Rapid identification of minor active metabolites in extracts of marine organisms: A platform for efficient drug discovery

Efficient identification of biologically active metabolites present in complex crude extracts continues to be a significant challenge in natural products discovery. To overcome this obstacle, contemporary drug discovery programs have placed an emphasis on the development of multifaceted approaches to capture comprehensive biological and chemical data early in the isolation workflow. This information can be used to quickly characterize active metabolites and direct research efforts to those with the highest potential for development as drug leads. Here we outline a discovery platform used to rapidly generate and screen a large fraction library from extracts of marine organisms. Fractions are concurrently analyzed by high-resolution LC-MS/MS and assayed against a panel of human cancer cell lines. Analysis of aggregate biological and mass spectrometric data is combined with molecular networking to evaluate the structural diversity of active metabolites and direct future isolation efforts. To highlight the effectiveness of this platform, we describe the identification of dolastatin 10 and symplostatin 1, potent cytotoxic linear peptides, in multiple extracts of phylogenetically diverse organisms collected from a single geographic area. Production of these compounds is attributed to a cyanobacterial strain co-occurring in low abundance with the field collected organisms. Subsequent purification of both compounds, guided by the chemical information collected during library generation, allowed structural verification by NMR.