The structure-function relationships of nitrofluorenes and nitrofluorenones in the Salmonella mutagenicity and CHO sister-chromatid exchange assays

Abstract

Nitrofluorenes and nitrofluorenones are bacterial mutagens and are detected in a variety of environmental pollution sources. We tested a series of nitrosubstituted fluorenes and fluorenones for their genotoxicity using both Salmonella bacteria and Chinese hamster ovary (CHO) cells to determine if structure-function relationships observed in bacteria for mutation induction are similar to those for mutations and SCE induction in mammalian (CHO) cells. The compounds studied were 2-nitrofluorene (2-NF), 2,7-dinitrofluorene (2,7-DNF), 3-nitrofluorenone (3-NFone), 2-nitrofluorenone (2-NFone), 2,7-dinitrofluorenone (2,7-DNFone), 2,4,7-trinitrofluorenone (2,4,7-TNFone), and 2,4,5,7-tetranitrofluorenone (2,4,5,7-TNFone). In bacteria, the presence of carbonyl group to convert mono-nitrofluorenes to nitrofluorenones and the addition of a second nitro group to either mono-nitrofluorene or fluorenone to form the dinitro compounds increased mutagenic activity in the Ames test. Location of the nitro group relative to the carbonyl group was important in enhancing mutagenic activity as 2-nitrofluorenone was more mutagenic than 3-nitrofluorenone. In CHO cells, the di-, tri- and tetra-nitrofluorenones were cytotoxic and delayed the progression of CHO cells through the cell cycle. The degree of the cytotoxicity could be decreased by the addition of S9. None of the compounds produced mutations when tested in the CHO/HGPRT mutation assay with the addition of S9. Nonetheless, the current study did show that these compounds, both with and without the activation by S9, can interact with the DNA and produce SCE in CHO cells. The addition of a carbonyl group had no influence on SCE frequency since both 2-nitrofluorene and 2-nitrofluorenone induced a similar frequency of SCE either with or without S9. Additional nitro groups, forming di-, tri- or tetra-nitrofluorenones, increased the frequency of SCE induced, especially when tested with S9 which limits cytotoxicity. The addition of a single nitro group to 2-nitrofluorenone did not change the SCE frequency but did cause a large increase in the frequency of mutations in bacteria. In contrast, 2,4,7-TNFone and 2,4,5,7-TNFone were less mutagenic than the 2,7-DNFone in bacteria but were more effective in production of SCE in CHO cells. This study illustrates that structure-function relationships are dependent on both the compounds tested and the type of genetic change induced.