An Integrated Approach for Identification and Target Validation of Antifungal Compounds Active against Erg11p

Abstract

ABSTRACTSystemic life-threatening fungal infections represent a significant unmet medical need. Cell-based, phenotypic screening can be an effective means of discovering potential novel antifungal compounds, but it does not address target identification, normally required for compound optimization by medicinal chemistry. Here, we demonstrate a combination of screening, genetic, and biochemical approaches to identify and characterize novel antifungal compounds. We isolated a set of novel non-azole antifungal compounds for which no target or mechanism of action is known, using a screen for inhibition ofSaccharomyces cerevisiaeproliferation. Haploinsufficiency profiling of these compounds inS. cerevisiaesuggests that they target Erg11p, a cytochrome P450 family member, which is the target of azoles. Consistent with this, metabolic profiling inS. cerevisiaerevealed a buildup of the metabolic intermediates prior to Erg11p activity, following compound treatment. Further, human cytochrome P450 is also inhibited inin vitroassays by these compounds. We modeled the Erg11p protein based on the human CYP51 crystal structure, andin silicodocking of these compounds suggests that they interact with the heme center in a manner similar to that of azoles. Consistent with these docking observations,Candidastrains carrying azole-resistant alleles ofERG11are also resistant to the compounds in this study. Thus, we have identified non-azole Erg11p inhibitors, using a systematic approach for ligand and target characterization.