Hu, Ming2022-06-18December 22021-12December 2https://hdl.handle.net/10657/9305Objective: The objective of this project is to evaluate the chemoprevention efficacy of locally bioavailable and selective COX-2 inhibitor 6a1 by using Pirc rat model with DSS-accelerated polyps multiutility, and then to evaluate if epithelial COX-2 is a good target for preventing polyps development and growth in Pirc rats. Methods：The individual turnover number of COX-1 and COX-2 proteins were derived by PGE2 production and absolute quantification of protein amounts using newly developed LC-MS method. Taken together of the local protein amounts and turnover numbers of COX-1 and COX-2, the individual contribution of COX-1 and COX-2 to colon PGE2 production was assessed and compared. Absolute amount of COX-1 and COX-2 proteins and PGE2 levels were determined in Pirc rats at different ages. Pirc rats were treated with 3% DSS to induce COX-2 expression and accelerate polyps multiplicity. Celecoxib and 6a1 were given orally, and the local PGE2 level and COXs levels were determined by LC-MS methods. The COX/PGE2 inhibitory effects, polyps suppression efficacy of locally bioavailable and selective inhibitor 6a1 were calculated and evaluated in DSS/Pirc rat model. Results：An absolute quantification LC-MS method for COX-1 and COX-2 proteins were successfully developed and fully validated. In Pirc rats, colon epithelial COX-1 protein levels were 5- to 15-fold higher than COX-2 protein levels at all tested ages, and polyps protein levels of COX-1 and COX-2 were 1-fold and 3-fold higher than epithelium levels, respectively. Unexpectedly, both COX-2 protein and PGE2 levels were not increased with polyps development. 3% DSS treatment resulted in a 59-fold increment of epithelial COX-2 but no change in epithelial COX-1 protein levels. The contribution of elevated epithelial COX-2 protein caused a 10-fold increase of epithelium PGE2 levels, and then accelerated the polyps multiplicity up to 10-fold in Pirc rat model. Orally administration of a locally bioavailable and selective COX-2 inhibitor 6a1 can further diminish the COX-2 expression but failed to suppress epithelium PGE2 level in DSS-induced Pirc rats, and as a result failed to suppress polyps development and growth. Orally administration of a systemic and selective COX-2 inhibitor celecoxib at pharmacological doses (5, 20 and 70 mg/kg) to DSS-induced Pirc rats were too toxic to be tolerated by the Pirc rats. Conclusion：In Pirc rat model, epithelial COX-1 protein levels were always higher than epithelial COX-2 levels at different ages. They both remained stable with age or when polyps burden increased, suggesting high epithelial COX-2 level may not be required for polyps development in Pirc rats. Inhibition of COX-2 activities by a locally bioavailable COX-2 inhibitor 6a1 did not reduce PGE2 level nor polyps growth in DSS-induced or non-DSS treated Pirc rat models, suggesting the chemopreventive efficacy of 6a1 was not significant though it could effectively suppress COX-2 expression level. These data demonstrated that suppression of epithelial COX-2 alone is not enough for the prevention of polyps growth in DSS-induced or non-DSS treated Pirc rat models, invalidating colon epithelial COX-2 as a target for polyps chemoprevention.application/pdfengThe author of this work is the copyright owner. UH Libraries and the Texas Digital Library have their permission to store and provide access to this work. Further transmission, reproduction, or presentation of this work is prohibited except with permission of the author(s).Cyclooxygenase (COX), Prostaglandins, Locally bioavailable, Selective COX-2 inhibitors, Absolute quantification, Inflammation, Colitis, Colorectal cancer, DSS (dextran sulphate sodium), Pirc rats2022-06-18Thesisborn digital