Most drugs that reverse multidrug resistance also inhibit photoaffinity labeling of P-glycoprotein by a vinblastine analog.
Multidrug-resistant human KB carcinoma cells express a 170,000-dalton membrane glycoprotein (P-glycoprotein) that can be photoaffinity labeled with the vinblastine analog N-(p-azido-[3-125I]salicyl]-N'-(beta-aminoethyl)vindesine. Several agents that suppress the multidrug-resistant phenotype, including N-solanesyl-N,N'-bis(3,4-dimethylbenzyl)ethylenediamine, cepharanthine, quinidine, and reserpine, were found to inhibit photolabeling of P-glycoprotein at doses comparable to those that reverse multidrug resistance. However, the phenothiazines chlorpromazine and trifluoperazine, which also effectively reverse multidrug resistance, were poor inhibitors of the photoaffinity labeling of P-glycoprotein. Chloroquine, propranolol, or atropine, which only partially reversed the drug resistance, also did not inhibit photolabeling. Naphthalene sulfonamide calmodulin inhibitors, W7 and W5, as well as many other drugs that did not circumvent multidrug resistance, did not inhibit photolabeling. These studies suggest that most, but not all, agents that phenotypically suppress multidrug resistance also inhibit drug binding to a site on P-glycoprotein with which a photoaffinity analog of vinblastine interacts.
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000345:Affinity Labels / Q000378:metabolism*; D001386:Azides / Q000378:metabolism*; D004351:Drug Resistance; D006801:Humans; D007457:Iodine Radioisotopes; D007624:KB Cells / Q000187:drug effects; D008562:Membrane Glycoproteins / Q000378:metabolism*; D010640:Phenothiazines / Q000494:pharmacology; D014751:Vindesine / Q000031:analogs & derivatives* / Q000378:metabolism
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000345:Affinity Labels; D001386:Azides; D007457:Iodine Radioisotopes; D008562:Membrane Glycoproteins; D010640:Phenothiazines; C048695:N-(4-azido-3-iodosalicyl)-N'-beta-aminoethylvindesine; D014751:Vindesine