Blockage of drug resistance in vitro by disulfiram, a drug used to treat alcoholism

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 circum venting P-gp-mediated multidrug resistance, which complicates cancer chemot herapy and treatment of patients infected with human immunodeficiency virus . We examined the effect of disulfiram (Antabuse(TM)) 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 s ensitivity of the transfected cells to cytotoxic agents were determined. En zyme assays were used to determine the effects of disulfiram on the verapam il-stimulated adenosine triphosphatase (ATPase) activity of P-gp, Disulfira m modifies cysteine residues, and mutant forms of P-gp that lack individual cysteines were used to determine whether particular cysteine residues medi ate disulfiram's effects on P-gp activity. Maturation of recombinant P-gp w as followed on immnnoblots. Results: Disulfiram increased the sensitivity o f P-gp-transfected cells to vinblastine and colchicine and inhibited P-gp's verapamil-stimulated ATPase activity. Half-maximal inhibition of ATPase ac tivity occurred at 13.5 mu M disulfiram, Disulfiram (at 100 mu M) inhibited a P-gp mutant by 43% (95% confidence interval [CI] = 37% - 48%) when cyste ine was present at position 431 only and by 72% (95% CI = 66% - 77%) when c ysteine was present at position 1074 only. Treatment of P-gp-transfected ce lls with 50 nM disulfiram blocked maturation of recombinant P-gp, Conclusio ns: Disulfiram can potentially reduce P-gp-mediated drug resistance by inhi biting P-gp activity (possibly via cysteine modification) and/or by blockin g its maturation. These results suggest that disulfiram has the potential t o increase the efficacy of drug therapies for cancer and acquired immunodef iciency syndrome.