Radiosensitivity and recovery of mouse L cells during the cell cycle

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Abstract
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/D 0 and extrapolation numbern were found to vary during the cell cycle. TheD 0 has a maximum value of 176 ± 1 rad in the middle ofG 1 phase and a minimum of 71 ± 1 rad at theS/G 2 transition, while the extrapolation number is rather constant from the beginning ofG 1 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/G 2 transition. The values ofn in the various phases of cell cycle are compared with the respective values of the recovery factorγ determined after fractionated irradiation. - Cell survival after a single dose of 616 rad has minima for irradiation atG 1/S transition and in earlyG 2 phase; the survival in earlyG 2 being about 40 times smaller than in earlyG 1 phase. Implications for a cell cycle specific therapy are discussed.