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Journal of Biomedicine and Biotechnology
Volume 2006, Article ID 71659, 15 pages
Review Article

Delivery Systems for the Direct Application of siRNAs to Induce RNA Interference (RNAi) In Vivo

Department of Pharmacology and Toxicology, Philipps-University Marburg, Karl-v.-Frisch-Strasse 1, Marburg 35033, Germany

Received 14 January 2006; Accepted 27 February 2006

Copyright © 2006 Achim Aigner. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


RNA interference (RNAi) is a powerful method for specific gene silencing which may also lead to promising novel therapeutic strategies. It is mediated through small interfering RNAs (siRNAs) which sequence-specifically trigger the cleavage and subsequent degradation of their target mRNA. One critical factor is the ability to deliver intact siRNAs into target cells/organs in vivo. This review highlights the mechanism of RNAi and the guidelines for the design of optimal siRNAs. It gives an overview of studies based on the systemic or local application of naked siRNAs or the use of various nonviral siRNA delivery systems. One promising avenue is the the complexation of siRNAs with the polyethylenimine (PEI), which efficiently stabilizes siRNAs and, upon systemic administration, leads to the delivery of the intact siRNAs into different organs. The antitumorigenic effects of PEI/siRNA-mediated in vivo gene-targeting of tumor-relevant proteins like in mouse tumor xenograft models are described.