Systemically administered PRO051 showed dose-dependent molecular efficacy in patients with Duchenne's muscular dystrophy, with a modest improvement in the 6-minute walk test after 12 weeks of extended treatment. (Funded by Prosensa Therapeutics; Netherlands National Trial Register number, NTR1241.).

Intramuscular injection of antisense oligonucleotide PRO051 induced dystrophin synthesis in four patients with Duchenne's muscular dystrophy who had suitable mutations, suggesting that further studies might be feasible.

Duchenne muscular dystrophy (DMD) is caused by mutations in the dystrophin

Antisense oligonucleotides (AONs) are being developed as RNA therapeutic molecules for Duchenne muscular dystrophy. For oligonucleotides with the 2′-O-methyl-phosphorothioate (2OMePS) RNA chemistry, proof of concept has been obtained in patient-specific muscle cell cultures, the mouse and dog disease models, and recently by local administration in Duchenne patients. To further explore the pharmacokinetic (PK)/pharmacodynamic (PD) properties of this chemical class of oligonucleotides, we performed a series of preclinical studies in mice. The results demonstrate that the levels of oligonucleotides in dystrophin-deficient muscle fibers are much higher than in healthy fibers, leading to higher exon-skipping levels. Oligonucleotide levels and half-life differed for specific muscle groups, with heart muscle showing the lowest levels but longest half-life (~46 days). Intravenous (i.v.), subcutaneous (s.c.), and intraperitoneal (i.p.) delivery methods were directly compared. For each method, exon-skipping and novel dystrophin expression were observed in all muscles, including arrector pili smooth muscle in skin biopsies. After i.v. administration, the oligonucleotide peak levels in plasma, liver, and kidney were higher than after s.c. or i.p. injections. However, as the bioavailability was similar, and the levels of oligonucleotide, exon-skipping, and dystrophin steadily accumulated overtime after s.c. administration, we selected this patient-convenient delivery method for future clinical study protocols.