Marine Actinomyceten als neue Quelle für die Entdeckung von Medikamenten in der Krebstherapie
Zusammenfassung der Projektergebnisse
The goal of this research project was to identify novel agents for the treatment of cancer, derived from marine actinomycetes isolated from ocean sediments. These plentiful, yet virtually unexplored, organisms have evolved to produce collections of chemically unique, bioactive metabolites. The central hypothesis is that groups of evolutionarilyrelated marine actinomycetes (phylotypes) produce related suites of molecules (chemotypes). Vice versa: obtain and explore new phylotypes in culture is an effective method for the discovery of new natural products. Genome sequencing on marine bacteria reveals a complex secondary metabolome even beyond the observed chemotypes. The second hypothesis is that stimulated activation of silent gene clusters will lead to production of so far not observed secondary metabolites. We could show, that a smart combination of bio-informatics with classical chemical screening leads to the isolation of new natural products. This approach could dramatically increase the efficiency in microbial natural products discovery. The central hypothesis could be substantiated during the last 26 months by extensively studies of strain extracts derived from over 60 marine actinomycetes of rare or undefined phylotypes. The Fenical laboratory has established a high-throughput screening of crude extracts and fractions thereof against a colon cancer cell line (HCT-116). Positive hits of known compounds were fast and easily identified with a liquid chromatography-mass spectrometry system (LC-MS) compared with the in-house database, which stores characteristic UV-absorption and mass pattern as well as commercially available microbial databases. Un-identified positive hits were subjected to extensive chromatographic purification to yield in pure substance. Structure elucidation was done with mass spectrometry (MS), nuclear magnetic resonance (NMR), X-ray crystallography and chemical derivatization techniques to obtain the relative and absolute stereo-configuration of novel molecules. Surprisingly, despite the archive of known compounds in the LC-MS database library, the re-isolation observed rate of known was over 75%. During my project time, an NIH Grant to study antibiotic active marine metabolites got granted to the Fenical laboratory to install a test assay against methicillin-resistant Staphylococcus aureus (MRSA). Strains and fractions I worked on were subjected to both test assays. In combination with a bioactivity guided fractionation approach, 9 novel and bioactive metabolites, could be isolated. Interestingly, more antibiotic active metabolites could be found, isolated and characterized than anti-cancer active compounds.
