Short Antisense Oligonucleotides with Novel 2′−4′ Conformationaly Restricted Nucleoside Analogues Show Improved Potency without Increased Toxicity in Animals

The potency of second generation antisense oligonucleotides (ASOs) in animals was increased 3- to 5 -fold (ED₅₀ ≈ 2−5 mg/kg) without producing hepatotoxicity, by reducing ASO length (20-mer to 14-mer) and by employing novel nucleoside modifications that combine structural elements of 2′-<i>O</i>-methoxyethyl residues and locked nucleic acid. The ability to achieve this level of potency without any formulation agents is remarkable and likely to have a significant impact on the future design of ASOs as therapeutic agents