Biological Efficacy and Toxicity of Diamidines in Myotonic Dystrophy Type 1 Models.

Myotonic dystrophy type 1 (DM1) is a disease characterized by errors in alternative splicing, or "mis-splicing". The causative agent of mis-splicing in DM1 is an inherited CTG repeat expansion located in the 3' untranslated region of the DM protein kinase gene. When transcribed, CUG repeat expansion RNA sequesters muscleblind-like (MBNL) proteins, which constitute an important family of alternative splicing regulators. Sequestration of MBNL proteins results in the mis-splicing of its regulated transcripts. Previous work has demonstrated that pentamidine, a diamidine which is currently FDA-approved as an antiparasitic agent, was able to partially reverse mis-splicing in multiple DM1 models, albeit at toxic concentrations. In this study, we characterized a series of pentamidine analogues to determine their ability to reverse mis-splicing and their toxicity in vivo. Experiments in cell and mouse models demonstrated that compound 13, also known as furamidine, effectively reversed mis-splicing with equal efficacy and reduced toxicity compared to pentamidine.

Reducing levels of toxic RNA with small molecules.

Myotonic dystrophy (DM) is one of the most common forms of muscular dystrophy. DM is an autosomal dominant disease caused by a toxic gain of function RNA. The toxic RNA is produced from expanded noncoding CTG/CCTG repeats, and these CUG/CCUG repeats sequester the Muscleblind-like (MBNL) family of RNA binding proteins. The MBNL proteins are regulators of alternative splicing, and their sequestration has been linked with mis-splicing events in DM. A previously reported screen for small molecules found that pentamidine was able to improve splicing defects associated with DM. Biochemical experiments and cell and mouse model studies of the disease indicate that pentamidine and related compounds may work through binding the CTG*CAG repeat DNA to inhibit transcription. Analysis of a series of methylene linker analogues of pentamidine revealed that heptamidine reverses splicing defects and rescues myotonia in a DM1 mouse model.