Evaluation of 8-Hydroxyquinoline Derivatives as Hits for Antifungal Drug Design.

Clioquinol is an 8-hydroxyquinoline derivative that was widely used from the 1950s to 1970s as an oral antiparasitic agent. In 1970, the oral forms were withdrawn from the market due to reports of toxicity, but topical formulations for antifungal treatment remained available. Thus, the purpose of this study was to evaluate the toxicity, anti-Candida and antidermatophyte activity and to determine pharmacodynamic characteristics of clioquinol and other 8-hydroxyquinoline derivatives (8-hydroxy-5-quinolinesulfonic acid and 8-hydroxy-7-iodo-5-quinolinesulfonic acid). Antifungal activity was tested by broth microdilution and the fungicidal or fungistatic effect was checked by a time-kill assay. Permeation and histopathological evaluation were performed in Franz diffusion cells with ear skin of pigs and examined under light microscopy. An HET-CAM test was used to determine the potential irritancy. The three compounds were active against all isolates showing anti-Candida and antidermatophyte activity, with MIC ranges of 0.031-2 μg/ml, 1-512 μg/ml, and 2-1024 μg/ml for clioquinol, 8-hydroxy-5-quinolinesulfonic acid, and 8-hydroxy-7-iodo-5-quinolinesulfonic acid, respectively. All compounds showed fungistatic effect for Candida, 8-hydroxy-5-quinolinesulfonic acid, and 8-hydroxy-7-iodo-5-quinolinesulfonic acid showed a fungicidal effect for M. canis and T. mentagrophytes, and clioquinol showed a fungicidal effect only for T. mentagrophytes. Furthermore, they presented a fungicidal effect depending on the time and concentration. The absence of lesions was observed in histopathological evaluation and no compound was irritating. Moreover, clioquinol and 8-hydroxy-5-quinolinesulfonic acid accumulated in the epithelial tissue, and 8-hydroxy-7-iodo-5-quinolinesulfonic acid had a high degree of permeation. In conclusion, 8-hydroxyquinoline derivatives showed antifungal activity and 8-hydroxy-5-quinolinesulfonic acid demonstrated the potential for antifungal drug design.