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  • Title: Characterization of resistance to cytosine arabinoside (Ara-C) in NALM-6 human B leukemia cells.
    Author: Kanno S, Hiura T, Ohtake T, Koiwai K, Suzuki H, Ujibe M, Ishikawa M.
    Journal: Clin Chim Acta; 2007 Feb; 377(1-2):144-9. PubMed ID: 17097625.
    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.
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