Poly-L-glutamic acid derivatives as vectors for gene therapy

Cationic Hydrogels Modulate Neural Stem and Progenitor Cell Proliferation and Differentiation Behavior in Dependence of Cationic Moiety Concentration in 2D Cell Culture

The central nervous system (CNS) has a limited regenerative capacity because a hostile environment prevents tissue regeneration after damage or injury. Neural stem/progenitor cells (NSPCs) are considered a potential resource for CNS repair, which raises the issue of adequate cultivation and expansion procedures. Cationic charge supports the survival and adhesion of NSPCs. Typically, tissue culture plates with cationic coatings, such as poly-l-ornithine (PLO), have been used to culture these cell types (NSPCs). Yet presently, little is known about the impact of cationic charge concentration on the viability, proliferation, and differentiation capacity of NSPCs. Therefore, we have recently developed well-defined, fully synthetic hydrogel systems G1 (gel 1) to G6 (gel 6) that allow for the precise control of the concentration of the cationic trimethylaminoethyl acrylate (TMAEA) molecule associated with the polymer in a range from 0.06 to 0.91 μmol/mg. When murine NSPCs were cultured on these gels under differentiation conditions, we observed a strong correlation of cationic charge concentration with NSPC survival. In particular, neurons were preferentially formed on gels with a higher cationic charge concentration, whereas astrocytes and oligodendrocytes favored weakly charged or even neutral gel surfaces. To test the properties of the gels under proliferative conditions, the NSPCs were cultivated in the presence of fibroblast growth factor 2 (FGF2). The cytokine significantly increased the number of NSPCs but delayed the differentiation toward neurons and glia cells. Thus, the hydrogels are compatible with the survival, expansion, and differentiation of NSPCs and may be useful to create supportive environments in transplantation approaches.

Interaction of γ-Polyglutamic Acid/Polyethyleneimine/Plasmid DNA Ternary Complexes with Serum Components Plays a Crucial Role in Transfection in Mice

Typical examples of non-viral vectors are binary complexes of plasmid DNA with cationic polymers such as polyethyleneimine (PEI). However, problems such as cytotoxicity and hemagglutination, owing to their positively charged surfaces, hinder their in vivo use. Coating binary complexes with anionic polymers, such as γ-polyglutamic acid (γ-PGA), can prevent cytotoxicity and hemagglutination. However, the role of interactions between these complexes and serum components in in vivo gene transfer remains unclear. In this study, we analyzed the contribution of serum components to in vivo gene transfer using PEI/plasmid DNA binary complexes and γ-PGA/PEI/plasmid DNA ternary complexes. In binary complexes, heat-labile components in the serum greatly contribute to the hepatic and splenic gene expression of the luciferase gene. In contrast, serum albumin and salts affected the hepatic and splenic gene expression in the ternary complexes. Changes in physicochemical characteristics, such as increased particle size and decreased absolute values of ζ-potential, might be involved in the enhanced gene expression. These findings would contribute to a better understanding of in vivo non-viral gene transfer using polymers, such as PEI and γ-PGA.

Nanoengineered Polymeric RNA Nanoparticles for Controlled Biodistribution and Efficient Targeted Cancer Therapy

RNA nanotechnology, including rolling circle transcription (RCT), has gained increasing interest as a fascinating siRNA delivery nanoplatform for biostable and tumor-targetable RNA-based therapies. However, due to the lack of fine-tuning technologies for RNA nanostructures, the relationship between physicochemical properties and siRNA efficacy of polymeric siRNA nanoparticles (PRNs) with different sizes has not yet been fully elucidated. Herein, we scrutinized the effects of size/surface chemistry-tuned PRNs on the biological and physiological interactions with tumors. PRNs with adjusted size and surface properties were prepared using sequential engineering processes: RCT, condensation, and nanolayer deposition of functional biopolymers. Through the RCT process, nanoparticles of three sizes with a diameter of 50-200 nm were fabricated and terminated with three types of biopolymers: poly-l-lysine (PLL), poly-l-glutamate (PLG), and hyaluronic acid (HA) for different surface properties. Among the PRNs, HA-layered nanoparticles with a diameter of ∼200 nm exhibited the most effective systemic delivery, resulting in superior anticancer effects in an orthotopic breast tumor model due to the CD44 receptor targeting and optimized nanosized structure. Depending on the type of PRNs, the in vivo siRNA delivery with protein expression inhibition differed by up to approximately 20-fold. These findings indicate that the types of layered biopolymers and the PRNs size mediate efficient polymeric siRNA delivery to the targeted tumors, resulting in high RNAi-induced therapeutic efficacy. This RNA-nanotechnology-based size/surface editing can overcome the limitations of siRNA therapeutics and represents a potent built-in module method to design RNA therapeutics tailored for targeted cancer therapy.

