Simple SummaryThe tumor microenvironment of pancreatic cancer consists of dense fibrotic stroma, which, to a certain extent, accounts for the relative drug resistance of this malignancy. Activated pancreatic stellate cells (PSC) and myofibroblasts are responsible for this fibrosis, and strategies to target the fibrosis or render the stellate cells quiescent have been investigated in order to improve therapies for pancreatic cancer. Many have studied TGF-β and other pathways involved in fibrosis. In this work, we study the role of a novel cholecystokinin receptor signaling pathway in pancreatic cancer fibrosis. Treatment with a CCK receptor antagonist, proglumide, induced plasticity of activated mouse and human fibroblasts to revert the cells to a quiescent state with decreased migration, proliferation, and production of collagenous proteins of the tumor microenvironment. Interruption of the CCK-B receptor pathway provides a novel strategy to alter the extracellular matrix in pancreatic cancer by changing PSCs from an activated state to quiescence.AbstractCCK receptors are expressed on pancreatic cancer epithelial cells, and blockade with receptor antagonists decreases tumor growth. Activated pancreatic stellate cells or myofibroblasts have also been described to express CCK receptors, but the contribution of this novel pathway in fibrosis of the pancreatic cancer microenvironment has not been studied. We examined the effects of the nonselective CCK receptor antagonist proglumide on the activation, proliferation, collagen deposition, differential expression of genes, and migration in both murine and human PSCs. CCK receptor expression was examined using western blot analysis. Collagen production using activated PSCs was analyzed by mass spectroscopy and western blot. Migration of activated PSCs was prevented in vitro by proglumide and the CCK-B receptor antagonist, L365,260, but not by the CCK-A receptor antagonist L365,718. Proglumide effectively decreased the expression of extracellular matrix-associated genes and collagen-associated proteins in both mouse and human PSCs. Components of fibrosis, including hydroxyproline and proline levels, were significantly reduced in PSC treated with proglumide compared to controls. CCK peptide stimulated mouse and human PSC proliferation, and this effect was blocked by proglumide. These investigations demonstrate that targeting the CCK-B receptor signaling pathway with proglumide may alter the plasticity of PSC, rendering them more quiescent and leading to a decrease in fibrosis in the pancreatic cancer microenvironment.