To search for potential non-viral nucleic acids carriers, a series of novel cationic polymers, multi-armed poly(aspartate-graft-oligoethylenimine) (MP-g-OEI) copolymers were designed and synthesized by grafting different types of oligoethylenimine (OEI) to a multi-armed poly(l-aspartic acid) backbone. The as-synthesized MP-g-OEI copolymers were characterized by Fourier transform infrared spectroscopy, nuclear magnetic resonance and gel permeation chromatography. These MP-g-OEI copolymers (MP423, MP600 and MP1800) exhibited good capacity in condensing nucleic acids (pDNA or siRNA) into nanosized particles (90–150 nm) with positive surface charges. Gene transfection activity of the MP-g-OEI copolymers (especially MP1800) showed improved performance compared with PEI25k in both HeLa and CHO cell lines. The silencing efficiency of MP600/siRNA and MP1800/siRNA complexes showed a superior knockdown effect in CT26 and Huh-7 cell lines. Moreover, the MP-g-OEI copolymers exhibited much lower cytotoxicity than PEI25k. Flow cytometric analysis showed that MP-g-OEI copolymers could efficiently mediate the entry of nucleic acids into cells. These results suggest that MP-g-OEI copolymers may be potential non-viral gene carriers for the delivery of nucleic acids in future gene therapy.
A novel pH-sensitive charge-conversion shielding system was designed by the electrostatic binding of polyethylenimine (PEI)-poly(l-lysine)-poly(l-glutamic acid) (PELG), PEI, and cis-aconityl-doxorubicin (CAD). Doxorubicin (DOX) was modified by cis-aconityl linkage to form acid-sensitive CAD, which was then adsorbed by the positively charged PEI. The PEI/CAD complexes were subsequently shielded with the pH-responsive charge-conversion PELG. In normal tissues, the PELG/PEI/CAD complexes were negatively charged; in acidic tumor tissues, the shielding PELG was positively charged and detached from the PELG/PEI/CAD complexes. The resulting positively charged PEI/CAD complexes thus became exposed and were endocytosed. CAD was then cleaved in the acidic intracellular environment of endosomes and lysosomes, and converted back into DOX. The charge reversal of the PELG/PEI/CAD complexes was verified by zeta potential analysis at different pH values. Moreover, DOX release increased with decreasing pH. Cell uptake and confocal laser scanning microscopy analyses showed that, at pH 6.8, PELG/PEI/CAD had the highest endocytosis rate and more DOX entered cell nuclei. More importantly, the system showed remarkable cytotoxicity against cancer cells. These results revealed that the combination of pH-sensitive charge-conversion shielding with pH-sensitive drug release is a potential drug delivery system for tumor treatment.
Two copolymers are designed and synthesised for siRNA delivery based on polyethylenimine by grafting hydrophilic acrylamide segments and hydrophobic poly(γ-benzyl L-glutamate). The amphiphilic PEI-PBLG/siRNA complex demonstrates high gene silencing efficiency in the absence or presence of 10 vol% and 50 vol% sera in vitro. The anti-tumor effects in vivo are evaluated in luciferase-bearing mice expressing CT26 tumors. PEI-PBLG/siVEGF complex provides a higher and more sustained suppressive effect by reducing VEGF mRNA expression in the tumors, leading to higher tumor growth inhibition efficacy. Further studies on the potential use of the PEI-PBLG carrier system in mediating the silencing of genes other than VEGF or in other tumor models are recommended.
A polyethylenimine-poly(hydroxyethyl glutamine) copolymer (PEI-PHEG) was designed and synthesized as a gene delivery system. The molecular structure of PEI-PHEG was characterized using nuclear magnetic resonance. Moreover, PEI-PHEG/pDNA complexes were fabricated and characterized by gel retardation assay, particle size analysis, and zeta potential analysis. The transfection efficiency and cytotoxicity of PEI-PHEG were evaluated using human cervical carcinoma (HeLa), human embryonic kidney (HEK293), and murine colorectal adenocarcinoma (CT26) cells in vitro. The results show that PEI-PHEG could effectively form positively charged nano-sized particles with pDNA; the particle size was in a range of 130.2 to 173.0 nm and the zeta potential was in a range of 27.6 to 41.0 mV. PEI-PHEG exhibited much lower cytotoxicity and higher gene transfection efficiency than PEI-25K with different cell lines in vitro. An animal test was also conducted on a Lewis Lung Carcinoma tumor model in C57/BL6 mice by using subcutaneous intratumoral administration. The results show that in vivo transfection efficiency of PEI-PHEG was improved greatly compared with that of commercial PEI-25K. These results demonstrate that PEI-PHEG can be a potential nonviral vector for gene delivery systems both in vitro and in vivo. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012
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