Abstract C084: Oncogenic KRAS signaling drives the activation of tissue-resident fibroblasts and is required to maintain CAF heterogeneity in pancreatic cancer
Authors: Caligiuri Giuseppina , Thalappillil Jennifer S. , Shakiba Mojdeh , Nadella Sandeep , Hinds Juliene , Courtois Elise , Flynn William F. , Alagesan Brinda , Yordanov Georgi N. , Kaminow Benjamin , Robson Paul , Perez-Mancera Pedro A. , Preall Jonathan , Dobin Alexander , Park Youngku , Tuveson David A. 
Published: November 2022

Abstract
The complexity of the tumor microenvironment (TME) is one of the distinguishing features of pancreatic ductal adenocarcinoma (PDA) and is responsible for patients’ poor response to therapies. The heterogeneity of cancer-associated fibroblasts (CAFs) has been correlated to the key features of the stroma that contribute to making PDA the third-leading cause of cancer-related deaths in the United States. The recent development of FDA-approved drugs against oncogenic KRAS opened a new therapeutic avenue for the treatment of tumors that have KRAS as their driver oncogene, such as PDA. However, the precise mechanisms driving the development of the TME and the contribution of KRAS to these processes have yet to be elucidated. This poses a challenge for the prediction of the effects of KRAS inhibition on established PDA tumors. By employing spatial transcriptomic technologies on various murine models recapitulating different stages of tumor initiation and progression, from acute and chronic inflammation to PanIN and overt PDA, we were able to observe distinctive changes in the activation status of pancreatic fibroblasts. These resident activated fibroblasts (RAFs) display expression of discrete markers brought upon by inflammation (inflammatory RAFs, iRAFs) or specific to oncogenic KRAS activation (myofibroblastic RAFs, myRAFs). Importantly, these RAF populations are maintained in established tumors and are identifiable in human PDA. To assess the consequences of the disruption of KRAS signaling on CAFs and RAFs, we employed a PDA mouse model that allows for the irreversible excision of KrasG12V, the FPC model (KrasFrt-LSL-G12V-Frt; p53LSL-R172H; PDX-CRE; Rosa26FlpOERT2). Through a combination of single-cell RNA sequencing (scRNA-seq), spatial transcriptomics and fluorescent in situ hybridization combined with immunofluorescence (immunoFISH) on FPC mice before and after KrasG12V deletion, we demonstrate the profound impact of Kras ablation on the TME composition. A deep remodeling of the stroma as well as significant changes in the proportion of CAF subtypes were evident. Interestingly, we observed a decrease in CAFs with a concomitant increase in RAFs. Our results suggest that the activation of oncogenic Kras in pre-neoplastic lesions drives a unique paracrine signaling that shapes the TME and is required to maintain the CAF population in PDA.
Citation Format: Giuseppina Caligiuri, Jennifer S. Thalappillil, Mojdeh Shakiba, Sandeep Nadella, Juliene Hinds, Elise Courtois, William F. Flynn, Brinda Alagesan, Georgi N. Yordanov, Benjamin Kaminow, Paul Robson, Pedro A. Perez-Mancera, Jonathan Preall, Alexander Dobin, Youngku Park, David A. Tuveson. Oncogenic KRAS signaling drives the activation of tissue-resident fibroblasts and is required to maintain CAF heterogeneity in pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer; 2022 Sep 13-16; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2022;82(22 Suppl):Abstract nr C084.