Reversal Activity and Toxicity of Heparin-Binding Copolymer after Subcutaneous Administration of Enoxaparin in Mice

Uncontrolled bleeding after enoxaparin (ENX) is rare but may be life-threatening. The only registered antidote for ENX, protamine sulfate (PS), has 60% efficacy and can cause severe adverse side effects. We developed a diblock copolymer, heparin-binding copolymer (HBC), that reverses intravenously administered heparins. Here, we focused on the HBC inhibitory activity against subcutaneously administered ENX in healthy mice. BALB/c mice were subcutaneously injected with ENX at the dose of 5 mg/kg. After 110 min, vehicle, HBC (6.25 and 12.5 mg/kg), or PS (5 and 10 mg/kg) were administered into the tail vein. The blood was collected after 3, 10, 60, 120, 360, and 600 min after vehicle, HBC, or PS administration. The activities of antifactors Xa and IIa and biochemical parameters were measured. The main organs were collected for histological analysis. HBC at the lower dose reversed the effect of ENX on antifactor Xa activity for 10 min after antidote administration, whereas at the higher dose, HBC reversed the effect on antifactor Xa activity throughout the course of the experiment. Both doses of HBC completely reversed the effect of ENX on antifactor IIa activity. PS did not reverse antifactor Xa activity and partially reversed antifactor IIa activity. HBC modulated biochemical parameters. Histopathological analysis showed changes in the liver, lungs, and spleen of mice treated with HBC and in the lungs and heart of mice treated with PS. HBC administered in an appropriate dose might be an efficient substitute for PS to reverse significantly increased anticoagulant activity that may be connected with major bleeding in patients receiving ENX subcutaneously.

Surface-Displayed Porcine IFN-λ3 in Lactobacillus plantarum Inhibits Porcine Enteric Coronavirus Infection of Porcine Intestinal Epithelial Cells

Interferon (IFN)-λ plays an essential role in mucosal cells which exhibit strong antiviral activity. Lactobacillus plantarum (L. plantarum) has substantial application potential in the food and medical industries because of its probiotic properties. Alphacoronaviruses, especially porcine epidemic diarrhea virus (PEDV) and transmissible gastroenteritis virus (TGEV), cause high morbidity and mortality in piglets resulting in economic loss. Co-infection by these two viruses is becoming increasingly frequent. Therefore, it is particularly important to develop a new drug to prevent diarrhea infected with mixed viruses in piglets. In this study, we first constructed an anchored expression vector with CWA (C-terminal cell wall anchor) on L. plantarum. Second, we constructed two recombinant L. plantarum strains that anchored IFN-λ3 via pgsA (N-terminal transmembrane anchor) and CWA. Third, we demonstrated that both recombinant strains possess strong antiviral effects against coronavirus infection in the intestinal porcine epithelial cell line J2 (IPEC-J2). However, recombinant L. plantarum with the CWA anchor exhibited a more powerful antiviral effect than recombinant L. plantarum with pgsA. Consistent with this finding, Lb.plantarum-pSIP-409-IFN-λ3-CWA enhanced the expression levels of IFN-stimulated genes (ISGs) (ISG15, OASL, and Mx1) in IPEC-J2 cells more than did recombinant Lb.plantarum-pSIP-409-pgsA'-IFN-λ3. Our study verifies that recombinant L. plantarum inhibits PEDV and TGEV infection in IPEC-J2 cells, which may offer great potential for use as a novel oral antiviral agent in therapeutic applications for combating porcine epidemic diarrhea and transmissible gastroenteritis. This study is the first to show that recombinant L. plantarum suppresses PEDV and TGEV infection of IPEC-J2 cells.

