ANTIFUNGAL ASSESSMENTS, CHEMOGENOMIC AND TRANSCRIPTOMIC ANALYSES, AND STRUCTURE-ACTIVITY RELATIONSHIPS OF BIOACTIVE AURONE COMPOUNDS

Abstract

Candida spp. as commensal colonizers of mucocutaneous surfaces in humans are the major fungal cause of bloodstream infections, resulting in 50,000 deaths every year. Because of the paucity of fundamental antifungal treatments along with the recurrent emergence of resistant strains, the urgency for new antifungal agents with selective and novel targets necessitates the efforts of laboratory research. Complementary to such attempts for identification of novel anti-Candida agents, two synthetically aurones, SH1009 and SH9051, have shown significant inhibitory activities against Candida spp. The main goal of this research was to assess antifungal activity and mammalian cell cytotoxicity and comprehensively characterize the modes of action for aurones SH1009 and SH9051. Aurone SH1009 exhibited significant antifungal activity against Candida spp., including resistant isolates, with fungistatic pharmacodynamic properties. SH1009 treatment of a pooled genome-wide set of Saccharomyces cerevisiae deletion mutants demonstrated a set of sensitive and resistant growth responses in mutants encoding cell cycle-dependent organization of actin cytoskeleton. Accordingly, phenotypic studies revealed cell cycle arrest at the G1 phase in SH1009-treated Candida albicans along with abnormally interrupted actin dynamics and enlarged, unbudded cells, validating the chemical genetic interaction and suggesting a novel mode of action for aurone SH1009 as an antifungal. In vitro cytotoxicity assays using human cell lines showed selective toxicity of SH1009 toward fungal cells and less selectivity in SH9051-treated cells. In an attempt to increase antifungal activity by combining both aurones, antifungal synergy was detected as an indifferent interaction, suggesting different modes of action for the aurones. To interpret these differences, transcriptome changes in SH1009- and SH9051-treated C. albicans were analyzed, revealing common and unique pathways enriched consistently based on the chemical structure of each aurone. A reverse genetic approach coupled with structure-activity relationship analyses demonstrated that trehalose was uniquely responsible for SH1009 resistance. SH9051 uniquely stimulated sulfur amino acid catabolism, and the core chemical structure of both aurones commonly promoted intracellular oxidative stress. The results of these studies determined a selectively novel molecular target, for aurone SH1009 as a promising antifungal and revealed cellular effects for different functional groups of the aurone, paving the way for future development and investigation.