Abstract 3455: Mesenchymal tumors direct macrophage-mediated vascular editing and premetastatic remodeling to promote PDAC metastasis

Abstract Background: Patients with pancreatic ductal adenocarcinoma (PDAC) often have metastatic disease at diagnosis and respond poorly to therapies. High myeloid-to-T cell ratios correlate with worse prognoses, but a more detailed, integrated understanding of mechanisms by which myeloid cells regulate metastasis is critically needed. Using high-parameter spatial profiling, we recently observed that a highly metastatic tumor cell line utilizes mesenchymal invasion and harbors a tumor microenvironment with increased endothelial cell abundance, lower M1-like to M2-like tumor associated macrophage (TAM) ratios, and Arginase-1+ TAMs situated closer to tumor and endothelial cells, compared to a less metastatic model. These models were further interrogated to study the myeloid drivers of metastasis in the primary and metastatic sites. Methods: We used two murine cell lines driven by KrasG12D and Trp53R172H under Pdx1-Cre, KPCY 2838c3 (“c3”) and KPCY 6419c5 (“c5”), which exhibit low-metastatic and high-metastatic propensities, respectively. Imaging mass cytometry was used to determine the changes in the primary tumor and pre-metastatic microenvironments. TAMs and endothelial cells from the primary site were evaluated using RNAseq. In vitro tube formation assays were performed to evaluate the potential factors driving vascularization. Results: In the pancreatic site, the highly metastatic c5 model was significantly enriched for metastasis- and angiogenesis-promoting pathways, including the RANK/RANKL axis. In vitro tube formation assays revealed that c5-derived TAMs induce greater tube formation over those from the c3 model and that RANKL significantly promotes tube formation. Moreover, in the hepatic premetastatic site, the c5 tumors expanded Kupffer, stellate, and endothelial cells to a greater extent than c3 tumors. Finally, the c5 tumors recruit fewer lymphocytes and more granulocytes to the liver, suggesting poorer immune protection against metastasis. Conclusions: Our study highlights multiple tumor-intrinsic and extrinsic factors responsible for metastasis, and that TAMs serve as a critical integration point. Interestingly, we found the RANK/RANKL axis, for which there is already an inhibitory agent that is clinically used, to be a potential mechanism underlying the TAM-endothelial crosstalk. Together, these data prompt further exploration of the observed TAM-endothelial relationship and the premetastatic remodeling in human PDAC, as well as the targetability of the RANK/RANKL axis for disrupting PDAC metastasis. Citation Format: Nicole Elizabeth Gross, Soren Charmsaz, Tiffany Chu, Jae W. Lee, Emma Kartalia, Yiyang Gao, Alexei G. Hernandez, Sarah M. Shin, Erin M. Coyne, Courtney Cannon, Xuan Yuan, Cheng-Chieh Huang, James Leatherman, Pei-Hsun Wu, Laura D. Wood, Elizabeth M. Jaffee, Won Jin Ho. Mesenchymal tumors direct macrophage-mediated vascular editing and premetastatic remodeling to promote PDAC metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 3455.