Discovery of a Novel Antifungal Agent in the Pathogen Box François L. Mayer, James W. Kronstad Michael Smith Laboratories, Department of Microbiology and Immunology, University of British Columbia, Vancouver, British Columbia, Canada ABSTRACT Human fungal pathogens cause over 2 million infections per year and are major drivers of morbidity and mortality. Cryptococcus neoformans and Candida albicans are two of the most common fungal pathogens of humans, together ac- counting for a staggering 1.4 million infections annually, with very high mortality rates. Patients with dysfunctional immune systems, such as individuals with HIV/ AIDS, are particularly susceptible to fungal infections. Unfortunately, relatively few antifungal drugs are currently available and fungi frequently develop resistance, fur- ther complicating treatment approaches. In this study, we screened the Pathogen Box chemical library (Medicines for Malaria Venture, Switzerland) in an effort to iden- tify novel antifungal compounds. This approach led to the discovery of a novel, highly potent antifungal agent with activity against both C. neoformans and C. albi- cans. Our initial study of the mechanism of action suggested that this novel com- pound prevents fungal proliferation by targeting the ability of C. neoformans to withstand stress at the plasma membrane and cell wall. Because this compound had previously been shown to have low toxicity for mammalian cells, we propose that it represents an attractive lead compound for further antifungal drug development. IMPORTANCE Cryptococcus neoformans and Candida albicans are two major human fungal pathogens and together account for over 1.4 million infections annually, with very high mortality rates. These fungi often infect immunocompromised individuals, such as HIV/AIDS patients. In an effort to identify novel drugs with antifungal activ- ity, we have screened the Pathogen Box for compounds with anticryptococcal and anticandidal activities. This approach led to the discovery of a promising lead com- pound (MMV688271) with strong antifungal potency under nutrient-limited condi- tions. KEYWORDS antifungal drug, Candida albicans, Cryptococcus gattii, Cryptococcus neoformans, Pathogen Box F ungal pathogens have recently been estimated to contribute to as many human deaths as malaria or tuberculosis (1, 2). Cryptococcus neoformans and Candida al- bicans are two of the major human fungal pathogens, together accounting for over 1.4 million infections annually. Mortality rates vary between 20 and 75% but are generally very high (2). C. neoformans alone, for example, is estimated to cause over 600,000 deaths per year (3). Usually, a weakened immune system predisposes people to fungal diseases. Indeed, HIV/AIDS patients, individuals with severe burns, patients undergoing chemotherapy, and neonates are particularly at risk of such infections (2). C. neoformans is naturally found in the environment on trees, in soil, and in bird droppings (4). In general, the fungus establishes an initial pulmonary infection upon inhalation of spores or desiccated yeast cells, with subsequent dissemination to the brain to cause meningoencephalitis (5). C. neoformans usually does not infect immu- nocompetent individuals; however, a related species, Cryptococcus gattii, recently Received 9 March 2017 Accepted 20 March 2017 Published 12 April 2017 Citation Mayer FL, Kronstad JW. 2017. Discovery of a novel antifungal agent in the Pathogen Box. mSphere 2:e00120-17. https:// doi.org/10.1128/mSphere.00120-17. Editor Aaron P. Mitchell, Carnegie Mellon University Copyright © 2017 Mayer and Kronstad. This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International license. Address correspondence to James W. Kronstad, kronstad@msl.ubc.ca. RESEARCH ARTICLE Therapeutics and Prevention crossm March/April 2017 Volume 2 Issue 2 e00120-17 msphere.asm.org 1