title: Defective sterol C5-6 desaturation and azole resistance: a new hypothesis for the mode of action of azole antifungals.
abstract: Two azole resistant isolates of Saccharomyces cerevisiae carried mutations allelic to erg 3 and were blocked to differing degrees at the C5-6 desaturation step of ergosterol biosynthesis. When treated with the sterol 14 alpha-demethylation inhibitor fluconazole the wild-type sensitive strain accumulated lanosterol and 14 alpha-methyl-erogosta-8,24(28)-dien-3 beta, 6 alpha-diol (14-methyl-3,6 diol). The stringent desaturase mutant, A2, accumulated 14 alpha-methyl-8,24(28)-dien-3 beta-ol (14-methyl fecosterol) and lanosterol as the major sterol components when treated with fluconazole. Resistant isolate A3 accumulated 14-methyl-3,6-diol, 14-methyl fecosterol, and lanosterol and was only partially blocked at sterol C5-6 desaturation. We conclude that functional sterol C5-6 desaturase is required for the synthesis of 14-methyl-3,6-diol under conditions of azole inhibition. We present a new hypothesis for the mode of action of azole antifungals based on the inability of 14-methyl-3,6-diol to support growth, and suggest that growth can occur through utilisation of 14-methyl fecosterol, produced by a combination of azole inhibition and defective sterol C5-6 desaturation.
authors.affiliation: University Department of Pharmacology and Therapeutics, Sheffield University, UK.
authors.forename: P F
authors.initials: PF
authors.lastname: Watson
authors.forename: M E
authors.initials: ME
authors.lastname: Rose
authors.forename: S W
authors.initials: SW
authors.lastname: Ellis
authors.forename: H
authors.initials: H
authors.lastname: England
authors.forename: S L
authors.initials: SL
authors.lastname: Kelly
mesh_terms: D000935:Antifungal Agents / Q000494:pharmacology*; D001393:Azoles / Q000494:pharmacology*; D004352:Drug Resistance, Microbial / Q000235:genetics; D015725:Fluconazole / Q000494:pharmacology*; D008401:Gas Chromatography-Mass Spectrometry; D009154:Mutation; D010088:Oxidoreductases / Q000235:genetics*; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000235:genetics*; D013261:Sterols / Q000378:metabolism*
chemical_list: D000935:Antifungal Agents; D001393:Azoles; D013261:Sterols; D015725:Fluconazole; D010088:Oxidoreductases; C039306:sterol delta-5 desaturase