Spherical, well-defined core-shell nanoparticles that consist of poly(methyl methacrylate) (PMMA) cores and branched poly(ethylenimine) shells (PEI) were synthesized via a graft copolymerization of methyl methacrylate from branched PEI induced by a small amount of tert-butyl hydroperoxide. The PMMA-PEI core-shell nanoparticles were between 130 to170 nm in diameter and displayed zeta-potentials near +40 mV at pH 7 in 1 mM aqueous NaCl. Plasmid DNA (pDNA) was mixed with nanoparticles and formed complexes of approximately 120 nm in diameter and was highly monodispersed. The complexes were characterized with respect to their particle size, zeta-potential, surface morphology, and DNA integrity. The complexing ability of the nanoparticles was strongly dependent on the molecular weight of the PEI and the thickness of the PEI shells. The stability of the complexes was influenced by the loading ratio of the pDNA and the nanoparticles. The condensed pDNA in the complexes was significantly protected from enzymatic degradation by DNase I. Cytotoxity studies using MTT colorimetric assays suggested that the PMMA-PEI (25 kDa) core-shell nanoparticles were three times less toxic than the branched PEI (25 kDa). Their transfection efficiencies were also significantly higher. Thus, the PEI-based core-shell nanoparticles show considerable potential as carriers for gene delivery.
"An efficient gene delivery system must be able to protect DNA from degradation by nucleases in serum and in the extracellular matrix.35 As shown in Figure 6, after incubation with DNase I, the naked DNA and the DNA in PEI 800-DNA complexes were all completely degraded, while the DNA in SP-DNA complexes or PEI 25,000-DNA complexes remained intact, indicating that both SP-DNA complexes and PEI 25,000-DNA complexes can effectively protect DNA from degradation by DNase I. Quantification of the intact DNA (ImageJ, NIH) revealed that 93.0% and 94.4% of the loaded DNA was recovered from the SP-DNA complexes and PEI 25,000-DNA complexes, respectively, indicating that the ability of SP to protect DNA from enzymatic cleavage is comparable with that of PEI 25,000. "
[Show abstract][Hide abstract] ABSTRACT: A new amphiphilic comb-shaped copolymer (SP) was synthesized by conjugating poly(styrene-co-maleic anhydride) with low molecular weight polyethyleneimine for gene delivery. Fourier transform infrared spectrum, (1)H nuclear magnetic resonance, and gel permeation chromatography were used to characterize the graft copolymer.
The buffering capability of SP was similar to that of polyethyleneimine within the endosomal pH range. The copolymer could condense DNA effectively to form complexes with a positive charge (13-30 mV) and a small particle size (130-200 nm) at N/P ratios between 5 and 20, and protect DNA from degradation by DNase I. In addition, SP showed much lower cytotoxicity than polyethyleneimine 25,000. Importantly, the gene transfection activity and cellular uptake of SP-DNA complexes were all markedly higher than that of complexes of polyethyleneimine 25,000 and DNA in MCF-7 and MCF-7/ADR cell lines.
This work highlights the promise of SP as a safe and efficient synthetic vector for DNA delivery.
International Journal of Nanomedicine 09/2012; 7:4961-72. DOI:10.2147/IJN.S32069 · 4.38 Impact Factor
"Polymeric NPs have an advantage over both liposomes and lipid reagents because of their ease of manipulation, control over DNA release profiles, and biological stability in vivo . In addition, the properties of these NPs can be easily modified, for example, by addition of functional polymer groups to increase uptake or improve release of cargo genetic material   . One of the major drawbacks to gene encapsulation in synthetic polymers for delivery using bottom-up techniques is the incorporation of plasmid DNA (pDNA) into the particles during the synthesis phase. "
[Show abstract][Hide abstract] ABSTRACT: Poly(D,L-lactide-co-glycolide-) (PLGA-)chitosan nanoparticles are becoming an increasingly common choice for the delivery of nucleic acids to cells for various genetic manipulation techniques. These particles are biocompatible, with tunable size and surface properties, possessing an overall positive charge that promotes complex formation with negatively charged nucleic acids. This study examines properties of the PLGA-chitosan nanoparticle/plasmid DNA complex after formation. Specifically, the study aims to determine the optimal ratio of plasmid DNA:nanoparticles for nucleic acid delivery purposes and to elucidate the location of the pDNA within these complexes. Such characterization will be necessary for the adoption of these formulations in a clinical setting. The ability of PLGA-chitosan nanoparticles to form complexes with pDNA was evaluated by using the fluorescent intercalating due OliGreen to label free plasmid DNA. By monitoring the fluorescence at different plasmid: nanoparticle ratios, the ideal plasmid:nanoparticle ration for complete complexation of plasmid was determined to be 1:50. Surface-Enhanced Raman Spectroscopy and gel digest studies suggested that even at these optimal complexation ratios, a portion of the plasmid DNA was located on the outer complex surface. This knowledge will facilitate future investigations into the functionality of the system in vitro and in vivo.
Journal of Nanomaterials 01/2011; 2011. DOI:10.1155/2011/952060 · 1.64 Impact Factor
"Secondly, instead of mixing water-soluble polycations and DNA (or siRNA) to form complexes, which would result in the formation of uncontrollable large particles , micellar nanoparticles with positive charge allows nucleic acid loading post nanoparticles formation. This is believed to be favorable for the construction of size-controllable and monodispersed nucleic acid loaded nanoparticles, which may display unique advantage for in vivo applications . In addition, such preparation method may be convenient for expansion to meet large quantity requirement for therapeutic applications. "
[Show abstract][Hide abstract] ABSTRACT: A novel amphiphilic and cationic triblock copolymer consisting of monomethoxy poly(ethylene glycol), poly(epsilon-caprolactone) (PCL) and poly(2-aminoethyl ethylene phosphate) denoted as mPEG(45)-b-PCL(100)-b-PPEEA(12) was designed and synthesized for siRNA delivery. The copolymers were well characterized by (1)H NMR spectroscopy and gel permeation chromatography. Micelle nanoparticles' (MNPs) formation of this amphiphilic copolymer in aqueous solution was studied by dynamic light scattering, transmission electron microscopy and fluorescence technique. MNPs took uniform spherical morphology with zeta potential of around 45 mV and were stabilized by hydrophobic-hydrophobic interaction in the PCL core, exhibiting the critical micelle concentration at 2.7 x 10(-3) mg/mL. Such MNPs allowed siRNA loading post nanoparticle formation without change in uniformity. The average diameter of nanoparticles after siRNA binding ranged from 98 to 125 nm depending on N/P ratios. The siRNA loaded nanoparticles can be effectively internalized and subsequently release siRNA in HEK293 cells, resulting in significant gene knockdown activities, which was demonstrated by delivering two siRNAs targeting green fluorescence protein (GFP). It effectively silenced GFP expression in 40-70% GFP-expressed HEK293 cells and it was observed that higher N/P ratio resulted in more effective silence which was likely due to better cell internalization at higher N/P ratio. MTT assay demonstrated that neither MNPs themselves nor siRNA loaded MNPs showed cytotoxicity even at high concentrations. Such cationic MNPs made from biocompatible and biodegradable polymers are promising for siRNA delivery.
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