Metformin Downregulates PD-L1 Expression in Esophageal Squamous Cell Catrcinoma by Inhibiting IL-6 Signaling Pathway

Yao Lu; Dao Xin; Lulu Guan; Mengli Xu; Yalan Yang; Yu Chen; Yuanyuan Yang; Andrea Wang-Gillam; Li Wang; Shanggang Zong; Feng Wang

doi:10.3389/fonc.2021.762523

Metformin Downregulates PD-L1 Expression in Esophageal Squamous Cell Catrcinoma by Inhibiting IL-6 Signaling Pathway

Front Oncol. 2021 Nov 22:11:762523. doi: 10.3389/fonc.2021.762523. eCollection 2021.

Authors

Yao Lu¹, Dao Xin¹, Lulu Guan¹, Mengli Xu¹, Yalan Yang¹, Yu Chen¹, Yuanyuan Yang¹, Andrea Wang-Gillam², Li Wang³, Shanggang Zong³, Feng Wang¹

Affiliations

¹ Department of Oncology, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, China.
² Department of Oncology, Washington University School of Medicine, St. Louis, MO, United States.
³ Henan Academy of Medical Sciences, Zhengzhou, China.

Abstract

Purpose: To characterize the mechanism by which metformin inhibits PD-L1 expression in esophageal squamous cell carcinoma (ESCC) and to evaluate the effect of metformin on the antitumor immune response.

Methods: The Cancer Genome Atlas (TCGA) database was used to analyze the correlations between IL-6 and prognosis and between IL-6 and PD-L1 gene expression in esophageal cancer. Reverse transcription-quantitative polymerase chain reaction (RT-PCR), Western blotting and immunofluorescence were used to study the mechanism by which metformin affects PD-L1 expression. Additionally, T cell function was assessed in a coculture system containing ESCC cells and peripheral blood mononuclear cells (PBMCs) treated with metformin or IL-6. In an in vivo assay, we used a model established with NPIdKO™ mice, which have a reconstituted immune system generated by transplanting PBMCs through intravenous injection, to evaluate the effect of metformin on tumors.

Results: The TCGA esophageal cancer data showed that IL-6 expression was positively correlated with PD-L1 expression and that patients with high IL-6 expression had a significantly lower overall survival rate than patients with low IL-6 expression. PD-L1 expression in ESCC cell lines was significantly inhibited by metformin via the IL-6/JAK2/STAT3 signaling pathway but was not correlated with the canonical AMPK pathway. In the coculture system, the metformin pretreatment group showed higher T cell activation and better T cell killing function than the control group. Animal experiments confirmed that metformin downregulated PD-L1 expression and that combination treatment with metformin and PD-1 inhibitors synergistically enhanced the antitumor response.

Conclusions: Metformin downregulated PD-L1 expression by blocking the IL-6/JAK2/STAT3 signaling pathway in ESCC, which enhanced the antitumor immune response.

Keywords: IL-6/JAK2/STAT3 signaling pathway; PD-L1; anti-PD-1 antibody; esophageal squamous cell carcinoma; metformin.