Abstract
Herein, we have demonstrated that the siRNA activity could be enhanced by incorporating the guide strand in the RISC complex through thermodynamic asymmetry caused by m(3)U-based destabilizing modifications. A nuclease stability study revealed that 2'-OMe-m(3)U and 2'-OEt-m(3)U modifications slightly improved the half-lives of siRNA strands in human serum. In the in vitro gene silencing assay, 2'-OMe-m(3)U modification at the 3'-overhang and cleavage site of the passenger strand in anti-renilla and anti-Bcl-2 siRNA duplexes were well-tolerated and exhibited improved gene silencing activity. However, gene silencing activity was attenuated when these modifications were incorporated at position 3 in the seed region of the antisense strand. The molecular modeling studies using these modifications at the seed region with the MID domain of hAGO2 explained that the 2'-alkoxy group makes steric interactions with the amino acid residues of the hAGO2 protein.