title: Multiple Drug Transport Pathways through Human P-Glycoprotein.
abstract: P-Glycoprotein (P-gp) is a plasma membrane efflux pump that is commonly associated with therapy resistances in cancers and infectious diseases. P-gp can lower the intracellular concentrations of many drugs to subtherapeutic levels by translocating them out of the cell. Because of the broad range of substrates transported by P-gp, overexpression of P-gp causes multidrug resistance. We reported previously on dynamic transitions of P-gp as it moved through conformations based on crystal structures of homologous ABCB1 proteins using in silico targeted molecular dynamics techniques. We expanded these studies here by docking transport substrates to drug binding sites of P-gp in conformations open to the cytoplasm, followed by cycling the pump through conformations that opened to the extracellular space. We observed reproducible transport of two substrates, daunorubicin and verapamil, by an average of 11-12 Å through the plane of the membrane as P-gp progressed through a catalytic cycle. Methylpyrophosphate, a ligand that should not be transported by P-gp, did not show this movement through P-gp. Drug binding to either of two subsites on P-gp appeared to determine the initial pathway used for drug movement through the membrane. The specific side-chain interactions with drugs within each pathway seemed to be, at least in part, stochastic. The docking and transport properties of a P-gp inhibitor, tariquidar, were also studied. A mechanism of inhibition by tariquidar that involves stabilization of an outward open conformation with tariquidar bound in intracellular loops or at the drug binding domain of P-gp is presented.
authors.affiliation: Center for Drug Discovery, Design and Delivery, Center for Scientific Computing, and Department of Biological Sciences, Southern Methodist University, Dallas, Texas 75275-0376, United States.
authors.forename: James W
authors.initials: JW
authors.lastname: McCormick
authors.affiliation: Center for Drug Discovery, Design and Delivery, Center for Scientific Computing, and Department of Biological Sciences, Southern Methodist University, Dallas, Texas 75275-0376, United States.
authors.forename: Pia D
authors.initials: PD
authors.lastname: Vogel
authors.affiliation: Center for Drug Discovery, Design and Delivery, Center for Scientific Computing, and Department of Biological Sciences, Southern Methodist University, Dallas, Texas 75275-0376, United States.
authors.forename: John G
authors.initials: JG
authors.lastname: Wise
mesh_terms: D018435:ATP Binding Cassette Transporter, Subfamily B / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism; D000889:Anti-Arrhythmia Agents / Q000378:metabolism; D000903:Antibiotics, Antineoplastic / Q000378:metabolism; D001665:Binding Sites; D001692:Biological Transport; D003630:Daunorubicin / Q000378:metabolism; D006801:Humans; D008024:Ligands; D062105:Molecular Docking Simulation; D056004:Molecular Dynamics Simulation; D004364:Pharmaceutical Preparations / Q000378:metabolism*; D011487:Protein Conformation; D011804:Quinolines / Q000378:metabolism; D014700:Verapamil / Q000378:metabolism
chemical_list: C513055:ABCB1 protein, human; D018435:ATP Binding Cassette Transporter, Subfamily B; D000889:Anti-Arrhythmia Agents; D000903:Antibiotics, Antineoplastic; D008024:Ligands; D004364:Pharmaceutical Preparations; D011804:Quinolines; D014700:Verapamil; C402343:tariquidar; D003630:Daunorubicin