Abstract PR-03: Canonical Notch signaling in cancer-associated fibroblasts supports an immunosuppressive pancreatic tumor microenvironment

Abstract Notch is a contact-dependent signaling pathway that plays critical roles in spatiotemporal patterning during embryogenesis. Beyond its role in development, Notch signaling can regulate tissue patterning in adult organs in response to tissue injury or cancer. In pancreatic cancer, Notch signaling drives pancreatic tumor epithelial growth and regulates myeloid function in the tumor microenvironment (TME). Its role in pancreatic cancer-associated fibroblasts (CAFs) is less clear. CAFs are a central component of the pancreatic TME and demonstrate significant phenotypic and functional differences depending on their spatial arrangement in pre-neoplastic and tumor tissue. Using Notch signaling reporter mice CBF: H2B-Venus bred into KC (Ptf1a cre/+;Kras LSL-G12D/+) and KPC (Ptf1a cre/+;Kras LSL-G12D/+;p53 flox/+) backgrounds, we demonstrate that canonical Notch signaling is activated in CAFs at different stages of neoplastic progression. Notably, Notch signaling appears to be most active in aSMA+ CAFs spatially located adjacent to pre-neoplastic/cancer cells, suggesting that Notch ligands expressed by pre-neoplastic/cancer cells are critical for this activation. To test the functional role of canonical Notch signaling in CAFs, we generated a fibroblast-specific, tamoxifen-inducible model of Notch inhibition that utilizes a dominant-negative form of the Notch transcriptional co-activator MAML1 (PDGFRa CreERT2/+ ,Rosa26 LSL-DNMAML). Using an orthotopic model of pancreatic cancer (50,000 cells; KPC) we demonstrate that inhibition of Notch signaling in CAFs results in smaller tumors. These CAFs expressed lower levels of the myofibroblastic marker aSMA+. Additionally, tumors from PDGFRa CreERT2/+, Rosa26 LSL-DNMAML mice had fewer Arg1+ macrophages and a dramatic influx of CD8+ T cells. Collectively, these results suggest that Notch signaling in CAFs regulates their phenotype and supports tumor progression by inducing an immunosuppressive tumor microenvironment. Citation Format: Allison Bischoff, Wei Yan, Filip Bednar, Marina Pasca di Magliano. Canonical Notch signaling in cancer-associated fibroblasts supports an immunosuppressive pancreatic tumor microenvironment [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research; 2024 Sep 15-18; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(17 Suppl_2):Abstract nr PR-03.