Abstract 1384: Highly metastatic PDAC adopts mesenchymal morphology and spatially coordinates endothelial cells with macrophages

Abstract Background: Patients with pancreatic ductal adenocarcinoma (PDAC) often have metastatic disease at diagnosis and are highly resistant to cytotoxic and immunotherapies. Increased presence of myeloid cells, specifically high myeloid-to-T cell ratios, correlates with worse prognoses. However, mechanisms by which myeloid cells regulate cancer invasion and metastasis remain poorly understood. To study the role of immunosuppressive myeloid cells in driving metastasis, we employed murine PDAC models in conjunction with organoid systems and imaging mass cytometry (IMC). Methods: We used two murine cell lines driven by KrasG12D and Trp53R172H under Pdx1-Cre, KPCY 2838c3 and KPCY 6419c5, which exhibit low-metastatic and high-metastatic propensities, respectively. To characterize differences in the metastatic cascade between these cell lines, flow cytometry, histological analysis, and 3D organoid modeling were used. IMC was also used to interrogate the tumor microenvironment and identify spatial relationships. Results: These cell lines were orthotopically injected into syngeneic C57BL/6J mice to generate tumors that naturally metastasize to the liver. Flow cytometry analysis of livers from mice bearing 2838c3 or 6419c5 pancreatic tumors validated the higher propensity for metastasis with the 6419c5 cells (p=0. 0484). Furthermore, the steps along the metastatic cascade contrasted significantly between 6419c5 and 2838c3. Highly metastatic PDAC adopted mesenchymal rather than collective invasion, increased intravasation, and more robust metastatic outgrowth. Notably, IMC revealed that highly metastatic PDAC had increased endothelial cell abundance (***p ≤ 0. 001), lower cytotoxic CD8+ T cell to CD4+ regulatory T cell ratios (***p ≤ 0. 001), and lower M1-like to M2-like tumor associated macrophage (TAM) ratios (*p ≤ 0. 05). Furthermore, spatial analysis demonstrated that highly metastatic PDAC excluded lymphocytes from the tumor and situated Arginase-1+ TAMs near Ki67+ tumor cells and CD31+ endothelial cells. In contrast, low-metastatic PDAC had closer lymphocyte proximities to tumor and greater distances between Arginase-1+ TAMs, tumor, and endothelial cells. Conclusions: The highly metastatic PDAC tumor line utilizes mesenchymal invasion, has increased intravasation, and robust metastatic outgrowth compared to the low-metastatic PDAC cells. The TME of the highly metastatic model had disproportionate abundances of T regulatory cells and M2-like macrophages, poor lymphocyte infiltration, and enhanced vascularization. These overabundant M2-like macrophages (Arginase-1+) were also spatially coordinated with proliferating tumor cells and vasculature, suggesting a potential role for macrophages in tumor cell invasion and/or angiogenesis. Citation Format: Nicole E. Gross, Soren Charmsaz, Jae W. Lee, Cheng-Chieh Huang, Alexei G. Hernandez, Sarah M. Shin, Erin M. Coyne, Courtney Cannon, Xuan Yuan, Laura D. Wood, Elizabeth M. Jaffee, Won Jin Ho. Highly metastatic PDAC adopts mesenchymal morphology and spatially coordinates endothelial cells with macrophages abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 1384.