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.     

Enhancement of gene expression by polyamidoamine dendrimer conjugates with alpha-, beta-, and gamma-cyclodextrins.

To improve the transfection efficiency of nonviral vector, we synthesized the starburst polyamidoamine dendrimer conjugates with alpha-, beta-, and gamma-cyclodextrins (CDE conjugates), expecting the synergistic effect of dendrimer and cyclodextrins (CyDs). The (1)H NMR spectroscopic data indicated that alpha-, beta-, and gamma-CyDs are covalently bound to dendrimer in a molar ratio of 1:1. The agarose gel electrophoretic studies revealed that CDE conjugates formed the complexes with plasmid DNA (pDNA) and protected the degradation of pDNA by DNase I in the same manner as dendrimer. CDE conjugates showed a potent luciferase gene expression, especially in the dendrimer conjugate with alpha-CyD (alpha-CDE conjugate) which provided the greatest transfection activity (approximately 100 times higher than those of dendrimer alone and of the physical mixture of dendrimer and alpha-CyD) in NIH3T3 and RAW264.7 cells. In addition, the gene transfer activity of alpha-CDE conjugate was superior to that of Lipofectin. The enhancing gene transfer effect of alpha-CDE conjugate may be attributable to not only increasing the cellular association, but also changing the intracellular trafficking of pDNA. These findings suggest that alpha-CDE conjugate could be a new preferable nonviral vector of pDNA.     

Effects of structure of polyamidoamine dendrimer on gene transfer efficiency of the dendrimer conjugate with alpha-cyclodextrin

To improve gene transfer activity of a new nonviral vector, a polyamidoamine dendrimer (G2) conjugate with alpha-cyclodextrin (alpha-CDE conjugate (G2)), we prepared alpha-CDE conjugates with dendrimer having different generations (G3 and G4), and their gene transfer activities were compared with those of alpha-CDE conjugate (G2) and TransFast, a novel transfection reagent. alpha-CDE conjugates (G2, G3, and G4) formed the complexes with pDNA, changing the zeta-potential and particle size of pDNA complexes and the protection of pDNA from DNase I in a charge ratio-dependent manner, although their differences at higher charge ratios (vector/pDNA) were small. The gene transfer activity of alpha-CDE conjugates (G2, G3, and G4) was higher than that of the corresponding dendrimer alone in NIH3T3 and RAW264.7 cells. Of these CDE conjugates, alpha-CDE conjugate (G3) had a superior gene transfer activity which was comparable to that of TransFast in NIH3T3 cells. The intracellular distribution of pDNA after application of the pDNA complex with alpha-CDE conjugate (G3) to NIH3T3 cells was different from that with dendrimer alone (G3), although the cellular association of pDNA was almost comparable among all vectors. alpha-CDE conjugate (G3) strongly interacted with a fluorescence probe, 2-(p-toluidinyl)-naphthalene-6-sulfonate (TNS), suggesting that the conjugate possesses the inclusion ability with biomembrane constituents such as phospholipids after transfection. These results suggest that alpha-CDE conjugates, particularly the G3 conjugate, could be novel nonviral gene transfer agents.     

Preferences for uptake of carbohydrate-coated liposomes by C-type lectin receptors as antigen-uptake receptors

We evaluated the carbohydrate preferences of the C-type lectin receptors (CLRs) SIGNR1, SIGNR3, and Langerin as pathogen-uptake receptors based on uptake of liposomes consisting of cholesterol, DPPC, and various neoglycolipids at molar ratios of 10:10:1 and 10:7:4, respectively, using non-phagocytic CHO cells that express these receptors transiently. SIGNR1-expressing cells ingested liposomes coated with neoglycolipids with terminal mannose residues, such as Man2-, Man3-, and Man5-DPPE, and with a terminal N-acetylglucosamine. SIGNR1 mediated uptake of Man3-DPPE-coated liposomes most efficiently. Uptake of liposomes with lower neoglycolipid content by SIGNR3- or Langerin-expressing cells was slight or negligible, but uptake into these cells was detected for liposomes with higher neoglycolipid content. SIGNR1-expressing cells clearly ingested liposomes coated with Lewis X antigen, whereas SIGNR3- or Langerin-expressing cells barely ingested these liposomes, even at the higher neoglycolipid content. In contrast, SIGNR3 or Langerin, but not SIGNR1, mediated uptake of liposomes coated with blood group H antigen. These results indicate that CLRs with similar carbohydrate-recognition characteristics have distinct properties as pathogen-uptake receptors for carbohydrate-decorated particles.     

