title: Inhibition of cell-mediated cytolysis and P-glycoprotein function in natural killer cells by verapamil isomers and cyclosporine A analogs.
abstract: We have previously shown that among normal leukocytes, CD56+ and CD8+ cells express relatively high levels of P-glycoprotein (P-gp), a transmembrane efflux pump. While the physiologic significance of P-gp expression in leukocytes is unknown, the relatively high levels of P-gp in CD56+ and CD8+ cells suggest that P-gp may function in cell-mediated cytolysis. To explore this possibility we examined the effect of four inhibitors of P-gp efflux [(R)-verapamil (R-ver), (S)-verapamil (S-ver), cyclosporine A (CsA), and PSC833 (PSC)] on both the inhibition of natural killer cell (NK) function and on P-gp efflux. NK function was assayed by measuring the lysis of 51Cr-labeled K562 target cells in the presence and absence of inhibitors. All four P-gp efflux inhibitors inhibited NK-mediated cytolysis in a dose-dependent manner. The stereoisomers of verapamil were more potent inhibitors of cell-mediated cytolysis than the cyclosporines CsA and PSC. In contrast, CsA and PSC were more potent as inhibitors of P-gp-mediated rhodamine 123 dye efflux than the verapamil isomers. Both CsA and PSC maximally inhibited P-gp efflux at 3 microM, but only minimally inhibited cell-mediated cytolysis. The verapamil compounds demonstrated closer correlation between efflux inhibition of NK-mediated cytolysis. The data support a role for P-gp in NK-mediated cytolysis; however, these studies also suggest that the NK cytolytic process is multifaceted and that inhibition of the P-gp-mediated efflux mechanism only partially abrogates this process.
authors.affiliation: Arizona Cancer Center, University of Arizona, Tucson 85724, USA.
authors.forename: W T
authors.initials: WT
authors.lastname: Klimecki
authors.forename: C W
authors.initials: CW
authors.lastname: Taylor
authors.forename: W S
authors.initials: WS
authors.lastname: Dalton
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000037:antagonists & inhibitors* / Q000097:blood / Q000276:immunology; D000818:Animals; D003524:Cyclosporins / Q000494:pharmacology*; D003602:Cytotoxicity, Immunologic / Q000187:drug effects*; D006801:Humans; D007694:Killer Cells, Natural / Q000187:drug effects* / Q000276:immunology; D004915:Leukemia, Erythroblastic, Acute / Q000276:immunology; D007962:Leukocytes / Q000378:metabolism; D051379:Mice; D014407:Tumor Cells, Cultured; D014700:Verapamil / Q000031:analogs & derivatives / Q000494:pharmacology*
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D003524:Cyclosporins; D014700:Verapamil