Optimizing splice-switching oligomer sequences using 2'-O-methyl phosphorothioate chemistry

Optimization of 2',4'-BNA/LNA-Based Oligonucleotides for Splicing Modulation In Vitro

Antisense oligonucleotide-mediated splicing modulation is an attractive strategy for treating genetic disorders. In 2016, two splice-switching oligonucleotides (SSOs) were approved by the FDA. To date, various types of novel artificial nucleic acids have been developed, and their potential for splicing modulations has been demonstrated. To apply these novel chemistries to SSOs, it is necessary to determine the appropriate design for each artificial nucleic acid such as the length of the SSO and number of modifications. In this protocol, we focus on SSOs modified with 2'-O,4'-methylene-bridged nucleic acid (2',4'-BNA)/locked nucleic acid (LNA), which is an artificial nucleic acid that shows extremely high binding affinity to target RNA strands. We describe our typical protocol for the optimization of 2',4'-BNA-based SSOs.

Evaluation of anhydrohexitol nucleic acid, cyclohexenyl nucleic acid and d-altritol nucleic acid-modified 2'-O-methyl RNA mixmer antisense oligonucleotides for exon skipping in vitro

Antisense oligonucleotide (AO) mediated exon skipping has been widely explored as a therapeutic strategy for several diseases, in particular, for rare genetic disorders such as Duchenne muscular dystrophy (DMD). To date, the potential of anhydrohexitol nucleic acid (HNA), cyclohexenyl nucleic acid (CeNA) and altritol nucleic acid (ANA) has not been explored in exon skipping. For the first time, in this study we designed and synthesised HNA, CeNA and ANA-modified 2'-O-methyl (2'-OMe) mixmer AOs on a phosphorothioate (PS) backbone, and evaluated their potential to induce exon 23 skipping in mdx mouse myotubes, as a model system. Our results clearly showed that all three AO candidates modified with HNA, CeNA and ANA could efficiently induce Dmd exon 23 skipping in vitro in parallel to the fully modified 2'-OMePS AO with reduced dual exon 22/23 skipping. In addition, they showed high nuclease resistance and no cytotoxicity compared to the 2'-OMePS AO, demonstrating the applicability of HNA, CeNA and ANA nucleotide-modified AOs in exon skipping.

Pro-apoptotic effects of splice-switching oligonucleotides targeting Bcl-x pre-mRNA in human glioma cell lines

Alternative splicing is a near-ubiquitous phenomenon with important roles in human diseases, including cancers. Splice-switching oligonucleotides (SSOs) have emerged as a class of antisense therapeutics that modulate alternative splicing by hybridizing to the pre-mRNA splice site. The Bcl-x gene is alternatively spliced to express anti‑apoptotic Bcl-xL and pro-apoptotic Bcl-xS. Bcl-xL expression is upregulated in many cancers and is considered a general mechanism by which cancer cells evade apoptosis. By redirecting Bcl-x pre-mRNA splicing from Bcl-xL to Bcl-xS, SSO exerted pro-apoptotic and chemosensitizing effects in various cancer cell lines. In this study, we investigated the effects of SSO targeting Bcl-x pre-mRNA in human glioma cell lines. First, we performed reverse transcription-polymerase chain reaction (RT-PCR) and western blotting to determine the mRNA and protein expression levels of Bcl-xL in glioma cell lines (U87 and U251) and a normal human astrocyte cell line (HA1800). Then, the Bcl-x SSO was designed to bind to the downstream 5' alternative splice site of exon 2 in Bcl-x pre-mRNA and was modified using 2'-O-methoxyethyl-phosphorothioate. An oligonucleotide targeting aberrantly spliced human β-globin intron was used as a negative control. The SSOs were delivered with a cationic lipid into glioma and astrocyte cell lines. The antitumor effects of the SSOs were assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays and flow cytometry, and the switch in production from Bcl-xL to Bcl-xS was analyzed by RT-PCR and western blotting. Bcl-xL mRNA and protein were highly expressed in both glioma cell lines. The Bcl-x SSO modified Bcl-x pre-mRNA splicing and had pro-apoptotic effects on the glioma cell lines. By contrast, the lipid alone and the control SSO did not affect Bcl-xL expression or induce apoptosis. Our study demonstrated the antitumor activity of an SSO that targets Bcl-x pre-mRNA splicing in glioma cell lines. Bcl-x SSO may be a potential strategy for treating gliomas.