Fusarielin A

Using the OSMAC (One Strain MAny Compounds) approach, the fungal endophyte Fusarium tricinctum was cultivated on fruit and vegetable juice-supplemented solid rice media. This led to an up to 80-fold increase in the accumulation of the new natural product fusarielin J (1), as well as to the induction of two new natural products fusarielin K (2) and fusarielin L (3) and the known derivatives fusarielins A (4) and B (5). Compounds 2-5 were not detected when the fungus was grown on rice media lacking either fruit or vegetable juice. The highest increase in the accumulation of compound 1 was observed in the presence of apple and carrot juice, whereas the stimulating effect was weaker for banana juice. Compound 1 exhibited cytotoxicity against the human ovarian cancer cell line A2780, with an IC50 value of 12.5 μM.

The fusarielins are a group of metabolites found in several Aspergillus and Fusarium species that have been reported to have with weak antifungal, antibiotic and cytotoxic effects. This study identifies fusarielin A, F, G and H isolated from Fusarium as mycoestrogens. Mycoestrogens are compounds from fungi that bind to the estrogen receptors and induce an estrogenic response in targeted cells. All four tested fusarielins stimulate MCF-7 cell proliferation with fusarielin H as the most potent, able to stimulate cell proliferation 4-fold in a resazurin metabolism assay at 25μM. MDA-MB-231 cells without the estrogen receptor-α and MCF-10a cells without estrogen receptors were not stimulated by fusarielins. Furthermore, the stimulation was prevented in MCF-7 cells when fusarielins were incubated in the presence of the estrogen receptor antagonist fulvestrant. These observations suggest that fusarielins bind to the estrogen receptor and act as weak mycoestrogens.

Fusarielins constitute a relative unexplored group of secondary metabolites, which have been isolated mainly from unidentified Aspergillus and Fusarium strains. In the present study we show that the ability to produce fusarielins is restricted to a few Fusarium species. Among the 15 analyzed species fusarielins were identified only in extracts from Fusarium graminearum and Fusarium tricinctum. The influence of different carbon sources on fusarielin biosynthesis was examined and the results showed that disaccharides and dextrin in combination with arginine as sole nitrogen source increased fusarielin production. When arginine was replaced with nitrate the fusarielins were produced on a wider selection of carbon sources including all monosaccharides. Production of fusarielins in F. graminearum was also influenced by pH, cultivation time, temperature and fructose concentration with the optimal conditions being: pH6, 25°C, 26days and 60mg fructose/mL. Wheat spikes were inoculated with F. graminearum to determine whether fusarielins are produced in infected cereals and fusarielin H was detected in all samples ranging from 392 to 1865ng/g (mean: 989ng/g) indicating that fusarielins are produced during infection. The study shows that even though fusarielins are produced by a narrow list of Fusarium species, they potentially can be present in infected cereals.