Antifungal activity, mode of action variability, and subcellular distribution of coumarin-based antifungal azoles

Azole antifungals inhibit the biosynthesis of ergosterol, the fungal equivalent of cholesterol in mammalian cells. Here we report an investigation of the activity of coumarin-substituted azole antifungals. Screening against a panel of Candida pathogens, including a mutant lacking CYP51, the target of antifungal azoles, revealed that this enzyme is inhibited by triazole-based antifungals, whereas imidazole-based derivatives have more than one mode of action. The imidazole-bearing antifungals more effectively reduced trailing growth associated with persistence and/or recurrence of fungal infections than triazole-based derivatives. The imidazole derivatives were more toxic to mammalian cells and more potently inhibited the activity of CYP3A4, which is one of the main causes of azole toxicity. Using live cell imaging, we showed that regardless of the type of azole ring fluorescent 7-diethylaminocoumarin-based azoles localized to the endoplasmic reticulum, the organelle that harbors CYP51. This study suggests that the coumarin is a promising scaffold for development of novel azole-based antifungals that effectively localize to the fungal cell endoplasmic reticulum.