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

Objective: Patients with cancer pain are highly dependent on morphine analgesia, but studies have shown a negative correlationbetween morphine demand and patient outcomes. The long-term use of morphine may result in abnormally elevated serummorphine-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 onhuman cytotoxic T lymphocytes (CTL) cytotoxicity and INF-γ release was also detected. Finally, the LLC murine lung adenocarcinomacell 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). M3Gactivated the PI3K and the NFκB signaling pathways, and this effect was antagonized by a TLR4 pathway inhibitor. A PI3K pathwayinhibitor reversed the M3G-mediated PD-L1 upregulation. M3G inhibited the cytotoxicity of CTL on A549 cells and decreased thelevel of INF-γ. Repeated M3G intraperitoneal injections promoted LLC tumor growth and lung metastasis through the upregulationof 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 PI3K signalingpathway, thereby inhibiting CTL cytotoxicity and finally promoting tumor immune escape.