Design of noninflammatory synthetic siRNA mediating potent gene silencing in vivo

Mol Ther. 2006 Mar;13(3):494-505. doi: 10.1016/j.ymthe.2005.11.002. Epub 2005 Dec 15.


Targeted silencing of disease-associated genes by synthetic short interfering RNA (siRNA) holds considerable promise as a novel therapeutic strategy. However, unmodified siRNA can be potent triggers of the innate immune response, particularly when associated with delivery vehicles that facilitate intracellular uptake. This represents a significant barrier to the therapeutic development of siRNA due to toxicity and off-target gene effects associated with this inflammatory response. Here we show that immune stimulation by synthetic siRNA can be completely abrogated by selective incorporation of 2'-O-methyl (2'OMe) uridine or guanosine nucleosides into one strand of the siRNA duplex. These noninflammatory siRNA, containing less than 20% modified nucleotides, can be readily generated without disrupting their gene-silencing activity. We show that, coupled with an effective systemic delivery vehicle, 2'OMe-modified siRNA targeting apolipoprotein B (apoB) can mediate potent silencing of its target mRNA, causing significant decreases in serum apoB and cholesterol. This is achieved at therapeutically viable siRNA doses without cytokine induction, toxicity, or off-target effects associated with the use of unmodified siRNA. This approach to siRNA design and delivery should prove widely applicable and represents an important step in advancing synthetic siRNA into a broad range of therapeutic areas.

MeSH terms

  • Animals
  • Cells, Cultured
  • DNA Methylation
  • Gene Silencing* / immunology
  • Humans
  • Immunosuppressive Agents / administration & dosage
  • Immunosuppressive Agents / chemical synthesis*
  • Inflammation Mediators / administration & dosage
  • Inflammation Mediators / chemical synthesis*
  • Inflammation Mediators / physiology
  • Leukocytes, Mononuclear / metabolism*
  • Leukocytes, Mononuclear / pathology
  • Mice
  • Mice, Inbred BALB C
  • Mice, Inbred ICR
  • Molecular Sequence Data
  • RNA Interference / immunology
  • RNA, Small Interfering / administration & dosage*
  • RNA, Small Interfering / chemical synthesis*
  • RNA, Small Interfering / physiology


  • Immunosuppressive Agents
  • Inflammation Mediators
  • RNA, Small Interfering

Associated data

  • RefSeq/NM_008084
  • RefSeq/XM_137955