Abstract PO-102: Fibroblast-derived interleukin-33 promotes pancreatic ductal adenocarcinoma as a result of tumor cell KRASG12D

Pancreatic ductal adenocarcinoma (PDA) is a deadly disease that is difficult to detect early and limited in its therapeutic options. As a result, the five-year survival rate of PDA is only 10%. Expression of the oncogene KRAS is present in over 94% of PDA cases, with the most common KRAS mutation being KRASG12D. Another hallmark of PDA is its reactive, fibroinflammatory tumor microenvironment, which is established in tandem with the earliest stages of tumorigenesis and is essential to the growth and maintenance of the tumor. In this work, we have endeavored to uncover the ways by which tumor cell KRASG12D expression influences extracellular signals that shape the tumor microenvironment to the benefit of the disease, with the overall goal of identifying new potential therapeutic vulnerabilities downstream of KRAS signaling. Importantly, using genetically engineered mouse models (GEMMs) and in vitro assays by which tumor cell expression of KrasG12D can be turned on and off, we have found that tumor cell KRASG12D activity stimulates the expression of Interleukin-33 (IL33) in pancreatic fibroblasts through a mechanism requiring both JAK/STAT3 and Focal Adhesion Kinase (FAK) signaling. Through immunohistochemical staining and single cell RNA sequencing of patient tumor samples, we have also confirmed the expression of IL33 in the cancer-associated fibroblast compartment of human PDA. IL33 is a dual function cytokine - it is sequestered in the nucleus where it can impact the cellular transcriptome, and it can also be released to signal to cells expressing its receptor, ST2L. Across the cancer biology field, IL33 expression has been reported to be regulated by different signaling factors, and its impact can be either tumor promoting or tumor restricting depending on the tissue context. In PDA, the role of IL33 is currently unclear, with recent publications alternatively describing it as anti- or pro-tumor. While previous studies have focused on epithelial IL33, we have used a Pdgfra-CreERT2/+;Il33f/f GEMM to knock out Il33 in fibroblasts prior to orthotopic implantation of syngeneic PDA cells. Tumor growth in Il33-deficient mice was reduced, and we observed fewer infiltrating immune cells, including macrophages. As our group and others have previously shown that macrophages are a significant driver of immunosuppression required for the maintenance of PDA, we hypothesized that fibroblast-derived Il33 promotes pancreatic tumorigenesis through either direct or indirect recruitment of immunosuppressive macrophages. As we continue to dissect the role of IL33 in the pancreatic tumor microenvironment, we aim to fully understand the biological role of IL33 during the onset of carcinogenesis and in advanced disease. Overall, this work will shed new light on the ways by which fibroblasts and macrophages are co-opted by tumor cells as a result of KRASG12D, further elucidating prospective therapeutic avenues that may be exploited in the future. Citation Format: Katelyn Donahue, Wenting Du, Carlos Espinoza, Eileen Carpenter, Kristee Brown, Nina Steele, Marina Pasca di Magliano. Fibroblast-derived interleukin-33 promotes pancreatic ductal adenocarcinoma as a result of tumor cell KRASG12D [abstract]. In: Proceedings of the AACR Virtual Special Conference on Pancreatic Cancer; 2021 Sep 29-30. Philadelphia (PA): AACR; Cancer Res 2021;81(22 Suppl):Abstract nr PO-102.