Treatment and Prevention of Systemic Candidiasis

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ABSTRACT Objective: We propose an innovative approach towards the discovery of new targets for anti-Candida drug development. Our approach is based on the concept that, although invasive C. albicans infections typically originate from commensal populations populating the host gut mucosa and skin, the critical transition from superficial to invasive infection is absent from the standard intravenous injection model of virulence. Therefore, we will develop improved animal models that better represent the natural history of disseminated candidiasis and to exploit the new systems to identify much-needed antifungal drug targets. Rationale: Candida albicans is a yeast component of the human microbiome that persists stably on mucocutaneous surfaces of the gut, skin, and genitourinary tract for the lifetime of the host. It is also a pathogen that causes highly morbid invasive infections in patients with certain risk factors, such as exposure to antibiotics, immunosuppressants, parenteral nutrition, or intravenous catheters. Candida spp. are the fourth most common cause of bloodstream infections in US hospitals, and mortality from candidemia remains high at ~40%. The most important therapeutic intervention in treatment of bloodstream candidiasis is the early initiation of antifungal antibiotics, such that mortality increases with each day that appropriate therapy is delayed. Unfortunately, our antifungal armamentarium is currently limited to only a handful of drugs. Moreover, the choice of drugs in debilitated patients is often further limited by significant toxicities (e.g. amphotericin, azoles), restricted tissue distribution (e.g. echinocandins), and complex drug-drug interactions (e.g. azoles). These issues and the emergence of drug resistance in selected clinical isolates have created an urgent need for additional, potent, safe antifungal drugs. Unlike many microbial pathogens, C. albicans infections typically originate from the commensal population, when yeasts on the skin or in the gut manage to penetrate through epithelial barriers. We propose that the specific pathogen functions required for this transition have been missed by current methods for investigating virulence. To test this hypothesis, we have initiated development of animal models of invasive candidiasis that include 1) the transition from localized skin infection (cellulitis) to bloodstream infection and 2) invasion of gut commensals through the gastrointestinal mucosa to surrounding organs. We propose to exploit these models to screen C. albicans mutant collections for functions required for disseminated disease. Our functional screens and focused follow up studies will identify novel targets for the prevention and treatment of invasive candidiasis.