Abstract C064: Mapping Cellular Plasticity Through the Lens of FRA1 During Kras G12D Mediated Pancreatic Acinar to Ductal Metaplasia

Abstract Introduction: Acinar cells have been proposed as a cell-of-origin for pancreatic ductal adenocarcinoma (PDAC) after undergoing acinar to ductal metaplasia (ADM). ADM can be triggered by pancreatitis causing acinar cells to de-differentiate to a ductal-like state. We identify FRA1 (gene name Fosl1) as the most active transcription factor during Kras G12D acute pancreatitis-mediated injury. Herein, we explore the role of the FRA1 in the onset of ADM and neoplastic transformation. Methods: We generated tamoxifen (TAM)-inducible Ptf1aCre ERT ;Kras G12D ; Rosa26 YFP/YFP (TAM-KCY Fosl1 WT ) mice and bred in the Fosl1 fl/fl allele to create TAM- KCY Fosl1 KO mice and subjected them to caerulin (CCK analog) induced acute pancreatitis. First, we performed a time course of hematoxylin and eosin (H&E) images from mice either with Fosl1 WT or Fosl1 KO after induction of acute pancreatitis to understand the functional role of FRA1 during acinar de-differentiation. Next, after snap-freezing pancreata at the Day 5 post-caerulein timepoint and extracting nuclei, we sorted YFP+ nuclei for snATAC sequencing and bulk-RNA sequencing. We developed a pseudotime model and gene-regulatory network (GRN) to understand the dynamic landscape as cells transitioned from normal acinar to late ADM. Finally, to determine the functional role of in tumorigenesis, we bred an inducible mutant p53 R172H gain- of-function allele into TAM-KCY Fosl1 WT/KO mice to create TAM-KPCY Fosl1 WT/KO mice. These mice were subjected to the same tamoxifen and acute pancreatitis protocol as TAM-KCY Fosl1 WT/KO mice and monitored for tumor growth and overall survival. Results: A time course of H&E images demonstrated that FRA1 depletion slowed progression to maximum ADM in the first 5 days after caerulein treatment. We additionally observed a dramatic reduction in the amount of PanIN lesions formed between TAM-KCY Fosl1 WT and TAM-KCY Fosl KO mice, which occurred on day 7 in this caerulein model. Pseudotime analysis proposed a time point when FRA1 becomes active to prime ADM cells for recovery from inflammation and simultaneously undergo PanIN transformation. Furthermore, GRN analysis validated the differentially active transcription factors identified by pseudotime analysis of snATAC-seq. To elaborate on further timepoints, we observed a delay in the progression of TAM-KCY Fosl KO PanIN lesions at later Day 21, 8-week and 12-week timepoints. In the survival analysis, TAM-KPCY Fosl1 WT mice had a median survival time of 25.86 weeks, while TAM-KPCY Fosl1 KO mice survived for almost twice as long with a median survival time of 40.57 weeks. Histologically, the percentage of Ki-67- positive cells in TAM-KPCY Fosl1 WT tumors was significantly higher than in TAM-KPCY Fosl1 KO tumors, suggesting the loss of FRA1 reduce tumor aggressiveness. Conclusions: Our findings reveal that FRA1 is a critical mediator of ADM progression to PanIN and PDAC. Fosl1 genetic depletion can alter the kinetics of ADM formation and lead to a decrease in PanIN and eventual malignant transformation. Citation Format: Alina Li, Noriyuki Nishiwaki, Kensuke Sugiura, Kensuke Suzuki, Constanza Nicole Tapia Contreras, Dorsay Sadeghian, Anirban Maitra, Jason R Pitarresi, Rohit Chandwani, Peter A Sims, Anil K Rustgi. Mapping cellular plasticity through the lens of FRA1 during Kras G12D mediated pancreatic acinar to ductal metaplasia [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research; 2024 Sep 15-18; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(17 Suppl_2):Abstract nr C064.