Metabolism and nucleic acid binding of 7-fluoro-2-acetamidofluorene in rats: Oxidative defluorination and apparent dissociation from hepatocarcinogenesis of 8-( N-arylamide)guanine adducts on DNA

Abstract

The significance in hepatocarcinogenesis of various arylamine/amide adducts with nucleic acid was investigated by the use of comparison studies on several different parameters. Female Fischer and Sprague-Dawley rats are comparably sensitive to hepatocarcinogenesis by 2-acetamidofluorene (AAF), while male rats are more sensitive. 7-Fluoro-AAF is more carcinogenic in Sprague-Dawley rats than is AAF, but is strikingly so toward the liver of the female rat. Based on these observations, binding of both compounds to liver nucleic acids was determined for male and female Fischer rats at 1 and 3 days after a single injection of carcinogen, and in female Sprague-Dawley rats from 1 to 28 days after a single injection. As shown by others, no 8-( N-2-fluorenylacetamido)guanine adduct could be found in RNA or DNA of female Sprague-Dawley rats treated with AAF (nor was the corresponding 7-fluoro derivative detectable). These adducts were present, however, in comparable amounts in both male and female Fischer rats. The binding of 7-fluoro-AAF derivatives was higher than that of AAF derivatives in female Sprague-Dawley rats. Feeding of either AAF or 7-fluoro-AAF to Sprague-Dawley rats for 4 weeks before a single injection of [ 3H]7-fluoro-AAF resulted in reduction of the 8-( N-2-(7-fluoro)fluorenylacetamido)guanine adduct in males to undetectable levels in DNA and to 10% of control level in RNA. Non-acetylated adducts were increased in males, but decreased in females by AAF prefeeding; 7-fluoro-AAF prefeeding resulted in little change in adduct formation in females and in a major increase in non-acetylated adducts in males. AAF adducts disappeared from DNA more rapidly than did 7-fluoro-AAF adducts. Assay of the urinary metabolites from the animals in the prefeeding experiment showed that all compounds fed (including the non-hepatocarcinogens 4-acetamidobiphenyl and 2-acetamidophenanthrene) increased the proportion of N-hydroxy-7-fluoro-AAF among the metabolites. Defluorination of 7-fluoro-AAF to 7-hydroxy-AAF was also demonstrated and the ratio of 7-hydroxy-AAF to 5-hydroxy-7-fluoro-AAF was comparable to that observed for 7-hydroxy-AAF/5-hydroxy-AAF and AAF itself, suggesting that fluoro substitution does not increase activity by preventing detoxication.