Discovery of natural products potentially active against myotonic dystrophy type 1

Myotonic dystrophy type 1 (DM 1) is a genetically inherited muscle disorder that is characterised by progressive muscle wasting and weakening, cataracts, and cardiac conduction defects. At present there is no cure or effective treatment for this disabling disease. In this context, a collection of 70 pure compounds and 2100 extracts from different plants and fungal strains were screened with a novel DM 1-based biochemical assay for their ability to inhibit the formation of the pathogenic complex formed between (CUG)n-RNA and the splicing-factor muscleblind-like 1 (MBNL1). As a result, eight extracts from different plant species were found to be active (≥50% inhibition at 100 µg/mL). Active constituents were tracked using HPLC-based activity profiling, an approach which combines bioactivity data, structural information from online HPLC-UV-MS and offline microprobe NMR analyses, and database searches. Methylenetanshinquinone and 1,2-dihydrotanshinquinone were found to be the most active compounds in Salvia miltiorrhiza. The β-carboline alkaloid harmine was responsible for the activity of Peganum harmala, and the iridoid-glycoside auroside was identified as the active constituent in Lamium album. The HPLC profiles suggested the presence of tannins in the remaining five active extracts. Retesting of these extracts after tannin removal by filtration over polyamide confirmed the nonspecific interaction of the original extracts with the protein-based screen. In addition, the protoberberine alkaloid berberine was identified as a potent hit from the library of pure compounds. Overall, this study identified several small molecules of natural origin which are promising hit compounds in (CUG)n-MBNL1 complex inhibition. In a secondary cellular assay some of the identified small molecules partially reversed the splicing defects associated with DM 1. Detailed secondary in vitro and in vivo investigations on these compounds are ongoing.