1-beta-D-arabinofuranosylcytosine (
ara-C) is a
deoxycytidine analog with activity in
leukemia, which requires phosphorylation by
deoxycytidine kinase (dCK) to allow formation of its active
phosphate 1-beta-D-arabinofuranosylcytosine
triphosphate, but can be deaminated by
deoxycytidine deaminase. Altered membrane transport is also a mechanism of drug resistance. In order to facilitate
ara-C uptake and prolong retention in the cell, lipophilic
prodrugs were synthesized.
Fatty acid groups with a varying acyl chain length and number of double bonds were esterified at the 5' position on the
sugar moiety of
ara-C. The compounds were tested in two pairs of
ara-C resistant leukemic cell lines (murine L1210 and rat BCLO and their resistant variants L4A6 and Bara-C, respectively) and two pairs of cell lines with a resistance to
gemcitabine, another
deoxycytidine analog (human
ovarian cancer A2780 and murine
colon cancer C26-A and their resistant variants AG6000 and C26-G, respectively). L4A6, Bara-C and AG6000 have varying degrees of decreased dCK activity, while the mechanism for C26-G is not yet clear. In the parent cell lines,
ara-C was more active, but in the resistant variants several of the analogs were more active, while the degree of cross-resistance varied. In AG6000 with a total dCK deficiency, all compounds were inactive. Structure-activity relation analysis showed that
ara-C derivatives with shorter acyl chains and more double bonds were more active in the parental and
drug resistant cells. Further mechanistic studies were performed with the
elaidic acid derivative of
ara-C (CP-4055).
CP-4055 inhibited deamination of dCyd partly and induced
DNA synthesis inhibition effectively in C26-A and C26-G cells, but the retention of inhibition was much longer for
CP-4055 than for
ara-C. In contrast to
ara-C,
CP-4055 inhibited
RNA synthesis for 60% after
drug exposure. In conclusion,
CP-4055 seems to be a promising
prodrug, whose effects were different and longer lasting than for the parent
drug.