Broad-spectrum antifungal activities and mechanism of drimane sesquiterpenoids

Eight drimane sesquiterpenoids including (-)-drimenol and (+)-albicanol were synthesized from (+)-sclareolide and evaluated for their antifungal activities. Three compounds, (-)-drimenol, (+)-albicanol, and (1R,2R,4aS,8aS)-2-hydroxy-2,5,5,8a-tetramethyl-decahydronaphthalene-1-carbaldehyde (4) showed strong activity against C. albicans. (-)-Drimenol, the strongest inhibitor of the three, (at concentrations of 8 – 64 μg/ml, causing 100% death of fungi), acts not only against C. albicans as a fungicidal manner, but also inhibits other fungi such as Aspergillus, Cryptococcus, Pneumocystis, Blastomyces, Fusarium, Rhizopus, Saksenaea and FLU resistant strains of C. albicans, C. glabrata, C. krusei, C. parapsilosis and C. auris. These observations suggest drimenol is a broad-spectrum antifungal agent. At high concentration (100 μg/ml), drimenol caused a rupture of the fungal cell wall/membrane. In a nematode model of C. albicans infection, drimenol rescued the worms from C. albicans-mediated death, indicating drimenol is tolerable and bioactive in a metazoan. Genome-wide fitness profiling assays of both S. cerevisiae (nonessential homozygous and essential heterozygous) and C. albicans (Tn-insertion mutants) collections revealed putative genes and pathways affected by drimenol. Using a C. albicans mutants spot assay, the Crk1 kinase associated gene products, Ret2, Cdc37, and novel putative targets orf19.759, orf19.1672, and orf19.4382 were revealed to be the potential targets of drimenol. Further, computational modeling results suggest possible modification of the structure of drimenol including the A ring for improving antifungal activity.