Autoradiographic and cytophotometric analyses of the resting stages of the L1210 ascites tumor.

SUMMARY In the murine Ll2lO ascites tumor the resting stages were investigated on Days 5, 6, and 8 after transplantation of l0@ cells. The experimental work consisted of continuous labeling with thymidine-3 H combined with cytophotometric deter mination of the single-cell DNA content of unlabeled tumor cells. The present experimental data and earlier experiments with percentage of labeled mitoses and continuous labeling were analyzed by a computer method based on 2 alternative mathematical models for the cell kinetics in the tumor. In the 5-day tumor, no resting cells were found, while 4.2 and 44.8% were noncycling cells in the 6-and 8-day tumors, respectively. The new finding was the demonstration of a small but significant fraction of noncycling cells with G2 DNA content in the 6-and 8-day tumors (0.6 and 0.9%, respectively). Furthermore, the investigations confirmed the previous fmding of noncycling cells with G1 DNA content in the 6-and 8-day tumors (3.6 and 43.9%, respectively). The study provided evidence in support of the assumption of cell loss in the Ll210 tumor as an age-specific elimination of resting cells with G1 DNA content.