PROJECT SUMMARY/ABSTRACT Despite significant advances in cancer care, pancreatic ductal adenocarcinoma (PDAC) remains the third leading cause of cancer death in the United States with a 5-year survival rate of ~10%. Obesity and high fat diet (HFD) consumption increase PDAC risk in human cohorts and accelerate PDAC progression in mice, but the mechanistic basis for these relationships is not well understood. Given the rapid rise in both the worldwide prevalence of obesity and consumption of dietary fat, deciphering mechanisms of obesity-driven PDAC could broadly impact human health. The translational relevance of prior diet research, however, has been limited by uncontrolled variations in fat source and intake across human populations and mouse experiments. Therefore, whether and how specific dietary fats promote pancreatic tumorigenesis remain critical unanswered questions of great societal importance. Leveraging a unique isocaloric panel of HFDs differing only in fat source, we identified a correlation between consumption of diets high in oleic acid – a monounsaturated fatty acid typically associated with good health – and enhanced tumor development in a genetic model of PDAC that faithfully mimics the genetic and histologic progression of the human disease. We further observed that tumorigenesis correlated with increased incorporation of oleic acid into specific phospholipids in tissues, including the pancreas. In this proposal, we aim to test the hypothesis that excess dietary oleic acid directly incorporates into cellular lipids in the pancreas to drive PDAC development. The studies in Aim 1 utilize sophisticated genetic, pharmacologic, and dietary approaches to modulate systemic oleic acid levels and establish whether excess oleic acid is necessary and sufficient to promote pancreatic tumorigenesis. The proposed work in Aim 2 uses lipidomic analyses to clarify the relationship between dietary fatty acids and pancreatic lipid composition during PDAC progression and tests whether specific resultant unsaturated lysophospholipids drive tumorigenesis. Finally, the experiments in Aim 3 combine metabolic and radioactive isotope tracer analyses with conditional knockout models to decipher the mechanisms by which dietary oleic acid is directly taken up by the pancreas and whether inhibition of fatty acid uptake pathways in pancreatic cells blocks the pro-tumorigenic effects of oleic acid. Together, these studies will link fatty acid consumption to specific changes in pancreatic lipid composition as driving forces in PDAC progression. Results from this work have transformative potential to identify novel targeted dietary and pharmacologic strategies for the prevention of a largely incurable cancer.