Azole Drug Import into the Pathogenic Fungus Aspergillus fumigatus

The fungal pathogen Aspergillus fumigatus causes serious illness and often death when it invades tissues, especially in immuno-compromised individuals. The azole class of drugs is the most commonly prescribed treatment for many fungal infections and acts on the ergosterol biosynthesis pathway. One commonmechanism of acquired azole drug resistance in fungi is the preven-tion of drug accumulation to toxic levels in the cell. While drug efflux is a well-known resistance strategy, reduced azole import would be another strategy to maintain low intracellular azole levels. Recently, azole uptake in Candida albicans and other yeasts was analyzed using [3H]fluconazole. Defective drug import was suggested to be a potential mechanism of drug resistance in sev-eral pathogenic fungi, including Cryptococcus neoformans, Candida krusei, and Saccharomyces cerevisiae. We have adapted and developed an assay to measure azole accumulation in A. fumigatus using radioactively labeled azole drugs, based on previous work done with C. albicans. We used this assay to study the differences in azole uptake in A. fumigatus isolates under a variety of drug treatment conditions, with different morphologies and with a select mutant strain with deficiencies in the sterol uptake and biosynthesis pathway. We conclude that azole drugs are specifically selected and imported into the fungal cell by a pH- and ATP-independent facilitated diffusionmechanism, not by passive diffusion. This method of drug transport is likely to be conserved across most fungal species. The fungal pathogen Aspergillus fumigatus is one of the mostcommon andubiquitous environmentalmolds.Aspergillus in-fections represent a significant human health burden. Aspergillu