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Autoradiographic and Cytophotometric Analyses of the Resting Stages of the L1210 Ascites Tumor¹

Finsen Laboratory [N. R. H.] and Department of Internal Medicine [P. D.], Finsen Institute, DK-2100 Copenhagen, Denmark

In the murine L1210 ascites tumor the resting stages were investigated on Days 5, 6, and 8 after transplantation of 10⁵ cells.

The experimental work consisted of continuous labeling with thymidine-³H combined with cytophotometric determination 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 finding 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 L1210 tumor as an age-specific elimination of resting cells with G₁ DNA content.

¹ This investigation was supported by grants from the Daell Foundation; The Danish Hospital Foundation for Medical Research, Region of Copenhagen; The Danish Medical Research Council; the Hasselbalch Foundation; and the Michaelsen Foundation.

Received 12/27/73. Accepted 8/26/74.