The oxygen enhancement ratio for radiation lethality in ataxia telangiectasia cells

The radiotoxicity of iodine-125 in ataxia telangiectasia fibroblasts

Normal and ataxia telangiectasia fibroblast strains were labeled with 3H- or 125I-labelled iododeoxyuridine, were stored at -75 degrees C to accumulate damage, and were thawed for survival assays. X-ray survival of frozen, unlabeled cells was also determined. The ataxia telangiectasia strains were about twice as sensitive as normal (based upon survival curve slopes) when irradiated with X-rays or 3H decays under frozen conditions. Accumulated 125I decays, while about 13 times more toxic than 3H decays, also killed ataxia telangiectasia cells about twice as efficiently as normal cells. These results indicate that a large proportion of 125I-induced damage--at least 50%--is subject to repair in normal cells. In addition, they suggest that ataxia telangiectasia cells less capably repair a lesion that is induced in common by X-rays and 125I, but in larger porportion by the latter--probably a DNA double-strand break.

Normal repair of DNA single-strand breaks in patients with ataxia telangiectasia

The repair of DNA single-strand breaks induced by X-rays or bleomycin was investigated in diploid fibroblasts isolated from normal individuals and from patients with ataxia telangiectasia by the technique of alkaline elution. No difference was observed between these cell strains in the rate of rejoining of DNA strand breaks induced by low or moderate doses of X-rays or by treatment with bleomycin. Owing to the sensitivity of the technique employed, the possibility that ataxia telangiectasia cells are deficient in DNA single-strand break repair appears unlikely.