Chinese hamster ovary cells grown in vitro were treated with bleomycin or irradiated with high doses of 60Co gamma rays (200 and 400 Gy). DNA strand breaks in single cells were analysed by using our newly introduced microelectrophoretic technique. Bleomycin seems to act in a selective manner so that in some cells the DNA is heavily degraded while in others there is only moderate or no measurable damage. In contrast, a uniform response was found after gamma irradiation. To achieve the same magnitude of DNA fragmentation as in the most severely bleomycin-damaged cells, irradiation with more than 200 Gy is required. Some 8000 double-strand breaks per cell are produced by 200 Gy which will convert the molecular weight of the DNA to the range of 10(8)-10(9) dalton, and free migration of DNA fragments occurs during electrophoresis. We include also a detailed study of the DNA migration pattern following doses of 0-100 Gy gamma rays.
Aspiration biopsy specimens were taken from malignant tumours--1 Hodgkin's lymphoma, 3 non-Hodgkin lymphomas, 1 squamous cell carcinoma and 1 adenocarcinoma-before and after irradiation. Individual cells were analysed by micro-electrophoresis, a new technique which estimates radiation-induced DNA strand breaks. The cells were embedded in agarose gel; after lysis of the cells in a neutral detergent solution, an electric field (5 V/cm) was applied for five minutes. DNA showed a tendency to migrate, some cell diameters, and was more pronounced in irradiated than in control cells. The DNA migration was evaluated by a microscope photometer which estimated the fluorescence in cells stained with acridine orange. This technique was found to be suitable for human material in vivo as only a few cells are needed and no radioactive prelabelling is necessary.
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