DNA DOUBLE-STRAND BREAKS, CHROMOSOME BREA KS AND RADIATION-INDUCED LETHALITY OF HUMAN-CELLS

DNA double-strand breaks (DSB) are the likely event which may explain the radiation-induced killing effect in mammalian cells. An overview o f the litterature shows that, to the exception of a small group of hum an tumours, the repair defect rather than the induction rate of DSB pl ays the major role. However, the arguments supporting the relationship between DSB and intrinsic radiosensitivity are most often indirect. O ur results dealing with intrinsic radiosensitivity, residual DNA DSB a nd chromosome breaks have been achieved with untransformed human fibro blasts (5 control and 18 hypersensitive cell lines). We describe a qua ntitative relationship between the intrinsic radiosensitivity and the residual breaks. The death of a human fibroblast is linked to 1.3 unre paired chromsome break and 6.6 unrepaired DSB.