Cell cycle kinetics of synchronized EAT-cells after irradiation in various phases of the cell cycle studied by DNA distribution analysis in combination with two-parameter flow cytometry using acridine orange

Synchronized Ehrlich ascites tumor cells were irradiated with X-rays in various phases of the cell cycle (G1, G1/S, S, G2 and M-phase) and the progression through the remainder of the cell cycle and the following cell cycle was studied by DNA distribution analysis. Radiation-induced delays were observed in S- and G2-phase during the cell analysis. Radiation-induced delays were observed in S- and G2-phase during the cell cycle. After the first division of irradiated cells, DNA distributions showed a broadening of the G1-peak which complicated evaluation of DNA histograms. Synchronized cells irradiated in various phases of the cell cycle were used to study the dose dependent broadening of the G1-peak after division. A linear increase of the coefficient of variation was observed as function of radiation dose (1-9 Gy). Using two-parameter flow cytometry after acridine orange staining, the fraction of cells in mitosis after irradiation could also be measured. Combining this technique with DNA distribution analysis it could be shown that only a proportion of a population of synchronized cells irradiated in M-phase underwent division. A dose dependent fraction of these cells did not divide but entered a polyploid state. Cells irradiated in G1-, G1/S- or S-phase also showed a dose dependent polyploidization but to a lesser extent. (orig./AJ)