Morphine-3-glucuronide upregulates PD-L1 expression via TLR4 and promotes the immune escape of non-small cell lung cancer

摘要

Objective:Patients with cancer pain are highly dependent on morphine analgesia,but studies have shown a negative correlation between morphine demand and patient outcomes.The long-term use of morphine may result in abnormally elevated serum morphine-3-glucuronide(M3G)levels.Hence,the effects of M3G on tumor progression are worth studying.Methods:The effects of M3G on PD-L1 expressions in human non-small cell lung cancer(NSCLC)cell lines were first evaluated.Activation of TLR4 downstream pathways after M3G treatment was then determined by Western blot.The effects of M3G on human cytotoxic T lymphocytes(CTL)cytotoxicity and INF-γrelease was also detected.Finally,the LLC murine lung adenocarcinoma cell line were used to establish a murine lung cancer model,and the effects of M3G on tumor growth and metastasis were determined.Results:M3G promoted the expressions of PD-L1 in the A549 and H1299 cell lines in a TLR4-dependent manner(P<0.05).M3G activated the PI3 K and the NFκB signaling pathways,and this effect was antagonized by a TLR4 pathway inhibitor.A PI3 K pathway inhibitor reversed the M3G-mediated PD-L1 upregulation.M3G inhibited the cytotoxicity of CTL on A549 cells and decreased the level of INF-γ.Repeated M3G intraperitoneal injections promoted LLC tumor growth and lung metastasis through the upregulation of tumor expressed PD-L1 and the reduction of CTL in the tumor microenvironment.Conclusions:M3G specifically activated TLR4 in NSCLC cells and upregulated PD-L1 expression through the PI3 K signaling pathway,thereby inhibiting CTL cytotoxicity and finally promoting tumor immune escape.