Gene silencing by 2'-O-methyldithiomethyl-modified siRNA, a prodrug-type siRNA responsive to reducing environment.

RNAs bearing various 2'-modifications have been synthesized in an effort to improve nuclease resistance. However, the gene silencing activity of small interfering RNAs (siRNAs) has been decreased or sometimes completely suppressed by the chemical modifications. We previously developed a post-synthetic approach for the synthesis of 2'-O-methyldithiomethyl-modified RNA, which can be converted into unmodified RNA under reducing conditions, and named it Reducing-Environment-Dependent Uncatalyzed Chemical Transforming RNA (REDUCT RNA). Here, the gene silencing activity of REDUCT siRNA bearing 2'-O-methyldithiomethyl groups was evaluated. REDUCT siRNA showed more effective gene silencing than unmodified siRNA regardless of the modification site. This result suggests that REDUCT siRNA is converted into unmodified siRNA inside cells as a prodrug-type siRNA.