Gemcitabine (dFdC) and cisplatin (CDDP) act synergistically by an increase in platinum-DNA adduct formation. Since ribonucleotide (NTP) and deoxyribonucleotide (dNTP) levels are essential for DNA-synthesis and repair of DNA damage, we investigated whether disturbances might account for differences in effects between sensitive and resistant cell lines. The human ovarian cancer cell line A2780, its CDDP-resistant variant ADDP and its dFdC-resistant variant AG6000 were exposed for 24 h to dFdC or CDDP alone, or a combination causing moderate to strong growth inhibition. In AG6000 cells UTP levels were 2-fold lower and in ADDP cells almost 2-fold higher than in A2780 cells. Levels of dTTP, dATP and dCTP were 2-5-fold lower in the resistant cell lines. Drug treatment affected NTP and dNTP levels most pronounced in A2780 cells. dFdC alone, at 1.5 nM to 1 µM increased ATP, GTP and CTP pools 1.2 to 2.0-fold, while 10 µM dFdC increased UTP 2.5-fold. Combination of dFdC and CDDP increased all NTP levels at low dFdC and CDDP concentrations more than 1.2-fold, but at 20 µM CDDP only CTP increased 2.4-fold. Only 1.5 nM dFdC increased all dNTP pools more than 1.6-fold, but at 0.1 and 1 µM dFdC, dATP and dGTP decreased down to 10-fold, while dTTP increased 3-5-fold. CDDP and the combination increased all dNTP pools over 1.4 and 1.9-fold, respectively. In AG6000 cells dFdC and CDDP hardly affected the NTP and dNTP status, except at the high concentrations, which decreased ATP, GTP and UTP levels 1.2-1.8-fold. Both CDDP alone and the combination increased dTTP, dCTP and dATP pools up to 1.6-fold. In ADDP cells NTP and most dNTP levels were hardly affected, except dGTP levels which decreased to non-detectable levels. In conclusion, both dFdC and CDDP induce concentration and combination dependent changes in NTP and dNTP pools.

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