Abstract

Background The immunosuppressive microenvironment severely constrains the efficacy of immunotherapy for colorectal cancer with peritoneal metastasis (CPM), urgently demanding strategies to reprogram it. Here, we aim to evaluate natural compound neogambogic acid (NGA) for its potential to modulate CPM progression and reshape the tumor immune microenvironment. Methods CPM mouse models were established via intraperitoneal injection of murine colorectal cancer cells, and then treated with NGA. Tumor burden and ascites, and immune microenvironment were assessed. Flow cytometry and RT-qPCR were performed to determine the impact of NGA on the differentiation of monocytic myeloid-derived suppressor cells (M-MDSCs) into M1 macrophages. Network pharmacology was used to screen the potential targets of NGA, and molecular docking, cellular thermal shift assay (CTESA) and drug affinity responsive target stability (DARTS) assays were employed to validate the interaction between NGA and STAT3. Finally, the synergistic effect of NGA combined with anti-PD-1/anti-CD47 blockade on inhibiting CPM progression was evaluated. Results NGA significantly reduced tumor burden, suppressed ascites formation, and reshaped immunosuppressive microenvironment by decreasing M-MDSCs, increasing tumor-infiltrating CD4 + /CD8 + T cells and M1 macrophage frequency. Notably, NGA promoted the differentiation of M-MDSCs toward M1 macrophages. Mechanically, NGA directly bound to STAT3 and inhibited its phosphorylation (pSTAT3). Therapeutically, NGA synergized with anti-PD-1/anti-CD47 combination therapy, leading to a marked reduction in tumor burden in CPM models. Conclusion NGA, a multi-targeted agent that prominently targets STAT3, enhances the immunotherapy efficacy in CPM by reshaping the immunosuppressive microenvironment through M-MDSC-to-M1 macrophage conversion. These findings provide a promising preclinical basis for NGA-based combinatorial strategies in advanced colorectal cancer.