Exon 44 skipping in Duchenne muscular dystrophy: NS-089/NCNP-02, a dual-targeting antisense oligonucleotide

Exon-skipping therapy mediated by antisense oligonucleotides (ASOs) is expected to provide a therapeutic option for Duchenne muscular dystrophy (DMD). ASOs for exon skipping reported so far target a single continuous sequence in or around the target exon. In the present study, we investigated ASOs for exon 44 skipping (applicable to approximately 6% of all DMD patients) to improve activity by using a novel ASO design incorporating two connected sequences. Phosphorodiamidate morpholino oligomers targeting two separate sequences in exon 44 were created to simultaneously target two splicing regulators in exon 44, and their exon 44 skipping was measured. NS-089/NCNP-02 showed the highest skipping activity among the oligomers. NS-089/NCNP-02 also induced exon 44 skipping and dystrophin protein expression in cells from a DMD patient to whom exon 44 skipping is applicable. We also assessed the in vivo activity of NS-089/NCNP-02 by intravenous administration to cynomolgus monkeys. NS-089/NCNP-02 induced exon 44 skipping in skeletal and cardiac muscle of cynomolgus monkeys. In conclusion, NS-089/NCNP-02, an ASO with a novel connected-sequence design, showed both in vitro and in vivo exon-skipping activity.