title: In vitro flow cytometry method to quantitatively assess inhibitors of P-glycoprotein.
abstract: P-glycoprotein (Pgp)-mediated drug efflux is a major factor contributing to the variance of absorption and distribution of many drugs. A simple and reliable in vitro method to identify inhibitors of Pgp helps to prevent the potential of drug interactions. Using daunorubicin as a fluorescent marker and vanadate as a positive control compound, a functional flow cytometry method for assessing the ability of a drug to inhibit Pgp-mediated drug efflux from CR1R12 multidrug-resistant cells has been evaluated. Quantitation of the relative fluorescence was used to compare potency of individual inhibitors. Known Pgp inhibitors, such as cyclosporin A, nicardipine, verapamil, quinidine, terfenadine, tamoxifen, and vinblastine were demonstrated to inhibit the Pgp-mediated efflux of daunorubicin. Cyclosporin A and terfenadine were the most potent inhibitors among the compounds tested. Tetraphenylphosphonium and alpha-tocopherol had little inhibitory effect. Progesterone produced significant inhibition at relatively high concentrations. This study demonstrated that this in vitro flow cytometry method is a simple, sensitive, and quantitative tool to assess the capacity of a drug to inhibit Pgp transporters, and is useful for screening or identifying inhibitors of Pgp as well as evaluation of potential for drug interactions.
authors.affiliation: Department of Drug Metabolism and Pharmacokinetics, Schering-Plough Research Institute, Lafayette, New Jersey 07848-0032, USA.
authors.forename: E J
authors.initials: EJ
authors.lastname: Wang
authors.forename: C N
authors.initials: CN
authors.lastname: Casciano
authors.forename: R P
authors.initials: RP
authors.lastname: Clement
authors.forename: W W
authors.initials: WW
authors.lastname: Johnson
mesh_terms: D018435:ATP Binding Cassette Transporter, Subfamily B / Q000037:antagonists & inhibitors* / Q000378:metabolism; D000903:Antibiotics, Antineoplastic / Q000037:antagonists & inhibitors / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D003630:Daunorubicin / Q000037:antagonists & inhibitors / Q000494:pharmacology; D018432:Drug Resistance, Multiple; D019008:Drug Resistance, Neoplasm; D005434:Flow Cytometry; D006801:Humans; D008856:Microscopy, Fluorescence; D014407:Tumor Cells, Cultured; D014638:Vanadates / Q000494:pharmacology; D014700:Verapamil / Q000494:pharmacology
chemical_list: D018435:ATP Binding Cassette Transporter, Subfamily B; D000903:Antibiotics, Antineoplastic; D002121:Calcium Channel Blockers; D014638:Vanadates; D014700:Verapamil; D003630:Daunorubicin