Microbial Natural Product Drug Discovery Through Systematic Sampling of Diverse Texas Soils

Purpose: To proof a concept of discovering microbial natural products through systemic sampling of diverse Texas soils by constructing and screening a pilot library of secondary metabolites produced by Texas soil-derived microbes for cytotoxicity. Methods: Secondary metabolites were extracted from soil-derived microbial isolates using methanol and ethyl acetate. These metabolites ("crude extract") were preliminarily fractionated through reversed-phase flash chromatography and screened for cytotoxicity against MIA PaCa-2, SH-SY5Y, and COLO 829 using an ATP-luciferase assay. Following further activity-guided HPLC purification, isolated active compounds were identified through methods including TOF-MS, MS/MS, NMR, and X-ray crystallography. Results: Malformin, a bicyclic pentapeptide which has been shown to elicit potent anti-cancer effects was purified and helped to validate our methodology. Subsequently, two related compounds, aspergillin PZ and trichoderone B, exhibiting anti-cancer effects were purified from Aspergillus flavipes sp.. These two compounds were enrolled in the National Cancer Institute 60 human tumor cell line anticancer drug screen (NCI60) which showed similar cytotoxic profiles and low potency at 10 µM. Though a >25% reduction in growth was seen in UACC-257, HOP-92, A498, and SNB-75. Conclusions: While a previously unidentified compound has not yet been discovered through this pilot study, bioactive secondary metabolites have been re-discovered which not only validates our methodology but also provides opportunity to address gaps in scientific understanding of previously reported compounds. Theoretically, enlarging our library size should afford new and active natural products.