Effect of different dosing regimens of exon skipping antisense oligonucleotides on functional outcome in the mdx mouse model of Duchenne muscular dystrophy

Antisense oligonucleotide (AON) therapies for Duchenne muscular dystrophy (DMD) are aimed at inducing skipping of specific exons during pre-mRNA splicing. This results in restoration of the reading frame and consequently synthesis of a shorter yet functional version of the dystrophin protein, as has been demonstrated in healthy control and DMD patient-derived muscle cell cultures, various DMD mouse and dog models, and recently in DMD patients treated with eteplirsen or drisapersen. The aim of this study was to investigate the effect of different dosing regimens of an exon skipping AON on functional outcome in vivo in the mdx DMD mouse model. The AON applied in these experiments was M23D, a mouse-specific 2′-O-methyl phosphorothioate RNA inducing skipping of exon 23 of mouse dystrophin. The effect of different durations of dosing, different administration routes (subcutaneous vs intravenous) and inclusion of a loading dose in the first week were investigated in relation to AON tissue levels, exon skip levels, dystrophin protein levels, serum creatine kinase levels and a variety of functional outcome measures including muscle lesions, muscle perfusion and motor performance. Different dosing regimens differentially affected several downstream parameters such as percentage exon skip as determined by quantitative digital droplet PCR. In addition, different dosing regimens displayed differential effects on muscle perfusion as measured by MRI, which may represent changes in muscle leakiness.