Terconazole, a new broad spectrum antimycotic
triazole derivative, has been shown to have potent activity against Candida albicans in vitro and to be effective in animal models of yeast
infections. The present study explored a possible mechanism of anticandidal activity of
terconazole. The compound inhibited production of 14 alpha-desmethyl
sterols (e.g.
ergosterol) in C. albicans at concentrations (IC50 = 3-6 x 10(-9) M) lower than those inhibiting the in-vitro growth of the yeast. There was concomitant accumulation of methylated
sterols, (e.g.
lanosterol), which are considered detrimental to normal yeast cell membrane function.
Terconazole stimulated incorporation of 14C-acetate into
triglycerides, but had no other effect on C. albicans lipid metabolism. At concentrations greater than or equal to 10(-6)M
terconazole inhibited the oxidation of 14C-acetate into 14CO2 in C. albicans although the mechanism for this effect remains unclear. These data indicate that
terconazole is a specific inhibitor of yeast C-14 desmethyl
sterol production in C. albicans. Furthermore,
terconazole reduced
cytochrome P-450 levels in yeast microsomes at concentrations 10,000-fold below those at which it showed effects on rabbit liver microsomes. These data indicate a species specificity for the biochemical actions of
terconazole. The C-14 alpha-desmethylase system in yeast cell membranes is
cytochrome P-450 associated. Thus,
terconazole, was a potent inhibitor of C-14 desmethyl
sterol synthesis. This effect could contribute to the anticandidal activity of the
drug.