Emestrin

This research aimed to investigate the anticancer properties of emestrin, a major constituent of Emericella nidulans ATCC 38163 through the induction of apoptosis in Huh-7 human hepatocellular carcinoma cells. In this study, this fungus was isolated from the fresh leaves of Ruprechtia salicifolia (Cham. & Schltdl.) C.A. Mey, and identified by morphology and 18S rDNA followed by large-scale fermentation in liquid biomalt broth medium. Epidithiodioxopiperazine derivative emestrin along with ten known metabolites were isolated and identified from the fungal extract. The cytotoxic assay revealed that emestrin had the strongest cytotoxicity against Huh-7 and A-549 cells with IC50 values of 4.89 and 6.3 μM, respectively. Using annexin V-FITC assay, treatment of Huh-7 cells with 4.89 µM for 24 h resulted in a significant increase in the percentage of early and late apoptosis (3.16% and 22.84%, respectively) compared to untreated cells. Additionally, Bax and bcl-2 protein levels were regulated, which induced apoptosis in treated cells. These results indicate that emestrin induces mitochondrial pathway to stimulate apoptosis and inhibits cell proliferation in hepatocellular carcinoma.

Four emestrin hybrid polymers, asperemestrins A-D (1-4, respectively), were isolated from the fungus Aspergillus nidulans. Asperemestrins A-C are the first examples of emestrin-sterigmatocystin heterodimers bearing a 7/5/6/6/5/5/6/6/6 nonacyclic system with a 2,5-diazabicyclo[2.2.2]octane-3,6-dione core, while asperemestrin D features an unprecedented 2,15-dithia-17,19-diazabicyclo[14.2.2]icosa-4,8-diene-12,18,20-trione core skeleton. Their structures were determined by extensive spectroscopic data, electronic circular dichroism calculations, and single-crystal X-ray diffraction. Asperemestrin B showed moderate cytotoxicity against cancer cell lines, including SU-DHL-2, HEPG2, and HL-60.

In the search for new antibiotics, several fungal endophytes were isolated from the medicinal plant Leontopodium nivale subsp. alpinum (Edelweiss). The extract from one of these fungi classified as Akanthomyces sp. displayed broad-spectrum antibiotic activity against gram-negative bacteria and fungi. Further investigation into the composition of this extract using bioactivity-guided fractionation, HRMS, and nuclear magnetic resonance revealed two new 4-hydroxy-2-pyridone alkaloids (1, 2) and emestrin (3), an epidithiodioxopiperazine not previously known to be produced by a member of Cordycipitaceae. Further testing of purified compounds 1 and 2 proved that they are devoid of antibiotic activity, and all the activities observed in the crude extract could be assigned to emestrin (3), whose configuration was confirmed by crystallographic data. This study demonstrates, for the first time, that endophytic fungi from Edelweiss can produce new compounds, prompting further investigation into them for drug discovery.