Polyplex Micelles Research Articles

Gene Transfer Using Micellar Nanovectors Inhibits Corneal Neovascularization In Vivo

The efficacy of gene therapy using nonviral vector based on polyplex micelle has been studied against corneal neovascularization in mice. A block copolymer, poly(ethylene glycol) (PEG)-block-polycation carrying ethylenediamine units in the side chain (PEG-b-P[Asp(DET)]), was prepared. PEG-b-P[Asp(DET)] formed a polyplex micelle through the polyion complex formation with plasmid DNA. To evaluate in vivo gene transfer efficiency, PEG-b-P[Asp(DET)] micelle was injected into the subconjunctival space of mice, and the expression of the reporter gene was assessed. Furthermore, mouse corneal neovascularization models were treated with the PEG-b-P[Asp(DET)] polyplex micelle containing expression plasmid vector of soluble vascular endothelial growth factor receptor 1 (sflt-1). Subconjunctival injection of the PEG-b-P[Asp(DET)] polyplex micelle containing a reporter gene showed prolonged gene expression with low cytotoxicity. Also, gene transfer into subconjunctival space by the polyplex micelle containing sflt-1 plasmid showed significant inhibition of corneal neovascularization in mice. Nonviral gene therapy using PEG-b-P[Asp(DET)] polyplex micelle may have potential for safe and effective therapeutic treatment of corneal neovascularization.

Enhanced gene expression promoted by the quantized folding of pDNA within polyplex micelles

Selective packaging of plasmid DNA (pDNA) into folded rod or collapsed sphere structures in polyplex micelles was demonstrated by modulating the PLys segment length of poly(ethylene glycol)- block- poly( l-lysine) (PEG-PLys) block catiomers used for micelle formation. The two basic packaging structures correlated well to the integrity of double-stranded DNA contained within the micelles. Rod structures formed by the quantized folding mechanism, which results in dissociation of double-stranded DNA only at each fold. Collapsed sphere structures formed by substantial random disruption of the double-stranded DNA structure. Analysis of gene expression in a cell-free transcription/translation system, cultured cells and also skeletal muscle of mice showed that micelles containing pDNA packaged by quantized folding exhibited higher gene expression than naked pDNA and micelles containing collapsed pDNA. These results indicate that controlled packaging of pDNA into an appropriate structure is critical for achieving effective gene expression. Improved gene transfection and expression resulting from the quantized folding of pDNA within polyplex micelles is promising for application in therapeutic gene delivery systems.

Effect of integrin targeting and PEG shielding on polyplex micelle internalization studied by live-cell imaging

α vβ 3 and α vβ 5 integrins are attractive target structures for cancer therapy as they are upregulated in tumor and tumor associated host cells and play a pivotal role for tumor growth and metastasis. Gene vectors such as polyplex micelles consisting of thiolated PEG-block-poly(lysine) copolymers complexed with plasmid DNA can be targeted to these specific integrins by equipment with a cyclic RGD peptide. In this study, we analyzed the effect of the RGD ligand on micelle endocytosis by comparing fluorescently labeled, targeted and untargeted micelles in live-cell imaging experiments with highly sensitive fluorescence microscopy and flow cytometry. Two micelle types with 12 kDa (PEG12) and 17 kDa (PEG17) PEG shell layers were examined to evaluate the influence of surface shielding on the internalization characteristics. Our results reveal three major effects: First, the RGD ligand accelerates the internalization of micelles into integrin expressing HeLa cells without changing the uptake pathway of the micelles. Both targeted as well as untargeted micelles are predominantly internalized via clathrin mediated endocytosis. Second, the PEG shielding of micelles has an important effect on their targeting specificity. At high PEG shielding selective endocytosis of integrin targeted micelles occurs, whereas at low PEG shielding targeted and untargeted micelles show comparable internalization. In addition, PEG17 RGD(+) micelles induce the highest reporter gene expression. Third, our data demonstrate a clear influence of the applied micelle dose on the internalization of integrin targeted micelles. We propose that PEG17 shielded micelles equipped with a cyclic RGD ligand are the favored system of choice for clinical therapy as they exhibit higher transgene expression, a higher specificity for integrin-dependent endocytosis compared to PEG12 shielded micelles, and are functional at low doses as well.

