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Effects of A-Methopterin on Formate Incorporation into the Nucleic Acids of Susceptible and Resistant Leukemic Cells^*

( Southern Research Institute, Birmingham, Ala., and National Cancer Institute, National Institutes of Health, U.S. Public Health Service, Bethesda, Md.)

It has been demonstrated that A-methopterin inhibits formate incorporation into nucleic acid purines and thymine in leukemic cells which are sensitive to this compound and also in viscera of mice bearing these susceptible leukemic cells. A-methopterin, however, causes a significant increase in formate incorporation into the nucleic acids of leukemic cells which have become dependent on A-methopterin for optimal growth while inhibiting formate incorporation in the visceral nucleic acids of mice bearing the dependent strain of leukemia.

Possible mechanisms involved are discussed.

^* This work was supported by the American Cancer Society upon recommendation of the Committee on Growth, and by the Southern Research Institute.

Received 5/22/52.