title: Characterization of resistance to cytosine arabinoside (Ara-C) in NALM-6 human B leukemia cells.
abstract: BACKGROUND
  Cytosine arabinoside (1-beta-D-arabinofuranosylcytosine;Ara-C) is the most important antimetabolite used for acute leukemia. We established Ara-C (0.003-1 micromol/l)-resistant NALM-6 leukemia cells, and attempted the characterization of their resistance.
  
  
  METHODS
  The Ara-C-resistant cell lines were developed by stepwise increases in the drug. The mRNA expressions were analyzed by reverse transcription-polymerase chain reaction (RT-PCR). The uptake of Ara-C, deoxycytidine kinase (dCK) activity and cytidine deaminase (CDA) activity were measured using radioisotope methods. Cytotoxicity was evaluated using the MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide] assay.
  
  
  RESULTS
  The mRNA expression of human equilibrative nucleoside transporter-1 (hENT-1), which is an uptake transporter of Ara-C, was initially decreased during the acquisition of resistance to Ara-C. The expression of dCK, an activation enzyme, and of CDA, an inactivation enzyme, was decreased and increased in the late phase, respectively. The cytotoxic effect of Ara-C on parental NALM-6 cells was ameliorated by hENT-1 inhibitors. There were no differences in the cytotoxic effect of other anticancer drugs, but there was similar resistance to nucleoside analogues via hENT-1 between the parental and resistant cells.
  
  
  CONCLUSIONS
  Decreased hENT-1 expression and function is causatively responsible for the acquisition of Ara-C resistance and alterations in dCK and CDA contribute to the higher concentration range.
authors.affiliation: Department of Pharmacology and Toxicology, Cancer Research Institute, Tohoku Pharmaceutical University, and Department of Pathology and Laboratory Medicine, National Hospital Organization, Sendai Medical Center, Japan. syu-kan@tohoku-pharm.ac.jp
authors.forename: Syu-ichi
authors.initials: S
authors.lastname: Kanno
authors.forename: Takako
authors.initials: T
authors.lastname: Hiura
authors.forename: Takaharu
authors.initials: T
authors.lastname: Ohtake
authors.forename: Kimiko
authors.initials: K
authors.lastname: Koiwai
authors.forename: Hiroyoshi
authors.initials: H
authors.lastname: Suzuki
authors.forename: Mayuko
authors.initials: M
authors.lastname: Ujibe
authors.forename: Masaaki
authors.initials: M
authors.lastname: Ishikawa
mesh_terms: D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D003561:Cytarabine / Q000494:pharmacology* / Q000633:toxicity; D003564:Cytidine Deaminase / Q000378:metabolism; D019610:Cytoprotection / Q000187:drug effects; D003842:Deoxycytidine Kinase / Q000378:metabolism; D004176:Dipyridamole / Q000494:pharmacology; D019008:Drug Resistance, Neoplasm; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D007938:Leukemia / Q000201:enzymology / Q000473:pathology*; D012333:RNA, Messenger / Q000235:genetics; D013868:Thioinosine / Q000031:analogs & derivatives / Q000494:pharmacology
chemical_list: D012333:RNA, Messenger; D003561:Cytarabine; D013868:Thioinosine; D004176:Dipyridamole; D003842:Deoxycytidine Kinase; D003564:Cytidine Deaminase; C001789:4-nitrobenzylthioinosine