Impact of polyplex micelles installed with cyclic RGD peptide as ligand on gene delivery to vascular lesions

Gene therapy is expected to open a new strategy for the treatment of refractory vascular diseases, so the development of appropriate gene vectors for vascular lesions is needed. To realize this requirement with a non-viral approach, cyclo(RGDfK) peptide (cRGD) was introduced to block copolymer, poly(ethylene glycol)-block-polycation carrying ethylenediamine units (PEG-PAsp(DET)). cRGD recognizes α(v)β(3) and α(v)β(5) integrins, which are abundantly expressed in vascular lesions. cRGD-conjugated PEG-PAsp(DET) (cRGD-PEG-PAsp(DET)) formed polyplex micelles through complexation with plasmid DNA (pDNA) and the cRGD-PEG-PAsp(DET) micelles achieved significantly more efficient gene expression and cellular uptake as compared with PEG-PAsp(DET) micelles in endothelial cells and vascular smooth muscle cells. Intracellular tracking of pDNA showed that cRGD-PEG-PAsp(DET) micelles were internalized via caveolae-mediated endocytosis, which is associated with a pathway avoiding lysosomal degradation and that, PEG-PAsp(DET) micelles were transported to acidic endosomes and lysosomes via clathrin-mediated endocytosis. Further, in vivo evaluation in rat carotid artery with a neointimal lesion revealed that cRGD-PEG-PAsp(DET) micelles realized sustained gene expression, whereas PEG-PAsp(DET) micelles facilitated rapid, but transient gene expression. These findings suggest that introduction of cRGD to polyplex micelles might create novel and useful functions for gene transfer and contribute to the establishment of efficient gene therapy for vascular diseases.

Combination of chondroitin sulfate and polyplex micelles from Poly(ethylene glycol)-poly{N’-[N-(2-aminoethyl)-2-aminoethyl]aspartamide} block copolymer for prolonged in vivo gene transfection with reduced toxicity

Nonviral polycation-based gene carriers (polyplexes) have attracted attention as safe and efficient gene delivery systems. Polyplex micelles comprised of poly(ethyleneglycol)- block-poly{N’-[N-(2-aminoethyl)-2-aminoethyl]aspartamide} (PEG-PAsp(DET)) and plasmid DNA (pDNA) have shown high transfection efficiency with low toxicity due to the pH-sensitive protonation behavior of PAsp(DET), which enhances endosomal escape, and their self-catalytic degradability under physiological conditions, which reduces cumulative toxicity during transfection. In this study, we improved the safety and transfection efficiency of this polyplex micelle system by adding an anionic polycarbohydrate, chondroitin sulfate (CS). A quantitative assay for cell membrane integrity using image analysis software showed that the addition of CS markedly reduced membrane damage caused by free polycations in the micelle solution. It also reduced tissue damage and subsequent inflammatory responses in the skeletal muscle and lungs of mice following in vivo gene delivery with the polyplex micelles. Subsequently, this led to prolonged transgene expression in the target organs. This combination of polyplex micelles and CS holds great promise for safe and efficient gene introduction in clinical settings.

In situ quantitative monitoring of polyplexes and polyplex micelles in the blood circulation using intravital real-time confocal laser scanning microscopy

Surface modification using poly(ethylene glycol) (PEG) is a widely used strategy to improve the biocompatibility of cationic polymer-based nonviral gene vectors (polyplexes). A novel method based on intravital real-time confocal laser scanning microscopy (IVRTCLSM) was applied to quantify the dynamic states of polyplexes in the bloodstream, thereby demonstrating the efficacy of PEGylation to prevent their agglomeration. Blood flow in the earlobe blood vessels of experimental animals was monitored in a noninvasive manner to directly observe polyplexes in the circulation. Polyplexes formed distinct aggregates immediately after intravenous injection, followed by interaction with platelets. To quantify aggregate formation and platelet interaction, the coefficient of variation and Pearson's correlation coefficient were adopted. In contrast, polyplex micelles prepared through self-assembly of plasmid DNA with PEG-based block catiomers had dense PEG palisades, revealing no formation of aggregates without visible interaction with platelets during circulation. This is the first report of in situ monitoring and quantification of the availability of PEGylation to prevent polyplexes from agglomeration over time in the blood circulation. This shows the high utility of IVRTCLSM in drug and gene delivery research.

