Novel Zinc-Attenuating Compounds as Potent Broad-Spectrum Antifungal Agents with In Vitro and In Vivo Efficacy

Abstract

An increase in the incidence of rare but hard-to-treat invasive fungal pathogens as well as resistance to the currently available antifungal drugs calls for new broad-spectrum antifungals with a novel mechanism of action. Here we report the identification and characterization of two novel zinc-attenuating compounds, ZAC307 and ZAC989, which exhibit broad-spectrum in vitro antifungal activity and in vivo efficacy in a fungal kidney burden candidiasis model. The compounds were identified serendipitously as part of a drug discovery process aimed at finding novel inhibitors of the fungal plasma membrane proton ATPase Pma1. Based on their structure, we hypothesized that they might act as zinc chelators. Indeed, both fluorescence-based affinity determination and potentiometric assays revealed these compounds, subsequently termed zinc-attenuating compounds (ZACs), to have strong affinity for zinc, and their growth inhibitory effects on Candida albicans and Aspergillus fumigatus could be inactivated by the addition of exogenous zinc to fungal growth media. We determined the ZACs to be fungistatic, with a low propensity for resistance development. Gene expression analysis suggested that the ZACs interfere negatively with the expression of genes encoding the major components of the A. fumigatus zinc uptake system, thus supporting perturbance of zinc homeostasis as the likely mode of action. With demonstrated in vitro and in vivo antifungal activity, low propensity for resistance development, and a novel mode of action, the ZACs represent a promising new class of antifungal compounds, and their advancement in a drug development program is therefore warranted.

Zinc and Iron Homeostasis: Target-Based Drug Screening as New Route for Antifungal Drug Development

“…Several studies on adjunct treatment of metal chelators, such as EDTA, dibromoquinoline, or DIBI, and azoles showed markedly reduced susceptibility of fungi toward these combinations in comparison with antifungal monotherapy (Casalinuovo et al, 2017; Mohammad et al, 2018; Savage et al, 2018). While most of these studies focus on iron metabolism, targeting zinc homeostasis has also been proven to be a successful strategy (Cohrt et al, 2018).…”

Aspergillus fumigatus and Aspergillosis in 2019

“…Importantly, the ZafA-and ZrfC-like proteins are distributed exclusively among fungi, and no orthologs have been found in mammals. Consequently, the ZafA and ZrfC proteins can be considered specific fungal targets, since zinc-chelating compounds can inhibit fungal growth both in vitro and in vivo (372)(373)(374).…”

Promising Antifungal Targets Against Candida albicans Based on Ion Homeostasis

“…In recent years, the importance of zinc homeostasis has been highlighted due to its vital contribution to fungal pathogenesis and virulence. Researchers identified two novel zinc-attenuating compounds (ZACs) ZAC307 and ZAC989, which showed antifungal activity against C. albicans by chelating zinc in vitro (O'Hanlon Cohrt et al, 2018 ). ZAC307 and ZAC989 have a high-binding affinity for zinc.…”