Radiosensitivity and recovery of mouse L cells during the cell cycle

Summary Mouse fibroblasts, subline L-929 F were synchronized by mitotic detachment. The synchronized cell cultures were irradiated with 200 kVp X-rays at different time after mitosis, and age reponse functions and dose effect curves were determined using the colony test. The cell age in the mitotic cycle was obtained from a computer analysis of flow cytometric DNA histograms. Both intrinsic radiosensitivity 1/D₀ and extrapolation numbern were found to vary during the cell cycle. TheD₀ has a maximum value of 176 ± 1 rad in the middle ofG₁ phase and a minimum of 71 ± 1 rad at theS/G₂ transition, while the extrapolation number is rather constant from the beginning ofG₁ phase (1.9 ± 0.1) to the middle ofS phase (2.3 ± 0.1) and reaches a steep maximum of 9.3 ± 1.1 atS/G₂ transition. The values ofn in the various phases of cell cycle are compared with the respective values of the recovery factor determined after fractionated irradiation. - Cell survival after a single dose of 616 rad has minima for irradiation atG₁/S transition and in earlyG₂ phase; the survival in earlyG₂ being about 40 times smaller than in earlyG₁ phase. Implications for a cell cycle specific therapy are discussed.Supported by the Deutsche Forschungsgemeinschaft, Bonn-Bad Godesberg