Duchenne muscular dystrophy (DMD) is a progressive muscle-wasting disease caused by out-of-frame or nonsense mutation in the dystrophin gene. It begins with a loss of ambulation between 9 and 14 years of age, followed by various other symptoms including cardiac dysfunction. Exon skipping of patients’ DMD pre-mRNA induced by antisense oligonucleotides (AOs) is expected to produce shorter but partly functional dystrophin proteins, such as those possessed by patients with the less severe Becker muscular dystrophy. We are working on developing modified nucleotides, such as 2′-O,4′-C-ethylene-bridged nucleic acids (ENAs), possessing high nuclease resistance and high affinity for complementary RNA strands. Here, we demonstrate the preclinical characteristics (exon-skipping activity in vivo, stability in blood, pharmacokinetics, and tissue distribution) of renadirsen, a novel AO modified with 2′-O-methyl RNA/ENA chimera phosphorothioate designed for dystrophin exon 45 skipping and currently under clinical trials. Notably, systemic delivery of renadirsen sodium promoted dystrophin exon skipping in cardiac muscle, skeletal muscle, and diaphragm, compared with AOs with the same sequence as renadirsen but conventionally modified by PMO and 2′OMePS. These findings suggest the promise of renadirsen sodium as a therapeutic agent that improves not only skeletal muscle symptoms but also other symptoms in DMD patients, such as cardiac dysfunction.

Glycogen storage disease type 1a (GSD1a) is caused by a congenital deficiency of glucose-6-phosphatase-α (G6Pase-α, encoded by G6PC), which is primarily associated with life-threatening hypoglycemia. Although strict dietary management substantially improves life expectancy, patients still experience intermittent hypoglycemia and develop hepatic complications. Emerging therapies utilizing new modalities such as adeno-associated virus and mRNA with lipid nanoparticles are under development for GSD1a but potentially require complicated glycemic management throughout life. Here, we present an oligonucleotide-based therapy to produce intact G6Pase-α from a pathogenic human variant, G6PC c.648G>T, the most prevalent variant in East Asia causing aberrant splicing of G6PC. DS-4108b, a splice-switching oligonucleotide, was designed to correct this aberrant splicing, especially in liver. We generated a mouse strain with homozygous knockin of this variant that well reflected the pathophysiology of patients with GSD1a. DS-4108b recovered hepatic G6Pase activity through splicing correction and prevented hypoglycemia and various hepatic abnormalities in the mice. Moreover, DS-4108b had long-lasting efficacy of more than 12 weeks in mice that received a single dose and had favorable pharmacokinetics and tolerability in mice and monkeys. These findings together indicate that this oligonucleotide-based therapy could provide a sustainable and curative therapeutic option under easy disease management for GSD1a patients with G6PC c.648G>T.