Effect of single dose irradiation on the proliferation kinetics in a human malignant melanoma in athymic nude mice.

The effect of single dose irradiation on the proliferation kinetics in a human malignant melanoma grown in the athymic mutant nude mouse was analysed. DNA-histograms were obtained with flow cytofluorometry. Percentage labelled mitoses curves were established by the use of conventional autoradiographic techniques. Changes in the fraction of clonogenic cells with time after irradiation were measured in vitro in soft agar. In non-irradiated tumours the fraction of cells in G1/G0, S and G2 + M was 66.21 and 13 per cent, respectively. The median duration of G1, S, G2, M and Te was 19.0 h, 13.3 h, 5.0 h, 1.0 h and 41.4 h, respectively. The growth fraction was calculated as 0.66 and the cell loss factor as 0.67. The growth fraction was increased after irradiation and the cell cycle time reduced, due to a shortening of G1. These effects were dose dependent and decreased with time after exposure, but were still present after the tumours had resumed a continuous volume growth. The rate of volume growth was slower for irradiated tumours than for non-irradiated tumours of the same size, due to a larger cell loss factor for the former.