Rational Design of Short Locked Nucleic Acid-Modified 2′-O-Methyl Antisense Oligonucleotides for Efficient Exon-Skipping In Vitro

Locked nucleic acid is a prominent nucleic acid analog with unprecedented target binding affinity to cDNA and RNA oligonucleotides and shows remarkable stability against nuclease degradation. Incorporation of locked nucleic acid nucleotides into an antisense oligonucleotide (AO) sequence can reduce the length required without compromising the efficacy. In this study, we synthesized a series of systematically truncated locked nucleic acid-modified 2'-O-methyl AOs on a phosphorothioate (PS) backbone that were designed to induce skipping exon 23 from the dystrophin transcript in H-2K(b)-tsA58 mdx mouse myotubes in vitro. The results clearly demonstrated that shorter AOs (16- to 14-mer) containing locked nucleic acid nucleotides efficiently induced dystrophin exon 23 skipping compared with the corresponding 2'-O-methyl AOs. Our remarkable findings contribute significantly to the existing knowledge about the designing of short LNA-modified oligonucleotides for exon-skipping applications, which will help reduce the cost of exon-skipping AOs and potential toxicities, particularly the 2'-OMe-based oligos, by further reducing the length of AOs.