A 2′-modified uridine analog, 2'-O-(methylthiomethoxy)methyl uridine, for siRNA applications

The medicinal applications of siRNAs have been intensively examined but are still hindered by their low mo-lecular stability under biological conditions and off-target effects, etc. The introduction of chemical modifica-tions to the nucleoside is a promising strategy for solving these limitations. Herein, we describe the development of a new uridine analog, U*, that has a (methylthiomethoxy)methoxy group at the 2 & PRIME; position. The phosphor-amidite reagent corresponding to U* was easily synthesized and the RNA oligonucleotides containing U* were stably prepared using a standard protocol for oligonucleotide synthesis. The introduction of U* into the siRNA resulted in positive or negative effects on the targeted gene silencing in a position-dependent manner, and the positive effects were attributed to the improved stability under biological conditions. The thermodynamic analysis of the U*-modified RNAs revealed a slight destabilization of the dsRNA, based depending on which U was strategically utilized to restrain the off-target effects of the siRNA. This study describes a rare example of nucleoside analogs with a large substitution at the 2 & PRIME;-position in the context of an siRNA application and is informative for the development of other analogs to further improve the molecular properties of siRNAs for medicinal applications.

Automated summary

The medicinal applications of siRNAs have limitations in terms of molecular stability and off-target effects. Chemical modifications to the nucleoside, such as introducing a new uridine analog (U*), can improve the stability of siRNAs under biological conditions and have positive effects on target gene silencing. The study provides useful insights for the development of nucleoside analogs to enhance the molecular properties of siRNAs for medicinal applications.