Gene Transfer by DNA/mannosylated Chitosan Complexes into Mouse Peritoneal Macrophages

Chitosan is a biodegradable and biocompatible polymer and is useful as a non-viral vector for gene delivery. In order to deliver pDNA/chitosan complex into macrophages expressing a mannose receptor, mannose-modified chitosan (man-chitosan) was employed. The cellular uptake of pDNA/man-chitosan complexes through mannose recognition was then observed. The pDNA/man-chitosan complexes showed no significant cytotoxicity in mouse peritoneal macrophages, while pDNA/man-PEI complexes showed strong cytotoxicity. The pDNA/man-chitosan complexes showed much higher transfection efficiency than pDNA/chitosan complexes in mouse peritoneal macrophages. Observation with a confocal laser microscope suggested differences in the cellular uptake mechanism between pDNA/chitosan complexes and pDNA/man-chitosan complexes. Mannose receptor-mediated gene transfer thus enhances the transfection efficiency of pDNA/chitosan complexes.     

Polyion complex micelles of pDNA with acetal-poly(ethylene glycol)-poly(2-(dimethylamino)ethyl methacrylate) block copolymer as the gene carrier system: physicochemical properties of micelles relevant to gene transfection efficacy

An acetal-poly(ethylene glycol)-poly(2-(dimethylamino)ethyl methacrylate) (acetal-PEG-PAMA) block copolymer spontaneously associated with plasmid DNA (pDNA) to form water-soluble complexes (polyion complex micelle: PIC micelle) in aqueous solution. Physicochemical characteristics and transfection efficiency of the PIC micelles thus prepared were studied here, focusing on the residual molar mixing ratio (N/P ratio) of AMA units in acetal-PEG-PAMA to the phosphate units in pDNA. With the N/P ratio increasing to unity, acetal-PEG-PAMA cooperatively formed complex micelles with pDNA through electrostatic interaction, allowing pDNA to condense effectively. Dynamic light scattering measurements revealed that the PIC micelle at N/P > or = 3 had a constant size of approximately 90-100 nm. Eventually, acetal-PEG-PAMA/pDNA micelles underwent no precipitation even after long-term storage for more than 1 month at all N/P ratios. The PIC micelles were stable even in the presence of excess polyanions, poly(vinyl sulfate), in contrast to polyplexes based on the PAMA homopolymer, yet this stabilization effect was highly dependent on the N/P ratio to reach a plateau at N/P = 3-4. This character may be attributed to the increased hydrophobicity in the vicinity of the complexed pDNA. Furthermore, the pDNA in the micelle was adequately protected from DNase I attack. The transfection ability of the PIC micelles toward 293 cells was remarkably enhanced with an increasing N/P ratio as high as 25. The zeta-potential of the micelles with a high N/P ratio was an appreciably large positive value, suggesting a noncooperative micelle formation. This deviated micellar composition with an excess cationic nature as well as the presence of free acetal-PEG-PAMA may play a substantial role in the enhanced transfection efficiency of the PIC micelle system in the high N/P ratio (approximately 25) region.     

