c‐ MET Inhibition Is Accompanied by PD ‐ L1 Upregulation and Immunosuppression‐Related Tumor Microenvironment Changes in Esophageal Squamous Cell Carcinoma, With Enhanced Antitumor Activity in Combination With Anti‐ PD ‐1 Therapy

ABSTRACT Background c‐MET is implicated in ESCC progression, but whether c‐MET inhibition reshapes immune checkpoint expression and the tumor immune microenvironment remains unclear. Methods ESCC cell lines were treated with Tepotinib, and c‐MET and PD‐L1 expression were examined by Western blotting and immunofluorescence. MET knockdown was performed in TE‐1 and KYSE150 cells. AKR syngeneic subcutaneous tumor models were used to assess PD‐L1 and PD‐1 expression, immune cell composition, transcriptomic and proteomic changes, NF‐κB/p65 signaling, and the efficacy of Tepotinib combined with an anti‐PD‐1 antibody. Results Tepotinib decreased c‐MET expression and increased PD‐L1 expression in ESCC cells. MET knockdown produced a similar increase in PD‐L1. In vivo, Tepotinib increased PD‐L1 and PD‐1 expression in tumor tissues and increased PD‐L1 expression in the CD45 − non‐immune compartment, together with decreased CD8 + T cells and cDC1 cells, increased Treg cells, and increased CD206 expression in tumor‐associated macrophages. Dual immunofluorescence and quantitative analysis further showed an increased proportion of CD8 + PD‐1 + cells among total CD8 + cells in Tepotinib‐treated tumors. Transcriptomic and proteomic analyses indicated enrichment of inflammatory and immune‐related pathways, including NF‐κB, TNF, JAK–STAT, and immune checkpoint‐related signaling. Tepotinib increased p65 phosphorylation, whereas NF‐κB inhibition reduced p‐p65 and PD‐L1 expression. Tepotinib combined with anti‐PD‐1 antibody reduced tumor burden and delayed humane endpoint events compared with monotherapy. Conclusions c‐MET inhibition is accompanied by adaptive PD‐L1 upregulation and immunosuppression‐related changes in the tumor microenvironment in ESCC. NF‐κB/p65 signaling may participate in this response. The enhanced antitumor activity observed with Tepotinib plus anti‐PD‐1 therapy supports further investigation of this combination strategy.