CYP2S1: a novel regulator of PMN-MDSC recruitment and immunotherapy resistance in esophageal squamous cell carcinoma

Chemoimmunotherapy resistance significantly limits the clinical management of esophageal squamous cell carcinoma (ESCC). To identify tumor-intrinsic regulators associated with an immunosuppressive tumor microenvironment (TME) and treatment failure, we integrated proteomic profiling of clinical ESCC specimens (n=8) and single-cell RNA sequencing of three ESCC tumors and one normal control, identifying CYP2S1 as upregulated in chemoimmunotherapy-resistant tumors and predominantly expressed by malignant epithelial cells. Immunohistochemical and multiplex immunofluorescence analyses further showed that CYP2S1-high tumors contained increased numbers of phenotypically defined polymorphonuclear myeloid-derived suppressor cell (PMN-MDSC) cells. Consistent with a potential relationship between CYP2S1 expression and poor treatment response, the CYP2S1 immunohistochemical score was positively associated with Mandard tumor regression grade in 46 evaluable patients (linear regression R 2 = 0.271, P = 0.0002; Spearman ρ = 0.528, P < 0.001). Mechanistically, CYP2S1 knockdown reduced intracellular reactive oxygen species (ROS) levels and the expression of several myeloid-attracting chemokines, whereas CYP2S1 overexpression increased ROS and most consistently induced CXCL6 and CXCL8. In ROS-scavenging experiment, treatment with N-acetylcysteine attenuated CYP2S1 overexpression-associated ROS accumulation, reduced CXCL6 and CXCL8 mRNA induction, and decreased CXCL8 secretion, supporting a ROS-dependent component of this chemokine program. Collectively, these findings associate tumor cell CYP2S1 with a ROS-linked CXCL6/CXCL8 signaling axis, PMN-MDSC-like accumulation, and unfavorable chemoimmunotherapy response in ESCC.