Efficient gene transfection to the brain with ultrasound irradiation in mice using stabilized bubble lipopolyplexes prepared by the surface charge regulation method

Introduction

We previously developed anionic ternary bubble lipopolyplexes, an ultrasound-responsive carrier, expecting safe and efficient gene transfection. However, bubble lipopolyplexes have a low capacity for echo gas (C₃F₈) encapsulation (EGE) in nonionic solution such as 5% glucose. On the other hand, we were able to prepare bubble lipopolyplexes by inserting phosphate-buffered saline before C₃F₈ encapsulation. Surface charge regulation (SCR) by electrolytes stabilizes liposome/plasmid DNA (pDNA) complexes by accelerated membrane fusion. Considering these facts, we hypothesized that SCR by electrolytes such as NaCl would promote C₃F₈ encapsulation in bubble lipopolyplexes mediated by accelerated membrane fusion. We defined this hypothesis as SCR-based EGE (SCR-EGE). Bubble lipopolyplexes prepared by the SCR-EGE method (SCR-EGE bubble lipopolyplexes) are expected to facilitate the gene transfection because of the high amount of C₃F₈. Therefore, we applied these methods for gene delivery to the brain and evaluated the characteristics of transgene expression in the brain.

Methods

First, we measured the encapsulation efficiency of C₃F₈ in SCR-EGE bubble lipopolyplexes. Next, we applied these bubble lipopolyplexes to the mouse brain; then, we evaluated the transfection efficiency. Furthermore, three-dimensional transgene distribution was observed using multicolor deep imaging.

Results

SCR-EGE bubble lipopolyplexes had a higher C₃F₈ content than conventional bubble lipopolyplexes. In terms of safety, SCR-EGE bubble lipopolyplexes possessed an anionic potential and showed no aggregation with erythrocytes. After applying SCR-EGE bubble lipopolyplexes to the brain, high transgene expression was observed by combining with ultrasound irradiation. As a result, transgene expression mediated by SCR-EGE bubble lipopolyplexes was observed mainly on blood vessels and partially outside of blood vessels.

Conclusion

The SCR-EGE method may promote C₃F₈ encapsulation in bubble lipopolyplexes, and SCR-EGE bubble lipopolyplexes may be potent carriers for efficient and safe gene transfection in the brain, especially to the blood vessels.

Poly(HPMA)-DTPA/DOTA-Gd conjugates for magnetic resonance imaging

Poly(HPMA)-DTPA/DOTA-Gd conjugates were fabricated, and the cytotoxicity, hemocompatibility and T₁ relaxivity property were evaluated.

Diphenylpyrenylamine-functionalized polypeptides: secondary structures, aggregation-induced emission, and carbon nanotube dispersibility

In this study we prepared—through ring-opening polymerization of γ-benzyl-l-glutamate N-carboxyanhydride (BLG-NCA) initiated by N,N-di(4-aminophenyl)-1-aminopyrene (pyrene-DPA-2NH₂)—poly(γ-benzyl-l-glutamate) (PBLG) polymers with various degrees of polymerization (DP), each featuring a di(4-aminophenyl)pyrenylamine (DPA) luminophore on the main backbone. The secondary structures of these pyrene-DPA-PBLG polypeptides were investigated using Fourier transform infrared spectroscopy and wide-angle X-ray diffraction, revealing that the polypeptides with DPs of less than 19 were mixtures of α-helical and β-sheet conformations, whereas the α-helical structures were preferred for longer chains. Interestingly, pyrene-DPA-2NH₂ exhibited weak photoluminescence (PL), yet the emission of the pyrene-DPA-PBLG polypeptides was 16-fold stronger, suggesting that attaching PBLG chains to pyrene-DPA-2NH₂ turned on a radiative pathway for the non-fluorescent molecule. Furthermore, pyrene-DPA-2NH₂ exhibited aggregation-caused quenching; in contrast, after incorporation into the PBLG segments with rigid-rod conformations, the resulting pyrene-DPA-PBLG polypeptides displayed aggregation-induced emission. Transmission electron microscopy revealed that mixing these polypeptides with multiwalled carbon nanotubes (MWCNTs) in DMF led to the formation of extremely dispersible pyrene-DPA-PBLG/MWCNT composites. The fabrication of MWCNT composites with such biocompatible polymers should lead to bio-inspired carbon nanostructures with useful biomedical applications.

PBLG chains to pyrene-DPA-2NH₂ turned on a radiative pathway for the non-fluorescent molecule and TEM revealed these polypeptides with carbon nanotube to form PBLG/MWCNT composite.

