Science Tokyo develops new nucleic acid medicine technology for muscular dystrophy — Enhancing nuclear delivery efficiency with double-stranded nucleic acids

A research group led by Professor Emeritus Takanori Yokota and Part-time Lecturer Juri Hasegawa from the Department of Neurology and Neurological Science at the Institute of Science Tokyo and Project Junior Associate Professor Kotaro Yoshioka from the Nucleotide and Peptide Drug Discovery Center, Institute of Science Tokyo, in collaboration with Professor Satoshi Obika and Graduate Student Takenori Shimo (at the time of the research) from the Graduate School of Pharmaceutical Sciences at the University of Osaka, announced on May 22 that they have developed a new nucleic acid medicine technology called "Heteroduplex Splice-Switching Oligonucleotides (HDSSOs)" for Duchenne Muscular Dystrophy (DMD). High skipping activity was confirmed in model mice. The results are expected to lead to splicing control therapies not only for muscle tissue but also for various target tissues. The findings were published in the online edition of Molecular Therapy - Nucleic Acids on March 11.

DMD is an X-linked recessive genetic disorder where abnormalities in the dystrophin gene prevent the production of dystrophin protein, leading to progressive muscle degeneration and necrosis. In recent years, exon-skipping therapy, which bypasses abnormal exons within the dystrophin gene, has been applied to certain genetic mutations.

Splice-switching oligonucleotides (SSOs), a type of antisense oligonucleotide (ASO), have been approved for this therapy, but improvement in efficacy is needed due to short blood retention and rapid renal excretion.

The research group had previously developed HDO technology that significantly enhances the effects of antisense oligonucleotides, confirming its efficacy in model mice. This time, aiming to achieve efficient nuclear delivery necessary for enhancing exon-skipping efficiency, they worked on developing HDSSOs using nucleic acids with DNA and locked nucleic acids (LNA) as the basic backbone.

First, they examined whether HDSSO technology could be applied to LNA-based SSOs and 2'-OMe RNA-based SSOs. For each SSO targeting the dystrophin gene, they designed three types of complementary strands including DNA, RNA, and 2'-OMe RNA with phosphorothioate modification, and compared the exon-skipping activity of single-stranded SSOs and HDSSOs. All showed higher activity than single-stranded forms.

Next, using LNA-based SSOs, they set complementary DNA and complementary RNA strands and investigated the effects of length, PS linkage, and presence or absence of LNA modification on activity.

As a result, it became clear that HDSSO activity was highly dependent on the type, length, and modification of the complementary strand, and that the behavior of the complementary strand within cells affects activity.

HDSSOs designed based on this study showed higher exon-skipping activity compared with conventional SSOs, and the relationship between complementary strand structure and activity was also clarified. Furthermore, in experiments using DMD model mice, high exon-skipping activity was confirmed through HDO technology.

By applying this technology, improved target specificity through combination with drug delivery technologies using lipids and peptides is expected. Hasegawa commented, "Having experienced observing DMD patients in actual clinical settings, we conducted this research with the hope that we could somehow be of help. We would be pleased if this technology and other research outcomes could contribute even a little to the advancement of medicine."

Yoshioka added, "This new drug discovery technology was created by combining the efforts of chemical researchers from the University of Osaka and medical researchers from Science Tokyo. We would like to continue striving to create technologies that will bring hope to patients with intractable diseases through the power of such interdisciplinary collaboration."

Journal Information
Publication: Molecular Therapy - Nucleic Acids
Title: Effect of chemical modification on the exon-skipping activity of heteroduplex oligonucleotides
DOI: 10.1016/j.omtn.2025.102468