HMGA1 Chromatin Regulators in Pancreatic Carcinogenesis ABSTRACT Background: We propose to elucidate mechanisms mediated by High Mobility Group A1 (HMGA1) chromatin regulators in pancreatic carcinogenesis. Pancreatic ductal adenocarcinomas (PDAC) are highly lethal cancers characterized by invasive tumor cells and a dense desmoplastic stroma. HMGA1 gene expression is activated during embryogenesis, but silenced postnatally in most adult, differentiated tissues. In diverse, cancers, such as PDAC, HMGA1 becomes re-expressed where high levels portend adverse outcomes. HMGA1 the role of HMGA1 in pancreatic carcinogenesis is only beginning to emerge. Here, we focus on actionable pathways downstream of HMGA1 as novel therapeutic targets in PDAC. Our scientific premise that HMGA1 drives tumor progression in PDAC is based on the following preliminary results: 1) HMGA1 is highly overexpressed in PDAC where high levels predict decreased survival, 2) As we recently published (JCI, 2023), silencing HMGA1 blocks diverse oncogenic properties in PDAC cell lines while depleting tumor-initiator cells in xenografts, 3) In KPC mice with PDAC driven by mutant Kras and Tp53, deficiency of HMGA1 disrupts tumorigenesis while prolonging survival. 4) Surprisingly, loss of just a single Hmga1 allele within the pancreatic epithelium is sufficient to impair both tumor and stroma formation in KPC mice, 5) Mechanistically, HMGA1 functions as an epigenetic switch by activating transcriptional networks involved in proliferation and oncogenic transformation in PDAC cell line models, including the FGF19 growth factor gene, 6) Targeting FGF19 gene expression or function by FGFR4 receptor blockade in xenograft models disrupts tumor and stroma formation, 7) Most importantly, tumors with high expression of both HMGA1 and FGF19 define a molecular subclass of human PDAC with exceptionally poor outcomes. 8) In KPC mice, Hmga1 deficiency within pancreatic epithelium results in increasing immune cell infiltration in pancreatic tumors, suggesting that HMGA1 also drives immune evasion by Together, these intriguing results support the following hypotheses: 1) HMGA1 is required for PDAC progression and stroma formation through epigenetic alterations and gene networks that foster aberrant proliferation, differentiation, and TME signaling. 2) HMGA1 within tumor cells modulates the TME to promote immune evasion, 3) Targeting pathways governed by HMGA1 will provide novel therapeutic strategies. Aims/Approach: To test this, we propose the following Specific Aims: 1) To precisely define HMGA1- dependent mechanisms in tumor progression using KPC mice and primary human tumors, and, 2) To test targeting HMGA1 pathways for therapeutic efficacy in preclinical models. Impact: This work should reveal new paradigms for PDAC pathogenesis and lead to novel approaches to treat, or even prevent, these profoundly recalcitrant tumors.