Copper(II) and silver(I)-1,10-phenanthroline-5,6-dione complexes interact with double-stranded DNA: further evidence of their apparent multi-modal activity towards Pseudomonas aeruginosa

Tackling microbial resistance requires continuous efforts for the development of new molecules with novel mechanisms of action and potent antimicrobial activity. Our group has previously identified metal-based compounds, [Ag(1,10-phenanthroline-5,6-dione)₂]ClO₄ (Ag-phendione) and [Cu(1,10-phenanthroline-5,6-dione)₃](ClO₄)₂.4H₂O (Cu-phendione), with efficient antimicrobial action against multidrug-resistant species. Herein, we investigated the ability of Ag-phendione and Cu-phendione to bind with double-stranded DNA using a combination of in silico and in vitro approaches. Molecular docking revealed that both phendione derivatives can interact with the DNA by hydrogen bonding, hydrophobic and electrostatic interactions. Cu-phendione exhibited the highest binding affinity to either major (− 7.9 kcal/mol) or minor (− 7.2 kcal/mol) DNA grooves. In vitro competitive quenching assays involving duplex DNA with Hoechst 33258 or ethidium bromide demonstrated that Ag-phendione and Cu-phendione preferentially bind DNA in the minor grooves. The competitive ethidium bromide displacement technique revealed Cu-phendione has a higher binding affinity to DNA (K_app = 2.55 × 10⁶ M⁻¹) than Ag-phendione (K_app = 2.79 × 10⁵ M⁻¹) and phendione (K_app = 1.33 × 10⁵ M⁻¹). Cu-phendione induced topoisomerase I-mediated DNA relaxation of supercoiled plasmid DNA. Moreover, Cu-phendione was able to induce oxidative DNA injuries with the addition of free radical scavengers inhibiting DNA damage. Ag-phendione and Cu-phendione avidly displaced propidium iodide bound to DNA in permeabilized Pseudomonas aeruginosa cells in a dose-dependent manner as judged by flow cytometry. The treatment of P. aeruginosa with bactericidal concentrations of Cu-phendione (15 µM) induced DNA fragmentation as visualized by either agarose gel or TUNEL assays. Altogether, these results highlight a possible novel DNA-targeted mechanism by which phendione-containing complexes, in part, elicit toxicity toward the multidrug-resistant pathogen P. aeruginosa. Graphical abstract: [Figure not available: see fulltext.]