title: Modulation of resistance to idarubicin by the cyclosporin PSC 833 (valspodar) in multidrug-resistant cells.
abstract: Idarubicin (IDA) is an anthracycline anticancer drug utilized in the treatment of acute leukemias. There are conflicting data published with regard to the cross-resistance of IDA in multidrug-resistant (MDR) cells expressing P-glycoprotein (P-gp). We evaluated the cytotoxicity and cellular accumulation of IDA in a panel of anthracycline-selected MDR cell lines. Leukemia K562/R7 cells and sarcoma MES-SA/Dx5 cells expressing high levels of the MDR1 (ABCB1) gene were resistant to IDA (42-fold and 150-fold, respectively). In both of these cell lines, resistance to IDA was equivalent to that for doxorubicin, the drug used to select for the MDR variants. The P-gp inhibitor PSC 833 (valspodar) at 2 microM completely restored sensitivity to IDA. IDA accumulation was decreased 12-fold in MES-SA/Dx5 cells vs parental cell line, and drug uptake was restored to control levels by PSC 833. Reduced intracellular IDA was correlated with P-gp content by flow cytometry. Experiments in NIH3T3 murine cells transfected with the human MDR1 gene substantiated the findings of cross-resistance to IDA and reversal of resistance by PSC 833. Our data indicate that IDA is a high-affinity substrate for P-gp.
authors.affiliation: Oncology Division, Department of Medicine, Stanford University School of Medicine, CA 94305-5151, USA.
authors.forename: Norman J
authors.initials: NJ
authors.lastname: Lacayo
authors.forename: George E
authors.initials: GE
authors.lastname: Duran
authors.forename: Branimir I
authors.initials: BI
authors.lastname: Sikic
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000502:physiology*; D000903:Antibiotics, Antineoplastic / Q000494:pharmacology* / Q000627:therapeutic use; D003524:Cyclosporins / Q000494:pharmacology* / Q000627:therapeutic use; D004317:Doxorubicin / Q000494:pharmacology / Q000627:therapeutic use; D018432:Drug Resistance, Multiple; D019008:Drug Resistance, Neoplasm; D005434:Flow Cytometry; D006801:Humans; D015255:Idarubicin / Q000494:pharmacology* / Q000627:therapeutic use; D020014:K562 Cells / Q000187:drug effects*
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000903:Antibiotics, Antineoplastic; D003524:Cyclosporins; D004317:Doxorubicin; C070272:valspodar; D015255:Idarubicin