Dexniguldipine-HCl is a potent allosteric inhibitor of [3H]vinblastine binding to P-glycoprotein of CCRF ADR 5000 cells.
Cell membranes were prepared from the multidrug resistant, P-glycoprotein expressing human lymphoblastoid cell line CCRF-ADR 5000. The P-glycoprotein of these membranes possessed high affinity binding sites for [3H]vinblastine, with a Kd of 8 +/- 2 nM and Bmax of 17 +/- 8 pmol/mg of protein. The binding of [3H]vinblastine to P-glycoprotein was not ATP-dependent, and was inhibited by cytotoxic drugs with the following potency order; vincristine > doxorubicin > etoposide. The 1,4-dihydropyridine and multidrug resistance reversing agent, dexniguldipine-HCl, inhibited binding with a Ki value of 37 nM. The multidrug resistance reversing agent cyclosporin A, and the cytotoxics doxorubicin and etoposide did not alter the kinetics of [3H]vinblastine dissociation from P-glycoprotein; however, the 1,4-dihydropyridines dexniguldipine-HCl and nicardipine accelerated dissociation of [3H]vinblastine. These data suggest that P-glycoprotein possesses at least two allosterically coupled drug acceptor sites; receptor site 1 which binds vinblastine, doxorubucin, etoposide and cyclosporin A, and receptor site 2 which binds dexniguldipine-HCl and other 1,4-dihydropyridines.
Malkhandi
J
J
Department of Clinical Oncology, Queen Elizabeth Hospital, University of Birmingham, UK.
Ferry
D R
DR
Boer
R
R
Gekeler
V
V
Ise
W
W
Kerr
D J
DJ
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism*; D000494:Allosteric Regulation; D001667:Binding, Competitive / Q000187:drug effects; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D002455:Cell Division / Q000187:drug effects; D016572:Cyclosporine / Q000494:pharmacology; D004095:Dihydropyridines / Q000494:pharmacology*; D004317:Doxorubicin / Q000494:pharmacology; D018432:Drug Resistance, Multiple; D005047:Etoposide / Q000494:pharmacology; D006801:Humans; D007700:Kinetics; D008433:Mathematics; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000473:pathology; D014316:Tritium / Q000378:metabolism; D014407:Tumor Cells, Cultured; D014747:Vinblastine / Q000378:metabolism*; D014750:Vincristine / Q000494:pharmacology
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D002121:Calcium Channel Blockers; D004095:Dihydropyridines; D014316:Tritium; D014750:Vincristine; D014747:Vinblastine; D005047:Etoposide; D004317:Doxorubicin; D016572:Cyclosporine; C054074:niguldipine