Silver(I) and Copper(II) Complexes of 1,10-Phenanthroline-5,6-Dione Against Phialophora verrucosa: A Focus on the Interaction With Human Macrophages and Galleria mellonella Larvae

Abstract

Phialophora verrucosa is a dematiaceous fungus that causes mainly chromoblastomycosis, but also disseminated infections such as phaeohyphomycosis and mycetoma. These diseases are extremely hard to treat and often refractory to current antifungal therapies. In this work, we have evaluated the effect of 1,10-phenanthroline-5,6-dione (phendione) and its metal-based complexes, [Ag (phendione)2]ClO4 and [Cu(phendione)3](ClO4)2.4H2O, against P. verrucosa, focusing on (i) conidial viability when combined with amphotericin B (AmB); (ii) biofilm formation and disarticulation events; (iii) in vitro interaction with human macrophages; and (iv) in vivo infection of Galleria mellonella larvae. The combination of AmB with each of the test compounds promoted the additive inhibition of P. verrucosa growth, as judged by the checkerboard assay. During the biofilm formation process over polystyrene surface, sub-minimum inhibitory concentrations (MIC) of phendione and its silver(I) and copper(II) complexes were able to reduce biomass and extracellular matrix production. Moreover, a mature biofilm treated with high concentrations of the test compounds diminished biofilm viability in a concentration-dependent manner. Pre-treatment of conidial cells with the test compounds did not alter the percentage of infected THP-1 macrophages; however, [Ag(phendione)2]ClO4 caused a significant reduction in the number of intracellular fungal cells compared to the untreated system. In addition, the killing process was significantly enhanced by post-treatment of infected macrophages with the test compounds. P. verrucosa induced a typically cell density-dependent effect on G. mellonella larvae death after 7 days of infection. Interestingly, exposure to the silver(I) complex protected the larvae from P. verrucosa infection. Collectively, the results corroborate the promising therapeutic potential of phendione-based drugs against fungal infections, including those caused by P. verrucosa.

Metal Complexes as Antifungals? From a Crowd-Sourced Compound Library to the First In Vivo Experiments

“…The antifungal activity of metal compounds has been investigated even less than their antibacterial properties. ,,− Figure presents an overview of selected metal compounds with measured antifungal activity. Gasser and coworkers recently published an expansive review of the metal-based antifungals research field .…”

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

“…In addition, inorganic complexes with 1,10-phenanthroline (phen) ligands have had a resurgence as possible alternatives or additives to established antimicrobial therapeutics [ 13 , 14 , 15 ]. Transition metal complexes containing phen or its derivatives have demonstrated promising therapeutic capabilities against bacteria [ 16 , 17 ], fungi [ 18 , 19 , 20 ], parasites [ 21 , 22 , 23 ], and viruses [ 24 , 25 , 26 ].…”

Metal Complexes as Antifungals? – From a Crowd-Sourced Compound Library to First In Vivo Experiments

“…Over the last years a small number of reports have been published on several different antifungal metal complexes. 28,30,[34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51] Figure 1 presents an overview of selected metal compounds with measured antifungal activity. Gasser and coworkers recently published an expansive review of the metalbased antifungals research field.…”

“…Only a couple of studies so far have reported the in vivo evaluation of metal-based compounds. 28,30,35,51,[53][54] Gandra et al studied a series of phenanthroline complexes containing copper, manganese and silver. They demonstrated that these compounds showed no toxicity in a Galleria mellonella (moth larvae) in vivo model at 10 µg/larva.…”

“…41,53 Work by Granato et al showed that silver complexes with 1,10-phenanthroline-5,6dione were able to protect G. mellonella larvae from infection with Phialophora verrucose. 51 We recently published an antifungal study of a series of cobalt complexes that were initially discovered through the CO-ADD screening program. These compounds (e.g.…”