Abstract A030: Inactivation of <i>CDKN2A</i> <i>ARF</i> promotes p53-independent remodeling of the PDAC tumor microenvironment

Abstract The CDKN2A locus is one of the most frequent alterations in pancreatic ductal adenocarcinoma (PDAC). CDKN2A locus encodes two tumor suppressors, ARF and INK4A, which are rarely studied individually, limiting our understanding of their distinct roles in tumorigenesis. In addition, although ARF is an established positive regulator of the p53 tumor suppressor, it also has proposed p53-independent activities. The p53-dependent and p53-independent roles of ARF in the context of PDAC remain unclear. Here, we sought to understand ARF function in PDAC suppression. To this end, we first characterized expression and mutational patterns of the individual transcripts encoding ARF and INK4A using human TCGA data. Because the discrete roles of these transcripts have long been obscured by the shared CDKN2A locus nomenclature, we propose that future studies should analyze them independently and adopt CDKN2A ARF and CDKN2A INK4A as nomenclature that allows for their distinction. Notably, we found that CDKN2A ARF and CDKN2A INK4A are both commonly altered in human PDACs, through point mutation and/or deletion, suggesting that their combined inactivation contributes to human PDAC development. Next, to unequivocally interrogate a role for ARF as a PDAC suppressor, we used genetically-engineered mouse models (GEMMs). We found that Arf inactivation accelerated KRASG12D-driven PDAC development in GEMMs, both in the presence and absence of Trp53, demonstrating that ARF is a PDAC suppressor, and furthermore that it can act in a p53-independent manner. Transcriptomic analyses of PDACs from mice of various genotypes provided support for a p53-independent role for ARF, with ARF deficiency promoting extracellular matrix, collagen synthesis/assembly and epithelial-mesenchymal transition gene expression programs. Accordingly, ARF-deficient PDACs exhibited extensive remodeling of the tumor microenvironment (TME), associated with collagen deposition, increased tissue stiffness, and higher fibroblast content, all of which are characteristic of aggressive and treatment-resistant PDAC stroma. Similarly, transcriptomic analyses of human PDACs supported the notion that reduced ARF expression drives changes in the TME. Taken together, our findings reveal that ARF deficiency sculpts the PDAC TME and does so in a p53-independent fashion. Given the central role of the TME in PDAC progression and therapeutic resistance, our findings offer critical insights that may inform improved therapeutic strategies for PDAC. Moreover, our observations also underscore the importance of distinguishing between the two CDKN2A-encoded tumor suppressors, ARF and INK4A, and of studying both p53-dependent and p53-independent roles for ARF as they may have distinct and complementary roles in PDAC biology. Citation Format: Sofia Ferreira, Brittany M. Flowers, Won-Young Choi, Maria Farina-Morillas, Alberto Gatto, Sohinee Bhattacharyya, Gábor Boross, Ghmkin Hassan, Abigail S. Mulligan, Hannes Vogel, Laura D. Wood, Valerie M. Weaver, Monte M. Winslow, Dmitri Petrov, Mara H. Sherman, Hyo Young. Choi, D. Neil. Hayes, Andrew J. Aguirre, Jose A. Seoane, Laura D. Attardi. Inactivation of CDKN2A ARF promotes p53-independent remodeling of the PDAC tumor microenvironment [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research—Emerging Science Driving Transformative Solutions; Boston, MA; 2025 Sep 28-Oct 1; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2025;85(18_Suppl_3):Abstract nr A030.