The mutagenicity and interactions of 2- and 4-(acetylamino)fluorene with cytochrome P450 and the aromatic hydrocarbon receptor may explain the difference in their carcinogenic potency.

A study has been undertaken to identify the properties of 2-(acetylamino)fluorene which render it carcinogenic, in contrast to the 4-isomer, the carcinogenic potential of which is, at best, very weak. Compared to the 4-isomer, 2-(acetylamino)fluorene was a more potent inducer of cytochrome P450 1A (P450 1A) activity, as exemplified by the O-deethylation of ethoxyresorufin (P450 1A1), the metabolic activation of Glu-P-1 (P450 1A2), and immunoblot analysis. These findings were consistent with the relative affinity of these compounds for the cytosolic aromatic hydrocarbon receptor, determined by the displacement of tetrachlorodibenzo-p-dioxin. In the presence of Aroclor 1254-induced hepatic microsomal and cytosolic preparations 2-(acetylamino)-fluorene elicited a potent mutagenic response in the Ames test whereas the 4-isomer, in both cases, elicited a weak mutagenic response. Molecular orbital calculations of the relative energetics of the nitrenium ions revealed that the ion of the 2-isomer was more stable than the nitrenium ion of 4-(acetylamino)fluorene. Control hepatic microsomal and cytosolic fractions could activate 2-(acetylamino)fluorene to mutagens in the Ames test. Pretreatment of animals with 2-(acetylamino)fluorene enhanced both the microsome- and cytosol-mediated activation. In contrast, microsomal and cytosolic fractions from control animals could not activate 4-(acetylamino)fluorene, but following pretreatment with the compound itself, a weak mutagenic response in the presence of microsomes, but not of cytosol, was evident.(ABSTRACT TRUNCATED AT 250 WORDS)