1-β-d-Arabinofuranosylcytosine (cytarabine, araC) and 2′,2′-difluoro-2′-deoxycytidine (gemcitabine, dFdC), are effective cancer chemotherapeutic agents due to their ability to become incorporated into DNA and then subsequently inhibit DNA synthesis by replicative DNA polymerases. However, the impact of these 3′-modified nucleotides on the activity of specialized DNA polymerases has not been investigated. The role of polymerase β and base excision repair may be of particular importance due to the increased oxidative stress in tumors, increased oxidative stress caused by chemotherapy treatment, and the variable amounts of polymerase β in tumors. Here we directly investigate the incorporation of the 5′-triphosphorylated form of araC, dFdC, 2′-fluoro-2′- deoxycytidine (FdC), and cytidine into two nicked DNA substrates and the subsequent ligation. Opposite template dG, the relative kpol/K d for incorporation was dCTP > araCTP, dFdCTP ≫ rCTP. The relative kpol/Kd for FdCTP depended on sequence. The effect on kpol/Kd was due largely to changes in k pol with no differences in the affinity of the nucleoside triphosphates to the polymerase. Ligation efficiency by T4 ligase and ligase III/XRCC1 was largely unaffected by the nucleotide analogues. Our results show that BER is capable of incorporating araC and dFdC into the genome.
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