Repurposing an inhibitor of ribosomal biogenesis with broad anti-fungal activity

Nuo Sun,Yuhan Zhang,Richard Calderone,William Groutas,Kyle Killeen,Dongmei Li

doi:10.1038/s41598-017-17147-x

Abstract

The lack of new antifungal compounds with unique mechanisms of action is a concern for therapeutic management of patients. To identify inhibitors against human pathogenic fungi, we screened ~3000 compounds provided by the Developmental Therapeutics Program of NIH/NCI against a panel of pathogenic fungi including Candida species, Aspergillus fumigatus, and Cryptococcus neoformans. NSC319726 (a thiosemicarbazone) had broad antifungal activity in the range of 0.1–2.0 µg/ml and was also inhibitory to fluconazole-resistant isolates of Candida species. Synergy was demonstrated with NSC319726 and azoles, as well as caspofungin. The inhibitory concentration 50% (IC50) of NSC319726 was 35–800-fold higher than the Minimum Inhibitory Concentration 50% (MIC50 values), which indicates low compound toxicity to human cells in vitro. Transcriptome analysis of treated and untreated C. albicans using Gene Ontology (GO) revealed a large cluster of down regulated genes that encode translational proteins, especially those with ribosome biogenesis functions. As NSC319726 was first shown to have anti-cancer activity, its affects against human pathogenic fungi establish NSC319726 as a repurposed, off-patent compound that has potential antifungal activity. The minimal in vitro toxicity of lead optimized NSC319726 and its reasonable inhibitory activity against pathogens suggest advancing this compound to in vivo toxicity testing and protection studies against candidiasis.

Highlights

Invasive fungal infections remain common globally, and mortality caused by these pathogens now is equal to or exceeds drug resistant-Mycobacterium tuberculosis and malaria[1]
Three of the C. albicans strains (5674, TW17, and G5) as well as C. krusei were resistant to fluconazole (32–128 μg/mL) but susceptible to NSC319726 at concentrations less than 1 μg/mL
We found that NSC319726 caused an increase in reactive oxidant species (ROS) production in SC5314 C. albicans compared to untreated cells (Fig. 6A)

Summary

Introduction

Invasive fungal infections remain common globally, and mortality caused by these pathogens now is equal to or exceeds drug resistant-Mycobacterium tuberculosis and malaria[1]. Cryptococcus neoformans, as well as Aspergillus species have been added recently to the Federal Drug Administration (FDA) list of pathogens that constitute public health threats in the USA (https://www.federalregister.gov/documents/2014/06/05/2014-13023/ establishing-a-list-of-qualifying-pathogens-under-the-food-and-drug-administration-safety-and) This designation seeks to incentivize new drug discovery and fast-track compounds for therapeutic intervention. Many of the compounds from this library are known to have anti-cancer activity (or are active against other human diseases) and the mechanism of action of many has been suggested These compounds are referred to as repurposed, if additional activities (antifungal, for example) are identified[10,11]. A thiosemicarbazone compound, NSC319726, revealed broad antifungal activity against a panel of pathogenic fungi including Candida species, A. fumigatus, and C. neoformans in the range of 0.1–2.0 μg/ml. We suggest a mechanism of action (MOA) of NSC319726, which entails inhibition of ribosome biogenesis and the induction of oxidative stress

Methods

Results

Conclusion