title: Investigation of Fluorescein Derivatives as Substrates of Organic Anion Transporting Polypeptide (OATP) 1B1 To Develop Sensitive Fluorescence-Based OATP1B1 Inhibition Assays.
abstract: Organic anion transporting polypeptide (OATP) 1B1 plays an important role in the hepatic uptake of various drugs. Because OATP1B1 is a site of drug-drug interactions (DDIs), evaluating the inhibitory potential of drug candidates on OATP1B1 is required during drug development. For establishing a highly sensitive, high-throughput fluorescence-based OATP1B1 inhibition assay system, the present study focused on fluorescein (FL) and its derivatives and evaluated their uptake via OATP1B1 as well as OATP1B3 and OATP2B1 using the transporter-expressing human embryonic kidney 293 cells. We identified 2',7'-dichlorofluorescein (DCF), 4',5'-dibromofluorescein (DBF), and Oregon green (OG) as good OATP1B1 substrates with Km values of 5.29, 4.16, and 54.1 μM and Vmax values of 87.9, 48.1, and 187 pmol/min/mg protein, respectively. In addition to FL, fluo-3, and 8-fluorescein-cAMP, OG, and DBF were identified as OATP1B3 substrates. FL, OG, DCF, and DBF were identified as OATP2B1 substrates. Among the FL derivatives, DCF displayed the highest OATP1B1-mediated uptake. The Ki values of 14 compounds on OATP1B1 determined with DCF as a probe exhibited good agreement with those obtained using [(3)H]estradiol-17β-glucuronide (E2G) as a substrate, whereas [(3)H]estrone-3-sulfate and [(3)H]sulfobromophthalein yielded higher Ki values for all inhibitors than DCF. Mutually competitive inhibition observed between DCF and E2G suggested that they share the same binding site on OATP1B1. Therefore, DCF as well as E2G can be used as sensitive probes for in vitro OATP1B1 inhibition assays, which will help mitigate the risk of false-negative DDI predictions potentially caused by substrate-dependent Ki variations.
authors.affiliation: Drug Metabolism and Pharmacokinetics Japan, Tsukuba Research Laboratories, Eisai Co. Ltd., 5-1-3 Tokodai, Tsukuba-shi, Ibaraki 300-2635, Japan.
authors.forename: Saki
authors.initials: S
authors.lastname: Izumi
authors.affiliation: Drug Metabolism and Pharmacokinetics Japan, Tsukuba Research Laboratories, Eisai Co. Ltd., 5-1-3 Tokodai, Tsukuba-shi, Ibaraki 300-2635, Japan.
authors.forename: Yoshitane
authors.initials: Y
authors.lastname: Nozaki
authors.affiliation: Drug Metabolism and Pharmacokinetics Japan, Tsukuba Research Laboratories, Eisai Co. Ltd., 5-1-3 Tokodai, Tsukuba-shi, Ibaraki 300-2635, Japan.
authors.forename: Takafumi
authors.initials: T
authors.lastname: Komori
authors.affiliation: Modeling & Simulation, Clinical Pharmacology, Eisai Co., Ltd., 4-6-10 Koishikawa, Bunkyo-ku, Tokyo 112-8088, Japan.
authors.forename: Osamu
authors.initials: O
authors.lastname: Takenaka
authors.affiliation: Laboratory of Molecular Pharmacokinetics, Graduate School of Pharmaceutical Sciences, The University of Tokyo , 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
authors.forename: Kazuya
authors.initials: K
authors.lastname: Maeda
authors.affiliation: Laboratory of Molecular Pharmacokinetics, Graduate School of Pharmaceutical Sciences, The University of Tokyo , 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Kusuhara
authors.affiliation: Sugiyama Laboratory, RIKEN Innovation Center, Research Cluster for Innovation, RIKEN , 1-6 Suehiro-cho, Tsurumi-ku, Yokohama-shi, Kanagawa 230-0045, Japan.
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Sugiyama
mesh_terms: D001681:Biological Assay / Q000379:methods*; D001692:Biological Transport; D019793:Fluorescein / Q000737:chemistry / Q000378:metabolism*; D005453:Fluorescence; D057809:HEK293 Cells; D006801:Humans; D027381:Liver-Specific Organic Anion Transporter 1 / Q000037:antagonists & inhibitors* / Q000378:metabolism*
chemical_list: D027381:Liver-Specific Organic Anion Transporter 1; C503999:SLCO1B1 protein, human; D019793:Fluorescein
keywords: drug−drug interaction (DDI); fluorescent substrate; inhibition assay; organic anion transporting polypeptide (OATP)