4-aminoazobenzene and N,N-dimethyl-4-aminoazobenzene as equipotent hepatic carcinogens in male C57BL/6 X C3H/He F1 mice and characterization of N-(Deoxyguanosin-8-yl)-4-aminoazobenzene as the major persistent hepatic DNA-bound dye in these mice.

In contrast to the well-established requirement for an N-methyl group for efficient hepatic tumor induction by dietary administration of derivatives of 4-aminoazobenzene (AB) to adult rats, we have now observed that AB and its N-methyl and N,N-dimethyl derivatives have high and approximately equal hepatocarcinogenicity when given as a single i.p. dose to male 12-day-old C57BL/6 X C3H/ HeF1 (B6C3F1) mice. The hepatoma multiplicity induced by these dyes was approximately linearly related to the dose from 0.017 to 0.15 mumol/g body weight; at the high dose, an average of 11 hepatomas/mouse was observed at 10 months. Female B6C3F1 mice were resistant to tumor induction under these conditions. AB and its N-methyl derivative also induced the same incidences of hepatomas on administration of a single dose of 0.45 mumol/g body weight to 12-day-old male C3H/He mice (about 15 hepatomas/mouse) or C57BL/6 mice (about 1 hepatoma/mouse). Infant male Fischer rats were much less susceptible; less than 25% of the rats given 4 i.p. injections (0.3 to 0.4 mumol/g of body weight/injection) of N-methyl-4-amino-azobenzene and less than or equal to 5% of those given these doses of N,N-dimethyl-4-aminoazobenzene or AB before 22 days of age developed hepatic carcinomas by 24 months. Reverse-phase high-performance liquid chromatography of enzymatically hydrolyzed hepatic DNA from 12-day-old male B6C3F1 mice or Fischer rats given an i.p. dose (0.08 or 0.3 mumol/g of body weight) of [prime-ring-3H]AB showed a single major adduct which was chromatographically identical to N-( deoxyguanosin -8-yl)-4-aminoazobenzene synthesized by reaction at pH 7 of N-acetoxy-4-aminoazobenzene (formed in situ from N-hydroxy-4-aminoazobenzene and acetic anhydride) with deoxyguanosine. Mouse and rat liver DNA contained 20 and 0.5 pmol, respectively, of this adduct per mg 24 hr after administration of 0.3 mumol of [prime-ring-3H]AB/g of body weight. At 24 hr after administration of N,N-[prime-ring-3H]dimethyl-4-aminoazobenzene to male B6C3F1 mice, N-( deoxyguanosin -8-yl)-4-aminoazobenzene, N-( deoxyguanosin -8-yl)-N-methyl-4-aminoazobenzene, and 3-( deoxyguanosin -N2-yl)-N-methyl-4-aminoazobenzene were present in a ratio of approximately 4:2:1, respectively. Unlike the N-( deoxyguanosin -8-yl)-N-methyl-4-aminoazobenzene adducts, the N-( deoxyguanosin -8-yl)-4-aminoazobenzene adducts were relatively stable in the DNA; the level of the latter adducts decreased about 60% between 24 hr and 21 days.(ABSTRACT TRUNCATED AT 400 WORDS)