Lack of reversal of daunorubicin resistance in HL60/AR cells by cyclosporin A.
Cyclosporin A and verapamil are substrates for P-glycoprotein. Both agents are known to reverse multidrug resistance in cells overexpressing P-glycoprotein. In this investigation, we have examined the effects of cyclosporin A and verapamil on multidrug resistance in HL60/AR cells that lack P-glycoprotein. In addition, a correlation was sought between an alteration in plasma membrane potential as measured with cationic dye DIOC5 and overexpression of P-glycoprotein. HL60/AR cells accumulated 3 fold less daunorubicin than HL60 cells. The drug accumulation defect and drug resistance in HL60/AR cells were partially corrected by verapamil and buthionine sulfoximine. However, cyclosporin A had no detectable effect on daunorubicin accumulation or drug resistance in HL60/AR cells. The multidrug resistant P338/ADR cell line overexpressed P-glycoprotein and exhibited depolarization of plasma membrane when compared to its corresponding drug sensitive parental cell line. In contrast, HL60/AR cells lacked P-glycoprotein and plasma membrane potentials were similar to those of drug sensitive HL60 cells. These results suggest that [1] verapamil modulates daunorubicin transport by a mechanism independent of P-glycoprotein, [2] the mechanisms of reversal of multidrug resistance by verapamil and cyclosporin A are distinct, and [3] the plasma membrane depolarization in multidrug resistant cell lines that overexpress P-glycoprotein, as determined by DIOC5, may be due to an increased efflux of cationic dye by P-glycoprotein, rather than a true measurement of plasma membrane potential in multidrug resistant cells.
Gollapudi
S
S
Division of Basic and Clinical Immunology, University of California, Irvine 92717.
Gupta
S
S
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D019328:Buthionine Sulfoximine; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D016572:Cyclosporine / Q000494:pharmacology*; D003630:Daunorubicin / Q000494:pharmacology*; D004351:Drug Resistance / Q000502:physiology*; D006801:Humans; D007700:Kinetics; D015473:Leukemia, Promyelocytic, Acute; D008562:Membrane Glycoproteins / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects; D008717:Methionine Sulfoximine / Q000031:analogs & derivatives / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D014700:Verapamil / Q000494:pharmacology
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D008562:Membrane Glycoproteins; D008717:Methionine Sulfoximine; D019328:Buthionine Sulfoximine; D016572:Cyclosporine; D014700:Verapamil; D003630:Daunorubicin