[Anti-carcinogenic structural modification by fluorine-substitution in aza-polycyclic aromatic hydrocarbons]

One of the major goals of a series of our studies is to explore the availability of a method for anti-genotoxic modification of carcinogens by fluorine-substitution. Quinoline, a hepatocarcinogen, mutates bacterial tester strains in the presence of rat liver microsomal enzymes and induces GST-P (placental glutathione S-transferase)-positive foci in a medium-term bioassay system for hepatocarcinogenesis. On the other hand, 3-fluorinated quinoline (3-FQ) was neither mutagenic nor carcinogenic in the same assay system, whereas 5-fluoroquinoline (5-FQ) was mutagenic and carcinogenic. Quinoline, 3-FQ, and 5-FQ were also tested in an in vivo mutagenicity assay system using a lacZ-transgenic mouse (Muta Mouse). Mutation was induced by quinoline and 5-FQ only in the liver, the target organ of carcinogenesis by quinoline, but not in the other organs examined. 3-FQ was non-mutagenic in all of the organs. The results strongly indicate that fluorine-substitution at the position-3 of quinoline could be an anti-genotoxic structural modification of quinoline in a wide range of its genotoxic end-points. Additionally, seventeen mono- and di-fluorinated derivatives of 1,7-phenanthroline, 1,10-phenanthroline, benzo[h]quinoline, and benzo[f]quinoline were subjected to analysis of their structure-mutagenicity relationship. The results support that the enamine epoxide structure of the pyridine moiety, as well as the bay-region epoxide structure, is responsible for mutagenicity. These results suggest that the introduction of a fluorine atom to the molecule in question may be a useful tool to modify their mutagenic potency and to better understand the mechanism of mutation.