Abstract A051: Understanding the Arf-p53 axis in PDAC suppression

Abstract Understanding the gene regulatory networks that contribute to PDAC initiation and progression is critical for improving early detection and more effectively treating this disease. Activating mutations in KRAS are often accompanied by mutations in the TP53, CDKN2A, and SMAD4 tumor suppressor genes in ~72%, 30%, and 32% of PDAC cases (Raphael et al. 2017). Understanding the consequences of deletion of individual tumor suppressor genes can delineate specific genotype-phenotype correlations that can provide new clinical insights. Using a genetically engineered mouse PDAC model based on KrasG12D expression and tumor suppressor gene inactivation through Ptf1aCreER expression in adult acinar cells, we showed previously that p53 deletion or point mutation dramatically accelerates PDAC relative to mice with intact p53. To understand tumor evolution in mice with different p53 statuses, we analyzed the transcriptomic profiles of PDACs developing with intact or mutant p53 by spatial transcriptomics and both bulk and single cell RNA-sequencing. These experiments have provided insight into the pathways that become dysregulated as PDAC develops in the context of different p53 alleles. In addition, as oncogenic signals trigger p53 stabilization via the p19ARF (ARF) protein in some contexts, we sought to determine whether ARF acts upstream of p53 in PDAC suppression. Indeed, the frequent deletion of the CDKN2A locus, which encodes both the ARF and p16INK4A (p16) tumor suppressor genes, suggests the importance of both these genes in suppressing PDAC, but the specific role of ARF in PDAC suppression has not been tested. Using mouse models to definitively interrogate the importance of ARF in suppressing PDAC, we found that Arf inactivation promotes KrasG12D-driven PDAC, and with a latency similar to p53 inactivation. Interestingly, concurrent inactivation of both p53 and Arf accelerated oncogenic KRAS-driven PDAC development relative to p53 inactivation alone, suggesting a p53-independent role for ARF in PDAC suppression. Transcriptomic profiling of tumors from these mice revealed both p53-dependent and p53-independent programs of ARF-mediated tumor suppression, which provides insight into how tumors develop in the absence of ARF. Characterization of the immune and fibroblast components of the tumor microenvironment in tumors with intact tumor suppressors, p53 deficiency, Arf deficiency and combined p53;Arf deficiency reveals genotype-dependent differences, including different CAF profiles observed in tumors of different genotypes. Ongoing analysis of human PDAC will help to further parse the roles of ARF and p16 in human pancreatic cancer development. Together, these studies will help to illuminate how p53 and Arf inactivation contribute to cancer cell evolution and crosstalk with the tumor microenvironment during PDAC development, understanding with potential for improving clinical interventions in PDAC. Citation Format: Laura D. Attardi, Brittany M. Flowers, Kathryn Hanson, Abigail S. Mulligan, Sofia Ferreira, Sohinee Bhattacharyya, Hannes Vogel, Laura D. Wood, Mara Sherman. Understanding the Arf-p53 axis in PDAC suppression [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 A051.