Reparability of DNA double-strand breaks and radiation sensitivity in five mammalian cell lines.

We examined the relationship between gamma-ray-induced DNA double-strand breaks (dsb) and cell lethality in five mammalian cell lines differing in radiosensitivity; HA-1, HMV-I, L5178Y, M10 and LX830. These cells were derived from Chinese hamster, human melanoma, and mouse lymphoma (parent and its radiosensitive mutants), respectively. HA-1 cells were the most radioresistant and LX830 cells were the most radiosensitive among these five lines. Although the induction of dsb by gamma-rays for HA-1 was significantly different from other curves (p less than 0.05 for HMV-I and p less than 0.01 for L5178Y and M10), those for the other four lines were similar to one another. In addition, the most radioresistant cell line, HA-1, showed the highest dsb induction among five cell lines. Therefore, there is no correlation between radiosensitivity and the induction of dsb in these five lines. On the other hand, residual dsb after repair incubation (non-reparable dsb) do differ from each other. When the relative number of non-reparable dsb was plotted against the radiation dose, the dose-response curves for all the cell lines were concave, and the slopes of curves for M10 and LX830 were steeper than those for other cell lines. These curves are a mirror-image of the survival curves. The results suggest that there is a correlation between the radio-resistance in terms of cell killing and the capacity of cells to repair dsb.