Antifungal Chemical Compounds Identified Using a C. elegans Pathogenicity Assay

Abstract

There is an urgent need for the development of new antifungal agents. A facile in vivo model that evaluates libraries of chemical compounds could solve some of the main obstacles in current antifungal discovery. We show that Candida albicans, as well as other Candida species, are ingested by Caenorhabditis elegans and establish a persistent lethal infection in the C. elegans intestinal track. Importantly, key components of Candida pathogenesis in mammals, such as filament formation, are also involved in nematode killing. We devised a Candida-mediated C. elegans assay that allows high-throughput in vivo screening of chemical libraries for antifungal activities, while synchronously screening against toxic compounds. The assay is performed in liquid media using standard 96-well plate technology and allows the study of C. albicans in non-planktonic form. A screen of 1,266 compounds with known pharmaceutical activities identified 15 (∼1.2%) that prolonged survival of C. albicans-infected nematodes and inhibited in vivo filamentation of C. albicans. Two compounds identified in the screen, caffeic acid phenethyl ester, a major active component of honeybee propolis, and the fluoroquinolone agent enoxacin exhibited antifungal activity in a murine model of candidiasis. The whole-animal C. elegans assay may help to study the molecular basis of C. albicans pathogenesis and identify antifungal compounds that most likely would not be identified by in vitro screens that target fungal growth. Compounds identified in the screen that affect the virulence of Candida in vivo can potentially be used as “probe compounds” and may have antifungal activity against other fungi.

Drug repurposing screens and synergistic drug‐combinations for infectious diseases

“…Enoxacin, a broad‐spectrum fluoroquinolone antibacterial agent approved for treatment of urinary tract infections and gonorrhoea, showed antifungal activity in both a Caenorhabditis elegans assay and a murine model of candidiasis (Breger et al , 2007). Delamanid, a drug for tuberculosis, exhibited activity against visceral leishmaniasis (Patterson et al , 2016).…”

Prokaryote–eukaryote interactions identified by using Caenorhabditis elegans

“…Importantly, microbial virulence determinants found to be relevant in pathogenesis toward C. elegans have also been found to be important in pathogenesis toward other hosts, including mammals (7). Recently, Candida albicans, the most common human fungal pathogen, with an attributable patient mortality reaching 40% in the face of invasive disease (8), was shown to cause a persistent lethal infection of the C. elegans intestinal tract (9). C. albicans infection leads to overwhelming intestinal proliferation and filamentation through the worm cuticle (9).…”

“…Recently, Candida albicans, the most common human fungal pathogen, with an attributable patient mortality reaching 40% in the face of invasive disease (8), was shown to cause a persistent lethal infection of the C. elegans intestinal tract (9). C. albicans infection leads to overwhelming intestinal proliferation and filamentation through the worm cuticle (9). The ability to form biofilm and undergo a morphological transition from yeast to a filamentous form, are critical virulence determinants of C. albicans toward mammals and C. elegans (9)(10)(11)(12)(13).…”

Use of Caenorhabditis elegans as a non-mammalian model system to study Candida virulence

“…An example of this penetrative filamentation is shown in Figure 1A. In some ways, this has similarity to its proliferation in the human gastrointestinal tract and gut translocation to cause invasive disease 15 . Pukkila-Worley, Peleg and colleagues have also shown the successful use of C. elegans in elucidating C. albicans dimorphism 7 .…”

“…Although it has been challenging to find an appropriate non-mammalian model to study the role of filamentation in the pathogenesis of C. albicans, Breger and colleagues developed the C. elegans model to perform in vivo studies of C. albicans pathogenesis and antifungal compounds 15 . Using a standard feeding assay, C. albicans were ingested by adult C. elegans worms, and then worms were transferred into liquid media.…”