Impact of polyplex micelles installed with cyclic RGD peptide as ligand on gene delivery to vascular lesions

AbstractGene therapy is expected to open a new strategy for the treatment of refractory vascular diseases, so the development of appropriate gene vectors for vascular lesions is needed. To realize this requirement with a non-viral approach, cyclo(RGDfK) peptide (cRGD) was introduced to block copolymer, poly(ethylene glycol)-block-polycation carrying ethylenediamine units (PEG-PAsp(DET)). cRGD recognizes &x03B1;v&x03B2;3 and &x03B1;v&x03B2;5 integrins, which are abundantly expressed in vascular lesions. cRGD-conjugated PEG-PAsp(DET) (cRGD-PEG-PAsp(DET)) formed polyplex micelles through complexation with plasmid DNA (pDNA), and the cRGD-PEG-PAsp(DET) micelles achieved significantly more efficient gene expression and cellular uptake as compared with PEG-PAsp(DET) micelles in endothelial cells and vascular smooth muscle cells. Intracellular tracking of pDNA showed that cRGD-PEG-PAsp(DET) micelles were internalized via caveolae-mediated endocytosis, which is associated with a pathway avoiding lysosomal degradation, and that PEG-PAsp(DET) micelles were transported to acidic endosomes and lysosomes via clathrin-mediated endocytosis. Further, in vivo evaluation in rat carotid artery with a neointimal lesion revealed that cRGD-PEG-PAsp(DET) micelles realized sustained gene expression, while PEG-PAsp(DET) micelles facilitated rapid but transient gene expression. These findings suggest that introduction of cRGD to polyplex micelles might create novel and useful functions for gene transfer and contribute to the establishment of efficient gene therapy for vascular diseases.

Polyplex micelles prepared from ω-cholesteryl PEG-polycation block copolymers for systemic gene delivery

Polyplex micelles formed with plasmid DNA (pDNA) and poly(ethylene glycol) (PEG)- block-poly{ N-[ N-(2-aminoethyl)-2-aminoethyl]aspartamide} [PAsp(DET)] exhibit effective endosomal escaping properties based on di-protonation of diamine side chains with decreasing pH, which improves their transfection efficiency and thus are promising candidates for local in vivo gene transfer. Here, PEG-PAsp(DET) polyplex micelles were further improved as in vivo systemic vectors by introduction of cholesterol (Chole) into the ω-terminus of PEG-PAsp(DET) to obtain PEG-PAsp(DET)-Chole. Introduction of the cholesterol resulted in enhanced association of block copolymers with pDNA, which led to increased stability in proteinous medium and also in the blood stream after systemic injection compared to PEG-PAsp(DET) micelles. The synergistic effect between enhanced polymer association with pDNA and increased micelle stability of PEG-PAsp(DET)-Chole polyplex micelles led to high in vitro gene transfer even at relatively low concentrations, due to efficient cellular uptake and effective endosomal escape of block copolymers and pDNA. Finally, PEG-PAsp(DET)-Chole micelles achieved significant suppression of tumor growth following intravenous injection into mice bearing a subcutaneous pancreatic tumor using therapeutic pDNA encoding an anti-angiogenic protein. These results suggest that PEG-PAsp(DET)-Chole micelles can be effective systemic gene vectors for treatment of solid tumors.

Antiangiogenic Gene Therapy of Solid Tumor by Systemic Injection of Polyplex Micelles Loading Plasmid DNA Encoding Soluble Flt-1

In this study, a polyplex micelle was developed as a potential formulation for antiangiogenic gene therapy of subcutaneous pancreatic tumor model. Poly(ethylene glycol)-poly(l-lysine) block copolymers (PEG-PLys) with thiol groups in the side chain of the PLys segment were synthesized and applied for preparation of disulfide cross-linked polyplex micelles through ion complexation with plasmid DNA (pDNA) encoding the soluble form of vascular endothelial growth factor (VEGF) receptor-1 (sFlt-1), which is a potent antiangiogenic molecule. Antitumor activity and gene expression of polyplex micelles with various cross-linking rates were evaluated in mice bearing subcutaneously xenografted BxPC3 cell line, derived from human pancreatic adenocarcinoma, and polyplex micelles with optimal cross-linking rate achieved effective suppression of tumor growth. Significant gene expression of this micelle was detected selectively in tumor tissue, and its antiangiogenic effect was confirmed by decreased vascular density inside the tumor. Therefore, the disulfide cross-linked polyplex micelle loading sFlt-1 pDNA has a great potential for antiangiogenic therapy against subcutaneous pancreatic tumor model by systemic application.