Design of Poly-l-Glutamate-Based Complexes for pDNA Delivery

Due to the polyanionic nature of DNA, typically cationic or neutral delivery vehicles have been used for gene delivery. As a new approach, this study focuses on the design, development, and validation of nonviral polypeptide-based carriers for oligonucleotide delivery based on a negatively charged poly-l-glutamic acid (PGA) backbone partly derivatized with oligoaminoamide residues. To this end, PGA-derivatives modified with different pentameric succinyl tetraethylene pentamines (Stp₅ ) are designed. Optionally, histidines for modulation of endosomal buffer capacity and cysteines for pDNA complex stabilization are included, followed by characterization of biophysical properties and gene transfer efficiency in N2a neuroblastoma or 4T1 breast cancer cells.

Tumor delivery of liposomal doxorubicin prepared with poly-L-glutamic acid as a drug-trapping agent

CONTEXT

Poly-l-glutamic acid (PGA) is an anionic polymer with a large number of carboxyl groups that can interact electrostatically with cationic drugs such as doxorubicin (DOX).

OBJECTIVE

For stable encapsulation of DOX into liposomes, we prepared triethylamine (TEA)-PGA-liposomes using PGA as an internal trapping agent.

METHODS

We prepared TEA-PGA-liposomes by remote loading of DOX with a TEA gradient into preformed liposomes prepared with 1, 2, or 4 mg/mL PGA (molecular weights 4800, 9800, and 20 500), and evaluated their biodistribution and antitumor effects on Lewis lung carcinoma (LLC) tumor-bearing mice.

RESULTS

TEA-PGA-liposomes using the higher the molecular weight or concentration of PGA showed a slower release of DOX from the liposomes. TEA-PGA-liposomes prepared with a high concentration of PGA could enhance DOX accumulation in tumors and prolonged DOX circulation in the serum, indicating that DOX may be retained stably in the liposomal interior by interaction with PGA. Furthermore, injection of TEA-PGA-liposomes prepared with 4 mg/mL of PGA₉₈₀₀ or 2 mg/mL PGA₂₀₅₀₀ strongly inhibited tumor growth in LLC tumor-bearing mice.

CONCLUSIONS

PGA may be a potential trapping agent for liposomal DOX for tumor drug delivery.

Microbial production and chemical transformation of poly-γ-glutamate

Poly-γ-glutamate (PGA), a novel polyamide material with industrial applications, possesses a nylon-like backbone, is structurally similar to polyacrylic acid, is biodegradable and is safe for human consumption. PGA is frequently found in the mucilage of natto, a Japanese traditional fermented food. To date, three different types of PGA, namely a homo polymer of D-glutamate (D-PGA), a homo polymer of L-glutamate (L-PGA), and a random copolymer consisting of D- and L-glutamate (DL-PGA), are known. This review will detail the occurrence and physiology of PGA. The proposed reaction mechanism of PGA synthesis including its localization and the structure of the involved enzyme, PGA synthetase, are described. The occurrence of multiple carboxyl residues in PGA likely plays a role in its relative unsuitability for the development of bio-nylon plastics and thus, establishment of an efficient PGA-reforming strategy is of great importance. Aside from the potential applications of PGA proposed to date, a new technique for chemical transformation of PGA is also discussed. Finally, some techniques for PGA and its derivatives in advanced material technology are presented.

Polycation-based nanoparticle delivery of RNAi therapeutics: adverse effects and solutions

Small interfering RNA (siRNA) that silence genes by the process of RNA interference offers a new therapeutic modality for disease treatment. Polycation-based nanoparticles termed polyplexes have been developed to maximise extracellular and intracellular siRNA delivery, a key requirement for enabling the clinical translation of RNAi-based drugs. Medical applications are dependent on safety; therefore, detailed investigation into potential toxicity to the cell or organism is required. This review addresses potential adverse effects arising from cellular and tissue interactions, immune stimulation and altered gene expression that can be associated with the assembled polyplex or the polycation and siRNA component parts. A greater understanding of the cellular mechanisms involved allows design-based solutions for rationale development of safe, effective and clinically relevant polyplex-based RNAi drugs.

