Antisense oligonucleotides (ASOs) and small interfering RNA (siRNA) are both recognized therapeutic agents for the silencing of specific genes at the posttranscriptional level. Chemical modifications, particularly 2’-O-(2-Methoxyethyl)- oligoribonucleotides (2’-O-MOE bases) and 2’-O-Methyl bases are commonly used to confer nuclease resistance to an oligo designed for anti-sense, siRNA or aptamer-based research, diagnostic or therapeutic purposes, when specific 2’-OH is not required.
Nuclease resistance can be further enhanced by phosphorothiolation of appropriate phosphodiester linkages within the oligo. These modifications confers nuclease resistance, high binding affinity towards complementary RNA, reduced unspecific protein binding and extended half-life in tissues.
Gapmers. Currently, the mainstream of the ASO is gapmer design ASOs. Gapmer design oligonucleotides, contain two to
five chemically modified nucleotides (LNA, 2’-O methyl or 2’-O-MOE RNA) as “wings” at each terminus flanking a central 5- to10-base “gap” of DNA, enable cleavage of the target mRNA by RNase H, which recognizes DNA/RNA heteroduplexes. Usually all the phosphodiester linkages are converted to phosphorothioate.
Delivery. The development of effective delivery systems for antisense oligonucleotides is essential for their clinical therapeutic application. The most common delivery system involves a relatively hydrophobic molecule that can cross the lipid membrane. The following list of modifications are suitable for delivery system in addition to cell penetrating peptides.
Cholesterol
Tocopherol (alpha-tocopherol, a natural isomer of vitamin E)
PEG
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