Antiangiogenic gene therapy of experimental pancreatic tumor by sFlt-1 plasmid DNA carried by RGD-modified crosslinked polyplex micelles

Disulfide crosslinked polyplex micelles with RGD peptides were formed through ion complexation of thiolated c(RGDfK)-poly(ethylene glycol)- block-poly( l-lysine) (c(RGDfK)-PEG-P(Lys-SH)) and plasmid DNA encoding sFlt-1 and tested for their therapeutic effect in BxPC3 pancreatic adenocarcinoma tumor bearing mice. These micelles, systemically injected, demonstrated significant inhibition of tumor growth up to day 18, as a result of the antiangiogenic effect that was confirmed by vascular density measurements. Significant therapeutic activity of the 15% crosslinked micelle (c(RGDfK)-PEG-P(Lys-SH15)) was achieved by combined effect of increased tumor accumulation, interaction with endothelial cells and enhanced intracellular uptake through receptor-mediated endocytosis. These results suggest that RGD targeted crosslinked polyplex micelles can be effective plasmid DNA carriers for antiangiogenic gene therapy.

Enhanced Percolation and Gene Expression in Tumor Hypoxia by PEGylated Polyplex Micelles

In regard to gene vectors for cancer gene therapy, their percolation into the tumor tissue should be essential for successful outcome. Here, we studied the tumor penetrability of nonviral vectors (polyplexes) after incubation with the multicellular tumor spheroid (MCTS) models and intratumoral (i.t.) injection into subcutaneous tumors. As a result, polyethylene glycolated (PEGylated), core-shell type polyplexes (polyplex micelles) showed facilitated percolation and improved transfection inside the tumor tissue, whereas conventional polyplexes from cationic polymers exhibited limited percolation and localized transfection. Furthermore, the transfection of hypoxia-responsive plasmid demonstrated that polyplex micelles allowed the transfection to the hypoxic region of the tumor tissue in both in vitro and in vivo experiments. To the best of our knowledge, our results demonstrated for the first time that polyplex micelles might show improved tumor penetrability over cationic polyplexes, thereby achieving transfection into the inside of the tumor tissue.

Polyplex Micelles with Cyclic RGD Peptide Ligands and Disulfide Cross-Links Directing to the Enhanced Transfection via Controlled Intracellular Trafficking

Thiolated c(RGDfK)-poly(ethylene glycol)-block-poly(lysine) (PEG-PLys), a novel block polymer that has a cyclic RGD peptide in the PEG terminus and thiol groups in the PLys side chain, was prepared and applied to the preparation of targetable disulfide cross-linked polyplex micelles through ion complexation with plasmid DNA (pDNA). The obtained polyplex micelles achieved remarkably enhanced transfection efficiency against cultured HeLa cells possessing alpha(v)beta(3) integrin receptors, which are selectively recognized by cyclic RGD peptides, demonstrating the synergistic effect of cyclic RGD peptide ligands on the micelle surface and disulfide cross-links in the core to exert the smooth release of pDNA in the intracellular environment via reductive cleavage. This enhancement was not due to an increase in the uptake amount of polyplex micelles but to a change in their intracellular trafficking route. Detailed confocal laser scanning microscopic observation revealed that polyplex micelles with cyclic RGD peptide ligands were distributed in the perinuclear region in the early stages preferentially through caveolae-mediated endocytosis, which may be a desirable pathway for avoiding the lysosomal degradation of delivered genes. Hence, this approach to introducing ligands and cross-links into the polyplex micelles is promising for the construction of nonviral gene vectors that enhance transfection by controlling intracellular distribution.

Polyplex Micelles from Triblock Copolymers Composed of Tandemly Aligned Segments with Biocompatible, Endosomal Escaping, and DNA-Condensing Functions for Systemic Gene Delivery to Pancreatic Tumor Tissue

