Dissecting Mechanisms of Echinocandin Drug Resistance and Filamentation in the Fungal Pathogen Candida albicans

Invasive fungal infections have a devastating impact on human health worldwide, in part due to the limited repertoire of antifungal drugs available to treat these infections. Candida albicans is a primary cause of systemic mycoses with mortality rates of ~40%, even with current treatment options. Thus, the development of novel therapeutic strategies to combat fungal infections is of utmost importance. My research aims to explore novel therapeutic approaches to treat mycotic infections. This includes strategies to combat antifungal resistance and strategies to target a key C. albicans virulence trait, the ability to transition between yeast and filamentous states. To uncover novel therapies to combat resistance, I explored compounds that potentiate activity of the cell wall-targeting echinocandin antifungal drug caspofungin. A screen of 1,280 pharmacologically active compounds identified 19 that reduced caspofungin resistance. The most potent molecule was a chelator, DTPA, which potentiated echinocandin activity via chelation of magnesium, modulating signaling through the Hog1 stress response pathway. DTPA also induced C. albicans filamentation through zinc chelation, and the combination of caspofungin and DTPA had in vivo therapeutic utility in a murine model of candidiasis. Further, to explore genetic circuitry governing C. albicans morphogenesis, I characterized the role of the transcriptional regulator Mfg1 in mediating filamentous growth. Mfg1 is a core regulator of filamentation in the model yeast Saccharomyces cerevisiae and in C. albicans, and interacts with Flo8 and Mss11 to form a complex important for regulating morphogenesis. Unexpectedly, I identified divergent roles for these complex members in regulating C. albicans filamentation. Experimental evolution exploiting a novel selection strategy revealed triplication of chromosome 6, the genomic location of FLO8, as an adaptive mechanism enabling filamentation in the absence of MFG1. Collectively, this research uncovered new circuitry governing C. albicans drug resistance, evolution, and virulence, suggesting novel therapeutic strategies to treat fungal infections.