Synthesis and properties of a novel modified nucleic acid, 2'-N-methanesulfonyl-2'-amino-locked nucleic acid

Synthesis and properties of RNA constrained by a 2'-O-disulfide bridge

We recently reported the properties of RNA hairpins constrained by a dimethylene (DME) disulfide (S-S) linker incorporated between two adjacent nucleosides in the loop and showed that this linker locked the hairpin conformation thus disturbing the duplex/hairpin equilibrium. We have now investigated the influence of the length of the linker and synthesized oligoribonucleotides containing diethylene (DEE) and dipropylene (DPE) S-S bridges. This was achieved via the preparation of building blocks, namely 2'-O-acetylthioethyl (2'-O-AcSE) and 2'-O-acetylthiopropyl (2'-O-AcSP) uridine phosphoramidites, which were successfully incorporated into RNA sequences. Thermal denaturation analysis revealed that the DEE and DPE disulfide bridges destabilize RNA duplexes but do not disrupt the hairpin conformation. Furthermore, our investigation of the duplex/hairpin equilibrium indicated that sequences modified with DME and DEE S-S linkers predominantly lock the hairpin form, whereas the DPE S-S linker provides flexibility. These findings highlight the potential of S-S linkers to study RNA interactions.

A Systemically Administered Unconjugated Antisense Oligonucleotide Targeting DUX4 Improves Muscular Injury and Motor Function in FSHD Model Mice

Facioscapulohumeral muscular dystrophy (FSHD), one of the most common muscular dystrophies, is caused by an abnormal expression of the DUX4 gene in skeletal muscles, resulting in muscle weakness. In this study, we investigated MT-DUX4-ASO, a novel gapmer antisense oligonucleotide (ASO). MT-DUX4-ASO decreased the expression of DUX4 and its target genes in FSHD patient-derived myoblasts. For the first time, we demonstrated that a systemically administered ASO, even without a ligand for drug delivery, could significantly improve muscle injury and motor function in the ACTA1-MCM/FLExDUX4 (DUX4-TG) mouse model of FSHD. Tamoxifen (TMX) injection transiently induces skeletal-muscle-specific DUX4 expression in DUX4-TG mice, while the skeletal muscles of TMX-untreated DUX4-TG mice have leaky DUX4 expression in a small subset of myofibers similar to those of FSHD patients. Subcutaneous 10 mg/kg of MT-DUX4-ASO at two-week intervals significantly suppressed muscular DUX4 target gene expression, histological muscle injury, and blood muscle injury marker elevation in TMX-untreated DUX4-TG mice. Notably, MT-DUX4-ASO at 10 mg/kg every other week significantly prevented the TMX-induced declines in treadmill test running speed and muscle force in DUX4-TG mice. Thus, the systemically administered unconjugated MT-DUX4-ASO suppressed disease progression in DUX4-TG mice, extending the potential of unconjugated ASOs as a promising FSHD treatment strategy.