Systemic delivery of a splice-switching oligonucleotide heteroduplex corrects splicing in central nervous system and muscle in spinal muscular atrophy mice

Oligonucleotide therapeutics are an established class of drugs for the treatment of genetic disorders. Their clinical development is challenging, however, as they typically distribute poorly to extra-hepatic tissues after systemic injection. Here we tested the heteroduplex oligonucleotide (HDO) platform for systemic delivery of SMN2 splice-switching oligonucleotides of 2’- O- methoxyethyl phosphorothioate or phosphorodiamidate morpholino oligomer chemistries. We first showed that splice-switching HDO cargoes correct SMN2 splicing in cells derived from spinal muscular atrophy (SMA) patients, and validated extra-hepatic activity in spinal cord and muscle in a mouse model of SMA following systemic delivery. Our study raises prospects for delivery of nusinersen, the 2’- O- methoxylethyl phosphorothioate oligonucleotide therapy approved for SMA and currently delivered by intrathecal injection, by systemic injection exploiting the HDO chemistry platform. Our findings also suggest that oligonucleotide drugs lacking convincing in vivo efficacy in muscle tissue could be delivered effectively by the HDO technology. ### Competing Interest Statement F.H. and N.A. declare no competing financial interests. M.J.A.W. is a founder and shareholder of Evox Therapeutics and PepGen Ltd, companies dedicated to the commercialization of extracellular vesicle therapeutics and peptide-enhanced therapeutic oligonucleotide delivery, respectively.