In vitro and in vivo gene transfer by an optimized alpha-cyclodextrin conjugate with polyamidoamine dendrimer

The purpose of the present study is to optimize the structure of the polyamidoamine starburst dendrimer (dendrimer) conjugate with alpha-cyclodextrin (alpha-CDE conjugate) as a nonviral vector. alpha-CDE conjugates of dendrimer (generation 3, G3) with various average degrees of substitution (DS) of alpha-CyD of 1.1, 2.4, and 5.4 were prepared. alpha-CDE conjugates formed the complexes with pDNA, resulting in a change of the particle sizes of pDNA complexes, but the distinction of physicochemical properties among their vector/pDNA complexes was only very slight. The membrane-disruptive ability of alpha-CDE conjugates on liposomes encapsulating calcein and their cytotoxicity to NIH3T3 and HepG2 increased with an increase in the DS value of alpha-CyD. In vitro gene transfer activity of alpha-CDE conjugates in both NIH3T3 and HepG2 cells augmented as the charge ratio (vector/pDNA) increased, and the activity of alpha-CDE conjugate (DS 2.4) was the highest at higher charge ratios among dendrimer (G3), the three alpha-CDE conjugates, and TransFast. After intravenous administration of pDNA complexes in mice, alpha-CDE conjugate (DS 2.4) delivered pDNA more efficiently in spleen, liver, and kidney, compared with dendrimer and other alpha-CDE conjugates (DS 1.1 and 5.4). The potential use of alpha-CDE conjugate (G3, DS 2.4) could be expected as a nonviral vector in vitro and in vivo, and these data may be useful for design of alpha-CyD conjugates with other nonviral vectors.     

Lactosylated chitosan for DNA delivery into hepatocytes: the effect of lactosylation on the physicochemical properties and intracellular trafficking of pDNA/chitosan complexes

Chitosan is a useful nonviral vector for gene delivery. To make a pDNA/chitosan complex specific to hepatocytes, lactose-modified chitosan (lac-chitosan) was synthesized. When the percentage of lactose residues substituted was 8%, lac-chitosan showed excellent DNA-binding ability, good protection of DNA from nuclease, and the suppression of self-aggregation and serum-induced aggregation. Although the cellular uptake efficiency of the pDNA/lac-chitosan complex was almost the same as that of the pDNA/chitosan complex, the cell transfection efficiency of the former was greater for HepG2 cells having asialoglycoprotein receptors. Inhibitor of endocytosis such as bafilomycin A1 and nocodazole significantly reduced the transfection efficiency of the pDNA/lac-chitosan complex. Observations with a confocal laser scanning microscope indicated that the pDNA/lac-chitosan complexes traversed endocytic compartments more rapidly than the pDNA/chitosan complex. Furthermore, the pDNA/lac-chitosan complexes were delivered to the late endosome and have the advantage of delivering DNA to the perinuclear region.     

A smart nanoassembly consisting of acid-labile vinyl ether PEG-DOPE and protamine for gene delivery: preparation and in vitro transfection

The conception of a modular designed and viruslike nonviral vector has been presented for gene delivery. Recently, we constructed a new smart nanoassembly (SNA) with multifunctional components that was composed of a condensed core of pDNA with protamine sulfate (PS) and a dioleoyl phosphatidylethanolamine (DOPE)-based lipid envelope containing poly(ethylene glycol)--vinyl ether--DOPE (PVD). SNAs with mPEG 2000 (SNAs1) or mPEG 5000 (SNAs2) loading PS/DNA were prepared by the lipid film hydration technique. The particle size was about 160 nm for SNAs1 and 240 nm for SNAs2 loading PS/DNA (10:1 w/w), and the zeta potential was about 4 mV for two SNAs. The in vitro release experiment indicated that PVD possessed a good ability for self-dePEGylation, which could result in the recovery of an excellent fusogenic capacity of DOPE at low pH. SNAs showed a higher transfection efficiency and much lower cytotoxicity than did Lipofectamine 2000 on HEK 293, HeLa, and COS-7 cells. The cellular uptake and subcellular localization demonstrated that the superior transfection efficiency of SNAs could result from the fact that the DOPE-based lipid envelope containing PVD increased PS/DNA in the cytoplasm, and protamine enhanced the nuclear delivery or overcame the nuclear membrane barrier. These results implied that the PVD-based nanoassembly loading PS/DNA could be a promising gene delivery system.     

