Investigating the antibacterial activity of novel metal complexes against antimicrobial resistant pathogens

Antimicrobial resistance (AMR) is one of the serious global health challenges of our time. There is an urgent need to develop novel therapeutic agents to overcome AMR, preferably through alternative mechanistic pathways from conventional treatments. Interdisciplinary research in inorganic medicinal chemistry with biology is advancing the knowledge and implementation of transition metal complexes for therapy and is offering a realistic alternative to traditional antibiotics. Metal complexes with 1,10-phenanthroline (phen) ligands have demonstrated promising therapeutic capabilities with diverse biological activity. Consequently, there has been a resurgence in research of these complexes as possible alternatives or adjuvants to established antimicrobial clinical therapeutics. The antibacterial and anti-biofilm activity of novel metal complexes (metal = Cu(II), Mn(II), and Ag(I)) incorporating phen and various dicarboxylate ligands was the focus of this research. The Cu(II), Mn(II), and Ag(I) chelates incorporating both phen and the dianion of 3,6,9-trioxaundecanedioic acid (tdda) were the most effective, and the activity varied depending on the metal centre. All three metal-tdda-phen complexes showed comparable and often superior activity to the established antibiotic gentamicin clinical P. aeruginosa isolates from cystic fibrosis (CF) lungs of Irish patients, concerning biofilm formation and established biofilms. Combination studies presented synergistic activity between all three complexes and gentamicin, particularly for the post-treatment of established mature biofilms, and were supported by the reduction of the individual biofilm components examined. The efficacy of individual treatments of Cu-tdda-phen, Mn-tdda-phen, and Ag-tdda-phen and in combination with gentamicin were further examined in vivo, utilising the larvae of Galleria mellonella infected with CF isolates. All test complexes were tolerated by G. mellonella in concentrations up to 10 µg/larva and affected the host\u27s immune response by stimulating immune cells (hemocytes) and enhancing the expression of genes that encode for immune-related peptides. Combining the metal-tdda-phen complexes with gentamicin further intensified this response at lower concentrations, clearing a P. aeruginosa infection previously resistant to gentamicin alone. Therefore, this work highlights the anti-pseudomonal capabilities of metal-tdda-phen complexes alone and combined with gentamicin in a valuable pre-clinical in vivo model

The Antibacterial and Anti-biofilm Activity of Metal Complexes Incorporating 3,6,9- Trioxaundecanedioate and 1,10-Phenanthroline Ligands in Clinical Isolates of Pseudomonas Aeruginosa from Irish Cystic Fibrosis Patients

Chronic infections of Pseudomonas aeruginosa in the lungs of cystic fibrosis (CF) patients are problematic in Ireland where inherited CF is prevalent. The bacteria\u27s capacity to form a biofilm in its pathogenesis is highly virulent and leads to decreased susceptibility to most antibiotic treatments. Herein, we present the activity profiles of the Cu(II), Mn(II) and Ag(I) tdda-phen chelate complexes {[Cu(3,6,9-tdda)(phen)2].3H2O.EtOH}n (Cu-tdda-phen), {[Mn(3,6,9-tdda)(phen)2].3H2O.EtOH}n (Mn-tdda-phen) and [Ag2(3,6,9-tdda)(phen)4].EtOH (Ag-tdda-phen) (tddaH2 = 3,6,9-trioxaundecanedioic acid; phen = 1,10-phenanthroline) towards clinical isolates of P. aeruginosa derived from Irish CF patients in comparison to two reference laboratory strains (ATCC 27853 and PAO1). The effects of the metal-tdda-phen complexes and gentamicin on planktonic growth, biofilm formation (pre-treatment) and mature biofilm (post-treatment) alone and in combination were investigated. The effects of the metal-tdda-phen complexes on the individual biofilm components; exopolysaccharide, extracellular DNA (eDNA), pyocyanin and pyoverdine are also presented. All three metal-tdda-phen complexes showed comparable and often superior activity to gentamicin in the CF strains, compared to their activities in the laboratory strains, with respect to both biofilm formation and established biofilms. Combination studies presented synergistic activity between all three complexes and gentamicin, particularly for the post-treatment of established mature biofilms, and was supported by the reduction of the individual biofilm components examined

