Echinocandins Localized to the Target-Harboring Cell Surface AreNot Degraded but Those Entering the Vacuole Are

Echinocandin antifungal drugs have a broadspectrum of activities and excellent safety profiles. These agentsnoncompetitively inhibit the formation of the major polysaccharidecomponent of the fungal cell wall, a reaction catalyzed by themembrane-bound beta-glucan synthase (GS) protein complex. Wehave developedfluorescent probes of three echinocandin drugs:caspofungin (CSF), anidulafungin (ANF), and rezafungin (RZF).Fluorescent echinocandins had the same spectrum of activities asthe parent echinocandins, supporting the fact that conjugation ofthe dye did not alter their mode of action. Of the threeechinocandins, ANF has the most potent in vitro activity.Investigation of the subcellular distribution of thefluorescentechinocandins in liveCandidayeast cells revealed that despite their high structural similarity, each of the drug probes had a uniquesubcellular distribution pattern. Fluorescent CSF, which is the least potent of the three echinocandins, accumulated inCandidavacuoles;fluorescent ANF localized in the extracellular environment and on the yeast cell surface where the target GS resides; andfluorescent RZF was partitioned between the surface and the vacuole over time. Recovery offluorescent CSF fromCandidacellsrevealed substantial degradation over time; functional vacuoles were necessary for this degradation. Under the same conditions,fluorescent ANF was not degraded. This study supports thetarget-oriented drug subcellular localizationprinciple. In the case ofechinocandins, localization to the cell surface can contribute to improved potency and accumulation in vacuoles induces degradationleading to drug deactivation.

Automated summary

Echinocandin antifungal drugs have broad-spectrum activities and excellent safety profiles by inhibiting the formation of major polysaccharides in the fungal cell wall. Fluorescent echinocandins, including caspofungin, anidulafungin, and rezafungin, maintain the same spectrum of activities as their non-fluorescent counterparts, with each drug probe showing a unique subcellular distribution pattern in live Candida yeast cells.