Mycology
Fluvastatin potentiates the activity of caspofungin against Aspergillus fumigatus in vitro

Presented in part at the Interscience Conference on Antimicrobial Agents and Chemotherapy held in California (ICAAC, 2006), poster M304, board 491.
https://doi.org/10.1016/j.diagmicrobio.2007.10.015Get rights and content

Abstract

Statins (anticholesterol drugs) inhibit HMG-CoA reductase, which is a key rate-limiting enzyme in the synthesis of sterols in fungi. We therefore investigated the in vitro inhibitory activity of various statins against Aspergillus fumigatus alone and in combination with antifungal drugs. Fresh conidial suspensions from 10 clinical isolates of A. fumigatus were obtained. The MIC and minimum fungicidal concentration (MFC) were determined by the Clinical and Laboratory Standards Institute M-38A protocol and the fungicidal activity by time–kill study. Fluvastatin (FST) showed good activity (MIC, 2 mg/L; MFC, 4 mg/L) against A. fumigatus; other statins had no activity (MIC ≥256 mg/L). FST enhanced the activity of caspofungin (CFG) against A. fumigatus; subinhibitory concentrations of FST in combination with CFG showed >99.9% killing of A. fumigatus conidia, whereas either drug alone showed poor activity at subinhibitory concentrations. FST potentiated the antifungal activity of CFG but displayed no specific interaction with voriconazole or amphotericin B.

Introduction

Invasive aspergillosis is a life-threatening infection in immunocompromised patients especially following hematopoietic stem cell transplantation. Despite the availability of novel antifungal agents, the mortality rate from invasive aspergillosis still remains high, and innovative therapeutic approaches are worthy of pursuit (Lin et al., 2001). Combination therapy is one approach that could be used to improve the efficacy of antimicrobial therapy for difficult-to-treat infections (Marr et al., 2004, Wheat, 2003, Johnson et al., 2004). Previous in vitro and in vivo studies have suggested good outcomes when echinocandins were used in combination with triazoles or polyene for therapy of invasive aspergillosis (Kirkpatrick et al., 2002, Petraitis et al., 2003, Aliff et al., 2003, Kontoyiannis et al., 2003).

The anticholesterol agents, statins are competitive inhibitors of 3-methylglutaryl-CoA-reductase (HMG-CoA-reductase), which is the rate-limiting enzyme in cholesterol synthesis and a precursor in the fungal ergosterol pathway (Bard and Downing, 1981, Ferreira et al., 2005, Abeles, 1990, Wilding et al., 2000, Vanden Bossche, 1990).

Although statins are primarily designed for the treatment of various forms of hyperlipidemia, they do possess antifungal, antiinflammatory, and apoptotic properties as well (Miida et al., 2004). Fluvastatin (FST) and other statins have been reported to exhibit synergistic antifungal interaction with azoles against Saccharomyces cerevisiae, Candida spp. (including azole-resistant species), and Cryptococcus neoformans (Chin et al., 1997). Therefore, we examined the in vitro efficacy of statins alone and in combination with either caspofungin (CFG), voriconazole (VCZ), or amphotericin B (AMB) against Aspergillus fumigatus.

Section snippets

Antifungal drugs

VCZ, AMB, and CFG were obtained from Pfizer Pharmaceuticals, New York, NY; Sigma Chemical, St. Louis, MO; and Merck, Rahway, NJ, respectively. VCZ and AMB were dissolved in dimethylsulfoxide to make a stock solution of 1 g/L, and then stored as 0.25-mL aliquots at −20 °C. CFG was dissolved in sterile double-distilled water to a concentration of 10 g/L and was stored as 0.25-mL aliquots at −70 °C. Frozen stocks of the antifungal agents were thawed at room temperature and used within 24 h. The

Results

Among the statins tested, FST had a MIC of 2 mg/L against A. fumigatus, whereas the other statins had no meaningful activity with MIC >256 mg/L. The MFC for FST was 4 mg/L. All strains were highly susceptible to VCZ and AMB with an MIC range of 0.15 to 0.25 and 0.25 to 2 mg/L, respectively (Espinel-Ingroff et al., 2005). The MIC value for CFG was high in the range of 32 to >256 mg/L. However, the MEC values for CFG were in the range of 0.015 to 0.25 mg/L, which was about 8- to 16-fold lower

Discussion

In our current study, enhanced fungicidal activity was observed with the combination of FST and CFG. The concentration of FST used in FICI and kill–curve studies was within the range (0.5–1 mg/L) of serum concentrations of FST reported for humans (Tse et al., 1992) Extrapolating from our results, it could be postulated that the enhanced fungicidal activity observed with the combination of FST and CFG may be secondary to the drugs targeting different sites on the fungal cell. It is also

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    Ethics committee approval is not applicable. None of the authors have any conflict of interest or financial disclosures.

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