Mechanism of action of efinaconazole, a novel triazole antifungal agent

Abstract

The mechanism of action of efinaconazole, a new triazole antifungal, was investigated with Trichophyton mentagrophytes and Candida albicans. Efinaconazole dose-dependently decreased ergosterol production and accumulated 4,4-dimethylsterols and 4α-methylsterols at concentrations below its MICs. Efinaconazole induced morphological and ultrastructural changes in T. mentagrophytes hyphae that became more prominent with increasing drug concentrations. In conclusion, the primary mechanism of action of efinaconazole is blockage of ergosterol biosynthesis, presumably through sterol 14α-demethylase inhibition, leading to secondary degenerative changes.

Fig 1

Effect of efinaconazole on ergosterol biosynthesis in T. mentagrophytes and C. albicans. (A) Effect of efinaconazole on [¹⁴C]acetate incorporation into cell membrane lipids. Incorporation of radioactivity into each lipid component (●, 4-desmethylsterols [ergosterol]; □, 4α-methylsterols; △, 4,4-dimethylsterols [lanosterol]; ×, squalene) is expressed as a percentage of the total radioactivity in all four lipid components. (B) Effects of efinaconazole, itraconazole, and clotrimazole on ergosterol biosynthesis. Efinaconazole (●) was compared to itraconazole (○) or clotrimazole (△) in T. mentagrophytes or C. albicans, respectively. Ergosterol biosynthesis is expressed as a percentage of the radioactivity incorporated in the 4-desmethylsterol fraction of untreated control cultures. Each symbol represents the mean for duplicate cultures of T. mentagrophytes or data for a single culture of C. albicans.

Fig 2

Representative SEM and TEM images of T. mentagrophytes hyphae following 24 h of exposure to efinaconazole. Growth control (a), 0.001 μg/ml (b), 0.01 μg/ml (c), 0.1 μg/ml (d), 1 μg/ml (e), and 10 μg/ml (f) are shown. (A) Morphological changes included shortening of interseptal distance (b and c, arrows), globular swelling (b and c, arrowheads), nonuniform widths (d and e, double arrows), and flattening (d, e, and f, asterisks). S, septum. Bar, 1 μm. (B) Ultrastructural changes included thickening of the cell wall (b, c, and d, arrowheads), separation of the plasma membrane from the cell wall (c, d, e, and f, asterisks), accumulation of electron-dense granules in the space between the cell wall and the plasma membrane (d, e, and f, arrows), and discontinuity of the plasma membrane (d, e, and f, double arrows). CW, cell wall; PM, plasma membrane; N, nucleus; M, mitochondria. Bar, 200 nm.

Fig 3

Effect of efinaconazole and positive-control drugs on Pi leakage from T. mentagrophytes and C. albicans cells. Each bar represents the mean + SEM for triplicate cultures of T. mentagrophytes or data for a single culture of C. albicans.