Radiation-induced DNA damage and cellular lethality in cultured mammalian cells.

X ray-induced DNA scissions and their repair were studied by an alkaline separation method. DNA damage in Chinese hamster V79 cells was assigned to one of three groups based on a repair profile previously used for mouse L5178Y cells: fast-reparable ( $T_{1/2}=5$ min), slow-reparable ( $T_{1/2}=70$ min), and nonreparable. The three kinds of damage were investigated in relation to cellular lethality under conditions where radiosensitivity of cultured cells was modified: (1) different sensitivity in different cell lines, (2) cell cycle fluctuation of radiosensitivity, and (3) recovery after split-dose irradiation. Among the three types of lesions, only nonreparable damage or remaining lesions showed correlation to cell killing. The parallel relationship between non-reparable damage and cell killing implies that this type of damage could play an important role in radiation-induced cell death.