Magnetic and pH-sensitive nanoparticles for antitumor drug delivery

A dually responsive nanocarrier with multilayer core-shell architecture was prepared based on Fe(3)O(4)@SiO(2) nanoparticles coated with mPEG-poly(l-Asparagine). Imidazole groups (pK(a)∼6.0) were tethered to the side chains of poly(l-Asparagine) segments by aminolysis. These nanoparticles were expected to be sensitive to both magnetic field and pH environment. The obtained materials were characterized with FTIR, dynamic light scattering, ζ-potential, TEM, TGA and hysteresis loop analysis. It was found that this Fe(3)O(4)@SiO(2)-polymer complex can form nano-scale core-shell-corona trilayer particles (∼250 nm) in aqueous solution. The Fe(3)O(4)@SiO(2), poly(L-Asparagine) and mPEG segments serve as a super-paramagnetic core, a pH-sensitive shell, and a hydrophilic corona, respectively. An antitumor agent, doxorubicin (DOX), was successfully loaded into the nanocarrier via combined actions of hydrophobic interaction and hydrogen bonding. The drug release profiles displayed a pH-dependent behavior. DOX release rate increased significantly as the ambient pH dropped from the physiological pH (7.4) to acidic (5.5). This is most likely due to protonation and a change in hydrophilicity of the imidazole groups in the poly(l-Asparagine) segments. This new approach may serve as a promising platform to formulate magnetic targeted drug delivery systems.

Well-defined degradable cationic polylactide as nanocarrier for the delivery of siRNA to silence angiogenesis in prostate cancer

Well-defined tertiary amine-functionalized cationic polylactides (CPLAs) are synthesized by thiol-ene click functionalization of an allyl-functionalized polylactide, and utilized for the delivery of interleukin-8 (IL-8) siRNA via CPLA-IL-8 siRNA nanoplexes. The CPLAs possess remarkable hydrolytic degradability, and their cytotoxicity is relatively low. The CPLA-IL-8 siRNA nanoplexes can be readily taken up by prostate cancer cells, resulting in significant IL-8 gene silencing. It is found that the degradability and cytotoxicity of CPLAs, as well as the transfection efficiency of the CPLA-IL-8 siRNA nanoplexes, positively correlate with the amine mol% of CPLAs.

Polylysine copolymers for gene delivery

Polylysine and its copolymers have been extensively used as nonviral polymeric gene carriers. Although polylysine on its own is toxic to cells, when polyethylene glycol is covalently linked to polylysine, toxicity is reduced and DNA transfection efficiency is increased. A degradable polylysine analog, polyaminobutyl glycolic acid, has been synthesized. Stearyl polylysine shows strong hydrophobic interactions with low-density lipoprotein and these components can be combined with DNA to form a "terplex" system that allows delivery of DNA to targeted cells and significant levels of transfection both in vitro and in vivo.

A novel dendrimer based on poly (L-glutamic acid) derivatives as an efficient and biocompatible gene delivery vector

Non-viral gene delivery systems based on cationic polymers have faced limitations related to their relative low gene transfer efficiency, cytotoxicity and system instability in vivo. In this paper, a flexible and pompon-like dendrimer composed of poly (amidoamine) (PAMAM) G4.0 as the inner core and poly (L-glutamic acid) grafted low-molecular-weight polyethylenimine (PLGE) as the surrounding multiple arms was synthesized (MGI dendrimer). The novel MGI dendrimer was designed to combine the merits of size-controlled PAMAM G4.0 and the low toxicity and flexible chains of PLGE. In phosphate-buffered saline dispersions the well-defined DNA/MGI complex above a N/P ratio of 30 showed good stability with particle sizes of approximately 200 nm and a comparatively low polydispersity index. However, the particle size of the DNA/25 kDa polyethylenimine (DNA/PEI 25K) complex was larger than 700 nm under the same salt conditions. The shielding of the compact amino groups at the periphery of flexible PAMAM and biocompatible PLGE chains in MGI resulted in a dramatic decrease of the cytotoxicity compared to native PAMAM G4.0 dendrimer. The in vitro transfection efficiency of DNA/MGI dendrimer complex was higher than that of PAMAM G4.0 dendrimer. Importantly, in serum-containing medium, DNA/MGI complexes at their optimal N/P ratio maintained the same high levels of transfection efficiency as in serum-free medium, while the transfection efficiency of native PAMAM G4.0, PEI 25K and Lipofectamine 2000 were sharply decreased. In vivo gene delivery of pVEGF165/MGI complex into balloon-injured rabbit carotid arteries resulted in significant inhibition of restenosis by increasing VEGF165 expression in local vessels. Therefore, the pompon-like MGI dendrimer may be a promising vector candidate for efficient gene delivery in vivo.

