Molecular Pharmacology, Vol 5, 625-639, Copyright © 1969 by the American Society for Pharmacology and Experimental Therapeutics

Increased Selectivity of Interaction between Fluorenylamine Carcinogens and Liver Proteins during Hepatocarcinogenesis

¹ The Institute for Cancer Research, Fox Chase, Philadelphia, Pennsylvania 19111

The continued ingestion of a fluorenylamine hepatocarcinogen by rats results in a marked change toward a highly selective interaction between the carcinogen and particular target liver proteins. Adult male rats were fed for 5 weeks a diet lacking (control) or containing the liver carcinogen N-2-fluorenylacetamide (2-acetylaminofluorene, FAA). They were then given single doses of N-2-fluorenylacetamide-9-¹⁴C intragastrically and killed 48 hr later. The soluble liver proteins were resolved extensively by column electrophoresis. Control liver profiles displayed a diffuse distribution of fluorenyl-¹⁴C-proteins. In contrast, the profiles from rats previously fed the carcinogen displayed a highly localized concentration of bound ¹⁴C-labeled carcinogen at one or two weakly basic classes of proteins (fast h₂ and/or slow h₁). These regions contained about one-third of all the soluble fluorenyl-¹⁴C-proteins of liver, and represented a 3-4-fold increase over that in control profiles. Each of the two conjugates displayed a degree of electrophoretic homogeneity resembling that of a single macromolecule. The relative proportion of the two species varied considerably. The more anionic one (slow h₁) was labile.

The possibility that the specificity of protein binding in vivo resided in the activation of FAA by N-hydroxylation was examined by administration of the proximate carcinogen N-hydroxy-FAA-9-¹⁴C to rats likewise previously fed FAA. This premise was not supported by the finding of a similar h specificity of the distribution of radioactivity.

In contrast to the h specificity of the preneoplastic livers of FAA-fed rats, unperfused primary liver tumors induced by FAA contained mostly soluble fluorenyl-¹⁴C-proteins which were weakly acidic (A proteins) and had a mobility similar to that of serum albumin.