Abstract 117: Inhibition of Hedgehog signaling alters fibroblast composition in pancreatic cancer

Abstract Purpose: Pancreatic ductal adenocarcinoma (PDAC) is a deadly disease characterized by an extensive fibroinflammatory stroma, which includes abundant cancer-associated fibroblast (CAF) populations. PDAC CAFs are heterogeneous, but the nature of this heterogeneity is incompletely understood. The Hedgehog (HH) pathway functions in PDAC in a paracrine manner, with ligands secreted by cancer cells signaling to stromal cells in the microenvironment. Previous reports investigating the role of HH signaling in PDAC have been contradictory, with HH signaling alternately proposed to promote or restrict tumor growth. In light of the newly discovered CAF heterogeneity, we investigated how HH pathway inhibition reprograms the PDAC microenvironment. Experimental Design: We used a combination of pharmacologic inhibition, gain- and loss- of-function genetic experiments, CyTOF, and single cell RNA-sequencing to study the roles of HH signaling in PDAC. Results: We find that HH signaling is uniquely activated in fibroblasts and differentially elevated in myofibroblastic CAFs (myCAFs) compared to inflammatory CAFs (iCAFs). SHH overexpression promotes tumor growth, while HH pathway inhibition with the Smoothened antagonist LDE225 impairs tumor growth. Further, HH pathway inhibition reduces myCAF numbers and increases iCAF numbers, which correlates with a decrease in cytotoxic T cells and an expansion in Tregs, consistent with increased immune suppression. Conclusions: HH pathway inhibition alters fibroblast composition and immune infiltration in the pancreatic cancer microenvironment. Citation Format: Nina G. Steele, Giulia Biffi, Samantha Kemp, Yaqing Zhang, Donovan Drouillard, LiJyun Syu, Yuan Hao, Tobiloba Oni, Erin Brosnan, Ela Elyada, Abhishek Doshi, Christa Hansma, Carlos Espinoza, Ahmed Abbas, Stephanie The, Valerie Irizarry-Negron, Christopher Halbrook, Nicole Franks, Megan Hoffman, Eileen Carpenter, Zeribe Nwosu, Youngkyu Park, Howard Crawford, Costas Lyssiotis, Timothy Frankel, Arvind Rao, Filip Bednar, Andrzej Dlugosz, Jonathan Preall, David Tuveson, Benjamin Allen, Marina Pasca di Magliano. Inhibition of Hedgehog signaling alters fibroblast composition in pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 117.