Further Studies on the Clonal Growth of HeLa S3 Cells Treated with Tritiated Thymidine

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Abstract
The probability of colony development relative to the colony population and degree of variability in the generative cycle is discussed. Suppression of colony development is a function of the variability of the uptake of H3-thymidine by cells within clones. Those cells which had a somewhat longer generation time than the average (22 to 24 hours) did not incorporate the radioisotope during the first 24 hour growth period in radioactive medium and, subsequently, established normal clones in nonradioactive medium. Autoradiograms showed that in young cultures the percentage of clones in which all cells were labeled after a 24-hour growth period in medium containing 0.1 [mu]c of H3-thymidine per milliliter was much greater than in older cultures having an average of 40 cells per clone. Survival curves for S3 cells cultured in varying concentrations of H3-thymidine for 24 and 48 hours were established and compared. In cultures incubated for 48 hours in medium with 0.02 [mu]c of H3-thymidine per milliliter there was a significant lethal effect, and complete suppression of clonal growth occurred at a concentration of 0.1 [mu]c per ml.