Targeted delivery of siRNA

Targeted delivery of small interfering RNA (siRNA) allows precise delivery of siRNA molecules to a particular tissue, cell type, or cellular compartment within an organism. siRNAs are a class of small RNA molecules that can silence or downregulate specific genes by targeting complementary mRNA molecules for degradation. For siRNAs to reach their site of action in the cytosol, siRNA therapeutics need to overcome several barriers standing in their way.

The targeted delivery of siRNA is crucial for therapeutic applications because it allows for precise gene regulation while minimizing off-target effects. Without targeted delivery, siRNA molecules will quickly degrade in the bloodstream, fail to reach the intended target cells or organelle, or accumulate in non-specific tissues, leading to potential side effects.

Various approaches to achieve targeted delivery of siRNA are now available:

1.   Chemical modifications

Chemical modifications of siRNAs enhance their stability, reduce immune responses, and improve their ability to enter cells. Also, these modifications can increase siRNA's resistance to degradation and improve its pharmacokinetic properties.

2.   Nanoparticles

Nanoparticles used as carriers protect and deliver siRNA molecules. These nanoparticles can be engineered with specific properties to facilitate targeted delivery. For example, lipid-based, polymer-based, or inorganic nanoparticles can deliver siRNA to specific cells or tissues when formulated to encapsulate siRNA.

3.   Antibody conjugates

When conjugated to siRNA molecules, antibodies bind to cell surface receptors expressed on target cells. This approach takes advantage of antibodies' high specificity and affinity to deliver siRNA to specific cell types.

4.   Ligand-mediated targeting

Attaching ligands, such as peptides or small molecules, to siRNA molecules or nanoparticle carriers enable targeting specific receptors or transporters on the surface of target cells. These ligands can facilitate receptor-mediated endocytosis and enhance siRNA delivery to the desired cells.

5.   Cell-specific promoters

siRNA expressed from a DNA vector under the control of a cell-specific promoter allows the delivery to target cells, where it is transcribed and processed into siRNA molecules, enabling specific gene silencing within those cells.

These approaches, individually or in combination, offer strategies for achieving targeted delivery of siRNA to specific cells or tissues, thereby enhancing the therapeutic potential of siRNA-based therapies while minimizing off-target effects. Targeted delivery is critical when developing siRNA-based therapeutics for various diseases, including cancer, genetic disorders, and viral infections.

Table 1: Targeted siRNA delivery systems for brain, leukocytes, and tumors. Receptor-specific ligands are paired with the respective molecular targets and siRNA-formulations such as nanoparticles or bioconjugates (Source: Lorenzer et al. 2015).







Transferrin antibody

Transferrin receptor


I. van Rooy, E. Mastrobattista, G. Storm,W.E. Hennink, R.M. Schiffelers, Comparison  of five different targeting ligands to enhance accumulation of liposomes into the brain, J. Control. Release 150 (2011) 30–36. [Pubmed] 


Transferrin-targeted fusion peptide

Transferrin receptor

Peptide/siRNA complexes

P. Youn, Y. Chen, D.Y. Furgeson, A myristoylated cell-penetrating peptide bearing a transferrin receptor-targeting sequence for neuro-targeted siRNA delivery, Mol. Pharm. 11 (2014) 486–495. [PMC]




Rabies virus glycoprotein (RVG)

Not identified

Peptide/siRNA complexes

P. Kumar, H.Wu, J.L. McBride, K.-E. Jung, M. Hee Kim, B.L. Davidson, S. Kyung Lee, P. Shankar, N. Manjunath, Transvascular delivery of small interfering RNA to the central nervous system, Nature 448 (2007) 39–43. [nature]




