Life science
Medical & healthcare, Drug discovery

Towards the development of safe and effective therapeutic
antisense oligonucleotides

Life science

Laboratory of Bioorganic Chemistry, Graduate School of Pharmaceutical Sciences
Associate Professor Takao Yamaguchi		

https://researchmap.jp/takao-yamaguchi?lang=en

Professor Satoshi Obika						https://researchmap.jp/read0014368?lang=en

Abstract
Antisense oligonucleotide is designed to form duplex with target
RNA in a sequence-specific manner. It allows for various therapeutic approaches, such as reducing the expression levels ofdisease-causing mRNA or altering splicing to increase the expression of the targeted proteins. As of September 2023, this field has
grown to the point where 10 products have received approvals.
One of the significant features of antisense oligonucleotide is theability to quickly develop drugs based on the sequence informationof mRNA and pre-mRNA.
In our laboratory, we have been focusing on the developmentof artificial nucleic acids to enhance the safety and efficacy ofantisense oligonucleotide. In recent years, we have successfully
developed GuNA[t-Bu], AmNA, scpBNA, and 5′-cp. We are now
advancing their applications by incorporating them into therapeutic
antisense oligonucleotides.

▍ Background & Results
Two crucial properties in antisense oligonucleotide are stability against nucleases and ability to form duplex with the target
RNA. We have developed several artificial nucleic acids aimed
at improving these two properties and have been advancing theirapplications in antisense oligonucleotide. For example, AmNA andscpBNA have been developed as artificial nucleic acids that significantly enhance both of these properties, leading to a remarkableenhancement of the therapeutic efficacy of antisense oligonucleotide. We have also developed 5′-cp that enhances stability against
nucleases and improves the safety of antisense oligonucleotides.
In recent studies, we have discovered that GuNA[t-Bu], whichcontains a bulky tert-butyl group, significantly enhances the duplex-forming ability of oligonucleotide toward the complementary
single-stranded RNA. X-ray crystallography of the duplexes containing GuNA[t-Bu] revealed that the tert-butyl group fits into theminor groove of the duplexes. This result indicates that the tertbutyl group of GuNA[t-Bu] interacts with the minor groove and enhances duplex stability. Furthermore, incorporation of GuNA[t-Bu]
into oligonucleotide significantly increased stability against nucleases. Therefore, GuNA[t-Bu] is a good candidate for use in therapeutic antisense oligonucleotides.
We are also working on establishing a supply system for thesefour artificial nucleic acids (GuNA[t-Bu], AmNA, scpBNA, and5′-cp). We believe that these artificial nucleic acids are helpful fordeveloping therapeutic antisense oligonucleotides.

▍ Significance of the research and Future perspective
Development of therapeutic antisense oligonucleotides is becoming more active specially for genetic diseases that are difficult
to treat with small molecule drugs or antibody-based drugs. We
have developed several artificial nucleic acids that enhance thesafety and efficacy of therapeutic antisense oligonucleotides. We
are actively promoting the use of these artificial nucleic acids totherapeutic oligonucleotides, with the goal of expeditiously providing effective medications.

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rsCpq®•ükú¢†oFigure 1 Development of modified nucleic acids for therapeutic antisense oligonucleotides.

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Figure 2 The structure of GuNA[t-Bu] in duplex.

789:;<AJ ≠¶ú$ok•ipki•ú$ü°$hi<=jkClim$¢†$çiqûúÆ#P a t e n t Japanese Unexamined Patent Publication No.WO2011052436, No.WO2014046212, No.WO2015125783, No.WO2020158910
Yamaguchi, Takao; Obika, Satoshi et al. Mechanism of the extremely high duplex-forming ability of oligonucleotides modified with N-tert-butylguanidine- or
N-tert-butyl-N′-methylguanidine-bridged nucleic acids. Nucleic Acids Res. 2023, 51, 7749–7761. doi: 10.1093/nar/gkad608
Tr e a t i s e
Yamaguchi, Takao; Obika, Satoshi et al. Synthesis and properties of 2′-O,4′-C-spirocyclopropylene bridged nucleic acid (scpBNA), an analogue of 2′,4′-BNA/LNA bearing a cyclopropane ring. Chem. Commun. 2015, 51, 9737–9740. doi: 10.1039/c5cc02024g
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L https://www.phs.osaka-u.ac.jp/homepage/b007/en/index.html
K e y w o r d antisense, oligonucleotide therapeutics, drug discovery, RNA, DNA