Loss of silencing activity caused by 5′-terminal modification with d-/l-isonucleotide (isoNA) or locked nucleic acid (LNA) could not be restored by 5′-terminal phosphorylation

Isonucleotide incorporation into middle and terminal siRNA duplexes exhibits high gene silencing efficacy and nuclease resistance

In this study, we introduced a pair of nucleotide enantiomers, d-/l-isonucleotides (d-/l-isoNA), to examine the interactions between siRNAs and their related proteins. The serum stability and gene-silencing activity of the modified siRNAs were systematically evaluated. Gene-silencing activity had a site-specific effect, and the incorporation of a single d-isoNA at the 8th position (counting from the 5'-terminus) in the antisense strand improved the gene-silencing activity by improving RISC loading and affecting the movement of the PIWI domain. d-isoNA incorporated at the terminus of siRNA including the 2nd position in the antisense strand and 3'-overhangs in the sense strand, especially the latter, enhanced nuclease resistance and prolonged the silencing retention time. In addition, l-isoNA incorporation into the middle of the sense strand enhanced activity. These results provide a chemical strategy for the modulation of siRNA gene-silencing activity and nuclease resistance.

Spatial conservation studies of nucleobases in 10–23 DNAzyme by 2′-positioned isonucleotides and enantiomers for increased activity

d-/l-Isonucleotides were used to modify the catalytic core and recognition arms of 10–23 DNAzyme and prominently improved its bioactivity.