Theranostics 2013; 3(3):201-209. doi:10.7150/thno.5743

Research Paper

Optimized siRNA-PEG Conjugates for Extended Blood Circulation and Reduced Urine Excretion in Mice

Frank Iversen1,#, Chuanxu Yang1,#, Frederik Dagnæs-Hansen2, David H. Schaffert1, Jørgen Kjems1✉, Shan Gao1✉

1. Interdisciplinary Nanoscience Center (iNANO) and Department of Molecular Biology and Genetics, C.F. Møllers Alle, Building 1130, 8000 Aarhus C, Aarhus University.
2. Department of Biomedicine, Aarhus University, Bartholin Building Building 1240, Wilhelm Meyers Alle 4,8000 Aarhus C, Denmark.
# Contributed equally.

This is an open access article distributed under the terms of the Creative Commons Attribution (CC BY-NC) License. See for full terms and conditions.
Iversen F, Yang C, Dagnæs-Hansen F, Schaffert DH, Kjems J, Gao S. Optimized siRNA-PEG Conjugates for Extended Blood Circulation and Reduced Urine Excretion in Mice. Theranostics 2013; 3(3):201-209. doi:10.7150/thno.5743. Available from

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Some of the main concerns with in vivo application of naked small interfering RNA are rapid degradation and urinary excretion resulting in a short plasma half-life. In this study we investigated how conjugation of polyethylene glycol (PEG) with variable chain length affects siRNA pharmacokinetics and biodistribution.

The PEG chains were conjugated to chemically stabilized siRNA at the 5' terminal end of the passenger strand using click chemistry. The siRNA conjugate remained functionally active and showed significantly prolonged circulation in the blood stream after intravenous injection. siRNA conjugated with 20kDa PEG (PEG20k-siRNA) was most persistent, approximately 50% PEG20k-siRNA remained 1h post-injection, while the uncoupled siRNA was rapidly removed >90% at 15min. In vivo fluorescent imaging of the living animal showed increased concentration of siRNA in peripheral tissue and delayed urine excretion when coupled to PEG 20k. Biodistribution studies by northern blotting revealed equal distribution of conjugated siRNA in liver, kidney, spleen and lung without significant degradation 24 h post-injection. Our study demonstrates that PEG conjugated siRNA can be applied as a delivery system to improve siRNA bioavailability in vivo and may potentially increase the efficiency of siRNA in therapeutic applications.

Keywords: siRNA, PEGylation, blood circulation, urine excretion, in vivo imaging.