Anti-DMD monoclonal antibody, clone 2909

In skeletal muscle fibers, ubiquitous membrane trafficking pathways responsible for transporting newly synthesized proteins, recycling cell surface receptors, and organizing membrane compartmentation have adapted to the high needs of an extremely specialized cell under constant mechanical stress. Membrane remodeling proteins involved in ubiquitous mechanisms such as clathrin-mediated endocytosis, caveolae formation, and membrane fusion have evolved to produce new pathways with sometimes completely different functions such as adhesion and mechanoprotection. In this review, I discuss recent advances in understanding the specialized features of skeletal muscle clathrin-coated plaques, caveolae, and dysferlin-mediated membrane repair. A special emphasis is given on recent findings suggesting that membrane trafficking pathways have evolved to participate into the mechanisms responsible for sarcolemma resistance to mechanical stress and discuss how defects in these pathways result in muscle disease.

Antisense-mediated exon skipping constitutes a promising new modality for treatment of Duchenne Muscular Dystrophy (DMD), which is caused by gene mutations that typically introduce a translation stop codon in the dystrophin gene, thereby abolishing production of functional dystrophin protein. The exon removal can restore translation to produce a shortened, but still partially functional dystrophin protein. Peptide nucleic acid (PNA) as a potential antisense drug has previously been shown to restore the expression of functional dystrophin by splice modulation in the mdx mouse model of DMD. In this study, we compare systemic administration of a 20-mer splice switching antisense PNA oligomer through intravenous (i.v.) and subcutaneous (s.c.) routes in the mdx mice. Furthermore, the effect ofin situforming depot technology (BEPO(R)) and PNA-oligonucleotide formulation was studied.In vivofluorescence imaging analysis showed fast renal/bladder excretion of the PNA (t(1/2)similar to 20 min) for i.v. administration, while s.c. administration showed a two to three times slower excretion. The release from the BEPO depot exhibited biphasic kinetics with a slow release (t(1/2)similar to 10 days) of 50% of the dose. In all cases, some accumulation in kidneys and liver could be detected. Formulation of PNA as a duplex hybridization complex with a complementary phosphorothioate oligonucleotide increased the solubility of the PNA. However, none of these alternative administration methods resulted in significantly improved antisense activity. Therefore, either more sophisticated formulations such as designed nanoparticles or conjugation to delivery ligands must be utilized to improve both pharmacokinetics as well as tissue targeting and availability. On the other hand, the results show that s.c. and BEPO depot administration of PNA are feasible and allow easier, higher, and less frequent dosing, as well as more controlled release, which can be exploited both for animal model studies as well as eventually in the clinic in terms of dosing optimization.