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Small-Molecule Inhibitors of the Budded-to-Hyphal-Form Transition in the Pathogenic Yeast Candida albicans

ABSTRACT The pathogenic yeast Candida albicans can exist in multiple morphological states, including budded, pseudohyphal, and true hyphal forms. The ability to convert between the budded and hyphal forms, termed the budded-to-hyphal-form transition, is important for virulence and is regulated by multiple environmental and cellular signals. To identify inhibitors of this morphological transition, a microplate-based morphological assay was developed. With this assay, the known actin-inhibiting drugs latrunculin-A and jasplakinolide were shown to inhibit the transition in a dose-dependent and reversible manner. Five novel small molecules that reversibly inhibited the transition and hyphal elongation without affecting budded growth were identified. These molecules inhibited hyphal growth induced by Spider, Lee's, M199 pH 8, and 10% serum-containing media, with two molecules having a synergistic effect. The molecules also differentially affected the hyphal form-specific gene expression of HWP1 and endocytosis without disrupting the actin cytoskeleton or septin organization. Structural derivatives of one of the molecules were more effective inhibiters than the original molecule, while other derivatives had decreased efficacies. Several of the small molecules were able to reduce C. albicans-dependent damage to endothelial cells by inhibiting the budded-to-hyphal-form transition. These studies substantiated the effectiveness of the morphological assay and identified several novel molecules that, by virtue of their ability to inhibit the budded-to-hyphal-form transition, may be exploited as starting points for effective antifungal therapeutics in the future.