echinocandin-b and nikkomycin

A number of substances that directly or indirectly affect the cell walls of fungi have been identified. Those that actively interfere with the synthesis or degradation of polysaccharide components share the property of being produced by soil microbes as secondary metabolites. Compounds specifically interfering with chitin or beta-glucan synthesis have proven effective in studies of preclinical models of mycoses, though they appear to have a restricted spectrum of coverage. Semisynthetic derivatives of some of the natural products have offered improvements in activity, toxicology, or pharmacokinetic behavior. Compounds which act on the cell wall indirectly or by a secondary mechanism of action, such as the azoles, act against diverse fungi but are usually fungistatic in nature. Overall, these compounds are attractive candidates for further development.

Topics: Aminoglycosides; Amphotericin B; Animals; Anthracyclines; Anti-Bacterial Agents; Antibiotics, Antineoplastic; Antifungal Agents; Cell Wall; Chitin; Echinocandins; Fungal Proteins; Fungi; Glucans; Mice; Mycoses; Peptides; Peptides, Cyclic; Pyrimidine Nucleosides

The cell wall of budding yeast is a rigid structure composed of multiple components. To thoroughly understand its involvement in morphogenesis, we used the image analysis software CalMorph to quantitatively analyze cell morphology after treatment with drugs that inhibit different processes during cell wall synthesis. Cells treated with cell wall-affecting drugs exhibited broader necks and increased morphological variation. Tunicamycin, which inhibits the initial step of N-glycosylation of cell wall mannoproteins, induced morphologies similar to those of strains defective in α-mannosylation. The chitin synthase inhibitor nikkomycin Z induced morphological changes similar to those of mutants defective in chitin transglycosylase, possibly due to the critical role of chitin in anchoring the β-glucan network. To define the mode of action of echinocandin B, a 1,3-β-glucan synthase inhibitor, we compared the morphology it induced with mutants of Fks1 that contains the catalytic domain for 1,3-β-glucan synthesis. Echinocandin B exerted morphological effects similar to those observed in some fks1 mutants, with defects in cell polarity and reduced glucan synthesis activity, suggesting that echinocandin B affects not only 1,3-β-glucan synthesis, but also another functional domain. Thus our multivariate analyses reveal discrete functions of cell wall components and increase our understanding of the pharmacology of antifungal drugs.

Topics: Aminoglycosides; Antifungal Agents; Cell Shape; Cell Wall; Chitin Synthase; Echinocandins; Fungal Proteins; Morphogenesis; Mutation; Saccharomyces cerevisiae; Software; Tunicamycin

Echinocandins and nikkomycins are antibiotics that inhibit the synthesis of the essential cell wall polysaccharide polymers 1,3-beta-glucan and chitin, respectively. Some 40 echinocandin-resistant Saccharomyces cerevisiae mutants were isolated and assigned to five complementation groups. Four complementation groups contained mutants with 38 recessive mutations. The fifth complementation group comprised mutants with one dominant mutation, etg1-3 (strain MS10), and one semidominant mutation, etg1-4 (strain MS14). MS10 and MS14 are resistant to the semisynthetic pneumocandin B, L-733,560, and to aculeacin A but not to papulacandin. In addition, microsomal membranes of both mutant strains contain 1,3-beta-glucan synthase activity that is resistant to L-733,560 but not to papulacandin. Furthermore, MS14 is also supersensitive to nikkomycin Z. The echinocandin resistance and the nikkomycin Z supersensitivity of MS14 cosegregated in genetic crosses. The wild-type gene (designated ETG1 [C. Douglas, J. A. Marrinan, and M. B. Kurtz, J. Bacteriol. 176:5686-5696, 1994, and C. Douglas, F. Foor, J. A. Marrinan, N. Morin, J. B. Nielsen, A. Dahl, P. Mazur, W. Baginsky, W. Li, M. El-Sherbeini, J. A. Clemas, S. Mandala, B. R. Frommer, and M. B. Kurtz, Proc. Natl. Acad. Sci. USA, in press]) was isolated from a genomic library in the plasmid YCp50 by functional complementation of the nikkomycin Z supersensitivity phenotype. The cloned DNA also partially complements the echinocandin resistance phenotype, indicating that the two phenotypes are due to single mutations. The existence of a single mutation, in MS14, simultaneously affecting sensitivity to a glucan synthase inhibitor and a chitin synthase inhibitor implies a possible interaction between the two polymers at the cell surface.

Topics: Aminoglycosides; Anti-Bacterial Agents; Antifungal Agents; Drug Resistance, Microbial; Echinocandins; Fungal Proteins; Glucosyltransferases; Membrane Proteins; Mutation; Peptides; Peptides, Cyclic; Saccharomyces cerevisiae; Schizosaccharomyces pombe Proteins