© 2000 by Oxford University Press
Journal of the National Cancer Institute, Vol. 92, No. 11, 898-902,
June 7, 2000
© 2000 Oxford University Press
ACCELERATED DISCOVERY |
Blockage of Drug Resistance In Vitro by Disulfiram, a Drug Used to Treat Alcoholism
Affiliation of authors: Medical Research Council Group in Membrane Biology, Departments of Medicine and Biochemistry, University of Toronto, ON, Canada.
Correspondence to: David M. Clarke, Ph.D., Department of Medicine, University of Toronto, Rm. 7342, Medical Sciences Bldg., 1 King's College Circle, Toronto, ON M5S 1A8, Canada (e-mail: david.clarke{at}utoronto.ca).
Background: P-glycoprotein (P-gp) pumps a wide range of cytotoxic drugs out of cells. Inhibiting maturation of P-gp would be a novel method for circumventing P-gp-mediated multidrug resistance, which complicates cancer chemotherapy and treatment of patients infected with human immunodeficiency virus. We examined the effect of disulfiram (AntabuseTM) on the maturation and activity of P-gp. Methods: Embryonic kidney cells were transfected with a complementary DNA for the P-pg gene, and the effects of disulfiram on the sensitivity of the transfected cells to cytotoxic agents were determined. Enzyme assays were used to determine the effects of disulfiram on the verapamil-stimulated adenosine triphosphatase (ATPase) activity of P-gp. Disulfiram modifies cysteine residues, and mutant forms of P-gp that lack individual cysteines were used to determine whether particular cysteine residues mediate disulfiram's effects on P-gp activity. Maturation of recombinant P-gp was followed on immunoblots. Results: Disulfiram increased the sensitivity of P-gp-transfected cells to vinblastine and colchicine and inhibited P-gp's verapamil-stimulated ATPase activity. Half-maximal inhibition of ATPase activity occurred at 13.5 µM disulfiram. Disulfiram (at 100 µM) inhibited a P-gp mutant by 43% (95% confidence interval [CI] = 37%–48%) when cysteine was present at position 431 only and by 72% (95% CI = 66%–77%) when cysteine was present at position 1074 only. Treatment of P-gp-transfected cells with 50 nM disulfiram blocked maturation of recombinant P-gp. Conclusions: Disulfiram can potentially reduce P-gp-mediated drug resistance by inhibiting P-gp activity (possibly via cysteine modification) and/or by blocking its maturation. These results suggest that disulfiram has the potential to increase the efficacy of drug therapies for cancer and acquired immunodeficiency syndrome.
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