Protein kinase inhibitors and other cytotoxic metabolites from the fungal endophyte Stemphylium botryosum isolated from Chenopodium album

The endophytic fungus Stemphylium botryosum was isolated from leaves of the medicinal plant Chenopodium album collected in Egypt. Extracts of the fungus grown on rice exhibited considerable cytotoxicity when tested in vitro against L5178Y mouse lymphoma cells. Upon chemical investigation they afforded the macrocyclic lactones curvularin (1) and dehydrocurvularin (2), as well as altersolanol A (3), tetrahydroaltersolanol B (4), stemphyperylenol (5) and macrosporin (6). The structures of all isolated compounds were determined by 1D and 2D NMR spectroscopy and mass spectrometry as well as by comparison with published data. Compounds 1-3 exhibited considerable cytotoxicity against L5178Y cells with EC50 values of 16, 1.4 and 0.6 μM, respectively, whereas the remaining compounds showed only modest activity. All compounds were further tested for protein kinase inhibitory activity in an assay involving 24 different kinases. Compound 3 was the most potent inhibitor displaying EC50 values ranging between 1.9 and 29.4 μM toward individual kinases, followed by 6 (EC50 = 2.3 - 27.1 μM). Compounds 4 and 5 showed moderate activity, while 1 and 2 were inactive

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The hydroquinone-containing cytostatic compound avarol inhibits predominantly growth of those cell lines which have a low level of superoxide dismutase. The substrate of this enzyme, the superoxide anion, was found to be formed during the in vitro oxidation reaction of avarol to its semiquinone radical in the presence of oxygen. Under the same incubation conditions plasmid DNA (pBR322) was converted from the fully supercoiled circular form mainly to the nicked circular form, indicating that the compound causes primarily single-strand breaks. Using Friend erythroleukemia cells (FLC) it was found that avarol induces a dose-dependent DNA damage; the maximum number of DNA strand breaks was observed at 5 h after addition of the compound to the cells. Removal of avarol resulted in a rapid DNA rejoining with biphasic repair kinetics [first half-time, 8 min (90% of the breaks) and a second half-time, 40 min (10% of the breaks)]. When the degree of avarol-induced DNA damage in FLC was compared with the drug-caused inhibition of cell growth a close correlation was established. Avarol displayed no effect on dimethyl sulfoxide-induced erythrodifferentiation of FLC as determined by the benzidine reaction and by dot blot hybridization experiments. From incubation studies of FLC with [3H]avarol no hint was obtained for the formation of an adduct between DNA and the compound. The subcellular distribution of [3H]avarol was studied in liver cells after i.v. application of the compound. The predominant amount of the compound was present in the cytosolic fraction; little avarol was associated with plasma membranes, nuclei, and mitochondria. Using (a) oxidative phosphorylation and (b) oxygen uptake as parameters for mitochondrial function, no effect of the compound on the activity of this organelle was determined. These results suggest that avarol forms superoxide anions (and in consequence possibly also hydroxyl radicals) especially in those cells which have low levels of superoxide dismutase. Moreover, evidence is provided that the active oxygen species cause DNA damage resulting in the observed cytotoxic effect

Siliceous spicules in marine demosponges (example Suberites domuncula)

All metazoan animals comprise a body plan of different complexity. Since-especially based on molecular and cell biological data-it is well established that all metazoan phyla, including the Porifera (sponges), evolved from a common ancestor the search for common, basic principles of pattern formation (body plan) in all phyla began. Common to all metazoan body plans is the formation of at least one axis that runs from the apical to the basal region; examples for this type of organization are the Porifera and the Cnidaria (diploblastic animals). It seems conceivable that the basis for the formation of the Bauplan in sponges is the construction of their skeleton by spicules. In Demospongiae (we use the model species Suberites domuncula) and Hexactinellida, the spicules consist of silica. The formation of the spicules as the building blocks of the skeleton, starts with the expression of an enzyme which was termed silicatein. Spicule growth begins intracellularly around an axial filament composed of silicatein. When the first layer of silica is made, the spicules are extruded from the cells and completed extracellularly to reach their the final form and size. While the first steps Of spicule formation within the cells are becoming increasingly clear, it remains to be studied how the extracellularly present silicatein strings are formed. The understanding of especially this morphogenetic process will allow an insight into the construction of the amazingly diverse skeleton of the siliceous sponges animals which evolved between two periods of glaciations, the Sturtian glaciation (710-680 MYA) and the Varanger-Marinoan ice ages (605-585 MYA). Sponges are-as living fossils-witnesses of evolutionary trends which remained unique in the metazoan kingdom. (c) 2005 Elsevier Ltd. All rights reserved

A new tetrahydrofuran derivative from the endophytic fungus chaetomium sp isolated from otanthus maritimus

A hitherto unidentified endophytic strain of the genus Chaetomium, isolated from the medicinal plant Otanthus maritimus, yielded a new tetrahydrofuran derivative, aureonitolic acid (1), along with 5 known natural products, 2-6. The structure of 1 was determined by extensive spectroscopic analysis and comparison with reported data. Extracts of the fungus, grown either in liquid culture or on solid rice media, exhibited considerable cytotoxic activity when tested in vitro against L5178Y mouse lymphoma cells. Compounds 2 and 6 showed significant growth inhibition against L5178Y cells with EC50, values of 7.0 and 2.7 mu g/mL, respectively, whereas 1 was inactive