Search

Antisense therapy has been successful to skip targeted dystrophin exon with correction of frameshift and nonsense mutations of Duchenne muscular dystrophy (DMD). Systemic production of truncated but functional dystrophin proteins has been achieved in animal models. Furthermore, phase I/II clinical trials in United Kingdom and the Netherlands have demonstrated dystrophin induction by local and systemic administrations of antisense oligomers. However, long-term efficacy and potential toxicity remain to be determined. The present study examined 1-year systemic effect of phosphorodiamidate morpholino oligomers (PMO) treatment targeting mutated dystrophin exon 23 in mdx mice. PMO induced dystrophin expression dose-dependently and significantly improved skeletal muscle pathology and function with reduced creatine kinase (CK) levels by a regimen of 60 mg/kg biweekly administration. This regimen induced <2% dystrophin expression in the heart, but improved cardiac functions demonstrated by hemodynamics analysis. The results suggest that low levels of dystrophin induction may be able to provide detectable benefit to cardiac muscle with limited myopathy. Body weight, serum enzyme tests, and histology analysis showed no sign of toxicity in the mice treated with up to 1.5 g/kg PMO for 6 months. These results indicate that PMO could be used safely as effective drugs for long-term systemic treatment of DMD. [ABSTRACT FROM AUTHOR]

Steric-block antisense oligonucleotides (AONs) are able to target RNAs for destruction and splicing alteration. Reading frame restoration of the dystrophin transcript can be achieved by AON-mediated exon skipping in the dystrophic mdx mouse model. However, simple, unmodified AONs exhibit inefficient delivery systemically, leading to dystrophin induction with high variability in skeletal muscles and barely detectable in cardiac muscle. Here, we examined a Morpholino oligomer conjugated with a dendrimeric octaguanidine (Vivo-Morpholino) and demonstrated that the delivery moiety significantly improved dystrophin production in both skeletal and cardiac muscles in mdx mice in vivo. Single intravenous (IV) injections of 6 mg/kg Vivo-MorpholinoE23 (Vivo-ME23) generated dystrophin expression in skeletal muscles at the levels higher than the injection of 300 mg/kg unmodified ME23. Repeated injections at biweekly intervals achieved near 100% of fibers expressing dystrophin in skeletal muscles bodywide without eliciting a detectable immune response. Dystrophin protein was restored to ~50 and 10% of normal levels in skeletal and cardiac muscles, respectively. Vivo-Morpholinos showed no signs of toxicity with the effective dosages and regime, thus offering realistic prospects for the treatment of a majority of Duchenne muscular dystrophy (DMD) patients and many other diseases by targeting RNAs.Molecular Therapy (2009) 17 5, 864–871 doi:10.1038/mt.2009.38 [ABSTRACT FROM AUTHOR]