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Effects of 5-(3,3-Dimethyl-1-triazeno)imidazole-4-carboxamide and Its Metabolites on Novikoff Hepatoma Cells¹

Department of Human Oncology, University of Wisconsin Center for Health Sciences, Madison, Wisconsin 53706

Studies were undertaken to determine the effects of 5-(3,3-dimethyl-1-triazeno)imidazole-4-carboxamide (DTIC) and its metabolites on the growth and macromolecular synthesis of Novikoff hepatoma cells in culture. DTIC (3.0 mM) in light decreased the viable cell count by 90% within 96 hr. DTIC protected from light, 2-azahypoxanthine, dimethylamine, and 5-aminoimidazole-4-carboxamide, all at 3.0 mM, reduced the rate of cellular proliferation. 5-Diazoimidazole-4-carboxamide (1.0 mM) and 5-(3-methyl-1-triazeno)imidazole-4-carboxamide (3.0 mM) decreased the viable cell count by 99%.

Effects on macromolecular synthesis were determined by the rate of incorporation of the appropriate ³H-labeled precursor. Results after 6 hr are given as percentage of controls. DTIC (1.0 mM) in light inhibited DNA (8%), RNA (41%), and protein (63%) synthesis. DTIC (1.0 mM) protected from light inhibited DNA (12%) and RNA (57%) synthesis. 5-Diazoimidazole-4-carboxamide (0.1 mM) inhibited DNA (1%), RNA (9%), and protein (1%) synthesis. 5-(3-Methyl-1-triazeno)imidazole-4-carboxamide (1.0 mM) inhibited DNA (72%) and protein (65%) synthesis but stimulated RNA (127%) synthesis. 2-Azahypoxanthine (1.0 mM) inhibited DNA (43%), RNA (82%), and protein (28%) synthesis. 5-Aminoimidazole-4-carboxamide (3.0 mM) stimulated DNA (354%) and RNA (266%) synthesis.

These data show that DTIC is able to generate several toxic metabolites that may be responsible for its biological effects.

¹ Supported in part by USPHS Grants CA 13290 and CA 12491 from the National Cancer Institute. Preliminary reports of this work have been made (3, 4).

² To whom requests for reprints should be addressed.

³ Present address: Department of Pharmacology, Medical College of Wisconsin, Milwaukee, Wis. 53233.

Received 10/23/75. Accepted 5/10/76.