Rabies virus glycoprotein (RVG)


and p75NTR are possible targets

Polyethyleneimine complexes

Hwang DW, Son S, Jang J, Youn H, Lee S, Lee D, Lee YS, Jeong JM, Kim WJ, Lee DS. A brain-targeted rabies virus glycoprotein-disulfide linked PEI nanocarrier for delivery of neurogenic microRNA. Biomaterials. 2011 Jul;32(21):4968-75. doi: 10.1016/j.biomaterials.2011.03.047. [sciencedirect.com]


Y. Tao, J. Han, H. Dou; Brain-targeting gene delivery using a rabies virus glycoprotein peptide modulated hollow liposome: bio-behavioral study. J. Mater. Chem., 22 (2012), pp. 11808-11815. [RSC]

PAMAM nanoparticles

Y. Liu, R. Huang, L. Han, W. Ke, K. Shao, L. Ye, J. Lou, C. Jiang; Brain-targeting gene delivery and cellular internalization mechanisms for modified rabies virus glycoprotein RVG29 nanoparticles. Biomaterials, 30 (2009), pp. 4195-4202.

Targeted exosomes

Alvarez-Erviti, L., Seow, Y., Yin, H. et al. Delivery of siRNA to the mouse brain by systemic injection of targeted exosomes. Nat Biotechnol 29, 341–345 (2011).


Integrin antibody


Protamine-antibody/siRNA complexes

D. Peer, P. Zhu, C.V. Carman, J. Lieberman, M. Shimaoka; Selective gene silencing in activated leukocytes by targeting siRNAs to the integrin lymphocyte function-associated antigen-1. Proc. Natl. Acad. Sci. U. S. A., 104 (2007), pp. 4095-4100.



D. Peer, E.J. Park, Y. Morishita, C.V. Carman, M. Shimaoka; Systemic leukocyte-directed siRNA delivery revealing cyclin D1 as an anti-inflammatory target. Science, 319 (2008), pp. 627-630. [Science]

Tumor tissues



Polythyleneimine complexes

C. Dohmen, T. Frohlich, U. Lachelt, I. Rohl, H.-P. Vornlocher, P. Hadwiger, E. Wagner Defined folate-PEG-siRNA conjugates for receptor-specific gene silencing. Mol. Ther. Nucleic Acids, 1 (2012), p. e7 [sciencedirect]


H. Lee, A.K.R. Lytton-Jean, Y. Chen, K.T. Love, A.I. Park, E.D. Karagiannis, A. Sehgal, W. Querbes, C.S. Zurenko, M. Jayaraman, C.G. Peng, K. Charisse, A. Borodovsky, M. Manoharan, J.S. Donahoe, J. Truelove, M. Nahrendorf, R. Langer, D.G. Anderson Molecularly self-assembled nucleic acid nanoparticles for targeted in vivo siRNA delivery. Nat. Nanotechnol., 7 (2012), pp. 389-393. [Nature]


J.S. Kim, M.H. Oh, J.Y. Park, T.G. Park, Y.S. Nam; Protein-resistant, reductively dissociable polyplexes for in vivo systemic delivery and tumor-targeting of siRNA. Biomaterials, 34 (2013), pp. 2370-2379. [Sciencedirect]


PEG–siRNA conjugate

Li JM, Wang YY, Zhang W, Su H, Ji LN, Mao ZW. Low-weight polyethylenimine cross-linked 2-hydroxypopyl-β-cyclodextrin and folic acid as an efficient and nontoxic siRNA carrier for gene silencing and tumor inhibition by VEGF siRNA. Int J Nanomedicine. 2013;8:2101-17. [PMC]


Self-assembled nanoparticles

Julian Willibald, Johannes Harder, Konstantin Sparrer, Karl-Klaus Conzelmann, and Thomas Carell; Click-Modified Anandamide siRNA Enables Delivery and Gene Silencing in Neuronal and Immune Cells. Journal of the American Chemical Society 2012 134 (30), 12330-12333. [ACS]


Tumor tissues

Hyaluronic acid


Hyaluronic acid-graft-poly(dimethyl-aminoethyl methacrylate) (HPD) conjugate complexes