Spider silk-based gene carriers for tumor cell-specific delivery

The present study demonstrates pDNA complexes of recombinant silk proteins containing poly(L-lysine) and tumor-homing peptides (THPs), which are globular and approximately 150-250 nm in diameter, show significant enhancement of target specificity to tumor cells by additions of F3 and CGKRK THPs. We report herein the preparation and study of novel nanoscale silk-based ionic complexes containing pDNA able to home specifically to tumor cells. Particular focus was on how the THP, F3 (KDEPQRRSARLSAKPAPPKPEPKPKKAPAKK), and CGKRK, enhanced transfection specificity to tumor cells. Genetically engineered silk proteins containing both poly(L-lysine) domains to interact with pDNA and the THP to bind to specific tumor cells for target-specific pDNA delivery were prepared using Escherichia coli, followed by in vitro and in vivo transfection experiments into MDA-MB-435 melanoma cells and highly metastatic human breast tumor MDA-MB-231 cells. Non-tumorigenic MCF-10A breast epithelial cells were used as a control cell line for in vitro tumor-specific delivery studies. These results demonstrate that combination of the bioengineered silk delivery systems and THP can serve as a versatile and useful new platform for nonviral gene delivery.     

Dendritic poly(ether imine) based gene delivery vector

The nonviral vector based gene delivery approach is attractive due to advantages associated with molecular-level modifications suitable for optimization of vector properties. In a new class of nonviral gene delivery systems, we herein report the potential of poly(ether imine) (PETIM) dendrimers to mediate an effective gene delivery function. PETIM dendrimer, constituted with tertiary amine branch points, n-propyl ether linkers and primary amines at their peripheries, exhibits significantly reduced toxicities, over a broad concentration range. The dendrimer complexes pDNA effectively, protects DNA from endosomal damages, and delivers to the cell nucleus. Gene transfection studies, utilizing a reporter plasmid pEGFP-C1 and upon complexation with dendrimer, showed a robust expression of the encoded protein. The study shows that PETIM dendrimers are hitherto unknown novel gene delivery vectors, combining features of poly(ethylene imine)-based polymers and dendrimers, yet are relatively nontoxic and structurally precise.     

Evaluation by fluorescence resonance energy transfer of the stability of nonviral gene delivery vectors under physiological conditions

The stability in physiological medium of polyplex- and lipoplex-type nonviral gene vectors was evaluated by detecting the conformational change of complexed plasmid DNA (pDNA) labeled simultaneously with fluorescein (energy donor) and X-rhodamine (energy acceptor) through fluorescence resonance energy transfer (FRET). Upon mixing with cationic components, such as LipofectAMINE, poly(L-lysine), and poly(ethylene glycol)-poly(L-lysine) block copolymer (PEG-PLys), the fluorescence spectrum of doubly labeled pDNA underwent a drastic change due to the occurrence of FRET between the donor-acceptor pair on pDNA taking a globular conformation (condensed state) through complexation. The measurement was carried out also in the presence of 20% serum, under which conditions FRET from condensed pDNA was clearly monitored without interference from coexisting components in the medium, allowing evaluation of the condensed state of pDNA in nonviral gene vectors under physiological conditions. Serum addition immediately induced a sharp decrease in FRET for the LipofectAMINE/pDNA (lipoplex) system, which was consistent with the sharp decrease in the transfection efficiency of the lipoplex system in serum-containing medium. In contrast, the PEG-PLys/pDNA polyplex (polyion complex micelle) system maintained appreciable transfection efficiency even in serum-containing medium, and FRET efficiency remained constant for up to 12 h, indicating the high stability of the polyion complex micelle under physiological conditions.     

