β-Lapachone enhances the antifungal activity of fluconazole against a Pdr5p-mediated resistant Saccharomyces cerevisiae strain.

OBJECTIVES:The aim of this study was to evaluate the ability of lapachones in disrupting the fungal multidrug resistance (MDR) phenotype, using a model of study which an azole-resistant Saccharomyces cerevisiae mutant strain that overexpresses the ATP-binding cassette (ABC) transporter Pdr5p. METHODS:The evaluation of the antifungal activity of lapachones and their possible synergism with fluconazole against the mutant S. cerevisiae strain was performed through broth microdilution and spot assays. Reactive oxygen species (ROS) and efflux pump activity were assessed by fluorometry. ATPase activity was evaluated by the Fiske and Subbarow method. The effect of β-lapachone on PDR5 mRNA expression was assessed by RT-PCR. The release of hemoglobin was measured to evaluate the hemolytic activity of β-lapachone. RESULTS:α-nor-Lapachone and β-lapachone inhibited S. cerevisiae growth at 100 μg/ml. Only β-lapachone enhanced the antifungal activity of fluconazole, and this combined action was inhibited by ascorbic acid. β-Lapachone induced the production of ROS, inhibited Pdr5p-mediated efflux, and impaired Pdr5p ATPase activity. Also, β-lapachone neither affected the expression of PDR5 nor exerted hemolytic activity. CONCLUSIONS:Data obtained indicate that β-lapachone is able to inhibit the S. cerevisiae efflux pump Pdr5p. Since this transporter is homologous to fungal ABC transporters, further studies employing clinical isolates that overexpress these proteins will be conducted to evaluate the effect of β-lapachone on pathogenic fungi.