Biomedical Engineering Reference
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Fig. 15.6 Schematic of DNA strands for tetrahedron formation ( arrow head represents 5 0 end of
the nucleic acid strand) and representation showing site-specific hybridization of siRNA to the
self-assembled nanoparticles (Reprinted by permission from Macmillan Publishers Ltd: Nature
Nanotechnology, Ref. [ 12 ], copyright 2012)
of 0.1
M, and due to the immunostimulatory activity of CpG motifs, CpG-
functionalized nanostructures even slightly stimulated the growth of cells.
This functional CpG-DNA tetrahedron work showed that DNA tetrahedron
nanostructures have the potential to be used as universal drug delivery nanocarriers.
Most recently, Langer and Anderson's group used this DNA tetrahedron nanos-
tructure as targeted SiRNA nanocarrier in vivo [ 12 ]. The addressability of the DNA
3D nanostructure allowed them to have one nick site on each of the middle of edge
of the DNA tetrahedron. The overhangs at those nick sites are complementary to the
interested SiRNA strands. So each DNA tetrahedron can be attached with up to six
SiRNA strands (Fig. 15.6 ,Ref.[ 12 ]). Cell-targeting ligands (folate and peptides in
their study) can be attached to the outer ends of the SiRNA strands to differentiate
the cancerous cells from normal cells.
For their folate (FA)-mediated gene silencing, by mixing 35 nM dose of FA-
conjugated DNA tetrahedrons carrying siRNA-targeting GFP with folate receptor
overexpressing KB cells (expressing green fluorescent protein, GFP), they found a
reduction of .60% in GFP expression in KB cells. Also by utilizing the addressability
of this DNA tetrahedron nanostructure, they found that a minimum of three FAs
at a close distance on the DNA tetrahedron is essential for GFP silencing, which
proved that the density and location of ligands can greatly influence nanoparticle-
cell membrane interactions as well as intracellular uptake pathway.
Next they did a test on the in vivo delivery of DNA tetrahedrons, by tail-
vein injection, and they systemically delivered Cy5-labeled DNA tetrahedrons with
folate ligands into nude mice bearing KB xenograft tumors. The high-resolution
fluorescence images they got from fluorescence molecular tomography fused with
computed tomography (FMT-CT) over the course of 24 h clearly showed DNA
tetrahedrons accumulated primarily in the tumor and kidney (Fig. 15.7 ,Ref.[ 12 ]).
Their results also showed that the accumulation of ONPs in the tumor region as
early as 25 min post-injection. Also, the DNA tetrahedrons showed an almost
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