Analysis of variations in the cell population kinetics with tumor age in the L1210 ascites tumor.

The experimentally obtained data, growth curve, percentage of labeled mitoses curves, and continuous labeling curves have been analyzed by means of a computer method based on alternative mathematical models for the cell kinetics. The experimental doubling time determined from the growth curve is 10, 25, and 75 hr in the 5-, 6-, and 8-day tumors, respectively. From the models, growth fractions of 1.0, 0.96, and 0.56, respectively, are calculated for the same tumor ages. The calculated mean cell cycle time increases from 13.0 to 21.9 hr from Day 5 to 6, due to a proportional increase in the mean transit times of all phases in the cell cycle. In the 8-day tumor the mean cell cycle time surprisingly decreases to 15.3 hr and TQI becomes unappreciable. The cell loss is undetectable in the 5-day tumor, 0.1%/hr in the 6-day tumor, and 2.5%/hr in the 8-day tumor. The analysis makes it probable that the mode of cell loss is an age-specific elimination of noncycling cells with postmitotic DNA content.