Biomedical Engineering Reference
In-Depth Information
were fairly high, reaching almost 100% under optimal conditions. The calcium
phosphate core dissociated in the intracellular environment with appreciably
lowered calcium ion concentration compared to the exterior, allowing the
release of the incorporated siRNA in a controlled manner. Appreciable
silencing of GL3 luciferase gene expression (up to about 60%) was observed for
the siRNA-incorporated nanoparticles prepared over the polymer concentra-
tion range from 420 to 700 mgmL
-1
.
61
Other different micelle assembling block copolymers were further designed
for siRNA delivery. Compared with the water-soluble polycations, such
micellar nanoparticles exhibited their own advantages. Instead of mixing
water-soluble polycations and siRNA to form complexes, which would result
in the formation of uncontrollable large particles, micellar nanoparticles with a
positive charge allow nucleic acid loading after the formation of nanoparti-
cles.
62
This is believed to be favorable for the construction of size-controllable
and monodispersed nucleic acid loaded nanoparticles, which may display
unique advantages for in vivo applications.
63
In addition, such a preparation
method may be convenient for expansion to meet the large quantity
requirements for therapeutic applications.
62
The common copolymers for
siRNA delivery are those having polyester as core-forming blocks and PEG as
the shell-forming blocks, with cationic moieties in the polyester or PEG blocks.
The biocompatibility of both PEG and polyesters has been demonstrated.
PEG has been extensively used for coating different pharmaceuticals to modify
their pharmacokinetics, increase their safety, or lower their immunogeni-
city.
64,65
Polyesters, such as poly(e-caprolactone), polylactide, and poly(lac-
tide-co-glycolide), are proven biodegradable polymers and have a history of
safe application in absorbable biomedical devices such as sutures.
66,67
Xiong et al. developed a series of promising polymeric micelle carriers for
siRNA delivery based on degradable poly(ethylene oxide)-block-poly(e-
caprolactone) (PEO-b-PCL) containing polycationic side chains on their
polyester block, such as PEO-b-PCL with grafted spermine [PEO-b-P(CL-g-
SP)], tetraethylenepentamine [PEO-b-P(CL-g-TP)], and N,N-dimethyldipropy-
lenetriamine [PEO-b-P(CL-g-DP)]. Those polyamine-grafted PEO-b-PCL
polymers were found to effectively bind siRNA, self-assemble into micelles,
protect siRNA from degradation by nucleases, and be efficient in the delivery
of MDR-1 siRNA to silence P-glycoprotein (P-gp) expression in the resistant
human MDA435/LCC6 cancer cell line.
68
An advanced functional siRNA
carrier was based on PEO-b-P(CL-g-SP) decorated with integrin a
v
b
3
ligand
(RGD4C) and/or a cell-penetrating ligand (TAT) on the PEO shell, in order to
overcome the steric effect of the hydrophilic PEO shell that impeded the
attachment of the micellar carrier to cells (Figure 7.3). Increased cellular
uptake and effective endosomal escape of siRNA were demonstrated in those
delivered with the peptide-functionalized micelles, especially those with dual
functionality (RGD/TAT micelles) compared to unmodified micelles in
resistant MDA435/LCC6 cells. Transfection of MDR-1 siRNA formulated
in peptide-modified micelles led to P-gp downregulation both at the mRNA
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