Sirna Analogs Containing Phosphorodithioate Substitutions

Abstract

Chemically synthesized short interfering RNAs (siRNAs) mediate gene silencing in sequence-specific manner by utilizing the endogenous mechanism of RNA interference (RNAi). Synthetic siRNAs are often modified for improving their potency, stability, and for reducing undesirable “off-target” effects. Modification of the internucleotide bond in RNA chain, involving substitution of a single non-bridging phosphate oxygen with sulfur leads to the phosphorothioate (PS) derivatives of RNA. Substitution of both non-bridging phosphate oxygen atoms with sulfur gives rise to a phosphorodithioate (PS2) internucleotide linkage. We used a novel type of PS2-siRNA duplexes and tested their silencing activity, stability, and cellular up-take in comparison to PS- or unmodified duplexes. PS2-siRNAs show the A-type structure, characteristic for double-stranded RNA. Incorporation of PS2 substitutions into siRNA duplexes increases their serum stability. Gene silencing effect is strand- and position-dependent, with certain molecules showing significantly higher activity than PS or unmodified siRNAs. PS2 modifications are promising candidates in RNAi research and in therapeutic applications.

GRAPHICAL ABSTRACT

Keywords:

• RNA interference
• RNAi
• short interfering RNA
• siRNA
• phosphorothioates
• phosphorodithioates

Acknowledgments

We acknowledge the financial support from the Polish Ministry of Science and Higher Education, Grant Nr N N204 540039/2010-2013 to M Sierant, and U.S. National Institutes of Health grants of R43GM084552, R44GM084552, and R43CA141842 to X Yang.