NEUTRON-INDUCED CELL CYCLE-DEPENDENT ONCOGENIC TRANSFORMATION OF C3H 10T1 2 CELLS/

Exposure of synchronized populations of mouse C3H 10T1/2 cells to a si ngle dose (0.6 Gy) of 5.9 MeV neutrons at intervals after mitotic shak e-off results in a distinctive variation in the oncogenic transformati on frequency through the cell cycle. Previous findings show a sensitiv e window for X-ray-induced oncogenic transformants at late times after mitotic shake-off (14-16 h). Optimal sensitivity to neutrons was obse rved for cell populations irradiated soon after mitotic shake-off (4-6 h), where the majority of cells would be in the G(1) phase of the cel l cycle. Additionally, enhanced sensitivity was also found for that pe riod after shake-off (14-16 h) which was maximally sensitive to X rays corresponding to cell populations with a high proportion of G(2)-phas e cells. That is, low-LET radiation (250 kVp X rays) largely appears t o produce oncogenic transformants in G(2)-phase cells, while intermedi ate-LET radiation (5.9 MeV neutrons) is effective principally on G(1)- and, to a somewhat lesser extent, G(2)-phase cells. Cells irradiated with neutrons showed less variation for lethality through the cell cyc le than those irradiated with X rays, in agreement with previous findi ngs. The mechanistic basis for the difference in the response of cells in the different phases of the cell cycle to radiations of different quality is unknown but is suggestive of distinct (''signature'') molec ular changes leading to the observed oncogenic transformation response . (C) 1995 by Radiation Research Society