Mutagenic properties of N‐acetyl‐2‐aminofluorene and its metabolites in relation to the molecular mechanisms of carcinogenesis

The genetic properties of the carcinogen N‐acetyl‐2‐aminofluorene were compared with those of representatives of its suspected metabolites: the N‐hydroxylamine, its acetic and sulphuric acid oxy‐esters, as well as the 1‐ and 3‐hydroxylamines. Mutagenic activity was examined with respect to point‐mutations, gene eliminations and chromosome breakage, in both the euchromatic and heterochromatic parts of the genome. Selective mutagenicity was assayed on the basis of the specific mutational effects on the Minute (m), bobbed (bb) and 3 euchromatic loci relative to the overall X‐chromosome response (recessive lethals and visibles) in the same sample of treated gametes. The parent carcinogen and its N‐hydroxy derivatives (both the acetylated and non‐acetylated forms) were inactive as regards X‐chromosome recessive mutations and heterochromatic deletions involving both the m loci and the fertility genes, but were decisively active with respect to the bb's, thus indicating their virtual specificity for the r‐RNA genes. The genetic activity of the 3‐hydroxyamine was identical to that of the N‐hydroxylamine, to which it might be converted in vivo, but the I‐hydroxy derivative was mutagenically ineffective. The highest mutagenic activity among the present test compounds occurred with the chemically reactive amino‐oxy esters. The acetic acid derivative—N‐acetoxy‐2‐acetylaminofluorene—exerted a wide spectrum of mutational effects: X‐chromosome recessive mutations, heterochromatic gene eliminations (m's and bb's) and—to a lesser extent—chromosome structural rearrangements. Its yield of these mutational classes, however, was differential for the various germ cell stages, being maximal in the sperm for point‐mutations and in the spermatids for the m's and bb's. The sulphate ester—acetylaminofluorene‐N‐sulphate—was considerably more selective for the heterochromatin than the acetic acid analogue, as indicated by its high mutagenicity on the m loci and virtual inactivity with respect to the overall X‐chromosome mutations. A subtle correlation seemed to occur between the oncological and mutagenic selectivities manifested by the present test series. The hepatocarcinogenic parent amine and its N‐hydroxylamines were also virtually specific for the bb loci, and the acetoxy derivative, which exerted its carcinogenicity at the site of injection, produced the same order of bb‐selectivity as other direct carcinogens among the alkylating agents. This is in harmony with the concept that mutations at the r‐RNA genes might be significant in cancer initiation.