Randomly Distributed DNA Single Strand Breaks are not Lethal for Mammalian Cells

Abstract

1. The primary objective of this study was to assess whether randomly distributed DNA single strand breaks result in cytotoxicity.

2. The experimental approach was exposure of cultured Chinese hamster ovary cells to hydroxyl radicals generated either by X-rays (via water radiolysis) or from H₂O₂ (via the Fenton reaction).

3. An excellent inverse correlation was observed with X-rays: the higher the level of DNA breakage, the lower the cloning efficiency of the cells.

4. In the case of H₂O₂ the same correlation was found, however, single strand breaks produced by this agent appeared less toxic than those generated by X-irradiation.

5. Since considerable evidence indicates DNA damage as the major cause of X-ray- and H₂O₂-induced lethality, it is concluded that randomly distributed single strand breaks have hardly any effect in cell killing.