Theranostics 2017; 7(9):2495-2508. doi:10.7150/thno.19863

Research Paper

High-Yield Synthesis of Monomeric LMWP(CPP)-siRNA Covalent Conjugate for Effective Cytosolic Delivery of siRNA

Junxiao Ye1, 2, Ergang Liu1, 2, Junbo Gong2, Jianxin Wang3, Yongzhuo Huang4, Huining He1✉, Victor C. Yang1, 5✉

1. Tianjin Key Laboratory on Technologies Enabling Development of Clinical Therapeutics and Diagnostics, School of Pharmacy, Tianjin Medical University, Tianjin 300070, China;
2. Collaborative Innovation Center of Chemical Science and Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China;
3. Department of Pharmaceutics, School of Pharmacy, Fudan University
Key Laboratory of Smart Drug Delivery, Ministry of Education & PLA, Shanghai 201201, China
4. Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China;
5. Department of Pharmaceutical Sciences, College of Pharmacy, University of Michigan, Ann Arbor, Michigan 48109-1065, USA.

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.
Ye J, Liu E, Gong J, Wang J, Huang Y, He H, Yang VC. High-Yield Synthesis of Monomeric LMWP(CPP)-siRNA Covalent Conjugate for Effective Cytosolic Delivery of siRNA. Theranostics 2017; 7(9):2495-2508. doi:10.7150/thno.19863. Available from

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Because of the unparalleled efficiency and universal utility in treating a variety of disease types, siRNA agents have evolved as the future drug-of-choice. Yet, the inability of the polyanionic siRNA macromolecules to cross the cell membrane remains as the bottleneck of possible clinical applications. With the cell penetrating peptides (CPP) being discovered lately, the most effective tactic to achieve the highest intracellular siRNA delivery deems to be by covalently conjugating the drug to a CPP; for instance, the arginine-rich Tat or low molecular weight protamine (LMWP) peptides. However, construction of such a chemical conjugate has been referred by scientists in this field as the “Holy Grail” challenge due to self-assembly of the cationic CPP and anionic siRNA into insoluble aggregates that are deprived of the biological functions of both compounds. Based on the dynamic motion of PEG, we present herein a concise coupling strategy that is capable of permitting a high-yield synthesis of the cell-permeable, cytosol-dissociable LMWP-siRNA covalent conjugates. Cell culture assessment demonstrates that this chemical conjugate yields by far the most effective intracellular siRNA delivery and its corresponded gene-silencing activities. This work may offer a breakthrough advance towards realizing the clinical potential of all siRNA therapeutics and, presumably, most anionic macromolecular drugs such as anti-sense oligonucleotides, gene compounds, DNA vectors and proteins where conjugation with the CPP encounters with problems of aggregation and precipitation. To this end, the impact of this coupling technique is significant, far-reaching and wide-spread.

Keywords: cell penetrating peptide, siRNA delivery, covalent CPP-siRNA chemical conjugate, mass preparation.