RT Journal Article SR Electronic T1 Most drugs that reverse multidrug resistance also inhibit photoaffinity labeling of P-glycoprotein by a vinblastine analog. JF Molecular Pharmacology JO Mol Pharmacol FD American Society for Pharmacology and Experimental Therapeutics SP 144 OP 147 VO 33 IS 2 A1 S Akiyama A1 M M Cornwell A1 M Kuwano A1 I Pastan A1 M M Gottesman YR 1988 UL http://molpharm.aspetjournals.org/content/33/2/144.abstract AB 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.