Blood compatible N-maleyl chitosan-graft-PAMAM copolymer for enhanced gene transfection

To improve transfection efficiency, we prepared N-maleyl chitosan-graft-polyamidoamine (NMCTS-graft-PAMAM) copolymer. Self-assembled NMCTS-graft-PAMAM/pDNA complexes were prepared by complex coacervation method at different N/P (nitrogen to phosphate ratio) ratios. The copolymer effectively formed complexes with pDNA at lower N/P ratio (N/P ratio 1.0) than that of unmodified chitosan (N/P ratio 2.0) and the complexes were spherical with particle size of 100–150 nm. The copolymer showed significant protection of DNA from nuclease attack with lower toxicity against HeLa cell. The copolymer also showed no noticeable hemolytic effects up to 10 mg/mL indicating no detectable disturbance of the red blood cell membranes. The transfection efficiency of the copolymer was increased significantly compared to that of chitosan and reached up to 36 ± 2% at N/P ratio 7.0 which was higher than that of PEI (30 ± 3% at N/P ratio 10). Therefore, the copolymer may be a strong alternative candidate as effective nonviral vector.     

Biophysical characterization of the DNA binding and condensing properties of adenoviral core peptide mu.

Cationic peptides containing Lys and Arg residues interact with DNA via charge-charge interactions and are known to play an important role in DNA charge neutralization and condensation processes. In this paper, we describe investigations of the interaction of the cationic adenovirus core complex peptide mu with a dodecameric ODN (12 bp) and pDNA (7528 bp) using a combination of fluorescence spectroscopy, circular dichroism spectroscopy, isothermal titration calorimetry, and photon correlation spectroscopy. Comparisons are made with protamine, a cationic peptide well-known for DNA charge neutralization and condensation. Equilibrium dissociation constants are derived independently by both CD and ITC methods for the interaction between protamine or mu with pDNA (K(d) = 0.6-1 microM). Thermodynamic data are also obtained by ITC, indicating strong charge-charge interactions. The interaction of protamine with pDNA takes place with decreasing entropy (-28.7 cal mol(-1) K(-1)); unusually, the interaction of mu with pDNA takes place with increasing entropy (Delta S degrees (bind) = 11.3 cal mol(-1) K(-1)). Although protamine and mu appear to destabilize pDNA double helix character to similar extents, according to CD thermal titration analyses, PCS studies show that interactions between mu and pDNA result in the formation of significantly more size-stable condensed particles than protamine. The enhanced flexibility and size stability of mu-DNA (MD) particles (80-110 nm) compared to protamine counterparts suggest that MD particles are ideal for use as a part of new nonviral gene delivery vectors.     

Synthesis and characterization of a head-tail type polycation block copolymer as a nonviral gene vector

A head-tail type polycation block copolymer, which is composed of the polyamidoamine (PAMAM) dendron and poly(L-lysine) (PLL) blocks, was newly designed as a nonviral gene vector in this study. This block copolymer (PAMAM dendron-PLL) was successfully synthesized in two steps: the synthesis of the PAMAM dendron block and the polymerization of the PLL block from the PAMAM dendron block. PAMAM dendron and PLL blocks in block copolymer showed independent deprotonation behavior, and their pK(a) were determined to be 6.8 and 9.0, respectively. The complexation with pDNA was evaluated by gel retardation assay and dye exclusion assay, and both assays indicated that pDNA was selectively complexed with PLL block of block copolymer. Also, the PAMAM dendron-PLL poplyplexes showed 10(2) fold higher transfection efficiency to HeLa cells as that for PLL polyplexes. This might be due to the buffering effect of the PAMAM dendron block. This block copolymer could produce a function share in each block, i.e., tail block complexed with pDNA and head block showed a buffering effect. This molecular design of the head-tail type block copolymer might provide a new approach for realizing in vivo gene therapy.     

