USE OF CILOFUNGIN AS DIRECT FLUORESCENT-PROBE FOR MONITORING ANTIFUNGAL DRUG-MEMBRANE INTERACTIONS

Cilofungin is an antifungal cyclopeptide which inhibits cell wall (1,3 )-beta-glucan biosynthesis in fungal organisms, and its action against Candida albicans (1,3)-beta-glucan synthase has been widely studied. Since glucan synthase inactivation is thought to partially result from perturbations of the membrane lipid environment, the interaction of c ilofungin with fungal membranes and phosphatidylcholine membrane vesic les was studied. Cilofungin, which contains two independent aromatic g roups, has an excitation maximum of 270 nm and an emission maximum of 317 nm in aqueous solution. Comparison of the fluorescence properties of cilofungin with those of the analogs pneumocandin B-0, N-acetyl-tyr osinamide, and 4-hydrosybenzamide indicated that the emission of cilof ungin largely derived from the p-octyloxybenzamide side chain. Microso mal membranes from Saccharomyces cerevisiae, C. albicans, and phosphat idylcholine membrane vesicles induced a blue shift in the cilofungin e mission spectrum and increased the cilofungin steady-state emission an isotropy, providing direct evidence for a cilofungin membrane interact ion. Cilofungin interacted more strongly with membranes of C. albicans than with those of S. cerevisiae, correlating with previous findings that C. albicans is far more susceptible than S. cerevisiae to the act ion of cilofungin. These findings support the hypothesis that drug-ind uced inhibition of the (1,3)-beta-glucan synthesis results from the pe rturbation of the membrane environment and the interaction with the gl ucan synthase complex combined. The study demonstrated ways in which t he fluorescence propel ties of drugs can be used to directly evaluate drug-membrane interactions and structure-activity relationships.