograft model were used to detect the anti-tumor activity of erianin.First,the proteins,genes,and signal pathways related to erianin’s anti-tumor activity are explored using MTT experiments,western blotting,RT-PCR,homology modeling,flow cytometry,and immunoprecipitation assays.Lyso Tracker Red staining was performed to visualize the biological activity of lysosomes and explore the effect of the erianin on lysosomal activity.Secondly,transwell,wound healing,tube formation,colony formation and Ed U labelling assays were performed to determine cell proliferation,migration and invasion capabilities,respectively.Finally,a co-culture model of tumor cells and T lymphocytes was used to explore the effect of erianin on the viability of cytotoxic T lymphocytes.Results: Experimental data demonstrated that erianin inhibited PD-L1 expression and induced the lysosomal degradation of PD-L1.Erianin suppressed HIF-1α synthesis through m TOR/p70S6K/4EBP1 pathway,and inhibited RAS/Raf/MEK/MAPK-ERK pathway.Immunoprecipitation experiments demonstrated that erianin reduced the interaction between RAS and HIF-1α,thereby reducing the expression of PD-L1.Experiments using a co-cultivation system of T cells and He La cells confirmed that erianin restored cytotoxic T lymphocytes ability to kill tumor cells.Erianin inhibited PD-L1–mediated angiogenesis,proliferation,invasion and migration.The anti-proliferative effects of erianin were supported using in vivo xenotransplantation experiments.Conclusion: Collectively,these results revealed previously unknown properties of erianin and provided a new theory for improving the efficacy of immunotherapy against cervical cancer and other malignant tumors through PD-1/PD-L1 immune checkpoints.