title: Bivalent probes of the human multidrug transporter P-glycoprotein.
abstract: A small library of bivalent agents was designed to probe the substrate binding sites of the human multidrug transporter P-glycoprotein (P-gp). The bivalent agents were composed of two copies of the P-gp substrate emetine, linked by tethers of varied composition. An optimum distance between the emetine molecules of approximately 10 A was found to be necessary for blocking transport of the known fluorescent substrate rhodamine 123. Additionally, it was determined that hydrophobic tethers were optimal for bridging the bivalent compounds; hydrophilic or cationic moieties within the tether had a detrimental effect on inhibition of transport. In addition to acting as probes of P-gp's drug binding sites, these agents were also potent inhibitors of P-gp. One agent, EmeC5, had IC50 values of 2.9 microM for inhibiting transport of rhodamine 123 and approximately 5 nM for inhibiting the binding of a known P-gp substrate, [125I]iodoarylazidoprazosin. Although EmeC5 is an inhibitor of P-gp and was shown to interact directly with P-gp in one or more of the substrate binding sites, our data suggest that it is either not a P-gp transport substrate itself or a poor one. Most significantly, EmeC5 was shown to reverse the MDR phenotype of MCF-7/DX1 cells when co-administered with a cytotoxic agent, such as doxorubicin.
authors.affiliation: Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907-2084, USA.
authors.forename: Marcos M
authors.initials: MM
authors.lastname: Pires
authors.forename: Christine A
authors.initials: CA
authors.lastname: Hrycyna
authors.forename: Jean
authors.initials: J
authors.lastname: Chmielewski
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D001386:Azides / Q000378:metabolism; D003432:Cross-Linking Reagents / Q000378:metabolism; D019281:Dimerization; D004317:Doxorubicin / Q000494:pharmacology; D004640:Emetine / Q000138:chemical synthesis / Q000737:chemistry / Q000378:metabolism*; D005434:Flow Cytometry; D006801:Humans; D006868:Hydrolysis / Q000187:drug effects; D020128:Inhibitory Concentration 50; D008954:Models, Biological; D015335:Molecular Probes / Q000032:analysis / Q000737:chemistry / Q000378:metabolism*; D019920:Photoaffinity Labels; D011224:Prazosin / Q000031:analogs & derivatives / Q000378:metabolism; D020112:Rhodamine 123 / Q000494:pharmacology; D013379:Substrate Specificity / Q000187:drug effects; D014407:Tumor Cells, Cultured
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D001386:Azides; D003432:Cross-Linking Reagents; D015335:Molecular Probes; D019920:Photoaffinity Labels; D020112:Rhodamine 123; D004317:Doxorubicin; D000255:Adenosine Triphosphate; C041552:azidoprazosin; D004640:Emetine; D011224:Prazosin