Abstract C045: CA19-9-mediated remodeling of the pancreatic tumor microenvironment

Pancreatic ductal adenocarcinoma (PDA) is an intractable common malignancy with a pro-tumorigenic and immunosuppressive microenvironment (ME) that often limits treatment efficacy. The glycan CA19-9 is used to follow treatment response in PDA patients, but its functional role in PDA remained unknown until recently because rodents lack this carbohydrate. CA19-9 elevation in a KRAS-mutant background promotes rapid progression to invasive carcinoma and induces ME remodeling in mice. The tumor ME includes cancer associated fibroblasts (CAFs) and tumor associated macrophages (TAMs) that contribute to desmoplasia, immunosuppression, and therapeutic resistance. All prior work investigating the tumor ME in PDA mouse models was performed in a CA19-9 negative context, potentially missing a key element of PDA biology. Elevation of CA19-9 in mice caused expansion of both CAFs and TAMs, but the mechanisms by which CA19-9 contributes to ME remodeling remains largely unknown. We aim to uncover the direct and indirect mechanisms of CA19-9-mediated ME remodeling. We identified CA19-9 modified ligands by immunoprecipitation and mass spectrometry that may contribute to reprogramming of the PDA ME. In addition to exploring changes in abundance, localization, and protein interactions, we will functionally characterize these candidate effectors via CRISPR ablation and antibody blockade using a novel Macrophage, Organoid, and Fibroblast (MOrF) co-culture platform. MOrF co-cultures can be sustained for at least 10 days in defined media conditions and enable compartment specific delineation of paracrine and juxtacrine signals. While CA19-9 modification may play a direct role in stromal remodeling, we also investigate effectors that are altered in response to CA19-9 elevation. CA19-9 induction in KRAS-mutant organoid mono-cultures increased gene expression of IL1α, CSF1,and TGFβ. In addition, CA19-9 expression increased gene set enrichment of inflammatory programs inorganoid mono-culture and led to increased expression of CAF and TAM differentiation programs in MOrF co-culture. These results are being validated as discussed above as well as by evaluation in vivo in CA19-9 positive and negative syngeneic orthotopic transplantation and autochthonous genetically engineered mouse models using scRNA-seq, pharmacologic and genetic perturbation, as well as other approaches. Using these orthogonal approaches, we will identify the mechanisms by which CA19-9 directly and indirectly contribute