Cilofungin

Echinocandins are an interesting group of antifungals that were originally discovered in the early 1970s. They are a group of lipopeptides produced by fungi which consists of a large number of structural analogs of echinocandin B, the first echinocandin to be structurally characterized. All clinically used echinocandins are produced semi-synthetically. The cyclic peptide nuclear core is retained while the acyl chain is replaced to minimize toxicity and expand their spectrum of activity. It was not until 2002 with the introduction of caspofungin (Cancidas) into the clinics that their true worth was realized. Since the introduction of caspofungin, two other echinocandins, micafungin (Mycamine) and anidulafungin (Eraxis) have been introduced. They all function by inhibiting an enzyme unique for fungal cell wall production, which presumably accounts for their minimal side-effects. In this review, topics pertaining to their production, structural diversity, and use in the clinic along with the recent patents are discussed.

(1,3)β- d -Glucan synthase (EC 2.4.1.34. UDP-glucose: 1,3-β- d -glucan 3-β-glucosyltransferase) uses UDP-glucose as substrate and catalyzes the polymerization of glucose ([1,3]-β-linkages) to form the major carbohydrate component of the fungal cell wall. We have optimized in vitro assay conditions for (1,3)β-glucan synthase activity from Cryptococcus neoformans . Cells lysed in 50 mM Tris, pH 7.75, containing 20% glycerol, 2 mM NaF, 1 mM dithiothreitol, 0.1 mM phenylmethylsulfonyl fluoride, 5 mM MgCl 2 , 0.1% protease and phosphatase inhibitor cocktails, and 60 μM GTPγS produced maximum specific activity in vitro. We tested in vitro C. neoformans (1,3)β-glucan synthase activity against the (1,3)β-glucan synthase inhibitors, caspofungin and cilofungin, and have determined that (1,3)β-glucan synthase activity is very sensitive (apparent K i of 0.17 ± 0.02 μM and 22 ± 5.7 μM, respectively) to these echinocandins. Taken together with high MICs for C. neoformans (caspofungin MIC, 16 μg/ml; cilofungin MIC, 64 μg/ml), our results indicate that C. neoformans is resistant to caspofungin and cilofungin by a mechanism(s) unrelated to (1,3)β-glucan synthase resistance.