Fungicidal Potency and Mechanisms of θ-Defensins against Multidrug-Resistant Candida Species

Abstract

Systemic candidiasis is a growing health care concern that is becoming even more challenging due to the growing frequency of infections caused by multidrug-resistant (MDR) <i>Candida</i> species. Thus, there is an urgent need for new therapeutic approaches to candidiasis, including strategies bioinspired by insights into natural host defense against fungal pathogens. The antifungal properties of θ-defensins, macrocyclic peptides expressed in tissues of Old World monkeys, were investigated against a panel of drug-sensitive and drug-resistant clinical isolates of <i>Candida albicans</i> and non-<i>albicans Candida</i> species. Rhesus θ-defensin 1 (RTD-1), the prototype θ-defensin, was rapidly and potently fungicidal against drug-sensitive and MDR <i>C. albicans</i> strains. Fungal killing occurred by cell permeabilization that was temporally correlated with ATP release and intracellular accumulation of reactive oxygen species (ROS). Killing by RTD-1 was compared with that by histatin 5 (Hst 5), an extensively characterized anticandidal peptide expressed in human saliva. RTD-1 killed <i>C. albicans</i> much more rapidly and at a >200-fold lower concentration than that of Hst 5. Unlike Hst 5, the anticandidal activity of RTD-1 was independent of mitochondrial ATP production. Moreover, RTD-1 was completely resistant to <i>Candida</i> proteases for 2 h under conditions that rapidly and completely degraded Hst 5. MICs and minimum fungicidal concentrations (MFCs) of 14 natural θ-defensins isoforms against drug-resistant <i>C. albicans</i> isolates identified peptides that are more active than amphotericin B and/or caspofungin against fluconazole-resistant organisms, including MDR <i>Candida auris.</i> These results point to the potential of macrocyclic θ-defensins as structural templates for the design of antifungal therapeutics.