P264 Using antisense oligonucleotide therapy to rescue dystrophin (DMD) in the central nervous system in the mdx23 mouse model of Duchenne muscular dystrophy

Duchenne muscular dystrophy is a severe neuromuscular disorder caused by mutations in the DMD gene that disrupts the production of functional dystrophin proteins and leads to progressive muscle weakness. Neurobehavioral complications such as autism spectrum disorder (ASD) and anxiety have also been observed in more than a third of the patients, related to dystrophin deficiency in the brain. Mdx23 mouse model lacking the Dp427 isoform exhibits increased anxiety levels compared to wild-type mice in various behavioural tests. The exon-skipping phosphorodiamidate morpholino oligomer (PMO) antisense oligonucleotide (ASO) has been used to restore dystrophin expression in muscle. However, the effect of this PMO on brain's dystrophin expression and associated behavioural phenotype is unclear. Here, we investigate whether intracisternal magna injection (ICM) of the PMO, which induces skipping of exon 23, can restore dystrophin expression in the brain and lead to phenotypic improvement in the Mdx23 mouse. We used ICM injections due to their minimal invasiveness and potential for clinical translation. Male mdx23 mice were tested for restraint-induced fear response and anxiety after treatment with three ICM PMO injections starting at 6 weeks of age with three-day intervals. DMD exon skipping and protein restoration were analysed in micro-dissected brain regions, five and seven weeks after the last injection. Treated mdx23 mice exhibited a small but significant rescue of the enhanced fear response. PMO administration led to a low but detectable restoration of dystrophin protein expression and DMD exon skipping in micro-dissected brain regions, with the highest biodistribution in the olfactory bulb at both the RNA and protein level. We demonstrate that the ICM delivery of a PMO that leads to small dystrophin expression in brain does still provide modest behavioural phenotype in the mdx23 model. Duchenne muscular dystrophy is a severe neuromuscular disorder caused by mutations in the DMD gene that disrupts the production of functional dystrophin proteins and leads to progressive muscle weakness. Neurobehavioral complications such as autism spectrum disorder (ASD) and anxiety have also been observed in more than a third of the patients, related to dystrophin deficiency in the brain. Mdx23 mouse model lacking the Dp427 isoform exhibits increased anxiety levels compared to wild-type mice in various behavioural tests. The exon-skipping phosphorodiamidate morpholino oligomer (PMO) antisense oligonucleotide (ASO) has been used to restore dystrophin expression in muscle. However, the effect of this PMO on brain's dystrophin expression and associated behavioural phenotype is unclear. Here, we investigate whether intracisternal magna injection (ICM) of the PMO, which induces skipping of exon 23, can restore dystrophin expression in the brain and lead to phenotypic improvement in the Mdx23 mouse. We used ICM injections due to their minimal invasiveness and potential for clinical translation. Male mdx23 mice were tested for restraint-induced fear response and anxiety after treatment with three ICM PMO injections starting at 6 weeks of age with three-day intervals. DMD exon skipping and protein restoration were analysed in micro-dissected brain regions, five and seven weeks after the last injection. Treated mdx23 mice exhibited a small but significant rescue of the enhanced fear response. PMO administration led to a low but detectable restoration of dystrophin protein expression and DMD exon skipping in micro-dissected brain regions, with the highest biodistribution in the olfactory bulb at both the RNA and protein level. We demonstrate that the ICM delivery of a PMO that leads to small dystrophin expression in brain does still provide modest behavioural phenotype in the mdx23 model.