Effect of Folic Acid on in vitro Uptake of Labeled Thymidine by Leukemic Cells

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Abstract
The uptake of thymidine H3 by leukemic and non-leukemic tissues growing in tissue culture was studied under different nutritional conditions. The viral leukemias used were those of Drs. Gross, Friend, and Moloney. A transplantable leukemia, L1210, and a mouse lymphosarcoma were also used. Normal splenic explants served as controls. Bits of leukemic and normal tissues were grown on cover glasses in Eagle''s medium plus 15% horse serum. When growth was established, 0.1 uc/ml of thymidine H3 was added and the percentage of labeled cells determined by direct count 24 hours later. It was found that the uptake of thymidine by leukemic cells was lower (25% labeled cells) than that of normal spleen (40% labeled cells). However, when leukemic spleen explants from the three virus leukemias were grown in the presence of increased amounts of folic acid (10 mg/liter) the number of labeled cells increased, reaching the values of the normal spleen (40%). This effect was shown neither by the L1210 leukemia nor by the lymphosarcoma. Normal splenic cultures infected with the Friend leukemia virus gave an uptake of 17% as compared to the 40% of the non-infected spleen. When folic acid was added in increased amounts to the virus-infected splenic cultures, the percentage of labeled cells increased from 17% to 30%.