FR 179642

nidulans possess several chitin synthases; thus, the pool of UDP-N-acetylglucosamine produced in the first steps of chitin synthesis might have been utilised by different chitin synthases besides ChsB. As demonstrated by the work of Fujioka et al., several chitin synthase genes of A. nidulans were up-regulated upon cell wall damage induced by micafungin. Glucans are the more abundant polysaccharides in the cell wall. The main one, 1,3-b-glucan, forms long, poorly branched chains, covalently linked to chitin and other cell wall components. While the yeast Saccharomyces cerevisiae has two genes related to 1,3-b-glucan biosynthesis, A. nidulans has only one, fksA. The expression of this gene has been previously reported to increase upon treatment with cell wall damaging agents, e.g. micafungin.

Control and echinocandin surfaces exposed to reducing agent and washed with SDS at 70 1C were also characterized by multiple positive mass spectra (ToF-SIMS) for evidence of bound antifungal compounds. In this study principal component analysis (PCA) was used to extract information from the complex ToF-SIMS data and to aid in the data interpretation. Relationships between positive mass spectra for the control ALDpp surface and the surfaces of anidulafungin, micafungin and caspofungin derivatives are illustrated by scores plots shown in Fig. 4. The scores plots on PC1 and PC2 reveal that the positive mass spectra across the pairs ALDpp control-anidulafungin (trace A) and ALDpp control-micafungin (trace B) overlap. This reflects similar surface chemistries of ALDpp control and its modifications (exposed to echinocandins and washed). In contrast, the scores plot on PC1 and PC2 show the experimental points across the surfaces of ALDpp and its caspofungin derivative (trace C) from two well-separated clusters. This indicates the surfaces are chemically different. The interaction between the ALDpp surface and caspofungin after reductive amination is strong, reflecting its covalent nature. The spectra for individual samples form clusters with a very low internal scatter along PC1 - the PC that captures most of the data variance.

Despite the improvements brought by the allylamines, in order to further differentiate between mammalian and fungal cells, their distinct cell walls have been targeted by the echinocandins. This latest milestone in medical mycology provided us with caspofungin (CFG), micafungin (MFG), and anidulafungin (AFG), which were introduced in 2001, 2005, and 2006, respectively (Fig. 2). More specifically, these compounds target glucan synthesis, which is the most notable ab- erration between fungal and mammalian cells, by inhibiting the β-1,3-D-glucan synthase. The polymer β-glucan is an essential component of many fungal cell walls. As a result of this unique mechanism of action, the echinocandins addressed an important scientific challenge in medical mycology, which is selective toxicity against the eukaryotic fungal cell. Indeed, when comparing the rate of treatment discontinuation due to adverse effects, the aforementioned echinocandins were found to be more tolerable than AmB in all formulations, ITC, and VOR.

Caspofungin is the first approved semisynthetic echinocandin product followed by micafungin, and anidulafungin (Fig. 1). Though the mechanisms of action are similar, the spectrum of antifungal activity varies. For instance anidulafungin is effective against a wide range of azole or polyene resistant Candida sp and Aspergillus sp. Hence, these antifungal agents are truly life saving drugs. The frequency of echinocandin resistance remains low with Candida sp, as it facilitates escape through the formation of characteristic FKS hot-spot mutations. However, enchinocandin resistance has been observed in C. glabrata, thus this poses a serious clinical challenge in immunocompromised patients. Even though b-(1,3)-D-glucan synthase inhibitors are a significant alternative to ergosterol-binding antimycotic agents, poor oral bioavailabilty is their main limitation.