Characterization of resistance to cytosine arabinoside (Ara-C) in NALM-6 human B leukemia cells.
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.
Kanno
Syu-ichi
S
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
Hiura
Takako
T
Ohtake
Takaharu
T
Koiwai
Kimiko
K
Suzuki
Hiroyoshi
H
Ujibe
Mayuko
M
Ishikawa
Masaaki
M
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
D012333:RNA, Messenger; D003561:Cytarabine; D013868:Thioinosine; D004176:Dipyridamole; D003842:Deoxycytidine Kinase; D003564:Cytidine Deaminase; C001789:4-nitrobenzylthioinosine