title: Cyclosporin A is a broad-spectrum multidrug resistance modulator.
abstract: OBJECTIVE
  Overexpression of the multidrug resistance proteins P-glycoprotein (Pgp), multidrug resistance protein (MRP-1), breast cancer resistance protein (BCRP), and lung resistance protein (LRP) is associated with treatment failure in acute myeloid leukemia (AML) and other malignancies. The Pgp modulator cyclosporin A has shown clinical efficacy in AML, whereas its analogue PSC-833 has not. Cyclosporin A is known to also modulate MRP-1, and we hypothesized that broad-spectrum multidrug resistance modulation might contribute to its clinical efficacy.
  
  
  METHODS
  We studied the effects of cyclosporin A and PSC-833 on in vitro drug retention and cytotoxicity in resistant cell lines overexpressing Pgp, MRP-1, and BCRP and on nuclear-cytoplasmic drug distribution and cytotoxicity in cells overexpressing LRP. Cellular drug content was assessed by flow cytometry and nuclear-cytoplasmic drug distribution by confocal microscopy.
  
  
  RESULTS
  Cyclosporin A enhanced retention of the substrate drug mitoxantrone in cells overexpressing Pgp (HL60/VCR), MRP-1 (HL60/ADR), and BCRP (8226/MR20, HEK-293 482R) and increased cytotoxicity 6-, 4-, 4-, and 3-fold, respectively. Moreover, cyclosporin A enhanced nuclear distribution of doxorubicin in 8226/MR20 cells, which also express LRP, and increased doxorubicin cytotoxicity 12-fold without an effect on cellular doxorubicin content, consistent with expression of wild-type BCRP, which does not efflux doxorubicin. Cyclosporin A also enhanced nuclear doxorubicin distribution in a second cell line with LRP overexpression, HT1080/DR4. PSC-833 enhanced mitoxantrone retention and cytotoxicity in cells overexpressing Pgp, but had no effect in cells overexpressing MRP-1, BCRP, or LRP.
  
  
  CONCLUSIONS
  Cyclosporin A modulates Pgp, MRP-1, BCRP, and LRP, and this broad-spectrum activity may contribute to its clinical efficacy.
authors.affiliation: Leukemia Section, Department of Medicine, Roswell Park Cancer Institute, Elm & Carlton Streets, Buffalo, NY 14263, USA.
authors.forename: Misbah
authors.initials: M
authors.lastname: Qadir
authors.forename: Kieran L
authors.initials: KL
authors.lastname: O'Loughlin
authors.forename: Stacy M
authors.initials: SM
authors.lastname: Fricke
authors.forename: Nicole A
authors.initials: NA
authors.lastname: Williamson
authors.forename: William R
authors.initials: WR
authors.lastname: Greco
authors.forename: Hans
authors.initials: H
authors.lastname: Minderman
authors.forename: Maria R
authors.initials: MR
authors.lastname: Baer
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism; D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters / Q000378:metabolism; D000903:Antibiotics, Antineoplastic / Q000378:metabolism; D017209:Apoptosis / Q000187:drug effects*; D001943:Breast Neoplasms / Q000378:metabolism / Q000473:pathology; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D016572:Cyclosporine / Q000493:pharmacokinetics / Q000494:pharmacology*; D003593:Cytoplasm / Q000378:metabolism; D004317:Doxorubicin / Q000378:metabolism; D018432:Drug Resistance, Multiple; D019008:Drug Resistance, Neoplasm; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D018922:HL-60 Cells / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D007668:Kidney / Q000187:drug effects / Q000378:metabolism; D008942:Mitoxantrone / Q000378:metabolism; D009363:Neoplasm Proteins / Q000378:metabolism; D020394:Vault Ribonucleoprotein Particles / Q000378:metabolism; D000099187:Major Vault Protein
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters; D000903:Antibiotics, Antineoplastic; D016572:Cyclosporine; D004317:Doxorubicin; D004791:Enzyme Inhibitors; D008942:Mitoxantrone; D009363:Neoplasm Proteins; D020394:Vault Ribonucleoprotein Particles; D000099187:Major Vault Protein; C116614:ABCG2 protein, human