For systemic gene delivery to pancreatic tumor tissues, we prepared a three-layered polyplex micelle equipped with biocompatibility, efficient endosomal escape, and pDNA condensation functions from three components tandemly aligned; poly(ethylene glycol) (PEG), a poly(aspartamide) derivative with a 1,2-diaminoethane moiety (PAsp(DET)), and poly(L-lysine). The size and in vitro transfection efficacy of the polyplex micelles were determined by dynamic light scattering (DLS) and luciferase assay, respectively. The systemic gene delivery with the polyplex micelles was evaluated from enhanced green fluorescence protein (EGFP) expression in the tumor tissues. The polyplex micelles were approximately 80 nm in size and had one order of magnitude higher in vitro transfection efficacy than that of a diblock copolymer as a control. With the aid of transforming growth factor (TGF)-beta type I receptor (TbetaR-1) inhibitor, which enhances accumulation of macromolecular drugs in tumor tissues, the polyplex micelle from the triblock copolymer showed significant EGFP expression in the pancreatic tumor (BxPC3) tissues, mainly in the stromal regions including the vascular endothelial cells and fibroblasts. The three-layered polyplex micelles were confirmed to be an effective gene delivery system to subcutaneously implanted pancreatic tumor tissues through systemic administration.

PEG-Detachable Polyplex Micelles Based on Disulfide-Linked Block Catiomers as Bioresponsive Nonviral Gene Vectors

PEG-based polyplex micelles, which can detach the surrounding PEG chains responsive to the intracellular reducing environment, were developed as nonviral gene vectors. A novel block catiomer, PEG-SS-P[Asp(DET)], was designed as follows: (i) insertion of biocleavable disulfide linkage between PEG and polycation segment to trigger PEG detachment and (ii) a cationic segment based on poly(aspartamide) with a flanking N-(2-aminoethyl)-2-aminoethyl group, P[Asp(DET)], in which the Asp(DET) unit acts as a buffering moiety inducing endosomal escape with minimal cytotoxicity. The polyplex micelles from PEG-SS-P[Asp(DET)] and plasmid DNA (pDNA) stably dispersed in an aqueous medium with a narrowly distributed size range of approximately 80 nm due to the formation of hydrophilic PEG palisades while undergoing aggregation by the addition of 10 mM dithiothreitol (DTT) at the stoichiometric charge ratio, indicating the PEG detachment from the micelles through the disulfide cleavage. The PEG-SS-P[Asp(DET)] micelles showed both a 1-3 orders of magnitude higher gene transfection efficiency and a more rapid onset of gene expression than PEG-P[Asp(DET)] micelles without disulfide linkages, due to much more effective endosomal escape based on the PEG detachment in endosome. These findings suggest that the PEG-SS-P[Asp(DET)] micelle may have promising potential as a nonviral gene vector exerting high transfection with regulated timing and minimal cytotoxicity.

Cyclic RGD Peptide-Conjugated Polyplex Micelles as a Targetable Gene Delivery System Directed to Cells Possessing αvβ3 and αvβ5 Integrins

A cyclic RGD peptide-conjugated block copolymer, cyclo[RGDfK(CX-)]-poly(ethylene glycol)-polylysine (c(RGDfK)-PEG-PLys), was synthesized from acetal-PEG-PLys under mild acidic conditions and spontaneously associated with plasmid DNA (pDNA) to form a polyplex micelle in aqueous solution. The cyclic RGD peptide recognizes alphavbeta3 and alphavbeta5 integrin receptors, which play a pivotal role in angiogenesis, vascular intima thickening, and the proliferation of malignant tumors. The c(RGDfK)-PEG-PLys/pDNA polyplex micelle showed a remarkably increased transfection efficiency (TE) compared to the PEG-PLys/pDNA polyplex micelle for the cultured HeLa cells possessing alphavbeta3 and alphavbeta5 integrins. On the other hand, in the transfection against the 293T cells possessing no alphavbeta3 and a few alphavbeta5 integrins, the TE of the c(RGDfK)-PEG-PLys/pDNA micelle showed no increase compared to the TE of the PEG-PLys/pDNA micelle. Flow cytometric analysis revealed a higher uptake of the c(RGDfK)-PEG-PLys/pDNA micelle than the PEG-PLys/pDNA micelle against HeLa cells, consistent with the transfection results. Furthermore, a confocal laser scanning microscopic observation revealed that the pDNA in the c(RGDfK)-PEG-PLys micelle preferentially accumulated in the perinuclear region of the HeLa cells within 3 h of incubation. No such fast and directed accumulation of pDNA to the perinuclear region was observed for the micelles without c(RGDfK) ligands. These results indicate that the increase in the TE induced by the introduction of the c(RGDfK) peptide ligand was due to an increase in cellular uptake as well as facilitated intracellular trafficking of micelles toward the perinuclear region via alphavbeta3 and alphavbeta5 integrin receptor-mediated endocytosis, suggesting that the cyclic RGD peptide-conjugated polyplex micelle has promising feasibility as a site-specifically targetable gene delivery system.

