ABSTRACT:Evaluating biliary excretion, a major elimination pathway for many compounds, is important in drug discovery. The bile ductcannulated (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 intravenously 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 spectrometry. Biliary excretion was found to have a fairly good correlation 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 established based on physiochemical properties via a multiple linear regression. This model successfully predicted rat biliary excretion 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 calculations were conducted to verify the reliability of this computation 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 eliminated 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 (Masuda et al., 1997;Kurihara et al., 2005). Extensive biliary excretion can be linked to a high clearance (Arimori et al., 2003), enterohepatic recirculation (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 compounds 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 toxicology. 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 costineffective 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, consequently, cost. Furthermore, a...