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

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 40 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 Ki 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.