PEG-based block catiomers possessing DNA anchoring and endosomal escaping functions to form polyplex micelles with improved stability and high transfection efficacy

For the development of polyplex systems showing a high transfection efficacy without a large excess of polycations, a lysine (Lys) unit as a DNA anchoring moiety was introduced into the amino acid sequence in poly(ethylene glycol)- b-cationic poly( N-substituted asparagine) with a flanking N-(2-aminoethyl)-2-aminoethyl group (PEG- b-Asp(DET)) resulting in PEG- b-P[Lys/Asp(DET)], in which the Asp(DET) unit acts as a buffering moiety inducing endosomal escape with minimal cytotoxicity. PEG- b-P[Lys/Asp(DET)]/DNA polyplexes exhibited a narrow size distribution of ∼ 90 nm without secondary aggregates at the stoichiometric N/P 1, suggesting the formation of PEG-shielded polyplex micelles. The introduction of Lys units into the catiomer sequence facilitated cellular uptake and a 100-fold higher level of gene expression with PEG- b-P[Lys/Asp(DET)]/DNA polyplex micelles prepared even at a lowered N/P 2, possibly due to the enhanced association power of the anchoring Lys units.

Transfection study using multicellular tumor spheroids for screening non-viral polymeric gene vectors with low cytotoxicity and high transfection efficiencies

Polyplexes consisting of plasmid DNA and polycations have received much attention as promising vectors for gene transfer. For effective gene therapy, polycations with different polyamine structures in the side chain were developed to ensure their buffering capacity for endosomal escape, and their PEGylated block copolymers were developed to increase their stability and biocompatibility. The effects of the chemical structures of polycations and their PEGylation on transfection and cytotoxicity were elucidated by use of a three-dimensional multicellular tumor spheroid of human hepatoma HuH-7 cells. Various features of transfection with polyplex micelles, which have been hard to observe in conventional monolayer cultures, were revealed by the multicellular tumor spheroid (MCTS) model in terms of cytotoxicity and time-dependent behaviors of transfected gene expression under three-dimensional microenvironments. By using this system, the polyplex micelle from poly(ethylene glycol)- b-poly( N-substituted asparagine) copolymers having the N-(2-aminoethyl)-2-aminoethyl group in the side chain (PEG- b-P[Asp(DET)] polyplex micelle) was proved to achieve high transfection efficiencies as well as low cytotoxicity, both of which are critical properties for successful in vivo gene delivery.

Biocompatible micellar nanovectors achieve efficient gene transfer to vascular lesions without cytotoxicity and thrombus formation

Gene therapy, a promising treatment for vascular disease, requires appropriate gene vectors with high gene transfer efficiency, good biocompatibility and low cytotoxicity. To satisfy these requirements from the approach of nonviral vectors, a novel block copolymer, poly(ethylene glycol) (PEG)-block-polycation, carrying ethylenediamine units in the side chain (PEG-b-P[Asp(DET)]) was prepared. PEG-b-P[Asp(DET)] formed a polyplex micelle through polyion complex formation with plasmid DNA (pDNA). The PEG-b-P[Asp(DET)] polyplex micelle showed efficient gene expression with low cytotoxicity against vascular smooth muscle cells in vitro. It also showed reduced interactions with blood components, offering its feasibility of gene delivery via the vessel lumen. To evaluate in vivo gene transfer efficiency for vascular lesions, PEG-b-P[Asp(DET)] micelle was instilled into rabbit carotid artery with neointima by an intravascular method, and expression of the reporter gene in vascular lesions was assessed. Polyplexes from homopolymer P[Asp(DET)] and branched polyethyleneimine (BPEI) were used as controls. Ultimately, only the polyplex micelle showed appreciable gene transfer into vascular lesions without any vessel occlusion by thrombus, which was in strong contrast to BPEI and P[Asp(DET)] polyplexes which frequently showed occlusion with thrombus. These findings suggest that the PEG-b-P[Asp(DET)] polyplex micelle may have promising potential as a nonviral vector for the treatment of vascular diseases.

