The effect of folic acid on A-methopterin-induced inhibition of nucleic acid synthesis.

It has been observed that folie acid (2) or citrovorum factor (1) will prevent the anti-leukemic ac tion of folie acid antagonists. We have reported that desoxyribonucleic acid (5) and vitamin Bi2 (7) will partially prevent the anti-leukemic action of 4-aminopteroylglutamic acids, and have more re cently observed that a combination of thymidine, adenylic, guanylic, and cytidylic acids or DNA plus RNA plus Bi2 are more effective in preventing the anti-leukemic action of 4-amino-N10-methylpteroylglutamic acid (A-methopterin) than any of these materials administered alone.1 mice treated with A-methopterin and with folie acid plus A-methopterin (in immediate succession) were injected with C14-formate (1.0 MC-)>an(l &t 6 hours the viscera were excised, pooled, and the combined nucleic acids and then nucleic acid purines were isolated (8) and assayed for radioactivi ty (6). The dosage schedules and experimental re sults obtained are summarized in Table 1.