N-Hydroxylation in Aminostilbene Carcinogenesis

Abstract

FOLLOWING the original observation of Cramer, Miller and Miller (1960) that an N-hydroxylated metabolite of 2-acetamidofluorene (AAF) was formed in the rat, N-hydroxylation of a number of carcinogenic aromatic amines in susceptible species has been reported. Thus an N-hydroxylated metabolite of 4-acetamidobiphenyl was demonstrated in the rat (Miller, Wyatt, Miller and Hartmann, 1961) whilst similar metabolic conversions of 2-naphthylamine have been observed in both rat (Boyland, Manson and Nery, 1960) and man (Troll and Nelson, 1961).N-Hydroxylation of carcinogenic aromatic amines in vitro by tissue homogenates or sub-cellular fractions has also been reported. Hence IJehleke (1963) detected N-oxidation of several carcinogenic arylamines by rat liver microsomes and NADPH2 by estimation of the resulting hydroxyamino and nitroso compounds.The formation of N-hydroxy-AAF following incubation of AAF with rabbit liver microsomes has been demonstrated more directly by identification of the metabolite (Irving, 1964; Booth and Boyland, 1964) whilst Booth and Boyland (1964) also showed N-hydroxylation of 4-acetamidobiphenyl and N-acetylbenzidine.Investigations of the carcinogenicity of these compounds have shown that, in general, the N-hydroxy derivatives are more active than the parent amides. Thus N-hydroxy-2-acetamidofluorene was shown (Miller, Miller and Hartmann, 1961) to be more active than AAF towards rat liver and additionally, induced tumours at other sites including the peritoneum and forestomach. Similarly, N-hydroxy-4-acetamidobiphenyl proved to have an enhanced carcinogenic activity with a greater spectrum of action (Miller, Wyatt, Miller and Hartmann, 1961) and 2-naphthylhydroxylamine was a more potent carcinogen than the parent amide (Boyland, Dukes and Grover, 1963).trans-4-Aminostilbene and its derivatives, initally studied on account of their tumour inhibitory properties (Haddow, Harris, Kon and Roe, 1948), are highly carcinogenic in the rat inducing ear duct carcinomata following oral administration. These compounds thus provide a further class of aromatic amines for investigation of the significance of N-hydroxylation in carcinogepesis. The present paper describes the metabolic transformations of aminostilbene compounds in the rat particularly with reference to the formation of N-hydroxy-derivatives, and their further metabolic reactions.

The metabolism of 4-acetamidostilbene and its N-hydroxy derivative.

“…The residue was recrystallized four times from toluene and the product (yield 13 mg.) in ethanol solution stored in the dark. The radioactive compound (specific activity 0-74 mCi/m-mole) migrated with authentic N-hydroxy-4-acetamidostilbene on TLCs and gave the characteristic colour reaction with ferric chloride-potassium ferricyanide (Baldwin and Smith, 1965). A trace amount of 4-acetamidostilbene (1.0%) was detected by radioautography of TLCs.…”

“…The chromatographic properties of 4-aminostilbene compounds in these solvent systems have been described previously (Baldwin and Smith 1965). Metabolites were detected by their blue fluorescence under ultra-violet light or by spray reactions.…”

“…2380 C. and N-hydroxy-AAS, m.p. 2000 C. were prepared as previously described (Baldwin and Smith, 1965). 4'-Hydroxy-4-aminostilbene (4'-hydroxy-AS) m.p.…”

“…and treated with aluminium amalgam (60 mg.) as previously described (Baldwin and Smith, 1965). The mixture was filtered, the precipitate washed once with ether (5ml.)…”

Carcinogenic action of 4-acetamidostilbene and the N-hydroxy derivative in the rat

“…More recently it has been proposed (Schardein and Kaump, 1966) that lobular cystic dilation in the gland during aging contributes to tumour development. The direct involvement of carcinogen is supported, however, by the finding (Baldwin and Romeril, 1965) that radioactive material is localised in the ear duct glands in rats treated with 14C-labelled 4-acetamidostilbene or the N-hydroxy-derivative.…”