Abstract

The immunosuppressive tumor microenvironment (TME) limits the efficacy of immunotherapy in prostate cancer treatment. This study aims to investigate how melittin remodels the TME in prostate cancer and enhances the response mechanism to anti-PD-L1 therapy. The antitumor efficacy of melittin was evaluated using subcutaneous and orthotopic prostate cancer mouse models, in vitro co-culture systems of prostate cancer cells (PC-3, 22RV1) and THP-1-derived macrophages, and validation in primary bone marrow-derived macrophages (BMDMs). RNA sequencing, flow cytometry, qPCR, Western blot, ELISA, Transwell migration assays, CCK-8 viability analysis, and immunohistochemistry were employed to explore the underlying mechanisms. The synergistic effect of melittin combined with anti-PD-L1 antibody was assessed in vivo. Melittin significantly inhibited tumor growth in vivo and remodeled the tumor immune microenvironment by increasing CD8⁺ T cell infiltration while reducing macrophage accumulation. Mechanistically, melittin suppressed M2 macrophage polarization through inhibition of the JAK–STAT pathway, as evidenced by reduced phosphorylation of JAK1 and STAT3—an effect partially reversed by the JAK–STAT agonist RO8191 and mimicked by the JAK inhibitor Ruxolitinib. Melittin also attenuated macrophage recruitment via downregulation of tumor-derived CCL2, thereby compromising the CCL2–CCR2 chemotactic axis. In both subcutaneous and orthotopic models, melittin combined with anti-PD-L1 antibody synergistically reduced tumor burden, suppressed PD-L1 expression, and enhanced CD8⁺ T cell infiltration. Notably, melittin did not directly regulate PD-L1 expression in tumor cells in vitro, suggesting that its effects on PD-L1 in vivo are mediated through modulation of the TME. Melittin reverses the immunosuppressive TME in prostate cancer by inhibiting JAK-STAT mediated M2 polarization and CCL2-dependent macrophage recruitment.