Effects of 5′,8-Cyclodeoxyadenosine
Triphosphates on DNA Synthesis
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Abstract
Hydroxyl radicals generate a broad range of DNA lesions
in living cells. Cyclopurine deoxynucleosides (CPUs) are a biologically
significant class of oxidative DNA lesions due to their helical distortion
and chemically stability. The CPUs on DNA are substrates for the nucleotide
excision repair (NER) but not for base excision repair or direct damage
reversal. Moreover, these lesions block DNA and RNA polymerases, resulting
in cell death. Here, we describe the chemical synthesis of 5′<i>S</i> and 5′<i>R</i> isomers of 5′,8-cyclodeoxyadenosine
triphosphate (cdATP) and demonstrate their ability to be incorporated
into DNA by replicative DNA polymerases. DNA synthesis assays revealed
that the incorporation of the stereoisomeric cdATPs strongly inhibits
DNA polymerase reactions. Surprisingly, the two stereoisomers had
different mutagenic profiles, since the <i>S</i> isomer
of cdATP could be inserted opposite to the dTMP, but the <i>R</i> isomer of cdATP could be inserted opposite to the dCMP. Kinetic
analysis revealed that the <i>S</i> isomer of cdATP could
be incorporated more efficiently (25.6 μM<sup>–1</sup> min<sup>–1</sup>) than the <i>R</i> isomer (1.13
μM<sup>–1</sup> min<sup>–1</sup>) during DNA synthesis.
Previous data showed that the <i>S</i> isomer in DNA blocked
DNA synthesis and the exonuclease activity of DNA polymerase and is
less efficiently repaired by NER. This indicates that the <i>S</i> isomer has a tendency to accumulate on the genome DNA,
and as such, the <i>S</i> isomer of cdATP may be a candidate
cytotoxic drug