Synthetic Derivatives of Ciclopirox are Effective Inhibitors of .

Opportunistic fungal infections caused by are a significant source of mortality in immunocompromised patients. They are challenging to treat because of a limited number of antifungal drugs, and novel and more effective anticryptococcal therapies are needed. Ciclopirox olamine, a -hydroxypyridone, has been in use as an approved therapeutic agent for the treatment of topical fungal infections for more than two decades. It is a fungicide, with broad activity across multiple fungal species. We synthesized 10 -hydroxypyridone derivatives to develop an initial structure-activity understanding relative to efficacy as a starting point for the development of systemic antifungals. We screened the derivatives for antifungal activity against and and counter-screened for specificity in and two species. Eight of the ten show inhibition at 1-3 μM concentration (0.17-0.42 μg per mL) in both species and in , but poor activity in the species. In , the -hydroxypyridones are fungicides, are not antagonistic with either fluconazole or amphotericin B, and are synergistic with multiple inhibitors of the mitochondrial electron transport chain. They appear to function primarily by chelating iron within the active site of iron-dependent enzymes. This preliminary structure-activity relationship points to the need for a lipophilic functional group at position six of the -hydroxypyridone ring and identifies positions four and six as sites where further substitution may be tolerated. These molecules provide a clear starting point for future optimization for efficacy and target identification.