IN VIVO DELIVERY OF NAKED AND LIPID-COMPLEXED ANTISENSE OLIGOS IN MDX MICE: EFFECTS ON SKELETAL AND CARDIAC MUSCLE

Antisense-mediated exon skipping holds great potential for the treatment of DMD. In mdx mice, functional recovery of skeletal muscle has been reported upon systemic delivery of “naked” oligonucleotides or viral vectors encoding for antisense snRNAs. However, only one study achieved dystrophin restoration in cardiac muscle (using an adeno-associated vector). Here we report the in vivo delivery of morpholino oligos in aged mdx mice, both in skeletal muscle, via intra-arterial injection, and in cardiac muscle, via intramuscular injection. Intra-arterial delivery yielded levels of dystrophin restoration comparable to those reported in the literature with the intra-venous approach, but with smaller amounts of oligonucleotides. Intra-cardiac injections, on the other hand, showed that the level and duration of the skipping effect found in cardiac muscle were greatly decreased compared to skeletal muscle. This latter finding provides the first direct evidence that antisense-mediated dystrophin restoration in cardiac muscle might suffers from limitations that do not exist in skeletal muscle. All data published so far have indicated that systemic delivery via the vasculature requires large amount of naked oligos to achieve therapeutically significant results. Here we also report that the use of lipid carriers has the potential to greatly improve the delivery efficiency; in particular, we found that the use of lipid-encapsulated oligo RNA allowed to detect dystrophin re-expression with a single dose of ~40 µg of oligos per adult mdx mouse. Importantly, dystrophin restoration could be seen not only in skeletal and but also (albeit to a smaller extent) in cardiac muscle.