title: Reversal of P-glycoprotein-associated multidrug resistance by ivermectin.
abstract: P-Glycoprotein (P-gp) causes a multidrug resistance (MDR) phenotype in tumour cells. In some cancers, the expression of P-gp has been correlated with low clinical response to chemotherapy and survival of patients. Previous studies have shown that certain lipophilic drugs bind to P-gp and reverse the MDR phenotype of tumour cells. In this study, we extend that list of compounds and present evidence for the capacity of a potent and clinically safe anthelmintic, ivermectin (IVM), as an MDR-reversing drug. Using a highly drug-resistant human cell line, we compared IVM with other MDR-reversing agents and showed that IVM is 4- and 9-fold more potent than cyclosporin A and verapamil, respectively. The capacity of IVM to inhibit iodoaryl-azidoprazosin photolabeling of P-gp is consistent with direct binding to P-gp. Studies showed that [3H]IVM binding to membranes from resistant cells is specific and saturable with KD and Bmax values of 10.6 nM and 19.8 pmol/mg, respectively. However, while cyclosporin A or vinblastine inhibited [3H]IVM binding to membranes from drug-resistant but not drug-sensitive cells, neither verapamil nor colchicine had any effect. Furthermore, both IVM and cyclosporin A and, to a lesser extent, verapamil also inhibited [3H]vinblastine binding to membranes from drug-resistant cells. Drug transport studies showed that [3H]IVM is a substrate for the P-gp drug efflux pump. However, it was transported less efficiently by P-gp than [3H]vinblastine. Moreover, only cyclosporin A was effective in potentiating the accumulation of [3H]IVM in drug-resistant cells. Taken together, the high efficiency of MDR reversal by IVM combined with its low toxicity are consistent with the properties of an ideal MDR-reversing agent.
authors.affiliation: Institute of Parasitology of McGill University, Quebec, Canada.
authors.forename: J F
authors.initials: JF
authors.lastname: Pouliot
authors.forename: F
authors.initials: F
authors.lastname: L'Heureux
authors.forename: Z
authors.initials: Z
authors.lastname: Liu
authors.forename: R K
authors.initials: RK
authors.lastname: Prichard
authors.forename: E
authors.initials: E
authors.lastname: Georges
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000502:physiology*; D000345:Affinity Labels; D002478:Cells, Cultured; D018432:Drug Resistance, Multiple; D006801:Humans; D007559:Ivermectin / Q000493:pharmacokinetics / Q000494:pharmacology*; D014747:Vinblastine / Q000493:pharmacokinetics
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000345:Affinity Labels; D014747:Vinblastine; D007559:Ivermectin