DE-NOVO INDUCED MUTATIONS IN THE DEOXYCYTIDINE KINASE (DCK) GENE IN RAT LEUKEMIC CLONAL CELL-LINES CONFER RESISTANCE TO CYTARABINE (ARAC) AND 5-AZA-2'-DEOXYCYTIDINE (DAC)

We have investigated whether cytarabine (AraC) or decitabine (DAC) ind uce deficiency of deoxycytidine kinase (DCK) through different mutatio ns of the dck gene, related to their distinct interference with DNA re plication. Also, ii is not known whether mutations of the dck gene are the result of selection of mutants or de novo induction. To address t hese issues, three subclones of a rat leukemic cell line (RCL/O), sens itive to cytotoxicity mediated by AraC and DAC, were exposed to gradua lly increasing concentrations (from 0.1 to 10 mu M) of either AraC or DAC over a 140 days vs a 180 days period. During the course of resista nce induction DCK activity was monitored. We found that all clones acq uired irreversible cross-resistance, at marginally cytotoxic AraC or D AC concentrations of 0.1 to 0.4 times the IC,, for the parental clones . Furthermore, all resistant cell lines were DCK deficient and harbore d different mutations in the dck gene. AraC induced both rearrangement s and point mutations in the dck gene when administered over 140 days and 180 days, respectively. 140 days DAC induction yielded point mutat ions only. AH point mutations detected were nonrandomly distributed wi thin the dck coding region. SSCP analysis showed that in the majority of resistant clones more than one bandshift was present. The data sugg est the presence of multiple resistant clones, originating from one se nsitive clone and thus arguing against selection of mutants as a mecha nism for the development of AraC and DAC resistance.