In Silico Identification of Potential Cholestasis-Inducing Agents via Modeling of Na+-Dependent Taurocholate Cotransporting Polypeptide Substrate Specificity

Na+-dependent taurocholate cotransporting polypeptide (NTCP, SLC10A1) is the main transporter facilitating the hepatic uptake of bile acids from the circulation. Consequently, the interaction of xenobiotics, including therapeutic drugs, with the bile acid binding pocket of NTCP could lead to impairment of hepatic bile acid uptake. We pursued a 3D-pharmacophore approach to model the NTCP substrate and inhibitor specificity and investigated whether it is possible to identify compounds with intrinsic NTCP inhibitory properties. Based on known endogenous NTCP substrates, a 3D-pharmacophore model was built, which was subsequently used to screen two virtual libraries together containing the structures of 10 million compounds. Studies with Chinese hamster ovary cells overexpressing human NTCP, human hepatocytes, ex vivo perfused rat livers, and bile ductcannulated rats were conducted to validate the activity of the virtual screening hits. Modeling yielded a 3D-pharmacophore, consisting of two hydrogen bond acceptors and three hydrophobic features. Six out of 10 structurally diverse compounds selected in the first virtual screening procedure significantly inhibited taurocholate uptake in the NTCP overexpressing cells. For the most potent inhibitor identified, an anthraquinone derivative, this finding was confirmed in human hepatocytes and perfused rat livers. Subsequent structure and activity relationship studies with analogs of this derivative indicated that an appropriate distance between hydrogen bond acceptor features and presence of one or two negative charges appear critical for a successful NTCP interaction. In conclusion, pharmacophore modeling was successfully used to identify compounds that inhibit NTCP. Our approach represents an important first step toward the in silico flagging of potential cholestasis-inducing molecules.