Oxygen accessibility and iron levels are critical factors for the antifungal action of ciclopirox against Candida albicans

Objectives: Ciclopirox is a topical antifungal agent of the hydroxypyridone class whose mode of action is poorly understood. In order to elucidate the mechanism of action of ciclopirox, we analysed the growth, cellular integrity, biochemical properties, viability and transcriptional profile of the polymorphic yeast Candida albicans following exposure to this antifungal agent. Methods: Multiple biochemical assays served to identify factors that were critical for antifungal activity and to identify proteins whose activities changed in drug-exposed cells. Genome-wide transcriptional profiling was used to identify genes that were up-regulated in response to the cellular effects of the drug. Results: Ciclopirox inhibited growth of C. albicans yeast and hyphal cells in a dose-dependent manner. This effect was reduced (i) by the addition of iron ions or the metabolic inhibitor 2-deoxy-D-glucose to growth media, (ii) in media that lacked glucose, and (iii) for cells that were pre-incubated with hydrogen peroxide or menadione [which caused induction of proteins involved in detoxification of reactive oxygen species (ROS)]. In contrast, cells pre-cultured under poor oxygen conditions (which had decreased activity of proteins involved in ROS detoxification) were more susceptible to ciclopirox. Treatment with ciclopirox did not directly cause cell membrane damage and did not change intracellular levels of ATP. Finally, the transcriptional profiling pattern of drug-treated cells strongly resembled iron-limited conditions. Conclusions: These data indicate that metabolic activity, oxygen accessibility and iron levels are critical parameters in the mode of action of ciclopirox olamine.