P-glycoprotein possesses a 1,4-dihydropyridine-selective drug acceptor site which is alloserically coupled to a vinca-alkaloid-selective binding site.
[3H]Vinblastine bound with high affinity to surface membranes prepared from H69/LX4 cells which express P-glycoprotein (P-gp) and as a consequence are multidrug resistant (MDR). The KD was 9.8 +/- 1.5 nM and density of sites 31.2 +/- 8.6 pmol/mg of protein. [3H]Vinblastine binding was inhibited by cytotoxics and agents known to reverse MDR. 1,4-Dihydropyridine MDR reversing agents including nicardipine and nifedipine accelerated the dissociation of [3H]vinblastine from P-gp indicating a negative heterotropic allosteric effect. Cyclosporin A, vincristine and actinomycin D did not alter [3H]vinblastine dissociation kinetics. It is concluded that P-gp possesses at least two allosterically coupled drug acceptor sites, receptor site-1 that is selective for vinca alkaloids and cyclosporin A, and receptor site-2 that is selective for 1,4-dihydropyridines.
Department of Pharmacology, University of Birmingham, The Medical School, Edgbaston, United Kingdom.
D R
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Ferry
M A
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Russell
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Cullen
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000495:Allosteric Site; D000970:Antineoplastic Agents / Q000494:pharmacology*; D001665:Binding Sites; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism; D004095:Dihydropyridines / Q000378:metabolism*; D004351:Drug Resistance; D006801:Humans; D007700:Kinetics; D008175:Lung Neoplasms; D008562:Membrane Glycoproteins / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D014747:Vinblastine / Q000378:metabolism*
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000970:Antineoplastic Agents; D002121:Calcium Channel Blockers; D004095:Dihydropyridines; D008562:Membrane Glycoproteins; D014747:Vinblastine; C038806:1,4-dihydropyridine