PH-Responsive PEGylated nanogels as targetable and low invasive endosomolytic agents to induce the enhanced transfection efficiency of nonviral gene vectors

A pH-responsive PEGylated nanogel was successfully prepared by means of emulsion copolymerization of 2-(N,N-diethylamino)ethyl methacrylate (AMA) with heterobifunctional poly(ethylene glycol) (PEG) bearing a 4-vinylbenzyl group at the α-end and a lactose moiety at the ω-end in the presence of potassium persulfate and ethyleneglycol dimethacrylate as a cross-linker. Polyplex micelle composed of PEG-block-poly(l-lysine) copolymer and plasmid DNA (PEG-b-PLL/pDNA) exhibited a far more efficient transfection ability in the presence of lac-nanogel-8k-1.0% (PEG, Mn = 8000; cross-linking density, 1.0%) than the PEG-b-PLL/pDNA polyplex micelle alone (in the absence of lac-nanogel-8k-1.0%), suggesting that an appreciable fraction of lac-nanogel-8k-1.0% along with the PEG-b-PLL/pDNA polyplex micelle is taken up into the HuH-7 cells through the asialoglycoprotein receptor-mediated endocytosis process mediated by the cluster of a large number of lactose moieties on the surface of lac-nanogel-8k-1.0%, followed by the effective disruption of the endosome by the buffer effect of the unprotonated PAMA core in lac-nanogel-8k-1.0%.

PH-Responsive Three-Layered PEGylated Polyplex Micelle Based on a Lactosylated ABC Triblock Copolymer as a Targetable and Endosome-Disruptive Nonviral Gene Vector

Nonviral vectors for gene therapy have recently received an increased impetus because of the inherent safety problems of the viral vectors, while their transfection efficiency is generally low compared to the viral vectors. The lack of the ability to escape from the endosomal compartments is believed to be one of the critical barriers to the intracellular delivery of noviral gene vectors. This study was devoted to the design and preparation of a novel ABC triblock copolymer for constructing a pH-responsive and targetable nonviral gene vector. The copolymer, lactosylated poly(ethylene glycol)-block-poly(silamine)-block-poly[2-(N,N-dimethylamino)ethyl methacrylate] (Lac-PEG-PSAO-PAMA), consists of lactosylated poly(ethylene glycol) (A-segment), a pH-responsive polyamine segment (B-segment), and a DNA-condensing polyamine segment (C-segment). The Lac-PEG-PSAO-PAMA spontaneously associated with plasmid DNA (pDNA) to form three-layered polyplex micelles with a PAMA/pDNA polyion complex (PIC) core, an uncomplexed PSAO inner shell, and a lactosylated PEG outer shell, as confirmed by 1H NMR spectroscopy. Under physiological conditions, the Lac-PEG-PSAO-PAMA/pDNA polyplex micelles prepared at an N/P (number of amino groups in the copolymer/number of phosphate groups in pDNA) ratio above 3 were found to be able to condense pDNA, thus adopting a relatively small size (< 150 nm) and an almost neutral surface charge (zeta approximately +5 mV). The micelle underwent a pH-induced size variation (pH = 7.4, 132.6 nm --> pH = 4.0, 181.8 nm) presumably due to the conformational changes (globule-rod transition) of the uncomplexed PSAO chain in response to pH, leading to swelling of the free PSAO inner shell at lowered pH while retaining the condensed pDNA in the PAMA/pDNA PIC core. Furthermore, the micelles exhibited a specific cellular uptake into HuH-7 cells (hepatocytes) through asialoglycoprotein (ASGP) receptor-mediated endocytosis and achieved a far more efficient transfection ability of a reporter gene compared to the Lac-PEG-PSAO/pDNA and Lac-PEG-PAMA/pDNA polyplex micelles composed of the diblock copolymers and pDNA. The effect of hydroxychloroquine as an endosomolytic agent on the transfection efficiency was not observed for the Lac-PEG-PSAO-PAMA/pDNA polyplex micelles, whereas the nigericin treatment of the cell as an inhibitor for the endosomal acidification induced a substantial decrease in the transfection efficiency, suggesting that the protonation of the free PSAO inner shell in response to a pH decrease in the endosome might lead to the disruption of the endosome through buffering of the endosomal cavity. Therefore, the polyplex micelle composed of ABC (ligand-PEG/pH-responsive segment/DNA-condensing segment) triblock copolymer would be a promising approach to a targetable and endosome disruptive nonviral gene vector.