The effects of treatments with 5-(3,3-dimethyl-1-triazeno)imidazole-4-carboxamide in darkness and in light on survival and progression in Chinese hamster ovary cells in vitro.

The cytotoxic action of 5-(3,3-dimethyll-triazeno)imidazole-4-carboxamide in Chinese hamster ovary cells is enhanced considerably in the presence oflight, when 5-diazoimidazole-4-carboxamide is being continu ously generated. A broad shoulder threshold-type survival curve is seen when the cells are exposed to 5-(3,3-dimethyll-triazeno)imidazole-4-carboxamide (both in light anddark). The drug had only slight effects on the survival of cells treated in the dark for short times throughout the cell cycle. However, cells in the G! and early S phases were slightly more sensitive when treated with the drug in the light. Both light and dark treatments with the drug caused progression delay in S phase. Treatment in the light delayed cells at the G2-M boundary, whereas dark treatments delayed cells at the S-G2 boundary. Both light and dark treatments with the drug caused some G! cells to progress into S phase 1 hr early, while another fraction of the same population was delayed in G! phase.