Inhibition of DNA synthesis in HeLa cells by hydroxyurea.

The introduction of hydroxyurea as a potentially useful agent in leukemia chemotherapy (e.g., Ref. 21) has led to several studies of its effects at the cellular level. Mohler (8) found that this drug both inhibits division and causes death of Chinese hamster cells and that it inhibits division of HeLa S3 cells as well. Young and Hodas (24) reported that synthesis of DNA in HeLa cells is inhibited by hydroxyurea, that neither RNA nor protein synthesis is inhibited, and that the inhibition of DNA synthesis is readily reversible 30 min after the initiation of treatment. They suggested, as did Frenkel et al. (2), that inhibi tion of DNA synthesis arises from interference with ribonucleotide diphosphate reduction. Finally, Sinclair (18) has recently reported that the toxicity of hydroxyurea for Chinese hamster cells is restricted to cells in the DNA-synthesizing (S) phase of the division cycle. He also found that the drug is without effect on the progression of these cells through the non-DNA-synthesizing portions of the cycle, so that cells incubated in its presence accumulate at the end of the pre-DNA-synthetic (Gì) phase. This accumulation, together with the killing of the S-phase cells, suggested that hydroxyurea might be a useful agent for pro ducing synchronous populations of cells. The generality of the foregoing effects has not, however, been widely tested; indeed, Mohler (8) reported that while thymidine prevents the inhibitory action of hydroxyurea on Chinese hamster cells, it is without effect on hydroxyurea-inhibited HeLa S3 cells. It would appear, therefore, that different mammalian cell types may respond in qualitatively different ways to the drug. We have carried out the experiments reported here to define further the behavior of HeLa S3 cells treated with hy droxyurea, so as to assess its utility as a selective inhibitor of DNA synthesis.