Barwatt, J.W.

Abstract INTRODUCTION Candida auris has emerged as a global pathogenic yeast that disproportionately affects patients in healthcare settings. Infection ranges from localized skin infections to severe bloodstream infections. Multidrug resistance, hardiness on environmental surfaces, and the ability to persist as a colonizer in both sick and healthy patients enables it to spread rapidly in healthcare settings leading to significant morbidity and mortality. Multidrug resistance has led to limited effective therapies and necessitates the need for novel therapeutic options. Here we evaluate the efficacy of ISFP10, an antifungal compound with a novel mechanism of action, against C. auris. ISFP10 inhibits fungal phosphoglucomutase (PGM), an enzyme required for production of substrates for fungal cell wall synthesis (Figure 1). METHODSMIC Testing The compound ISFP10 was submitted to the National Institute of Allergy and Infectious Diseases Therapeutic Development Services for half-maximal and maximal inhibitory concentration (IC50/IC100) testing. C. auris isolates were tested using typical drug-dilution methods. Saccharomyces cerevisiae – C. auris PGM Growth Curve Testing This proof of mechanism assay was instituted to isolate PGM in Saccharomyces for growth curve testing. The Candida auris PGM was cloned into pYES2.1 downstream of an inducible galactose promoter. This plasmid was transformed into S. cerevisiae. C. auris PGM plasmid-containing S. cerevisiae was incubated for 24 hours in 2% glucose minimal media. Using absorbance readings, the inoculum was normalized to 5x105 cells/mL in galactose-containing media. The inoculum was plated onto a 96-well plate in a drug-dilution scheme with ISFP10 at concentrations ranging from 200uM to 6.25uM along with DMSO control wells. Plates were incubated at 30° C for 72 hours in a spectrophotometer with absorbance readings every hour. Growth curves were plotted using GraphPad Prism software. RESULTS The half-maximal inhibitory concentrations (IC50) and maximal inhibitory concentrations (IC100) were consistently low across the three C. auris isolates. The IC50 ranged from 0.5 µg/mL to 1.0 µg/mL, while the IC100 was 1.0 µg/mL for each of the three isolates (Table 1). Growth curves demonstrated concentration-dependent inhibition of C. auris PGM plasmid-containing S. cerevisiae. Figure 2 shows full inhibition of fungal growth at 25µM with dose-dependent delayed growth at lower concentrations. CONCLUSIONS ISFP10 shows promise for inhibiting C. auris PGM in a dose-dependent pattern. It's high in vitro activity and novel mechanism of action necessitates further investigation as a potential therapeutic for C. auris.