Hydroxyurea-induced cell death in human T lymphoma cells as related to imbalance in DNA/protein cycle and deoxyribonucleotide pools and DNA strand breaks.

Abstract

The aim of this study was to elucidate the mechanism(s) behind the cellular toxicity of therapeutic concentrations of hydroxyurea (HU). Treatment of human T lymphoma cells (CCRF-CEM) with 60-100 microM of HU for 24 h decreased the growth rate by 90% due to accumulation of cells in early S phase. It induced a marked imbalance in both the DNA/protein cycle (as measured by two-parameter flow cytometry) and the deoxyribonucleotide (dNTP) pools. HU treatment did not enhance the frequency of DNA single-strand breaks (SSBs), as measured by the alkaline unwinding technique. Cell viability was unaffected. However, removal of HU led to 10-15% cell loss during the following 12 h period in parallel with increasing SSBs, and a rapid progression of cells through S and G2 stages. The unbalanced DNA to protein content per cell and the dNTP pools were normalized 6-12 and 24 h after removal of HU, respectively. These results show that marked changes in the DNA to protein ratio and dNTP pools alone are not directly lethal, but when combined with a high replicative DNA synthesis rate, as found after removal of HU, apparently lead to elevated cell death.