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Rapid Membrane Filtration Technics for Studying the Action of 6-Thioguanine on Tumor Cells in Vitro^*

Frieda U. Brown, Morris Klein, T. S. Kandaswamy and H. George Mandel

( Department of Pharmacology, The George Washington University School of Medicine, Washington, D.C.)

Leukemia L1210 ascites cells sensitive to 6-thioguanine were incubated aerobically in a glucose-balanced salts medium supplemented with glutamine in the presence and and absence of the analog. The rates of incorporation and distribution of various isotopic precursors in this system were examined by radioassaying the various fractions of the tumor cells collected on membrane filters. This technic was extremely useful for the rapid assay of incorporation into tumor cells.

The incorporation of isotopic precursors represented net synthesis rather than exchange. Thioguanine decreased the uptake of formate-C¹⁴ and thymidine-C¹⁴H₃ into the acid-insoluble fraction of the cells by about one-half and one-third, respectively, but did not affect incorporation of methionine-S³⁵ or acetate-2-C¹⁴. The drug inhibited incorporation of formate-C¹⁴ into the nucleic acids, but proteins were only slightly affected. Molar activities of the isolated nucleic acid bases were reduced by the drug.

^* This research was supported by Research Grant CY-2978 from the National Cancer Institute, United States Public Health Service, Bethesda, Maryland.

Present address: 2801 Snow Road, Parma 34, Ohio.

Present address: Laboratory of Cellular Physiology, Department of Surgery, Albert Einstein College of Medicine, New York 61, N.Y.

Received 8/25/62.