Role of deoxycytidine kinase in an in vitro model for AraC- and DAC-resistance: substrate-enzyme interactions with deoxycytidine, 1-beta-D-arabinofuranosylcytosine and 5-aza-2'-deoxycytidine
Stegmann, A.P.; Honders, M.W.; Kester, M.G.; Landegent, J.E.; Willemze, R.
Leukemia 7(7): 1005-1011
1993
ISSN/ISBN: 0887-6924 PMID: 7686601 Document Number: 411349
Deoxycytidine kinase activity (dCk) was monitored in cell lines from a rat acute myeloid leukemia model of acquired resistance to cytosine arabinoside (AraC) and decitabine (DAC). In both AraC-resistant cell lines (RCL/A and its subclone RA/7), as well as in a DAC-resistant cell line (RCL/D) which we generated from the drug-sensitive RCL/10 cell line, a total deficiency of dCk activity and a cross-resistance for AraC and DAC was demonstrated. Furthermore, the metabolization of deoxycytidine (dC) was severely impaired in all these cell lines. K-m values for dC (9.4 mu-M in RCL/10 cells) had increased 70- to 100-fold in RCL/D (K-m = 673.2 mu-M), in RCL/A (K-m = 947.2 mu-M) and in RA/7 (K-m = 817.5 mu-M). V-max values were unaltered in RCL/D and RA/7, and twofold increased in RCL/A. Addition of hydroxyurea (HU) to cell cultures stimulated dCk salvage pathway activity in RCL/0 cells for dC, AraC, and DAC by increasing V-max values approximately 160% leaving K-m constants unchanged. In all resistant cell lines, HU pre-incubation did not influence the level of dCk activity, leaving K-m and V-max values unaltered. These data indicate that deficiency of dCk activity is crucial in the mechanism of drug resistance in this model.