Ahrens T, Assmann V, Fieber C, Termeer C, Herrlich P, Hofmann M, Simon JC. CD44 is the principal mediator of hyaluronic-acid-induced melanoma cell proliferation. J Invest Dermatol. 2001 Jan;116(1):93-101. doi: 10.1046/j.1523-1747.2001.00236.x. PMID: 11168803. [jidonline]

Tumor tissues


Antibody affibody

Her-2 receptor

Chitosan/quantum dot nanoparticles

Tan WB, Jiang S, Zhang Y. Quantum-dot based nanoparticles for targeted silencing of HER2/neu gene via RNA interference. Biomaterials. 2007 Mar;28(8):1565-71. doi: 10.1016/j.biomaterials.2006.11.018. Epub 2006 Dec 11. PMID: 17161865. [Science]

Bionanocapsule/liposome complexes

Yoon HY, Kim HR, Saravanakumar G, Heo R, Chae SY, Um W, Kim K, Kwon IC, Lee JY, Lee DS, Park JC, Park JH. Bioreducible hyaluronic acid conjugates as siRNA carrier for tumor targeting. J Control Release. 2013 Dec 28;172(3):653-61. [Sciencedirect]

Tumor tissues


Sigma receptor


Nishimura Y, Mieda H, Ishii J, Ogino C, Fujiwara T, Kondo A. Targeting cancer cell-specific RNA interference by siRNA delivery using a complex carrier of affibody-displaying bio-nanocapsules and liposomes. J Nanobiotechnology. 2013 Jun 24;11:19. doi: 10.1186/1477-3155-11-19. [PMC]

Lipid/protamine nanoparticles

Li SD, Chen YC, Hackett MJ, Huang L. Tumor-targeted delivery of siRNA by self-assembled nanoparticles. Mol Ther. 2008 Jan;16(1):163-9. [PMC]

Tumor tissues

Designed ankyrin repeat protein

Epithelial cell adhesion molecule


Winkler J, Martin-Killias P, Plückthun A, Zangemeister-Wittke U. EpCAM-targeted delivery of nanocomplexed siRNA to tumor cells with designed ankyrin repeat proteins. Mol Cancer Ther. 2009 Sep;8(9):2674-83. [PMC]

Tumor tissues

EGFR-targeted peptide


Chitosan nanoparticles

Nascimento AV, Singh A, Bousbaa H, Ferreira D, Sarmento B, Amiji MM. Mad2 checkpoint gene silencing using epidermal growth factor receptor-targeted chitosan nanoparticles in non-small cell lung cancer model. Mol Pharm. 2014 Oct 6;11(10):3515-27. doi: 10.1021/mp5002894. Epub 2014 Sep 26. PMID: 25256346; PMCID: PMC4186685. [PMC]

Tumor tissues

Bombesin-like histidine-rich peptide



Nakagawa O, Ming X, Carver K, Juliano R. Conjugation with receptor-targeted histidine-rich peptides enhances the pharmacological effectiveness of antisense oligonucleotides. Bioconjug Chem. 2014 Jan 15;25(1):165-70.  [PMC]

Tumor tissues

EGFR-, vimentin-targeted peptides



Lee, E. J., Lee, S. J., Kang, Y. S., Ryu, J. H., Kwon, K. C., Jo, E., Yhee, J. Y., Kwon, I. C., Kim, K., & Lee, J. (2015). Engineered proteinticles for targeted delivery of siRNA to cancer cells. Advanced Functional Materials25(8), 1279-1286. 


A proteinticle is a nanoscale particle constructed of proteins that self-assembles inside cells to form a constant structure and surface topology.


Lorenzer C, Dirin M, Winkler AM, Baumann V, Winkler J. Going beyond the liver: progress and challenges of targeted delivery of siRNA therapeutics. J Control Release. 2015 Apr 10; 203:1-15. https://www.sciencedirect.com/science/article/pii/S0168365915000930?via%3Dihub