Cytotoxic Peptaibols from Trichoderma guizhouense, a Fungus Isolated from an Urban Soil Sample

Soil sustains human life by nourishing crops, storing food sources, and housing microbes, which may affect the nutrition and biosynthesis of secondary metabolites, some of which are used as drugs. To identify lead compounds for a new class of drugs, we collected soil-derived fungal strains from various environments, including urban areas. As various human pathogens are assumed to influence the biosynthetic pathways of metabolites in soil fungi, leading to the production of novel scaffolds, we focused our work on densely populated urban areas and tourist attractions. A soil-derived fungal extract library was screened against MDA-MB-231 cells to derive their cytotoxic activity. Notably, 10 μg/mL of the extract of Trichoderma guizhouense (DS9-1) was found to exhibit an inhibitory effect of 71%. Fractionation, isolation, and structure elucidation efforts led to the identification of nine new peptaibols, trichoguizaibols A-I (1-9), comprising 14 amino acid residues (14-AA peptaibols), and three new peptaibols, trichoguizaibols J-L (10-12), comprising 18 amino acid residues (18-AA peptaibols). The chemical structures of 1-12 were determined based on their 1D and 2D NMR spectra, HRESIMS, electronic circular dichroism data, and results of the advanced Marfey's method. The 18-AA peptaibols were found to exhibit cytotoxicity against MDA-MB-231, SK-Hep1, SKOV3, DU145, and HCT116 cells greater than that of the 14-AA peptaibols. Among these compounds, 10-12 exhibited potent sub-micromolar IC₅₀ values. These results are expected to shed light on a new direction for developing novel scaffolds as anticancer agents.