Exploiting Diverse Chemical Collections to Uncover Compounds with Novel Activity Against Human Fungal Pathogens

Fungal pathogens are an underappreciated contributor to infectious disease related deaths, infecting billions and killing 1.6 million people annually. The rise in drug resistance amongst pathogenic fungi paired with the limited arsenal of antifungals available is an imminent threat to our medical system. To address this, I screened two distinct compound libraries to identify novel strategies to expand the antifungal armamentarium. The first collection, from Boston University, was screened to identify two types of compounds with activity against the highly drug-resistant pathogen Candida auris: those that were bioactive alone, and those that enhanced the efficacy of fluconazole, the most commonly administered systemic antifungal. Through these efforts I identified the rocaglates, a chemical class exhibiting single agent fungicidal activity. The rocaglates were found to inhibit translation initiation in C. auris but not in its close pathogenic relative Candida albicans. This species-specific activity was contingent on a single amino acid difference in the drug target, the translation initiation factor Tif1. Strikingly, rocaglate-mediated translation inhibition activated cell death in C. auris, but not in a rocaglate-sensitized C. albicans strain. From the fluconazole combination screen, I discovered a compound, subsequently termed azoffluxin, that enhanced fluconazole efficacy against C. auris through increasing its intracellular accumulation. This activity was through the inhibition of efflux pumps, indicating azoffluxin targets a key resistance mechanism. Furthermore, azoffluxin significantly reduced fungal burden alone and in combination with fluconazole in a mouse model of C. auris disseminated infection. The second chemical library screened, the RIKEN Natural Product Depository, was evaluated for antifungal activity against four major human fungal pathogens: C. auris, C. albicans, Candida glabrata, and Cryptococcus neoformans. One molecule, NPD6433, was prioritized for having broad-spectrum antifungal activity and minimal mammalian cytotoxicity. NPD6433 was determined to inhibit the enoyl reductase domain of the essential fungal enzyme fatty acid synthase 1, Fas1. Treatment with NPD6433 inhibited various virulence traits in multiple fungal species and rescued mammalian cell growth in a co-culture model with C. auris. Overall, this work identifies compounds with bioactivity against fungal pathogens, revealing important biology and paving the way for the critical development of new therapeutic strategies.Ph.D