Molecular Pharmacology, Vol 2, 275-283, Copyright © 1966 by the American Society for Pharmacology and Experimental Therapeutics

Studies on the Biochemical Mode of Action of a Cytotoxic Methylhydrazine Derivative, N-Isopropyl--(2-methylhydrazino)-p-toluamide

¹ Department of Pharmacology, Yale University School of Medicine, New Haven, Connecticut

N-Isopropyl--(2-methylhydrazino)-p-toluamide inhibited the incorporation of thymidine-³H, deoxycytidine-³H, formate-¹⁴C, adenine-8-¹⁴C, and 4-amino-5-imidazolecarboxamide-2-¹⁴C into DNA, and the utilization of orotic acid-6-¹⁴C and leucine-1-¹⁴C for the synthesis of RNA and protein, respectively, in L5178Y lymphoma cells. The site of the drug-induced blockade of the formation of DNA did not appear to reside at the level of thymidine kinase (ATP:thymidine 5'-phosphotransferase, EC 2.7.1.21), thymidine monophosphate kinase (ATP:thymidine monophosphate phosphotransferase, EC 2.7.4.9), or DNA nucleotidyltransferase (deoxynucleosidetriphosphate:DNA deoxynucleotidyltransferase, EC 2.7.7.7). Furthermore, treatment of cells with N-isopropyl--(2-methylhydrazino)-p-toluamide did not influence the rate of loss of thymine-³H from prelabeled DNA. Possible metabolic alterations which might explain the observed results are discussed. The inhibitions of the syntheses of nucleic acids and proteins that were measured were followed by a period during which most of the cell death occurred; this period corresponded with the development of a metabolic imbalance that was characterized by an accumulation of RNA and protein and an increase in cell volume.

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ACKNOWLEDGMENTS The authors wish to thank Dr. W. E. Scott, Hoffmann-La Roche, Inc. for a generous supply of MIH and Miss Sheila J. Feld for excellent technical assistance. This investigation was supported by USPHS Research Grant CA-02817 from the National Cancer Institute and by Grants ACS IN-31E-806 and ACS IN-31F-905 from the American Cancer Society. One of us (S.T.) gratefully acknowledges postdoctoral support from the Anna Fuller Fund.