title: Constitutive overexpression of P-glycoprotein, rather than breast cancer resistance protein or organic cation transporter 1, contributes to acquisition of imatinib-resistance in K562 cells.
abstract: OBJECTIVE
  The purpose of this study was to investigate the contribution of drug transporters in acquired imatinib-resistance. Specifically, we focused on the efflux transporters, P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP), and an influx transporter, organic cation transporter 1 (OCT1).
  
  
  METHODS
  We established imatinib-resistant K562 cells (K562/IM). Real-time PCR or Western blot analyses were performed to examine the mRNA or protein levels. Alamar blue method was used in the cytotoxicity assay. The transport activities and intracellular imatinib levels were measured by flow cytometry and HPLC, respectively.
  
  
  RESULTS
  K562/IM displayed a 47-fold increase in resistance to imatinib over the parent K562 cells. Both P-gp and BCRP were overexpressed in K562/IM relative to K562. Furthermore, the intracellular imatinib level was markedly reduced in K562/IM. Interestingly, cyclosporin A, a P-gp inhibitor, but not fumitremorgin C, a BCRP inhibitor, restored both imatinib-sensitivity and the intracellular imatinib level. By contrast, no significant difference in the expression and function of OCT1 was observed between K562/IM and K562.
  
  
  CONCLUSIONS
  P-gp, rather than BCRP or OCT1, is partially responsible for the development of imatinib-resistance due to constitutive and functional overexpression, leading to reduced intracellular accumulation of imatinib in K562/IM.
authors.affiliation: Department of Pharmacy, Kumamoto University Hospital, 1-1-1 Honjo, Kumamoto, 860-8556, Japan.
authors.forename: Chie
authors.initials: C
authors.lastname: Hirayama
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Watanabe
authors.forename: Reiko
authors.initials: R
authors.lastname: Nakashima
authors.forename: Takeru
authors.initials: T
authors.lastname: Nanbu
authors.forename: Akinobu
authors.initials: A
authors.lastname: Hamada
authors.forename: Akihiko
authors.initials: A
authors.lastname: Kuniyasu
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Nakayama
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Kawaguchi
authors.forename: Hideyuki
authors.initials: H
authors.lastname: Saito
mesh_terms: D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D000970:Antineoplastic Agents / Q000378:metabolism* / Q000494:pharmacology; D001549:Benzamides; D015153:Blotting, Western; D002470:Cell Survival; D002851:Chromatography, High Pressure Liquid; D016572:Cyclosporine / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D019008:Drug Resistance, Neoplasm / Q000187:drug effects / Q000235:genetics; D005434:Flow Cytometry; D006801:Humans; D000068877:Imatinib Mesylate; D007211:Indoles / Q000494:pharmacology; D020014:K562 Cells; D004915:Leukemia, Erythroblastic, Acute / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D027702:Organic Cation Transporter 1 / Q000235:genetics* / Q000378:metabolism; D010879:Piperazines / Q000378:metabolism* / Q000494:pharmacology; D016133:Polymerase Chain Reaction; D047428:Protein Kinase Inhibitors / Q000378:metabolism* / Q000494:pharmacology; D011743:Pyrimidines / Q000378:metabolism* / Q000494:pharmacology; D015854:Up-Regulation
chemical_list: C513055:ABCB1 protein, human; C116614:ABCG2 protein, human; D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters; D000970:Antineoplastic Agents; D001549:Benzamides; D007211:Indoles; D009363:Neoplasm Proteins; D027702:Organic Cation Transporter 1; D010879:Piperazines; D047428:Protein Kinase Inhibitors; D011743:Pyrimidines; D016572:Cyclosporine; D000068877:Imatinib Mesylate; C010522:tryptoquivaline