Identification, Ki determination and CoMFA analysis of nuclear receptor ligands as competitive inhibitors of OATP1B1-mediated estradiol-17β-glucuronide transport

Abstract

Evidence shows that drug-drug interactions can occur at the level of drug transporters such as the organic anion transporting polypeptides (OATPs), a group of membrane solute carriers that mediate the sodium-independent transport of a wide range of amphipathic organic compounds. The polyspecific OATP1B1 is exclusively expressed at the basolateral membrane of hepatocytes and mediates uptake of amphipathic organic compounds from blood into hepatocytes. Nuclear receptors are ligand-activated transcription factors that play an important role in xenobiotic disposition and human diseases. Quite a few nuclear receptor ligands interact with transport proteins.A high-resolution three-dimensional structure is critical to understand the polyspecificity of OATP1B1 to predict and prevent adverse drug-drug interactions. Unfortunately there are no crystal structures of OATPs/Oatps available to date. Therefore, in this study we attempted to elucidate the characteristics of the substrate binding site of OATP1B1 based on small molecules interacting with it. First, we identified inhibitors of the OATP1B1 model substrate estradiol-17β-glucuronide from about forty nuclear receptor ligands. Among them, GW1929, paclitaxel and troglitazone were strong inhibitors, while 5α-androstane, 5α-androstane-3β, 17β-diol-17-hexahydrobenzoate and estradiol-3-benzoate were weak inhibitors. Then, we selected 25 compounds and performed inhibition kinetic studies to identify competitive inhibitors and determine their K i values which ranged from submicromolar to submillimolar. Finally, we performed CoMFA analysis on the identified competitive inhibitors. The CoMFA results indicate that the substrate binding site of OATP1B1 consists of a large hydrophobic middle part with basic residues at both ends that could be very important for substrate binding.

The Development, Characterization, and Application of an OATP1B1 Inhibition Assay in Drug Discovery

“…The key molecular features identified in this two-dimensional quantitative structure activity relationship approach are consistent with the work of Chang et al (2005) who by use of a three-dimensional pharmacophore approach also identified hydrogen bond accepting and hydrophobicity as key features in OATP1B1 inhibition. These key interactions are further substantiated by Gui et al (2009) who by use of a comparative molecular field analysis approach identified hydrophobicity and basicity of the side chain residues as being critical for OATP1B1 inhibition. Badolo et al (2010) investigated the ability of 179 compounds to inhibit the uptake of estradiol-17␤-glucuronide in human hepatocytes to develop a structure-activity relationship for OATP1B1/1B3.…”

Molecular Characterization of Zebrafish Oatp1d1 (Slco1d1), a Novel Organic Anion-transporting Polypeptide

“…6. This type of analysis has been successfully used previously to determine the type of interaction for a wide range of physiological substrates and fibrates for OATP1B1 (22,23) and the interaction of OATP1B1, OATP1B3, and OATP1C1 with non-steroidal anti-inflammatory drugs (24,25). If an interacting compound is a competitive inhibitor of LY, we can assume that it is being transported by Oatp1d1, in which case the K i value of the interacting compound actually represents its K m value.…”

Kinetic Characterization of Rat Hepatic Uptake of 16 Actively Transported Drugs

“…To date, studies have primarily focused on single compounds or were not carried out over a sufficiently wide concentration range to achieve the above objectives. In contrast, there are several studies documenting inhibitory properties of many drugs against various hepatic transporters, particularly OATP1B1 (Hirano et al, 2006;Noe et al, 2007;Gui et al, 2009;Sharma et al, 2009). …”