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

Marcela Q Granato; Thaís P Mello; Renata S Nascimento; Marcos D Pereira; Thabatta L S A Rosa; Maria C V Pessolani; Malachy McCann; Michael Devereux; Marta H Branquinha; André L S Santos; Lucimar F Kneipp

doi:10.3389/fmicb.2021.641258

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

Front Microbiol. 2021 Apr 27:12:641258. doi: 10.3389/fmicb.2021.641258. eCollection 2021.

Affiliations

¹ Laboratório de Taxonomia, Bioquímica e Bioprospecção de Fungos (LTBBF), Instituto Oswaldo Cruz (IOC), Fundação Oswaldo Cruz (FIOCRUZ), Rio de Janeiro, Brazil.
² Laboratório de Estudos Avançados de Microrganismos Emergentes e Resistentes (LEAMER), Instituto de Microbiologia Paulo de Góes, Universidade Federal do Rio de Janeiro (UFRJ), Rio de Janeiro, Brazil.
³ Laboratório de Citotoxicidade e Genotoxicidade (LaCiGen), Instituto de Química, UFRJ, Rio de Janeiro, Brazil.
⁴ Laboratório de Microbiologia Celular, IOC/FIOCRUZ, Rio de Janeiro, Brazil.
⁵ Department of Chemistry, Maynooth University, National University of Ireland, Maynooth, Ireland.
⁶ Center for Biomimetic and Therapeutic Research, Focas Research Institute, Technological University Dublin, Dublin, Ireland.

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.

Keywords: 1,10-phenanthroline-5,6-dione; antifungal activity; cellular interaction; chromoblastomycosis; dematiaceous fungi.