In Silico Prediction of Biliary Excretion of Drugs in Rats Based on Physicochemical Properties Gang Luo, 1 Stephen Johnson, Mei-Mann Hsueh, Joanna Zheng, Hong Cai, Baomin Xin, Saeho Chong, Kan He, and Timothy W. Harper Pharmaceutical Candidate Optimization-Metabolism and Pharmacokinetics (G.L., M.-M.H., J.Z., H.C., B.X., S.C., K.H., T.W.H.) and Computer Assisted Drug Design (S.J.), Bristol-Myers Squibb Company, Pennington, New Jersey Received December 18, 2008; accepted December 3, 2009 ABSTRACT: Evaluating biliary excretion, a major elimination pathway for many compounds, is important in drug discovery. The bile duct- cannulated (BDC) rat model is commonly used to determine the percentage of dose excreted as intact parent into bile. However, a study using BDC rats is time-consuming and cost-ineffective. The present report describes a computational model that has been established to predict biliary excretion of intact parent in rats as a percentage of dose. The model was based on biliary excretion data of 50 Bristol-Myers Squibb Co. compounds with diverse chemical structures. The compounds were given intra- venously at <10 mg/kg to BDC rats, and bile was collected for at least 8 h after dosing. Recoveries of intact parents in bile were determined by liquid chromatography with tandem mass spec- trometry. Biliary excretion was found to have a fairly good cor- relation with polar surface area (r  0.76) and with free energy of aqueous solvation (G solv aq )(r 0.67). In addition, biliary excretion was also highly corrected with the presence of a carboxylic acid moiety in the test compounds (r  0.87). An equation to calculate biliary excretion in rats was then estab- lished based on physiochemical properties via a multiple linear regression. This model successfully predicted rat biliary excre- tion for 50 BMS compounds (r  0.94) and for 25 previously reported compounds (r  0.86) whose structures are markedly different from those of the 50 BMS compounds. Additional cal- culations were conducted to verify the reliability of this compu- tation model. Biliary excretion is a major elimination pathway for many drugs and discovery compounds both in humans and in preclinical animals. For example, pravastatin and losoxantrone were found to be mainly elimi- nated as intact parent through biliary excretion in humans (Hatanaka 2000; Joshi et al., 2001). In rats, pravastatin and methotrexate were minimally metabolized and were primarily excreted intact into bile (Ma- suda et al., 1997; Kurihara et al., 2005). Extensive biliary excretion can be linked to a high clearance (Arimori et al., 2003), enterohepatic recir- culation (Caldwell and Cline 1976; Rollins and Klaassen 1979), toxic gastrointestinal side effects (Kato et al., 2002), and potential drug-drug interactions (Luo et al., 2007). As a result, most lead discovery com- pounds are assessed for biliary excretion in selected preclinical animals early in the drug discovery and development process. Among the preclinical animal models, rats are the most commonly used model species for pharmacology, pharmacokinetics, and toxicol- ogy. The existing experimental models for determining rat biliary excretion include bile duct-cannulated rats and isolated perfused rat liver. However, these models are very time-consuming and cost- ineffective because of complicated preparation of test models and difficulty in bile sample analyses. Undoubtedly, a computational model for predicting rat biliary excretion could significantly reduce laboratory efforts and, conse- quently, cost. Furthermore, a computational model could enable scientists to determine the potential for biliary excretion of virtual compounds, thereby helping to prioritize synthetic efforts in drug discovery programs. However, such a model has not yet been reported, despite efforts to identify factors that critically influence rat biliary excretion. In previous work, molecular weight was commonly identified as a dominant factor influencing biliary ex- cretion (Millburn et al., 1967; Abou-El-Makarem et al., 1967a,b; Hirom et al., 1972a,b; Hughes et al., 1973a,b; Wright and Line 1980; Proost et al., 1997; Han et al., 2001), and a hypothesis of “molecular weight threshold” was proposed. For example, Wright and Line (1980) demonstrated in their study with 18 cephalosporin derivatives that a molecular weight of 450 was the threshold for rat biliary excretion; above that molecular weight threshold, biliary excretion increased in a generally progressive way and became the principal route of excretion of the higher-molecular-weight deriv- atives. Nevertheless, molecular weight alone cannot predict rat biliary excretion although it may indicate a trend toward increased biliary excretion. For example, the carboxylate and lactone forms of irinotecan have little difference in molecular weights, but the carboxylate exhibits much more biliary excretion than does the lactone (Arimori et al., 2003; Itoh et al., 2004). 1 Current affiliation: Covance Inc., Madison, Wisconsin. Article, publication date, and citation information can be found at http://dmd.aspetjournals.org. doi:10.1124/dmd.108.026260. ABBREVIATIONS: BMS, Bristol-Myers Squibb Co.; BDC, bile duct-cannulated; PSA, polar surface area; G solv aq , free energy of aqueous solvation; LC, liquid chromatography; MS/MS, tandem mass spectrometry; G solv DMSO , free energy of solvation in dimethyl sulfoxide; BMS- 182874, 5-(dimethylamino)-N-(3,4-dimethyl-5-isoxazolyl)-1-naphthalene sulfonamide. 0090-9556/10/3803-422–430$20.00 DRUG METABOLISM AND DISPOSITION Vol. 38, No. 3 Copyright © 2010 by The American Society for Pharmacology and Experimental Therapeutics 26260/3560831 DMD 38:422–430, 2010 Printed in U.S.A. 422 by guest on October 14, 2011 dmd.aspetjournals.org Downloaded from