Some Differences Among Various Mammalian Cell Lines in Reversal of Growth Inhibition by 5-Fluorouracil. ∗ †

Summary

Growth inhibition of HeLa and H. Ep. #1 cells by 5-fluorouracil and 5-fluorodeoxyuridine and reversal of inhibition by thymine and thymidine have been studied. Growth inhibition curves with 5-fluorouracil are similar in both cell lines while reversal studies reveal several differences. Thymine partially reverses inhibition by 5-fluorouracil and 5-fluorodeoxyuridine in HeLa but not in H. Ep. #1 cells. Thymidine reverses inhibition by 5-fluorodeoxyuridine in both H. Ep. #1 and HeLa cells but reverses inhibition by 5-fluorouracil only in HeLa cells. Partial reversal (about 30%) of inhibition by 5-fluorouracil in HeLa cells represents more closely a reduced growth rate by the whole cell population rather than a normal growth rate by a fraction of the population. Utilization of thymine-2-C¹⁴ for DNA thymine synthesis in HeLa cells was significantly increased in presence of 5-fluorouracil.