Multifaceted World of Chemically Modified Oligonucleotides for Nucleic Acid Therapeutics

Dear Colleagues,

The year 2023 marks the twin anniversary of nucleic acid therapeutics, i.e., 45 years since the publication (1978) of the celebrated paper written by Paul Zamecnik and Mary Stephenson, which heralded the advent of antisense technology, and 25 years since the approval of the first oligonucleotide drug, Vitravene (fomivirsen), in 1998. However, as 2023 nears the end, I believe another paper ought to be recalled: an early work by Nina Grineva et al. that appeared 55 years ago (Belikova et al., 1967, PMID 6073336). For the first time, it put forward the idea of exploiting the sequence-selective Watson–Crick duplex formation between an oligonucleotide and its complementary nucleic acid target (DNA in the paper) to achieve a therapeutic effect. Oligonucleotide synthesis was still in its infancy at that moment, although the same year (1967), Fritz Eckstein described the synthesis of the first ever enzymatically resistant phosphate mimic, replacing one of the nonbridging oxygen atoms of the phosphodiester group with sulfur—a dinucleoside phosphorothioate that, decades later, gave rise to first-generation antisense oligonucleotides such as fomivirsen. Consequently, it took over ten years for the Grineva concept to be experimentally verified in Zamecnik’s study, which firmly identified the biological target of antisense oligonucleotides to be an RNA molecule (mRNA in that case). At long last, chemically modified oligonucleotides received nearly universal recognition as precision tools for antisense- and RNAi-based gene therapies and more (e.g., mRNA vaccines, CRISPR/Cas, etc.). Every year since 2016 up until now, one, two or even three of these drugs would enter the pharmaceutical market, the latest being the siRNA Amvuttra (vutrisiran) in June 2022, and the morpholino antisense Amondys 45 (casimersen) in February 2021.

The aim of this Special Issue is to provide a snapshot of contemporary modified oligonucleotides, as well as their design, synthesis and applications as potential therapeutics. Suitable topics include, but are not limited to, oligonucleotides (including gapmers) with various phosphate/sugar/nucleobase modifications and terminal pendant groups, 2′-O-alkyl RNAs, bridged/locked nucleic acids (B/LNAs), peptide nucleic acids (PNAs), phosphorodiamidate morpholino oligonucleotides (PMOs), etc., cell/tissue-deliverable peptides, lipid and polymer/dendrimer conjugates, oligonucleotide-functionalized nanoparticles (spherical nucleic acids (SNAs), etc.), DNAzymes, DNA/RNA aptamers, CpG oligonucleotides, and therapeutic applications thereof, including genetic disorders/splice switching, neurodegenerative, cardiovascular and metabolic diseases, anticancer, antiviral, antibacterial, immunomodulatory, etc.

Dr. Dmitry A. Stetsenko
Guest Editor

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• DNA and RNA analogues
• phosphate mimics
• sugar-modified oligonucleotides
• base modifications
• nucleic acid therapeutics