Nitrated fluorene derivatives are potent frameshift mutagens

Area of Science:

• Environmental chemistry
• Molecular toxicology
• Genetics

Background:

• Nitrated fluorenes are known frameshift mutagens.
• Mutagenicity requires reduction of the nitro group to a hydroxylamine intermediate.
• Hydroxylamine intermediates are believed to esterify into electrophiles that bind DNA.

Purpose of the Study:

• To investigate the mechanism of mutagenicity for nitrated fluorenes.
• To explore the role of nitro group reduction and specific enzymes in mutagenicity.
• To determine how the number of nitro groups affects mutagenic potency.

Main Methods:

• Utilized bacterial tester strains with functional or deficient DNA repair (uvrB) and nitroreductase pathways.
• Assessed mutagenic activity of nitrated fluorenes with varying numbers of nitro substituents.

Main Results:

• Mutagenicity is dependent on the reduction of nitro groups, likely via hydroxylamine intermediates.
• The uvrB gene product and specific nitroreductases influence mutagenic expression.
• Mutagenic potency increases with additional nitro groups, peaking at trisubstituted fluorenes.
• A fourth nitro group reduces mutagenic activity.

Conclusions:

• The mechanism involves reduction of nitro groups to hydroxylamines, followed by DNA adduct formation.
• Enzymatic pathways, including nitroreductases and DNA repair systems, modulate the mutagenicity of nitrated fluorenes.
• Optimal mutagenic activity is observed with three nitro groups on the fluorene structure.