In Vivo Activity of Metal Complexes Containing 1,10-Phenanthroline and 3,6,9-Trioxaundecanedioate Ligands against Pseudomonas aeruginosa Infection in Galleria mellonella Larvae

Drug-resistant Pseudomonas aeruginosa is rapidly developing resulting in a serious global threat. Immunocompromised patients are specifically at risk, especially those with cystic fibrosis (CF). Novel metal complexes incorporating 1,10-phenanthroline (phen) ligands have previously demonstrated antibacterial and anti-biofilm effects against resistant P. aeruginosa from CF patients in vitro. Herein, we present the in vivo efficacy of {[Cu(3,6,9-tdda)(phen)2]·3H2O·EtOH}n (Cu-tdda-phen), {[Mn(3,6,9-tdda)(phen)2]·3H2O·EtOH}n (Mn-tdda-phen) and [Ag2(3,6,9-tdda)(phen)4]·EtOH (Ag-tdda-phen) (tddaH2 = 3,6,9-trioxaundecanedioic acid). Individual treatments of these metal-tdda-phen complexes and in combination with the established antibiotic gentamicin were evaluated in vivo in larvae of Galleria mellonella infected with clinical isolates and laboratory strains of P. aeruginosa. G. mellonella were able to tolerate all test complexes up to 10 µg/larva. In addition, the immune response was affected by stimulation of immune cells (hemocytes) and genes that encode for immune-related peptides, specifically transferrin and inducible metallo-proteinase inhibitor. The amalgamation of metal-tdda-phen complexes and gentamicin further intensified this response at lower concentrations, clearing a P. aeruginosa infection that were previously resistant to gentamicin alone. Therefore this work highlights the anti-pseudomonal capabilities of metal-tdda-phen complexes alone and combined with gentamicin in an in vivo model

Disarming Pseudomonas aeruginosa Virulence by the Inhibitory Action of 1,10-Phenanthroline-5,6-Dione- Based Compounds: Elastase B (LasB) as a Chemotherapeutic Target

negative pathogen Pseudomonas aeruginosa, and this enzyme orchestrates several physiopathological events during bacteria-host interplays. LasB is considered to be a potential target for the development of an innovative chemotherapeutic approach, especially against multidrug-resistant strains. Recently, our group showed that 1,10-phenanthroline-5,6-dione (phendione), [Ag(phendione)2]ClO4 (Ag-phendione) and [Cu(phendione)3](ClO4)2.4H2O (Cu-phendione) had anti-P. aeruginosa action against both planktonic- and biofilm-growing cells. In the present work, we have evaluated the effects of these compounds on the (i) interaction with the lasB active site using in silico approaches, (ii) lasB proteolytic activity by using a specific fluorogenic peptide substrate, (iii) lasB gene expression by real time-polymerase chain reaction, (iv) lasB protein secretion by immunoblotting, (v) ability to block the damages induced by lasB on a monolayer of lung epithelial cells, and (vi) survivability of Galleria mellonella larvae after being challenged with purified lasB and lasB-rich bacterial secretions. Molecular docking analyses revealed that phendione and its Ag+ and Cu2+ complexes were able to interact with the amino acids forming the active site of lasB, particularly Cu-phendione which exhibited the most favorable interaction energy parameters. Additionally, the test compounds were effective inhibitors of lasB activity, blocking the in vitro cleavage of the peptide substrate, aminobenzyl-Ala-Gly-Leu-Ala-p-nitrobenzylamide, with Cu- phendione having the best inhibitory action (Ki = 90 nM). Treating living bacteria with a sub-inhibitory concentration (1/2 × MIC value) of the test compounds caused a significant reduction in the expression of the lasB gene as well as its mature protein production/secretion. Further, Ag-phendione and Cu-phendione offered protective rg 1 August 2019 | Volume 10 | Article 1701 1,10-Phenanthroline-5,6-Dione-Based Compounds: As Anti-Virulence Drugs action for lung epithelial cells, reducing the A549 monolayer damage by approximately 32 and 42%, respectively. Interestingly, Cu-phendione mitigated the toxic effect of both purified lasB molecules and lasB-containing bacterial secretions in the in vivo model, increasing the survival time of G. mellonella larvae. Collectively, these data reinforce the concept of lasB being a veritable therapeutic target and phendione-based compounds (mainly Cu-phendione) being prospective anti-virulence drugs against P. aeruginosa