title: (R)- and (S)-verapamil differentially modulate the multidrug-resistant protein MRP1.
abstract: The multidrug-resistant protein MRP1 (involved in the cancer cell multidrug resistance phenotype) has been found to be modulated by racemic verapamil (through stimulation of glutathione transport), inducing apoptosis of human MRP1 cDNA-transfected baby hamster kidney 21 (BHK-21) cells and not of control BHK-21 cells. In this study, we show that the two enantiomers of verapamil have different effects on MRP1 activity. Only the S-isomer (not the R-isomer) potently induced the death of MRP1-transfected BHK-21 cells. The decrease in cellular glutathione content induced by the S-isomer, which was not observed with the R-isomer, was stronger than that induced by the racemic mixture, indicating that the R-isomer antagonized the S-isomer effect. Both enantiomers altered leukotriene C(4) and calcein transport by MRP1. Thus, the R-isomer behaved as an inhibitor, which was confirmed by its ability to revert the multidrug resistance phenotype toward vincristine. Molecular studies on purified MRP1 using fluorescence spectroscopy showed that both enantiomers bound to MRP1 with high affinity, with the binding being prevented by glutathione. Furthermore, conformational changes induced by the two enantiomers (monitored by sodium iodide accessibility of MRP1 tryptophan residues) were quite different, correlating with their distinct effects. (S)-Verapamil induces the death of potentially resistant tumor cells, whereas (R)-verapamil sensitizes MRP1-overexpressing cells to chemotherapeutics. These results might be of great potential interest in the design of new compounds able to modulate MRP1 in chemotherapy.
authors.affiliation: Laboratoire des Protéines de Résistance aux Agents Chimiothérapeutiques, Institut de Biologie et Chimie des Protéines, UMR 5086, IFR 128 BioSciences Lyon-Gerland, CNRS/Université de Lyon, 69367 Lyon Cedex 07, France.
authors.forename: Thomas
authors.initials: T
authors.lastname: Perrotton
authors.forename: Doriane
authors.initials: D
authors.lastname: Trompier
authors.forename: Xiu-Bao
authors.initials: XB
authors.lastname: Chang
authors.forename: Attilio
authors.initials: A
authors.lastname: Di Pietro
authors.forename: Hélène
authors.initials: H
authors.lastname: Baubichon-Cortay
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D006224:Cricetinae; D004305:Dose-Response Relationship, Drug; D018432:Drug Resistance, Multiple; D005452:Fluoresceins / Q000378:metabolism; D005456:Fluorescent Dyes / Q000378:metabolism; D005562:Formazans / Q000378:metabolism; D005978:Glutathione / Q000032:analysis / Q000378:metabolism; D020128:Inhibitory Concentration 50; D007668:Kidney / Q000166:cytology; D017997:Leukotriene C4 / Q000378:metabolism; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D011487:Protein Conformation; D012974:Sodium Iodide / Q000494:pharmacology; D013050:Spectrometry, Fluorescence; D013237:Stereoisomerism; D013778:Tetrazolium Salts / Q000378:metabolism; D014162:Transfection; D014364:Tryptophan / Q000378:metabolism; D014700:Verapamil / Q000633:toxicity*
chemical_list: D000251:Adenosine Triphosphatases; D005452:Fluoresceins; D005456:Fluorescent Dyes; D005562:Formazans; D005978:Glutathione; D017997:Leukotriene C4; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D012974:Sodium Iodide; D013778:Tetrazolium Salts; D014364:Tryptophan; D014700:Verapamil; C085925:calcein AM; C079782:MTT formazan; C421109:multidrug resistance-associated protein 1