Relationship between DNA double-strand breaks, cell killing, and fibrosis studied in confluent skin fibroblasts derived from breast cancer patients

Purpose: To investigate the relationship between DNA double-strand breaks ( dsbs), cell killing, and fibrosis using skin fibroblasts derived from breas t cancer patients who received postmastectomy radiotherapy. Methods and Materials: Experiments were performed with 12 lines of normal s kin fibroblasts derived from recurrence-free breast cancer patients. Cells were irradiated in confluence and cell survival was determined either after immediate or delayed (14 h) plating using a colony-forming assay. Dsbs wer e measured by constant-field gel electrophoresis, The "excess risk of fibro sis" was previously scored by Johansen et al. (IJRB 1994;66:407-412). Results: The 12 cell lines showed a typical spectrum of radiosensitivity. T he mean value of surviving fraction after 3.5 Gy (SF3.5) was 0.063 for imme diate and 0.174 for delayed plating with a coefficient of variation (CV) of 44 and 39%, respectively. There was also a broad variation in the extent o f recovery from potentially lethal damage (RPLD), which was not correlated with the immediate sensitivity. The number of initial dsbs as well as the h alf-times of dsb repair showed little variation, whereas there were conside rable differences in the number of residual dsbs (CV = 29%). The number of residual dsbs after 100 Gy was correlated significantly only with SF3.5 aft er delayed (r(2) = 0.59; p = 0.006) but not after immediate plating (r(2) = 0.21, p = 0.16). There was also no significant relationship between residu al dsbs and the "excess risk of fibrosis" determined for the respective pat ients. Conclusion: It is shown that the number of residual dsbs measured in conflu ent human fibroblast lines can be used to predict the cellular radiosensiti vity after delayed but not after immediate plating and also not to predict the excess risk of fibrosis of the respective breast cancer patients. (C) 2 000 Elsevier Science Inc.