Effects of Hydroxyurea and 1‐β‐D‐Arabinofuranosyl‐cytosine on Deoxyribonucleotide Pools in Mouse Embryo Cells

Abstract

Mouse embryo cells incubated in medium with 0.5% serum contain only few cells which synthesize DNA. When the serum concentration was raised, DNA synthesis was induced and the pools of the deoxyribonucleoside triphosphates expanded. In such cultures the pool of dGTP was the smallest of the deoxyribonucleoside triphosphate pools and its size corresponded to only approximately 30 sec of DNA synthesis. The dCTP pool was 10–20 times larger than the dGTP pool. Addition of hydroxyurea resulted in an almost instantaneous loss of the pool of dGTP and also in a decrease in the size of the dATP pool. In contrast the pools of dCTP and dTTP increased. However, the turnover of the dTTP pool was greatly diminished. Removal of hydroxyurea from the medium resulted in a rapid normalization of the triphosphate pools but only in a more gradual restoration of DNA synthesis. During incubation in 1‐β‐D‐arabinofuranosyl‐cytosine (arabinosyl‐cytosine), the pools of dATP, dGTP and dTTP expanded, while the pool of dCTP showed an initial decrease. The turnover of the dTTP pool was not markedly affected in spite of the fact that DNA synthesis was greatly reduced. When arabinosyl‐cytosine was removed the pools were normalized and DNA synthesis was slowly restored. Our results thus show that the inhibition of DNA synthesis by hydroxyurea is correlated with diminishing pools of dGTP and dATP and a decreased turnover of dTTP, indicating a generally decreased deoxyribonucleotide formation presumably due to the inhibition of the enzyme ribonucleoside‐diphosphate reductase. The inhibition of DNA synthesis by arabinosyl‐cytosine is not correlated with a similar depletion of deoxyribonucleoside triphosphate pools.