Rongjin Sun1, Lijun Zhu2, Li Li3, Wenjie Song2, Xia Gong2, Xiaoxiao Qi2, Ying Wang2, Romi Ghose3, Song Gao4, Ming Hu5, Zhongqiu Liu6. 1. Joint Laboratory for Translational Cancer Research of Chinese Medicine of the Ministry of Education of the People's Republic of China, International Institute for Translational Chinese Medicine, Guangzhou University of Chinese Medicine, Guangzhou 510006, Guangdong, China; Department of Pharmacological and Pharmaceutical Sciences, College of Pharmacy, University of Houston, 4901 Calhoun Street, Houston, TX 77204, United States. 2. Joint Laboratory for Translational Cancer Research of Chinese Medicine of the Ministry of Education of the People's Republic of China, International Institute for Translational Chinese Medicine, Guangzhou University of Chinese Medicine, Guangzhou 510006, Guangdong, China. 3. Department of Pharmacological and Pharmaceutical Sciences, College of Pharmacy, University of Houston, 4901 Calhoun Street, Houston, TX 77204, United States. 4. Department of Pharmaceutical and Environmental Health Sciences, Texas Southern University, 3100 Cleburne Street, Houston, TX 77004, United States. Electronic address: song.gao@tsu.edu. 5. Department of Pharmacological and Pharmaceutical Sciences, College of Pharmacy, University of Houston, 4901 Calhoun Street, Houston, TX 77204, United States. Electronic address: mhu4@central.uh.edu. 6. Joint Laboratory for Translational Cancer Research of Chinese Medicine of the Ministry of Education of the People's Republic of China, International Institute for Translational Chinese Medicine, Guangzhou University of Chinese Medicine, Guangzhou 510006, Guangdong, China. Electronic address: liuzq@gzucm.edu.cn.
Abstract
BACKGROUND AND PURPOSE: Irinotecan-induced diarrhea (IID) results from intestinal damages by its active metabolite SN-38. Alleviation of these damages has focused on lowering luminal SN-38 concentrations. However, it is unclear if the enteric bioavailability of SN-38 is mostly dependent on luminal SN-38 concentrations. EXPERIMENTAL APPROACH: Irinotecan (50 mg/kg, i.p. once daily for 6 days) was administered to female wildtype FVB, Mdr1a (-/-), Mrp2 (-/-) and Bcrp1 (-/-) mice for pharmacokinetic (PK), toxicokinetic (TK) and biodistribution studies. Plasma PK/TK profiles and tissues drug distribution were determined after first or sixth daily doses, along with activities of blood and gut esterases and intestinal Ugts. Caco-2 cells and bile-cannulate mice were used to further investigate intestinal and biliary disposition of irinotecan and its metabolites. KEY RESULTS: Significant differences in IID severity were observed with the susceptible rank of Bcrp1(-/-) > wildtype FVB > Mdr1a(-/-) > Mrp2(-/-). This rank order did not correlate with biliary excretion rates of SN-38/SN-38G. Rather, the severity was best correlated (R = 0.805) with the intestinal ratio of Css SN-38/SN-38G, a measure of gut Ugt activity. On the contrary, IID was poorly correlated with plasma AUC ratio of SN-38/SN-38G (R = 0.227). Increased intestinal esterase activities due to repeated dosing and gut efflux transporter functionality are the other key factors that determine SN-38 enteric exposures. CONCLUSION AND IMPLICATIONS: Intestinal SN-38 exposure is mainly affected by intestinal Ugt activities and blood esterase activities, and strongly correlated with severity of IID. Modulating intestinal SN-38 concentration and gut Ugt expression should be the focus of future studies to alleviate IID.
BACKGROUND AND PURPOSE: Irinotecan-induced diarrhea (IID) results from intestinal damages by its active metabolite SN-38. Alleviation of these damages has focused on lowering luminal SN-38 concentrations. However, it is unclear if the enteric bioavailability of SN-38 is mostly dependent on luminal SN-38 concentrations. EXPERIMENTAL APPROACH: Irinotecan (50 mg/kg, i.p. once daily for 6 days) was administered to female wildtype FVB, Mdr1a (-/-), Mrp2 (-/-) and Bcrp1 (-/-) mice for pharmacokinetic (PK), toxicokinetic (TK) and biodistribution studies. Plasma PK/TK profiles and tissues drug distribution were determined after first or sixth daily doses, along with activities of blood and gut esterases and intestinal Ugts. Caco-2 cells and bile-cannulate mice were used to further investigate intestinal and biliary disposition of irinotecan and its metabolites. KEY RESULTS: Significant differences in IID severity were observed with the susceptible rank of Bcrp1(-/-) > wildtype FVB > Mdr1a(-/-) > Mrp2(-/-). This rank order did not correlate with biliary excretion rates of SN-38/SN-38G. Rather, the severity was best correlated (R = 0.805) with the intestinal ratio of Css SN-38/SN-38G, a measure of gut Ugt activity. On the contrary, IID was poorly correlated with plasma AUC ratio of SN-38/SN-38G (R = 0.227). Increased intestinal esterase activities due to repeated dosing and gut efflux transporter functionality are the other key factors that determine SN-38 enteric exposures. CONCLUSION AND IMPLICATIONS: Intestinal SN-38 exposure is mainly affected by intestinal Ugt activities and blood esterase activities, and strongly correlated with severity of IID. Modulating intestinal SN-38 concentration and gut Ugt expression should be the focus of future studies to alleviate IID.
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