The induction of DNA strand breakage by nickel compounds in cultured Chinese hamster ovary cells

Both NiCl 2 and crystalline αNiS induced DNA strand breaks in cultured Chinese hamster ovary (CHO) cells. Alkaline sucrose gradient analysis of [ 3H]thymidine radiolabelled DNA isolated from cells exposed to NiCl 2 at 1 μg/ml for only 2 h indicated a high degree of DNA strand breakage. Similarly crystalline αNiS caused substantial strand breakage at 1 μg/ml following a 24-h treatment interval. These nickel compounds caused DNA strand breaks at concentrations which did not significantly impair normal cellular division. A concentration-dependent effect upon the number and average size of DNA fragments was obtained with both NiCl 2 and crystalline αNiS. Since DNA strand breakage occurred at such low concentrations, these results suggest that nickel compounds which cause cellular transformation have highly selective and specific effects upon DNA structure.