Posaconazole Is a Potent Inhibitor of Sterol 14α-Demethylation in Yeasts and Molds

Abstract

Posaconazole (POS; SCH 56592) is a novel triazole that is active against a wide variety of fungi, including fluconazole-resistant Candida albicans isolates and fungi that are inherently less susceptible to approved azoles, such as Candida glabrata. In this study, we compared the effects of POS, itraconazole (ITZ), fluconazole (FLZ), and voriconazole (VOR) on sterol biosynthesis in strains of C. albicans (both azole-sensitive and azole-resistant strains), C. glabrata, Aspergillus fumigatus, and Aspergillus flavus. Following exposure to azoles, nonsaponifiable sterols were extracted and resolved by liquid chromatography and sterol identity was confirmed by mass spectroscopy. Ergosterol was the major sterol in all but one of the strains; C. glabrata strain C110 synthesized an unusual sterol in place of ergosterol. Exposure to POS led to a decrease in the total sterol content of all the strains tested. The decrease was accompanied by the accumulation of 14␣-methylated sterols, supporting the contention that POS inhibits the cytochrome P450 14␣-demethylase enzyme. The degree of sterol inhibition was dependent on both dose and the susceptibility of the strain tested. POS retained activity against C. albicans isolates with mutated forms of the 14␣-demethylase that rendered these strains resistant to FLZ, ITZ, and VOR. In addition, POS was a more potent inhibitor of sterol synthesis in A. fumigatus and A. flavus than either ITZ or VOR.Fungal infections are a significant cause of morbidity and mortality among immunocompromised patients. The mortality rate for bone marrow transplant patients infected with Aspergillus fumigatus is approaching 90% (7). Similarly, Candida species are the fourth most common nosocomial bloodstream pathogen in the Unites States and in pediatric patients have a crude mortality rate of 20% (21). The current antifungal armamentarium, amphotericin B (AMB), fluconazole (FLZ), and itraconazole (ITZ), and the newer agents, caspofungin and voriconazole (VOR), have not satisfactorily met therapeutic needs, particularly in the case of mold infections. Consequently, there is an urgent need to develop new antifungal drugs.Posaconazole (POS; SCH 56592) is a potent new triazole antifungal compound with broad-spectrum activity both in vitro and in vivo (1, 15). Although POS is fungistatic against yeasts, it is fungicidal against A. fumigatus (8). Prior work had determined that triazoles inhibit the lanosterol 14␣-demethylase enzyme, resulting in a block in synthesis of ergosterol, the major sterol of the fungal cell membrane (3). Ergosterol is required for both membrane integrity (14) and for the function of some membrane-associated proteins (20). In addition to its role in maintaining membrane integrity, trace amounts of ergosterol are also thought to be required for the cell to progress through the cell cycle (5).Previously, we demonstrated that POS inhibited ergosterol synthesis in an azole-susceptible Candida albicans isolate (4).Here we extend these studies to compare the effect of POS, FLZ, ITZ, and VOR...

Correlation between Microdilution, E-test, and Disk Diffusion Methods for Antifungal Susceptibility Testing of Posaconazole against Candida spp

“…The azoles are inhibitors of the sterol 14-alpha-demethylase enzyme, blocking the production of the ergosterol component of the fungal cell membrane. Posaconazole, a triazole agent currently in clinical trials, is a more potent inhibitor of this enzyme than itraconazole and voriconazole in Aspergillus species and retains activity against the mutated enzyme responsible for resistance to fluconazole, itraconazole, and voriconazole in Candida (11). It has shown activity superior to fluconazole and itraconazole against Candida spp.…”

Match-making for posaconazole through systems thinking

“…Posaconazole (Nofaxil) was developed by Schering-Plough and was approved by the US Food and Drug Administration (FDA) for the treatment of invasive fungal infection in humans in 2006 [12]. Similar to other triazoles, posaconazole is a potent inhibitor of the Cyp450-dependent lanosterol 14a-demethylase (Cyp51) in yeasts and molds [13]. Inhibition of Cyp51 blocks the synthesis of ergosterol, which is an essential component in the cell membrane of fungal pathogens.…”

Role of posaconazole in the treatment of oropharyngeal candidiasis

“…Posaconazole inhibits the synthesis of ergosterol (a sterol component of fungal cell membranes) by inhibition of the enzyme, lanosterol 14-alpha demethylase, with accumulation of methylated sterol precursors. 7 In contrast with other azole antifungals, posaconazole is not extensively metabolized by the CYP450 enzymes. 8 In vitro tests have shown posaconazole to be active against Candida species, Aspergillus species, Coccidioides species, Fusarium species, Histoplasma capsulatum, Zygomycetes, Phaeohyphomycetes, and other filamentous fungi.…”