Determination of the intracellular targets and in vitro activity of a new class of chemical nuclease complexes derived from antibiotics of the quinolone family

Abstract

 Alteration of bacterial DNA structure and/or associated functions in vivo by [Cu(phen)(nal)]⁺, a metal complex of the type [Cu(phen)(antib)]⁺ (where antib is a quinolone or a fluoroquinolone), was demonstrated by the induction of a recA-lacZ fusion integrated at the amyE locus of a recombinant Bacillus subtilis strain. Using the same approach, nalidixic acid alone was shown to induce 14% of the β-galactosidase levels induced by [Cu(phen)(nal)]⁺; on the other hand none of the other components, i.e. copper, phenanthroline or the complex [Cu(phen)₂]²⁺ activated significantly the recA-directed β-galactosidase activity, suggesting that the intact structure of the complex is required to reach maximum levels of induction.

Results of in vitro experiments demonstrated that under reductive conditions [Cu(phen)(nal)]⁺ behaves as a powerful nuclease capable of degrading plasmid DNA; this activity was stronger than that of the chemical nuclease copper phenanthroline [Cu(phen)₂]²⁺. The nuclease activity putatively occurred by a mechanism involving hydroxyl radicals since the reaction was partially inhibited by catalase. These results support the hypothesis that the mechanism of action of quinolones could be mediated by a transition metal ion such as copper.