Inhibition of Ras1-MAPK pathways for hypha formation by novel drug candidates in Candida albicans

The opportunistic human fungal pathogen Candida albicans has morphogenesis as a virulence factor. The morphogenesis of C. albicans is closely related to pathogenicity (1). Ras1 in C. albicans is an important switch in the MAPK pathway for morphogenesis (2, 3). The MAPK pathway is important for the virulence, such as cell growth, morphogenesis, and biofilm formation (4, 5). Ume6 is a well-known transcriptional factor for hyphal-specific genes (6). Despite numerous studies, as a recent issue, it is necessary to develop a new drug that uses a different pathway mechanism to inhibit resistant C. albicans strains caused by chronic prescription of azole or echinocandin drugs, which are mainly used. Here, we show that the small carbazole derivatives attenuated the pathogenicity of C. albicans through inhibition of the Ras1/MAPK pathway. We found that the small molecules inhibit morphogenesis through repressing protein and RNA levels in Ras/MAPK related genes including UME6 and NRG1. Furthermore, we found the antifungal effect of the small molecules in vivo using a candidiasis murine model. We anticipate our findings are that the small molecules are the promising compounds for the development of new antifungal agents for the treatment of systemic candidiasis and possibly for other fungal diseases. Author summaryThe infection by the opportunistic human fungal pathogen Candida albicans occurs mainly in immunocompetent and immunocompromised humans, such as AIDS patients, immunosuppressant-treated organ transplant patients, and recent COVID-19 patients. Morphogenesis which the ability to switch between yeast and hyphal growth forms is one of the representative virulence factors of C. albicans. Here, we describe novel small molecules that show antifungal effects such as the inhibition of the morphogenesis and the biofilm formation, and maintenance of biofilm. Moreover, we found that these small molecules had antifungal activity in mouse experiments, and confirmed that they were also effective in drug-resistant C. albicans strains. Studies of some small molecules with structures similar to ours have already been reported to exhibit growth inhibitory activity against bacteria and Candida species. However, the mechanism of action of these molecules has not been elucidated. In this study, we demonstrated, for the first time, the mechanism by which these two small molecules inhibit C. albicans pathogenicity through inhibition of specific pathways. Our study, through the research of the mechanism of action of novel small molecules, provides new insights into the development of drug candidates not only for wild-type C. albicans, but also for strains resistant to existing drugs.