Azidopine noncompetitively interacts with vinblastine and cyclosporin a binding to P-glycoprotein in multidrug resistant cells

Ikumi Tamai, Ahmad Safa

Research output: Contribution to journalArticle

161 Citations (Scopus)

Abstract

It is believed that P-glycoprotein (P-gp) is an energy-dependent drug efflux pump responsible for decreased drug accumulation in multidrug resistant (MDR) cells. In this study, we investigated whether azidopine, a photoactive dihydropyridine calcium channel blocker, is transported by P-gp in MDR Chinese hamster lung cells, DC-3F/VCRd-5L, and whether its binding site(s) on P-gp are distinct from those of Vinca alkaloids and cyclosporins. The efflux of azidopine from MDR cells was energy-dependent and inhibited by the cytotoxic agent vinblastine (VBL). Cyclosporin A (CsA), a modulator of MDR, also increased azidopine accumulation in MDR cells by decreasing the energy-dependent efflux of azidopine. P-gp in these cells was the only protein specifically bound to [3H]azidopine in photo-affinity experiments. The specific photoaffinity labeling of P-gp by [3H]azidopine was inhibited by CsA, SDZ 33-243, nonradioactive azidopine, and VBL with median concentrations (IC50) of 0.5, 0.62, 1.7, and 25 μM, respectively. The equilibrium binding of azidopine to plasma membranes of MDR variant DC-3F/VCRd-5L cells showed a single class of specific binding sites having a dissociation constant of 1.20 MM and a maximum binding capacity of 4.47 nmol/mg of protein. Kinetic analysis indicated that the inhibitory effect of VBL and CsA on azidopine binding to plasma membranes of MDR cells was noncompetitive, indicating that azidopine binds to P-gp at a binding site(s) different from the binding site(s) of these drugs.

Original languageEnglish (US)
Pages (from-to)16796-16800
Number of pages5
JournalJournal of Biological Chemistry
Volume266
Issue number25
StatePublished - 1991
Externally publishedYes

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Vinblastine
P-Glycoprotein
Cyclosporine
Binding Sites
Cell membranes
Cyclosporins
Cell Membrane
azidopine
Pharmaceutical Preparations
Vinca Alkaloids
Cytotoxins
Calcium Channel Blockers
Cricetulus
Labeling
Modulators
Inhibitory Concentration 50
Proteins
Pumps
Lung
Kinetics

ASJC Scopus subject areas

  • Biochemistry

Cite this

Azidopine noncompetitively interacts with vinblastine and cyclosporin a binding to P-glycoprotein in multidrug resistant cells. / Tamai, Ikumi; Safa, Ahmad.

In: Journal of Biological Chemistry, Vol. 266, No. 25, 1991, p. 16796-16800.

Research output: Contribution to journalArticle

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