title: Effects of nonionic detergents on P-glycoprotein drug binding and reversal of multidrug resistance.
abstract: Multidrug-resistant cells are thought to maintain low intracellular cytotoxic drug concentration though the active efflux of drugs across the cell membrane. It is presently believed that P-glycoprotein mediates this energy-dependent drug efflux by interacting directly with various lipophilic compounds. In this report, we have used [3H]azidopine in a photoaffinity labeling assay to study the effect of detergents and denaturing agents on P-glycoprotein drug binding in intact cells. Nonionic detergents such as Triton X-100 or Nonidet P-40 at very low concentrations were found to completely abolish azidopine photolabeling to P-glycoprotein and are able to reverse the multidrug resistance phenotype. In contrast, high concentrations of the denaturing agent urea or the zwitterionic detergent 1-[(3-cholamidopropyl)dimethylamino]-1-propanesulfonate did not inhibit azidopine photolabeling to P-glycoprotein. A comparison between verapamil and Triton X-100 revealed that the latter was more effective in inhibiting azidopine photolabeling to P-glycoprotein while verapamil was more effective in potentiating [3H]vinblastine accumulation in drug-resistant cells. Drug transport studies showed that [3H]Triton X-100 accumulated in both drug-sensitive and -resistant cells, and its accumulation was not modulated by excess vinblastine, verapamil, or colchicine. Taken together, these findings suggest that low concentrations of Triton X-100 reverse the multidrug resistance phenotype by inhibiting P-glycoprotein drug binding. In addition, it is also suggested that the site(s) of P-glycoprotein drug binding is localized to sequences found within the lipid bilayer.
authors.affiliation: Institute of Parasitology, McGill University, Montreal, Quebec, Canada.
authors.forename: T
authors.initials: T
authors.lastname: Zordan-Nudo
authors.forename: V
authors.initials: V
authors.lastname: Ling
authors.forename: Z
authors.initials: Z
authors.lastname: Liu
authors.forename: E
authors.initials: E
authors.lastname: Georges
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D001386:Azides / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism*; D002478:Cells, Cultured; D002793:Cholic Acids / Q000494:pharmacology; D003902:Detergents / Q000494:pharmacology*; D004095:Dihydropyridines / Q000378:metabolism; D004351:Drug Resistance / Q000502:physiology*; D006801:Humans; D008562:Membrane Glycoproteins / Q000378:metabolism*; D017830:Octoxynol / Q000494:pharmacology; D014700:Verapamil / Q000494:pharmacology
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D001386:Azides; D002352:Carrier Proteins; D002793:Cholic Acids; D003902:Detergents; D004095:Dihydropyridines; D008562:Membrane Glycoproteins; C041130:azidopine; D017830:Octoxynol; D014700:Verapamil; C028213:3-((3-cholamidopropyl)dimethylammonium)-1-propanesulfonate