Problem addressed: Oligonucleotide based therapeutics have emerged as a new drug discovery platform. A range of oligonucleotide based drug candidates are being evaluated in late stage clinical trials. Chemical modifications of natural unmodified oligonucleotides are required to increase their half-life in serum, improving their binding affinity for targets and for delivering them to tissues of interest. Despite recent success these hurdles are far from fully solved and it is of utmost importance to develop new chemically modified oligonucleotides with better pharmacokinetic profile. We in this funding period developed a new class of chemically modified oligonucleotides termed as triazole-linked Locked Nucleic Acids. We replaced natural phosphodiester backbone with unnatural triazole inter-nucleotide linkages. Whilst triazole linkage increases the stability of a given oligonucleotides against nuclease degradation, these are not beneficial for binding to RNA targets. Locked nucleic acids (LNA) is a bi-cyclic nucleoside that contains an oxymethylene bridge between 2′- and 4′-carbons in the ribose ring. Oligonucleotide carrying LNAs bind to their complementary RNA targets high affinity and selectivity. We envisioned that oligonucleotides incorporating LNA and triazole-linkage should be highly resistant to degradation in vivo (triazole linkages) and will bind strongly to complementary RNA targets (LNA component). Thus, new dinucleosides with LNA on either side of the triazole linkages were prepared and incorporated into oligonucleotides. The resulting modified oligonucleotides are strikingly stable in biological media and showed enhanced binding to RNA targets.
Importance for Society: Oligonucleotide based therapeutics provide an opportunity to treat any disease of genetic disorder. In particular, this new platform is gathering momentum for treating rare diseases where small molecule drugs have failed to provide desired results. With more than 100 candidates in clinical trials and few recent FDA approvals, this platform has generated mew hopes for people diagnosed with rare diseases. The molecules we have developed during last two years are promising and may find applications as therapeutic/diagnostic oligonucleotides. Thus, this project and area of therapeutic oligonucleotides is of high importance for society.
Future perspective: Triazole-linked LNAs constitute a promising class of potential therapeutic oligonucleotides with excellent stability against nucleases and high RNA-binding affinity and RNA target specificity. The other advantage of t-LNAs is their reduced anionic charge (triazole-linkage being neutral). It will be of interest to see how the reduced anioninc charge will affect the cellular uptake of triazole-linked LNAs. Potential of this new class as splice switching oligonucleotides and siRNA is remains to be seen. Furthermore, this study showed that by combining two existing classed of modified nucleosides, new more potent nucleosides can be obtained. This strategy will potentially lead to novel chemical modification in coming years.
