Comparison of bleomycin and radiation in the G2 assay of chromatid breaks

Purpose: To compare bleomycin with radiation in the G2 chromatid break assay. Controversy exists in the literature about whether G2 bleomycin chromatid‐break sensitivity links with cancer predisposition in the same way as the G2 chromatid radiosensitivity test (the so‐called ‘G2 assay’). Although bleomycin is referred to as a ‘radiomimetic’ agent, it differs from radiation in the way the damage is induced. Materials and methods: Epstein–Barr virus‐immortalized lymphoblastoid cell lines from two head and neck squamous cell carcinoma patients, two breast cancer patients, two ataxia‐telangiectasia patients and two normal control persons were used. Chromosomal damage was determined in cells exposed to 0.3‐Gy radiation or 5 mU ml−1 bleomycin. The numbers of chromatid breaks per cell and of aberrations per cell (i.e. breaks and gaps) were determined. Results: A strong positive correlation was found between the two different damage inducers (r=0.99; p<0.001). This correlation was similar for both the breaks per cell and the total aberrations per cell. Inclusion of gaps in the scoring of chromatid breaks was associated with a higher variability of the data, but this did not influence the outcome of this study. Conclusions: Both bleomycin and radiation give the same sensitivity phenotypes as determined by the G2 assay of chromatid breaks. Thus, when no radiation facility is present, bleomycin seems to be a good alternative to radiation for this type of assay.