REPAIR OF CHROMOSOME AND DNA BREAKS VERSUS CELL-SURVIVAL IN CHINESE-HAMSTER CELLS

Clonogenic and non-clonogenic parameters of cell survival were compare d in irradiated Chinese hamster cells. Clonogenic survival, chromatid break and repair kinetics, as well as DNA damage and repair, were asse ssed in synchronized cells in different parts of the cell cycle. G(2) chromatid damage and repair was examined in metaphase chromosomes of c ells irradiated during S and G(2) phase, treated with or without inhib itors of DNA repair. Bromodeoxyuridine labelling of S phase cells star ting at the time of irradiation made it possible to determine precisel y, while scoring metaphase chromosomes, whether cells were irradiated in mid S, late S, or G(2) phases of the cycle. The results showed that chromatid breaks induced in S phase are efficiently repaired until th e moment cells progress into G(2), when repair stops abruptly. Chromat id damage in G(2) phase is not repaired. On the other hand, DNA double -strand breaks are repaired in all phases of the cycle, even during G( 2) phase which has no concurrent chromatid break repair. Finally, ther e is no consistent correlation between chromatid damage and repair, DN A damage and repair, and cell survival, thus indicating that the inter action of different parameters of radiosensitivity must be better unde rstood for them to be useful predictors of cell survival.