title: Tariquidar Is an Inhibitor and Not a Substrate of Human and Mouse P-glycoprotein.
abstract: Since its development, tariquidar (TQR; XR9576; N-[2-[[4-[2-(6,7-Dimethoxy-3,4-dihydro-1H-isoquinolin-2-yl)ethyl]phenyl]carbamoyl]-4,5-dimethoxyphenyl]quinoline-3-carboxamide) has been widely regarded as one of the more potent inhibitors of P-glycoprotein (P-gp), an efflux transporter of the ATP-binding cassette (ABC) transporter family. A third-generation inhibitor, TQR exhibits high affinity for P-gp, although it is also a substrate of another ABC transporter, breast cancer resistance protein (BCRP). Recently, several studies have questioned the mechanism by which TQR interfaces with P-gp, suggesting that TQR is a substrate for P-gp instead of a noncompetitive inhibitor. We investigated TQR and its interaction with human and mouse P-gp to determine if TQR is a substrate of P-gp in vitro. To address these questions, we used multiple in vitro transporter assays, including cytotoxicity, flow cytometry, accumulation, ATPase, and transwell assays. A newly generated BCRP cell line was used as a positive control that demonstrates TQR-mediated transport. Based on our results, we conclude that TQR is a potent inhibitor of both human and mouse P-gp and shows no signs of being a substrate at the concentrations tested. These in vitro data further support our position that the in vivo uptake of [(11)C]TQR into the brain can be explained by its high-affinity binding to P-gp and by it being a substrate of BCRP, followed by amplification of the brain signal by ionic trapping in acidic lysosomes.
authors.affiliation: Molecular Imaging Branch, National Institute of Mental Health, Bethesda, Maryland (L.D.W., P.K., R.B.I.); Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, Bethesda, Maryland (K.L.F., J.K.M., J.S.K., M.M.G., M.D.H.); and Karolinska Institutet, Department of Neuroscience, Stockholm, Sweden (L.D.W., J.M.).
authors.forename: Lora D
authors.initials: LD
authors.lastname: Weidner
authors.affiliation: Molecular Imaging Branch, National Institute of Mental Health, Bethesda, Maryland (L.D.W., P.K., R.B.I.); Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, Bethesda, Maryland (K.L.F., J.K.M., J.S.K., M.M.G., M.D.H.); and Karolinska Institutet, Department of Neuroscience, Stockholm, Sweden (L.D.W., J.M.).
authors.forename: King Leung
authors.initials: KL
authors.lastname: Fung
authors.affiliation: Molecular Imaging Branch, National Institute of Mental Health, Bethesda, Maryland (L.D.W., P.K., R.B.I.); Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, Bethesda, Maryland (K.L.F., J.K.M., J.S.K., M.M.G., M.D.H.); and Karolinska Institutet, Department of Neuroscience, Stockholm, Sweden (L.D.W., J.M.).
authors.forename: Pavitra
authors.initials: P
authors.lastname: Kannan
authors.affiliation: Molecular Imaging Branch, National Institute of Mental Health, Bethesda, Maryland (L.D.W., P.K., R.B.I.); Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, Bethesda, Maryland (K.L.F., J.K.M., J.S.K., M.M.G., M.D.H.); and Karolinska Institutet, Department of Neuroscience, Stockholm, Sweden (L.D.W., J.M.).
authors.forename: Janna K
authors.initials: JK
authors.lastname: Moen
authors.affiliation: Molecular Imaging Branch, National Institute of Mental Health, Bethesda, Maryland (L.D.W., P.K., R.B.I.); Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, Bethesda, Maryland (K.L.F., J.K.M., J.S.K., M.M.G., M.D.H.); and Karolinska Institutet, Department of Neuroscience, Stockholm, Sweden (L.D.W., J.M.).
authors.forename: Jeyan S
authors.initials: JS
authors.lastname: Kumar
authors.affiliation: Molecular Imaging Branch, National Institute of Mental Health, Bethesda, Maryland (L.D.W., P.K., R.B.I.); Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, Bethesda, Maryland (K.L.F., J.K.M., J.S.K., M.M.G., M.D.H.); and Karolinska Institutet, Department of Neuroscience, Stockholm, Sweden (L.D.W., J.M.).
authors.forename: Jan
authors.initials: J
authors.lastname: Mulder
authors.affiliation: Molecular Imaging Branch, National Institute of Mental Health, Bethesda, Maryland (L.D.W., P.K., R.B.I.); Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, Bethesda, Maryland (K.L.F., J.K.M., J.S.K., M.M.G., M.D.H.); and Karolinska Institutet, Department of Neuroscience, Stockholm, Sweden (L.D.W., J.M.).
authors.forename: Robert B
authors.initials: RB
authors.lastname: Innis
authors.affiliation: Molecular Imaging Branch, National Institute of Mental Health, Bethesda, Maryland (L.D.W., P.K., R.B.I.); Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, Bethesda, Maryland (K.L.F., J.K.M., J.S.K., M.M.G., M.D.H.); and Karolinska Institutet, Department of Neuroscience, Stockholm, Sweden (L.D.W., J.M.).
authors.forename: Michael M
authors.initials: MM
authors.lastname: Gottesman
authors.affiliation: Molecular Imaging Branch, National Institute of Mental Health, Bethesda, Maryland (L.D.W., P.K., R.B.I.); Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, Bethesda, Maryland (K.L.F., J.K.M., J.S.K., M.M.G., M.D.H.); and Karolinska Institutet, Department of Neuroscience, Stockholm, Sweden (L.D.W., J.M.) matthew.hall@nih.gov.
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Hall
mesh_terms: D016475:3T3 Cells; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000037:antagonists & inhibitors* / Q000378:metabolism; D018528:ATP-Binding Cassette Transporters / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D001921:Brain / Q000378:metabolism; D002460:Cell Line; D002461:Cell Line, Transformed; D006801:Humans; D007624:KB Cells; D061986:MCF-7 Cells; D051379:Mice; D011804:Quinolines / Q000378:metabolism* / Q000494:pharmacology*
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D018528:ATP-Binding Cassette Transporters; D011804:Quinolines; C541322:quinoline-3-carboxamide; D000251:Adenosine Triphosphatases; C402343:tariquidar