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

André Luis Souza Dos Santos,Anna Clara Milesi Galdino,Lívia Viganor,Sinéad O’Carroll,Marta Helena Branquinha,Matheus Mendonça Pereira,Malachy Mccann,Conor Bain,Michael Devereux,Georgia Menounou,Andrew Kellett,Zara Molphy

doi:10.1007/s00775-021-01922-3

Abstract

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 (Kapp = 2.55 × 106 M−1) than Ag-phendione (Kapp = 2.79 × 105 M−1) and phendione (Kapp = 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

Highlights

IntroductionThe therapeutic application of metal-based complexes has emerged against a multitude of human pathological disorders [1, 3]
The therapeutic application of metal-based complexes has emerged against a multitude of human pathological disorders [1, 3]. These treatments range from cisplatin in antineoplastic chemotherapy, gold-coordinated compounds for slowing the progression of rheumatoid arthritis, bismuth-based drugs for the treatment of ulcers, antimony-based metallodrugs in antiparasitic therapy, and silver-containing compounds with antimicrobial action [1,2,3,4]
The results showed that test compounds were able to bind to the DNA by means of hydrogen bonds and hydrophobic interactions

Summary

Introduction

The therapeutic application of metal-based complexes has emerged against a multitude of human pathological disorders [1, 3]. These treatments range from cisplatin in antineoplastic chemotherapy, gold-coordinated compounds for slowing the progression of rheumatoid arthritis, bismuth-based drugs for the treatment of ulcers, antimony-based metallodrugs in antiparasitic therapy, and silver-containing compounds with antimicrobial action [1,2,3,4]. With the addition of an o-quinoid group at the -5,6-position on the 1,10-phen backbone, 1,10-phenanthroline-5,6-dione (phendione) has exhibited increased antimicrobial activity when compared to 1,10-phen [10, 11]. Phendione-based complexes have demonstrated excellent antiproliferative activity against the: metronidazole-resistant Trichomonas vaginalis [12], dematiaceous fungus Phialophora verrucosa [13], clinically relevant yeast Candida albicans [14, 15], multidrug-resistant strains of Candida haemulonii species complex [16], filamentous fungus Scedosporium apiospermum [17], Escherichia coli [18], methicillin-resistant Staphylococcus aureus [18], carbapenemase-producing Acinetobacter baumannii [19], and multidrug-resistant bacterium Pseudomonas aeruginosa [9]

Methods

Results

Conclusion