Inhibition of Pancreatic Carcinoma Growth Through Enhancing ω-3 Epoxy Polyunsaturated Fatty Acid Profile by Inhibition of Soluble Epoxide Hydrolase

Background/Aim: Cytochrome P450 epoxygenase is a major enzyme involved in the metabolism of omega-3 polyunsaturated fatty acids (PUFAs) to produce biologically active omega-3 epoxy fatty acids (omega-3 epoxides). In general, all epoxy PUFAs including omega-3 epoxides are quickly metabolized/inactivated by soluble epoxide hydrolase (sEH) to form diol products. The aims of this study were to determine the effect and mechanism of fat-1 transgene, and omega-3 PUFA combined with sEH gene knockout or inhibitor on inhibiting pancreatic cancer and the related mechanisms involved. Materials and Methods: PK03-mutant Kras(G12D) murine pancreatic carcinoma cells were inoculated into mouse models including fat-1, sEH(-/-) and C57BL/6J mice. The mice were fed with AIN-76A diet with or without omega-3 PUFA supplementation or treated with sEH inhibitor. In addition to tumor growth (tumor size and weight), cell proliferation, mutant Kras-mediated signaling, inflammatory reaction and angiogenesis were analyzed immunohisto-chemically and by western blot assay. omega-3 PUFA metabolism, particularly focusing on omega-3 epoxy fatty acids (omega-3 epoxides), was measured using a liquid chromatography with tandem mass spectrometry (LC-MS/MS) approach. Results: Significant decreases of weight and size of the PK03 pancreatic carcinoma were observed in the fat-1 transgenic mice treated with sEH inhibitor compared to those of C57BL/6J control mice fed with AIN-76A diet (weight: 0.28 +/- 0.04 g vs. 0.58 +/- 0.06 g; size: 187.0 +/- 17.5 mm(3) vs. 519.3 +/- 60.6 mm(3)). In a separate experiment, sEH(-/-) mice fed omega-3 PUFA supplement and C57BL/6J mice treated with sEH inhibitor and fed omega-3 PUFA supplement exhibited a significant reduction in the weight and size of the pancreatic carcinoma compared to C57BL/6J control mice (weight: 0.26 +/-.26 g and 0.39 +/-.39 g vs. 0.69 +/- 0.11 g, respectively; size: 274.2 +/- 36.2 mm(3) and 296.4 +/- 99.8 mm(3) vs. 612.6 +/- 117.8 mm(3), respectively). Moreover, compared to the pancreatic tumors in C57BL/6J control mice, the tumors in fat-1 transgenic mice treated with sEH inhibitor showed a significant less inflammatory cell infiltrate (62.6 +/- 9.2/HPF (high power field) vs. 8.0 +/- 1.2/HPF), tumor cell proliferation (48.5 +/- 1.7% vs. 16.5 +/- 1.6%), and angiogenesis (micro-vessel density (MVD): 35.0 +/- 1.0 vs. 11.1 +/- 0.5) immunohistochemically, as well as significantly increased caspase-3 labeled apoptosis (0.44 +/- 0.06% vs. 0.69 +/- 0.06%, respectively). Using western blot approach, significant inhibition of mutant Kras-activated signals including phosphorylated Serine/threonine kinases (cRAF), Mitogen-activated protein kinase kinase (MEK), and extracellular signal-regulated kinase (ERK) were identified in pancreatic carcinoma of fat-1 transgenic mice treated with sEH inhibitor. Eicosanoic acid metabolic profiling of the serum specimens detected a significant increase of the ratios of epoxides to dihydroxy fatty acid (DiHDPE) for docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), and epoxides/dihydroxy octadecenoic acid (DiHOME) for arachidonic acid (ARA) and linoleic acid (LA), as well as a significant increase of epoxy metabolites of DHA, EPA, ARA and LA in fat-1 transgenic mice treated with a sEH inhibitor. Conclusion: omega-3 epoxy products from omega-3 PUFA metabolism play a crucial role in inhibiting pancreatic cancer growth, and use of omega-3 PUFAs combined with sEH inhibition is a strategy with high potential for pancreatic cancer treatment and prevention.