PURPOSE: To investigate the correlation between PCC fragments and cell killing. MATERIALS AND METHODS: Induction and repair of DNA fragments were measured in CHO, CHO-K1, xrs1 and xrs5 cells using the premature chromosome condensation (PCC) technique and cell survival was determined by a colony assay. RESULTS: The number of PCC fragments measured in cells immediately fused after X-irradiation was the same for CHO (3.4 +/- 0.16/cell/Gy) and CHO-K1 (3.6 +/- 0.12/cell/Gy) cells but significantly higher for xrs1 (4.9 +/- 0.07/cell/Gy) and xrs5 cells (7.0 +/- 0.4/cell/Gy). The repair curve of PCC fragments studied for CHO, CHO-K1 and xrs5 cells was best described by a monophasic exponential decline with a final plateau; the half-time of this decline was always about 30 min. The number of unrejoined PCC fragments, which was measured 14h after irradiation, increased linearly with dose. The steepest increase was found for xrs5 cells (5.5 +/- 0.3 fragments per cell and per Gy), the lowest for CHO/CHO-K1 (0.9 +/- 0.1; 1.0 +/- 0.1) and for xrs1 in between (3.3 +/- 0.1). For all four cell lines the relationship between cell killing and unrejoined fragments could be described by a single curve with a D0 of 2.5 +/- 0.4 unrejoined PCC fragments per lethal event. CONCLUSIONS: The data showed that the number of unrejoined PCC fragments can be used as an indicator of cellular radiosensitivity.
