Echinocandins have an alternative mode of action on biomimetic membranes that is not directly related to the functioning of (1,3) beta-glucan synthase

Echinocandins, one of five main classes of antifungal agents, are FDA-approved drugs for therapy of invasive candidiasis and aspergillosis. The exact mechanisms of echinocandins action are still under debates, in particular the role of target cell membranes in their function. In present study we analyzed the molecular mechanisms of action of echinocandins (anidulafungin, caspofungin, and micafungin) on the sterol-enriched lipid bilayers mimicking fungal and mammalian membranes. Calcein release assay and molecular dynamics simulations demonstrated the relation of the membrane permeability and echinocandin type. Moreover, we have shown for the first time the ability of echinocandins to form ion-permeable pores in sterol-containing membranes. Differential scanning microcalorimetry of the gel-to-liquid-crystalline lipid phase transition and confocal fluorescent microscopy of lipid domains revealed the ability of echinocandins to enhance phase segregation in membrane. Thus, echinocandins might affect the (1,3) beta-glucan synthase functioning by alteration in lipid microenvironment of target protein and cellular membrane permeability via formation of ion-selective leakage channels. We also found that small natural molecule, phloretin, potentiated the pore-forming activity of micafungin in the ergosterol-containing bilayers and significantly reduced the minimum inhibitory concentration of micafungin against fluconazole-resistant Candida albicans, C. tropicalis, and C.krusei.