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The Thymidine-¹⁴C and -³H Double-labeling Technic in the Study of the Cell Cycle of L1210 Leukemia Ascites Tumor in Vivo

Medicine Branch, National Cancer Institute, NIH Bethesda, Maryland 20014

A study was performed to evaluate the double-labeling technic with thymidine-¹⁴C and -³H in the determination of the duration of DNA synthesis, duration of mitosis, and generation time of LI210 leukemia ascites tumor. The results were comparable with data obtained from labeled mitoses curves. The average duration of DNA synthesis was 9.0 hours, and the average duration of mitosis was 0.20 hours.

Prolongation of generation time on the seventh day of tumor growth (18.1 hours) compared with the sixth day (13.3 hours) was noted. This difference is highly significant (P 0.001). Evidence was presented to suggest that the prolongation was related to a lengthened G₁.

Received 10/31/68. Accepted 4/10/69.