In vivo activity of nuclease-resistant siRNAs

TLDR

Chemical modifications can be added to siRNAs without compromising their gene‑silencing activity in cultured mammalian cells. The study evaluates the utility of 2′‑modified siRNAs in mammalian systems. 2′‑fluoro‑modified siRNAs are active in vitro and in mice, exhibit markedly higher plasma stability, yet this enhanced resistance does not lead to stronger or longer‑lasting gene knockdown compared to unmodified siRNAs.

Abstract

Chemical modifications have been incorporated into short interfering RNAs (siRNAs) without reducing their ability to inhibit gene expression in mammalian cells grown in vitro. In this study, we begin to assess the potential utility of 2′-modified siRNAs in mammals. We demonstrate that siRNA modified with 2′-flouro (2′-F) pyrimidines are functional in cell culture and have a greatly increased stability and a prolonged half-life in human plasma as compared to 2′-OH containing siRNAs. Moreover, we show that the 2′-F containing siRNAs are functional in mice and can inhibit the expression of a target gene in vivo. However, even though the modified siRNAs have greatly increased resistance to nuclease degradation in plasma, this increase in stability did not translate into enhanced or prolonged inhibitory activity of target gene reduction in mice following tail vein injection. Thus, this study shows that 2′-F modified siRNAs are functional in vivo, but that they are not necessarily more potent than unmodified siRNAs in animals.