Abstract B010: RUNX1/2-mediated chromatin accessibility governs the activation of cancer associated fibroblasts in pancreatic cancer

Abstract

Pancreatic ductal adenocarcinoma (PDAC) remains the deadliest cancer with only 13% of five-year survival rate in patients. However, effective drug delivery and administration of immunotherapy have been limited due to the dense fibrotic stroma in PDAC tumor microenvironment, majorly contributed by cancer-associated fibroblasts (CAFs). Unfortunately, targeting CAFs has not yet been successful due to the lack of understanding in CAF activation, heterogeneity, and plasticity. Of note, CAFs do not genetically differ from their origins, and they are interconvertible depending on external factors and signaling cues. This plasticity feature suggests that CAFs activation is regulated by epigenetic reprogramming. Using ATAC-seq and innovative PDAC organoid-CAF co-culture models, we revealed distinct chromatin accessibility profiles of two major CAF subtypes, myofibroblasts (myCAF) and inflammatory fibroblasts (iCAFs) in vitro. In parallel, snATAC-seq analysis on both patient samples and mouse models also indicated the role of chromatin accessibility in differentiating CAF subtypes. Interestingly, we discovered a universal inflammatory-to-fibroblastic process, in which fibroblasts were initially activated into iCAFs and gradually transitioned into late-stage LRRC15+ myCAFs. Notably, this activation towards myofibroblast is tightly regulated by RUNX1/2 transcription factors. Both pharmacological inhibition and genetic perturbation targeting RUNX1/2 significantly repressed CAF activation into either myCAFs or iCAFs and suppressed tumor organoid-fibroblast crosstalk in co-culture settings. Additionally, knocking out of Runx1/2 in fibroblasts markedly reduced collagen deposition and tumor growth in mice co-transplanted orthotopically with tumor organoids and fibroblasts. Overall, our study demonstrates the epigenetic basis of CAF plasticity and suggests a therapeutic strategy targeting the RUNX1/2 family to remodel the stroma and improve treatment outcomes.