Sodium butyrate inhibits colorectal cancer development by reducing M2 macrophage polarization and PD-L1 expression.

Short-chain fatty acids (SCFAs), produced by gut bacteria, are being recognized as an important form of anticancer therapy; however, their antitumor potency and underlying mechanisms remain unclear. Here, we used single-cell transcriptomics to identify the mechanism by which the SCFA sodium butyrate (NaB) inhibited the development of colorectal cancer (CRC) and explored new strategies for combining NaB with existing immunotherapies against CRC. An azoxymethane (AOM)/dextran sulfate sodium (DSS)-induced mouse model of colitis and a macrophage-deficient subcutaneous tumor model were used to determine NaB effects on CRC. RNA-sequencing profiled CRC immune landscape changes following NaB treatment. The potential synergy between NaB and programmed death receptor ligand 1 (PD-L1) blockade was explored in macrophage and CRC coculture systems. We showed that NaB markedly reduced inflammation, especially M2 macrophage polarization, tumor burden, histopathological damage, and disease activity index in AOM/DSS mice, and diminished PD-L1(+) tumor-associated macrophage (TAM) infiltration in CRC tissues. These effects depended on macrophage presence and HDAC/TLR4/MyD88 signaling. The synergy with PD-L1 blockade underscores the need for clinical evaluation of this combination therapy.IMPORTANCECRC remains a leading cause of cancer death worldwide, and new therapeutic approaches are urgently needed. Our study reveals that NaB, a natural gut-derived metabolite, can reshape the tumor immune environment by limiting pro-tumor M2 macrophages and reducing PD-L1(+) macrophage infiltration. By combining single-cell transcriptomics with mouse models, we pinpoint how butyrate acts through the HDAC/TLR4/MyD88 pathway and demonstrate its synergy with PD-L1 blockade. These findings highlight butyrate's potential as an accessible, low-toxicity agent to boost existing immunotherapies and offer a clear rationale for clinical trials exploring butyrate-immune checkpoint inhibitor combinations in CRC.