Abstract C025: Fibroblast-specific IL1R1-p38 MAPK signaling sustains stromal inflammation and contributes to therapeutic resistance in pancreatic cancer
Authors: Singh Samara P. , Dosch Austin R. , Mehra Siddharth , de Castro Silva Iago , Garrido Vanessa Tonin , Bianchi Anna , Amirian Haleh , Box Edmond W. , Datta Jashodeep , Nagathihalli Nagaraj S. , Merchant Nipun B. 
Published: January 2024

Abstract
Introduction: The desmoplastic stroma of pancreatic ductal adenocarcinoma (PDAC) perpetuates therapeutic resistance by impairing drug delivery and effector immune cell infiltration and activation. We have identified tumor cell-derived interleukin-1α (IL1α) as a critical activator of the stroma, comprised of cancer-associated fibroblasts (CAF), towards a pro-inflammatory phenotype via the IL1 receptor, IL1R1, and subsequent activation of p38 MAPK. Our hypothesis is that disruption of the CAF-specific IL1α/p38 MAPK signaling axis can improve chemotherapeutic resistance by remodeling the fibrotic stromal landscape and the overall immune microenvironment in PDAC. Methods: p38 MAPK was pharmacologically inhibited with pexmetinib and genetically with an shRNA lentiviral system. Bulk RNA and ATAC sequencing (RNAseq and ATACseq) were performed on human pancreatic stellate cells (hPSC). Gene set enrichment analyses and motif enrichment analyses were performed on the RNAseq and ATACseq datasets, respectively. Tumor cells (KPC-6694), derived from LSL-KrasG12D/+; LSL-Tp53R172H/+; Pdx1Cre/+ (KPC) murine tumors, were injected orthotopically into Col1a2Cre/+; Mapk14f/f and Col1a2Cre/+; Il1r1f/f mice, and tumors were harvested for downstream analysis. Ptf1aCre/+; LSL-KrasG12D/+; Tgfbr2flox/flox (PKT) mice were treated with pexmetinib (PEX, 30mg/kg, daily PO), anakinra (AKA, 50mg/kg IP, BID) or vehicle control for 2.5 weeks prior to sacrifice for downstream analyses and single-cell RNA sequencing (scRNA) on tumors. Results: In vitro inhibition of p38 MAPK prevented CAF activation into an inflammatory fibroblast, when stimulated with IL1α, demonstrated through bulk RNAseq and ATACseq. Bulk ATACseq revealed epigenetic regulation of the inflammatory CAF phenotype by IL1-mediated activation of p38 MAPK. Stromal-specific deletion of Il1r1 or Mapk14 resulted in signification reduction of tumor weight and intratumoral myeloid-derived suppressor cells. Additionally, pharmacologic blockade of both IL1R1 (AKA) and p38 MAPK inhibition (PEX) altered intratumoral immune cell and CAF populations, by flow cytometry and scRNA. Lastly, p38 inhibition or IL1R1 blockade combined with chemotherapy significantly reduced tumor burden and favorably altered the immune landscape in a PDAC genetically engineered mouse model. Conclusions: These findings provide important mechanistic data in preclinical PDAC models to explore p38 MAPK inhibition in combination therapy to target the fibrotic stroma and immunosuppressive tumor microenvironment.
Citation Format: Samara P. Singh, Austin R. Dosch, Siddharth Mehra, Iago de Castro Silva, Vanessa Tonin Garrido, Anna Bianchi, Haleh Amirian, Edmond W. Box, Jashodeep Datta, Nagaraj S. Nagathihalli, Nipun B. Merchant. Fibroblast-specific IL1R1-p38 MAPK signaling sustains stromal inflammation and contributes to therapeutic resistance in pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Pancreatic Cancer; 2023 Sep 27-30; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84(2 Suppl):Abstract nr C025.