Poly (glutamic acid)--an emerging biopolymer of commercial interest

Poly (γ-glutamic acid) (PGA) is water-soluble, anionic, biodegradable, and edible biopolymer produced by Bacillus subtilis. It has multifarious potential applications in foods, pharmaceuticals, healthcare, water treatment and other fields. The production of PGA has already been established on the industrial scale. Various studies regarding the fermentative production, downstream processing and characterization of PGA have been reported in the literature. This review provides updated information on fermentative production of PGA by various bacterial strains and effect of fermentation conditions and media component on production of PGA in submerged as well as solid state fermentation. Information on the application of genetic engineering for enhancement of yield of PGA, kinetic studies for production of PGA in submerged fermentation and recovery and purification of PGA is included. An attempt has also been made to review the current and potential applications of PGA. This review may contribute to further development of this commercially and academically interesting biopolymer.

A Biocompatible Arginine-based Polycation

Self assembly between cations and anions is ubiquitous throughout nature. Important biological structures such as chromatin often use polyvalent assembly between a polycation and a polyaninon. Biomedical importance of synthetic polycations arises from their affinity to polyanions such as nucleic acid and heparan sulfate. However, the limited biocompatibility of synthetic polycations hampers the realization of their immense potential. By examining biocompatible cationic peptides, we hypothesize that a biocompatible polycation should be biodegradable and made from endogenous cations. We designed an arginine-based biodegradable polycation and demonstrated that it was orders of magnitude more compatible than conventional polycations in vitro and in vivo. This biocompatibility diminishes when L-arginine is substituted with D-arginine or when the biodegradable ester linker changes to a biostable ether linker. We believe this design can lead to many biocompatible polycations that can significantly advance a wide range of applications including controlled release, tissue engineering, biosensing, and medical devices.

PEG- and PDMAEG-graft-modified branched PEI as novel gene vector: synthesis, characterization and gene transfection

The cytotoxicity of polyethylenimine (PEI) was a dominating obstacle to its application. Introduction of poly(ethylene glycol) (PEG) blocks to PEI is one of the strategies to alleviate the cytotoxocity of PEI. However, it is well known that the transfection efficiency of PEGylated PEI is decreased to some extent compared to the corresponding PEI. Thus, the aim of our study was to enhance the transfection efficiency of PEGylated PEI. A series of tri-block co-polymers, PEG-g-PEI-g-poly(dimethylaminoethyl L-glutamine) (PEG-g-PEI-g-PDMAEG), as novel vectors for gene therapy was synthesized and evaluated. PEG-g-PEI was first obtained by linking PEG and PEI using isophorone diisocyanate (IPDI) as coupling reagent. The anionic co-polymerization of gamma-benzyl-L-glutamate N-carboxyanhydride (BLG-NCA) using PEG-g-PEI as a macro-initiator was carried out, followed by aminolysis with 2-dimethylaminoethylamine to obtain the target water-soluble tri-block co-polymer. The structures of the polymers were confirmed by FT-IR and (1)H-NMR. The influence of the molecular weight of PEI and the length of the PDMAEG chain on the physicochemical properties and transfection activity of polymer/DNA was evaluated. All PEI derivates were revealed to compact plasmid DNA effectively to give polyplexes with suitable size (approx. 100 nm) and moderate zeta potentials (10-15 mV) at N/P ratios over 10. The PEG-g-PEI-g-PDMAEG tri-block co-polymers displayed particularly low cytotoxicity, even at high concentration, reflecting an improved safety profile compared to PEI 25k. Gene transfection efficiency of PEG-g-PEI-g-PDMAEG on HeLa in the presence and absence of serum was determined. Remarkably, the transfection activity of PEG-g-PEI (10k)-g-PDMAEG (PPP-4)/DNA polyplex formulations was nearly twofold higher than PEI 25k/DNA formulations in vitro, and the transfection efficiency was less affected by the presence of serum. These results indicated that the synthesized PEG-g-PEI-g-PDMAEG tri-block co-polymers are promising candidates as carriers for gene delivery.