Allosteric regulation of [3H]vinblastine binding to P-glycoprotein of MCF-7 ADR cells by dexniguldipine

Biochem Pharmacol. 1995 Jun 16;49(12):1851-61. doi: 10.1016/0006-2952(94)00517-p.


Plasma membranes were prepared from the P-glycoprotein expressing human breast cancer cell line MCF-7 ADR. [3H]Vinblastine bound to these membranes saturably with a Bmax of 24 pmol/mg of protein and KD of 23 nM. In contrast, membranes from the parent cells MCF-7 WT, which do not express P-glycoprotein, did not bind [3H]vinblastine with high affinity. Cytotoxics known to be transported by P-glycoprotein inhibited the binding of [3H]vinblastine, as did multidrug reversing agents including the 1,4-dihydropyridine, dexniguldipine-HCl (Ki, 15 nM). In dissociation kinetic experiments, dexniguldipine-HCl accelerated the dissociation of [3H]vinblastine from P-glycoprotein, indicating a negative heterotropic allosteric mechanism of action through a drug binding site distinct from that of vinblastine. Other 1,4-dihydropyridines tested also accelerated [3H]vinblastine dissociation from P-glycoprotein, however, multidrug reversing drugs of different chemical classes, including quinidine, verapamil and cyclosporin A did not. These results suggest that P-glycoprotein of MCF-7 ADR cell membranes possesses at least two drug acceptor sites which are allosterically coupled: receptor site-1 which binds vinca alkaloids, and receptor site-2 which binds 1,4-dihydropyridines such as dexniguldipine-HCl, which had the highest affinity of the tested derivatives.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • ATP Binding Cassette Transporter, Subfamily B, Member 1 / metabolism*
  • Allosteric Regulation
  • Cell Membrane / drug effects
  • Cell Membrane / metabolism
  • Dihydropyridines / pharmacology*
  • Drug Resistance, Multiple
  • Drug Synergism
  • Humans
  • Ions
  • Kinetics
  • Nucleotides
  • Protein Binding
  • Tritium
  • Tumor Cells, Cultured
  • Vinblastine / metabolism*


  • ATP Binding Cassette Transporter, Subfamily B, Member 1
  • Dihydropyridines
  • Ions
  • Nucleotides
  • Tritium
  • Vinblastine
  • niguldipine