P.11.1 Peptide-PMO induced exon-skipping restores muscle physiology in the mdx mouse

Abstract

Antisense directed exon-skipping has been shown to be a powerful method to induce expression of dystrophin in dystrophic muscle for a range of species including man. Dystrophin expression can be induced in the mdx mouse by oligonucleotides targeting exon 23 which removes the premature stop mutation in the murine dystrophin gene. We had previously shown improved resistance to eccentric exercise (10% length change of the active muscle) following intramuscular delivery of a phosphorodiamidate morpholino oligomer (PMO) targeting exon 23 in the mdx mouse (Sharp et al., 2011). Little improvement was seen in specific force which is commonly only 60% of wild-type in the mdx mouse. We now report similar physiology results following a single intravenous treatment with a peptide-PMO (PPMO) using the Pip6a peptide. Importantly, repeated intravenous PPMO treatment every two weeks starting at 12 weeks old and continuing for 10 doses, completely prevented the force drop associated with eccentric exercise and significantly improved the specific force, albeit not quite to wild-type levels. Both the acute and chronic dosing results correlated with the increased expression of dystrophin in muscle fibres and decreased levels of TIMP-1 in the serum. The chronic dosing study also showed a reduction in inflammation, restoration of a more normal fibre type pattern and reduction in fibre size variability. These studies show the potential of the PPMO formulation to significantly improve the results of exon-skipping in clinical trials.