Small Molecule Inhibitors of the Candida albicans Budded-to-Hyphal Transition Act through Multiple Signaling Pathways

Abstract

The ability of the pathogenic yeast Candida albicans to interconvert between budded and hyphal growth states, herein termed the budded-to-hyphal transition (BHT), is important for C. albicans development and virulence. The BHT is under the control of multiple cell signaling pathways that respond to external stimuli, including nutrient availability, high temperature, and pH. Previous studies identified 21 small molecules that could inhibit the C. albicans BHT in response to carbon limitation in Spider media. However, the studies herein show that the BHT inhibitors had varying efficacies in other hyphal-inducing media, reflecting their varying abilities to block signaling pathways associated with the different media. Chemical epistasis analyses suggest that most, but not all, of the BHT inhibitors were acting through either the Efg1 or Cph1 signaling pathways. Notably, the BHT inhibitor clozapine, a FDA-approved drug used to treat atypical schizophrenia by inhibiting G-protein-coupled dopamine receptors in the brain, and several of its functional analogs were shown to act at the level of the Gpr1 G-protein-coupled receptor. These studies are the first step in determining the target and mechanism of action of these BHT inhibitors, which may have therapeutic anti-fungal utility in the future.

Chemical screening identifies filastatin, a small molecule inhibitor of Candida albicans adhesion, morphogenesis, and pathogenesis

“…4E) and mediated by a complex transcriptional network (8,24). In addition to nutrient-poor Spider media, mammalian serum also induces hyphae (25,26), and we observed that filastatin inhibited the response to both these stimuli (Fig. 3B).…”

“…4E). Cells constitutively overexpressing the G protein-coupled receptor Gpr1 become hyperfilamentous on solid Spider media by PKA stimulation (26,28), and we observed that filastatin blocked hyphal morphogenesis in these cells (Fig. 4A).…”

“…For example, the modified sugar GlcNac also stimulates hyphal morphogenesis but does so independently of the cAMP-PKA pathway; instead, it activates the transcription factor Cph1 (26). On testing morphogenesis driven by GlcNac-containing media or constitutive overexpression of Cph1, we found that filastatin also inhibits formation of hyphae in these cases (Fig.…”

“…To explore the mechanism of filastatin action, we tested whether it would alter hyphal induction in hyperfilamentous mutants. For example, hyphal induction by Spider media requires the cAMP-PKA pathway (23,26) (Fig. 4E).…”

Minocycline Inhibits <i>Candida albicans</i> Budded-to-Hyphal-Form Transition and Biofilm Formation

“…Inhibition of the bud-to-hypha transition: The spider medium, N-acetylglucosamine (GlcNAc) medium, and Lee's medium were used for hyphal induction (10,11). C. albicans cells (10 6 mL) were added to each medium together with final concentrations 10 μg mL of each test compound, in 96-well plates.…”