Abstract B103: Interleukin-1 Receptor Accessory Protein (IL1RAP) is a Critical Determinant of Neutrophil Trafficking in Pancreatic Cancer

Abstract INTRODUCTION: A dominant mechanism of chemoimmunotherapy resistance in PDAC is the robust infiltration and persistence of neutrophilic or polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs). Interleukin-1 receptor accessory protein (IL1RAP) is the co-receptor for the IL-1 superfamily cytokines which drive inflammatory signaling in PDAC. Given its preferential expression in circulating PMN-MDSCs, we sought to determine how IL1RAP orchestrates trafficking to the tumor microenvironment (TME) and PMN-MDSC pathogenicity. METHODS: Single-cell RNA sequencing (scRNA-seq) and RNA velocity analysis of tumor and spleen derived from Ptf1a Cre/+ ; Kras LSL-G12D/+ ;Tgfbr2 flox/flox (PKT) genetically engineered mouse model (GEMM) at early vs late time points was performed. In-vitro cell migration assays assessed J774M chemotaxis upon genetic or pharmacologic IL1RAP inhibition. Fluorescently labeled J774M-gCTL or J774M-Il1rap KO cells were adoptively transferred into KPC tumor-bearing mice, followed by IVIS and flow cytometric analysis. Recombinant IL33 +/- Grk2 siRNA was used to examine CXCR2 regulation. An siRNA knockdown screen identified transcriptional regulators of Grk2. Orthotopic tumor-bearing Mrp8-Cre+/- Il1rap fl/fl and control mice were used to assess tumor burden by volume and weight measurements and CXCR2/GRK2 protein expression by immunofluorescence (IF). RESULTS: ScRNA-seq with RNA velocity in PKT tumors identified Il1rap as the top trajectory-defining gene in circulating terminal-state neutrophils. Genetic ablation of Il1rap in J774M cells significantly impaired transwell migration in vitro (p<0.01). Flow cytometry demonstrated that IL-33-IL1RAP signaling selectively induced CXCR2 expression and CXCR2-dependent trafficking in IL1RAP-competent J774M cells. In vivo, adoptively transferred J774M-Il1rap KO exhibited reduced trafficking and comprised significantly fewer CXCR2+ cells that migrated to the tumor (p<0.01). IL33/IL1RAP signaling induced GRK2 downregulation (p<0.001), maintaining CXCR2 surface stability in J774M. A targeted siRNA knockdown screen identified Nfkb1 (p50) as a transcriptional repressor of Grk2. IL33/IL1RAP signaling induces p105 phosphorylation, resulting in p50/p50 mediated repression of Grk2 which maintains CXCR2 surface stability. Treatment with Grk2 siRNA +/- recombinant IL33 enhanced CXCR2 surface expression, with maximal expression observed following combined treatment. Mrp8-Cre+/- Il1rap fl/fl exhibited significantly lower tumor weights (p<0.001) and volumes (p<0.01) than control Mrp8-Cre+/- mice; this arrest in tumor growth was associated with reduced CXCR2 (p<0.05) and higher GRK2 (p<0.01) expression in Ly6G+ cells from Mrp8-Cre+/- Il1rap fl/fl spleens. CONCLUSION: IL33-IL1RAP signaling appears a critical determinant of CXCR2-dependent neutrophil trafficking in PDAC. IL1RAP signaling induces p50-mediated Grk2 repression; the resulting decline in GRK2 stabilizes CXCR2 at the cell surface, a process reversed upon IL1RAP deletion. Targeting IL1RAP may mitigate neutrophil-derived immunosuppression in PDAC. Citation Format: Harper M. Marsh, Andrew Adams, Haleh Amirian, Karthik Rajkumar, Manan Patel, Luis Nivelo, Anuroop Allena, Erin M. Dickey, Elena Shersher, Kevin Van der Jeught, Anna Bianchi, Nipun Merchant, Jashodeep Datta. Interleukin-1 Receptor Accessory Protein (IL1RAP) is a Critical Determinant of Neutrophil Trafficking in Pancreatic Cancer [abstract]. In: Proceedings of the AACR Conference on Pancreatic Cancer: New Frontiers in Biology and Therapeutic Development; 2026 Sep 25-28; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(18_Suppl_2):Abstract nr B103.