Coixenolide Enhances Antitumor Immunity of Cytotoxic CD8+ T Cells by Inhibiting S100A8/A9-CD36 Axis in Obesity-Associated Pancreatic Adenocarcinoma.

Pancreatic adenocarcinoma (PAAD), characterized by an immunosuppressive tumor microenvironment (TME) and resistance to immunotherapy, exhibits a dismal prognosis further exacerbated by obesity. This study demonstrates the potent immunomodulatory and antitumor effects of coixenolide, a bioactive fatty acid ester from Coix lacryma-jobi L., particularly in obesity-associated PAAD. Utilizing high-fat diet (HFD)-fed mouse models, we found that coixenolide significantly inhibited tumor growth in HFD mice compared to control diet (CD) mice, correlating with enhanced intra-tumoral CD8+ T cell infiltration and cytotoxicity, reduced regulatory T cells (Tregs), and increased tumor cell apoptosis. Single-cell RNA sequencing (scRNA-seq) of PAAD tissues revealed that coixenolide specifically expanded and activated cytotoxic CD8+ T cells within the TME of HFD mice. Further analysis identified distinct malignant epithelial cell clusters enriched in HFD tumors, characterized by high expression of S100a8/a9 and stemness potential. Coixenolide treatment significantly reduced these S100a8/a9-expressing tumor cell populations and suppressed S100a8/a9 protein expression and secretion. Cell-cell communication analysis and functional assays revealed that tumor cell-derived S100a8/a9 interacted with Cd36 on CD8+ T cells. This interaction promoted CD36-mediated fatty acid uptake, leading to lipid peroxidation, ferroptosis, and functional exhaustion of CD8+ T cells. Coixenolide disrupted this axis by inhibiting tumor cell S100a8/a9, thereby downregulating CD36 on CD8+ T cells, reducing lipid peroxidation and ferroptosis, and restoring CD8+ T cell cytotoxicity. Genetic knockout (S100a9 KO) of tumor cells mimicked coixenolide's effects, enhancing CD8+ T cell function and suppressing tumor growth in vivo, especially in HFD mice. Clinical data confirmed elevated S100A8/A9 expression in human PAAD tumors correlated with poor survival, advanced stage, and higher histological grade, and scRNA-seq of patient samples showed S100A8/A9 expression in malignant ductal cells. Collectively, these results identify coixenolide as an immune-metabolic modulator that attenuates obesity-driven immunosuppression in PAAD at least in significant part through inhibition of the S100A8/A9-CD36 axis, with lipid peroxidation and ferroptosis of CD8+ T cells reduced. Other mechanisms potentially involving regulatory T cells warrant further investigation in the future. These findings suggest S100A8/A9-CD36-mediated intercellular crosstalk as a therapeutically actionable immune-metabolic vulnerability in obesity-associated PAAD.