Effective targeted gene delivery to dendritic cells via synergetic interaction of mannosylated lipid with DOPE and BCAT

The efficient delivery of plasmids encoding antigenic determinants into dendritic cells (DCs) that control immune response is a promising strategy for rapid development of new vaccines. In this study, we prepared a series of targeted cationic lipoplex based on two synthetic lipid components, mannose-poly(ethylene glycol, MW3000)-1,2-distearoyl-sn-glycero-3-phosphoethanolamine (Mannose-PEG3000-DSPE) and O-(2R-1,2-di-O-(1'Z-octadecenyl)-glycerol)-3-N-(bis-2-aminoethyl)-carbamate (BCAT), that were formulated with 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) for evaluation as nonviral vectors for transgene expression in DCs. First, we optimized the N/P ratio for maximum transfection and then screened the effects of mannose targeting for further enhancement of transfection levels. Our results indicate that efficient delivery of gWIZ GFP plasmid into DCs was observed for mannose compositions of ～10%, whereas low transfection efficiencies were observed with nontargeted formulations. Mannose-targeted lipofectamine complexes also showed high GFP expression levels in DCs relative to nontargeted lipofectamine controls. The best transfection performance was observed using 10 mol % Mannose-PEG3000-DSPE, 60 mol % BCAT, and 30 mol % DOPE, indicating that the most efficient delivery into DCs occurs via synergistic interaction between mannose targeting and acid-labile, fusogenic BCAT/DOPE formulations. Our data suggest that mannose-PEG3000-DSPE/BCAT/DOPE formulations may be effective gene delivery vehicles for the development of DC-based vaccines.     

Phase and surface properties of lipid bilayers containing neoglycolipids

The physical properties conferred to DPPC bilayers by including neoglycolipids composed by two different trisaccharides: mannose-mannose-mannose (3M) and glucose-mannose-glucose (GMG) attached to a cholesterol (cho) and a distearylglycerol (diC18) lipid moiety by a spacer were evaluated by means of the measurement of the electrokinetic potential and interfacial fluorescent probes. The phase properties measured with diphenylhexatriene (DPH) were correlated with the surface properties measured with merocyanine 540, dansyl, and Laurdan probes. The results show that the surface properties of large unilamellar vesicles depend on the sugar exposure to the water phase and also on the hydrocarbon moiety by which it is anchored to the bilayer. The combination of the cholesterol moiety with the saccharide attenuates the cooperativity decrease induced by the cholesterol moiety without the sugar portion. The neoglycolipid GMG-diC18 promotes opposite effects affecting slightly the cooperativity at the hydrocarbon core of DPPC and displacing the phase transition temperature to higher values. The presence of neoglycolipid with diC18 introduces defects in the packing at the interface of the membrane in the gel state. It is concluded that a relatively low proportion of neoglycolipids affects significantly the interfacial properties of DPPC bilayers in large unilamellar vesicles in the absence of changes at the membrane bulk at 25 degrees C.     

Amphiphilic peptides with arginines and valines for the delivery of plasmid DNA

A non-toxic and efficient gene carrier is one requirement for clinical gene therapy. In this study, amphiphilic peptides composed of arginines and valines were synthesized and characterized as plasmid DNA (pDNA) carriers. The peptides have a cationic region containing 1-4 arginines and a hydrophobic region containing 6 valines. The arginine-valine peptides (RV peptides) formed micelles in aqueous solution with a critical micelle concentration (CMC) of 1.35 mg/ml. In gel retardation assay, the RV peptides retarded all pDNA at weight ratios (pDNA:RV peptide) of 1:3 for R1V6, 1:2 for R2V6 and R3V6, and 1:1 for R4V6. A heparin competition assay showed that the R3V6 peptide formed tighter complexes with pDNA than poly-L-lysine (PLL). In vitro transfection assay into HEK293 cells showed that the R1V6 and R2V6 peptides had the highest transfection efficiencies at 1:30 weight ratios (pDNA:RV peptide), while the R3V6 and R4V6 peptides had the highest efficiencies at 1:20 weight ratios. Under optimal conditions, the R3V6 peptide had the highest transfection efficiency of all the RV peptides and PLL. MTT assay showed that the RV peptides did not have any detectable toxicity to cells. Therefore, the RV peptide may be useful for the development of non-toxic gene carriers.