Serum tolerance and endosomal escape capacity of histidine-modified pDNA-loaded complexes based on polyamidoamine dendrimer derivatives

Structure-activity relationship of dendrimers engineered with twenty common amino acids in gene delivery

Systematic explorations on the structure-activity relationship of surface-engineered dendrimers are essential to design high efficient and safe gene vectors. The chemical diversity of residues in naturally occurring amino acids allows us to generate a library of dendrimers with various surface properties. Here, we synthesized a total number of 40 dendrimers engineered with the twenty common amino acids and investigated their performances in gene delivery. The results show that gene transfection efficacy of the synthesized materials depends on both the type of amino acid and the conjugation ratio. Dendrimers engineered with cationic and hydrophobic amino acids possess relatively higher transfection efficacies. Engineering dendrimers with cationic amino acids such as arginine and lysine facilitates polyplex formation and cellular uptake, with histidine improves endosomal escape of the polyplexes, and with hydrophobic amino acids such as tyrosine and phenylalanine modulates the balance between hydrophobicity and hydrophilicity on dendrimer surface, which is beneficial for efficient cellular internalization. Dendrimers engineered with anionic or hydrophilic amino acids show limited transfection efficacy due to poor DNA binding capacity and/or limited cellular uptake. In the aspect of cytotoxicity, dendrimers engineered with arginine, lysine, tyrosine, phenylalanine and tryptophan show much higher cytotoxicity than other engineered dendrimers. These results are helpful for us to tailor the surface chemistry of dendrimers for efficient gene delivery.

STATEMENT OF SIGNIFICANCE

Cationic polymers such as dendrimers were widely used as gene vectors but are limited by relatively low delivery efficacy and high toxicity. To achieve efficient and low toxic gene delivery, the polymers were modified with various ligands. However, these ligand-modified polymers in gene delivery are reported by independent researchers using different polymer scaffolds and cell lines. It is hard to provide structure-function information of these materials based on current knowledge and experience, which are essential for the design of ideal polymeric vectors for gene delivery. Here, we prepared a small library of amino acid-modified dendrimers, which is used as a screening pool to discover efficient gene vectors. The results obtained from this study, especially the structure-activity relationship of the screened materials are helpful for us to further design efficient and biocompatible polymers for gene delivery. This manuscript will appeal to a wide readership such as nanomaterial chemist, dendrimer chemist, biological chemist, pharmaceutical scientist, and biomedical researchers.

Designed nucleus penetrating thymine-capped dendrimers: a potential vehicle for intramuscular gene transfection

A nucleus penetrating vehicle is indispensible when seeking to deliver plasmid DNA for gene transfection. In this study, dendrimers with terminal thymine groups were synthesized to meet this objective. Through modifications of the hydrophilic and neutral thymine moieties on hyperbranched peripheries, these dendrimers can achieve biosafety, efficient endosomal escape ability, cytosolic accessibility, and eventually, nuclear entry for the purposes of gene transfection. After optimization of the thymine coverages, better gene expression can only be achieved while replacing ∼50% of the amine groups of a dendrimer with thymine moieties. Presumably, a specific dendrimer comprising thymine and primary amines might possess a synergistic effect to promote pDNA condensation via the cooperation of electrostatic interaction and hydrogen bonding. In comparison, a dendrimer entirely capped by thymine can lose external amines, decreasing pDNA complexity and stability, which would cause poor gene transfection. The utility of specific thymine-capped dendrimers in vivo level was demonstrated to successfully and efficiently deliver plasmid DNA at a low complex ratio into mouse muscle by intramuscular injection. Upon the easy accessibility of intramuscular administration, the capability of thymine-capped dendrimers might be potentially used in immunotherapeutic gene transfection in the future.

A fluorinated dendrimer achieves excellent gene transfection efficacy at extremely low nitrogen to phosphorus ratios

Polymers have shown great promise in the design of high efficient and low cytotoxic gene vectors. Here we synthesize fluorinated dendrimers for use as gene vectors. Fluorinated dendrimers achieve excellent gene transfection efficacy in several cell lines (higher than 90% in HEK293 and HeLa cells) at extremely low N/P ratios. These polymers show superior efficacy and biocompatibility compared with several commercial transfection reagents such as Lipofectamine 2000 and SuperFect. Fluorination enhances the cellular uptake of the dendrimer/DNA polyplexes and facilitates their endosomal escape. In addition, the fluorinated dendrimer shows excellent serum resistance and exhibits high gene transfection efficacy even in medium containing 50% FBS. The results suggest that fluorinated dendrimers are a new class of highly efficient gene vectors and fluorination is a promising strategy to design gene vectors without involving sophisticated syntheses.

Enabling cytoplasmic delivery and organelle targeting by surface modification of nanocarriers

Nanocarriers are designed to specifically accumulate in diseased tissues. In this context, targeting of intracellular compartments was shown to enhance the efficacy of many drugs and to offer new and more effective therapeutic approaches. This is especially true for therapies based on biologicals that must be encapsulated to favor cell internalization, and to avoid intracellular endosomal sequestration and degradation of the payload. In this review, we discuss specific surface modifications designed to achieve cell cytoplasm delivery and to improve targeting of major organelles; we also discuss the therapeutic applications of these approaches. Last, we describe some integrated strategies designed to sequentially overcome the biological barriers that separate the site of administration from the cell cytoplasm, which is the drug's site of action.

Reduction-responsive cross-linked stearyl peptide for effective delivery of plasmid DNA

Low efficiency and significant toxicity are the main obstacles to successful gene delivery. We have developed a cationic reduction-responsive vector based on a disulfide cross-linked stearylated polyarginine peptide modified with histidine (C-SHR) for DNA delivery. The structure of the C-SHR was characterized, and the in vitro and in vivo transfection efficiency and cytotoxicity of C-SHR/plasmid DNA complexes were examined. Compared with non-cross-linked stearylated polyarginine peptide (SHR), C-SHR increased the intracellular uptake and dissociation behavior of the complexes. In addition, the gene transfection efficiency of C-SHR/plasmid DNA complexes in HEK293 and HeLa cells was improved and was comparable with that of bPEI-25K/plasmid DNA complexes, and the cytotoxicity of C-SHR was significantly less than that of bPEI-25K. Importantly, the in vivo gene transfection efficiency of C-SHR/plasmid DNA complexes was five fold higher than that of SHR/plasmid DNA complexes, suggesting that C-SHR is an efficient non-viral vector for DNA delivery.

Recent progress in biomedical applications of Pluronic (PF127): Pharmaceutical perspectives

Most of the administered anti-cancer drugs are hydrophobic in nature and are known to have poor water solubility, short residence time, rapid clearance from the body and systemic side effects. Polymeric-based targeted particulate carrier system has shown to directly deliver the encapsulated anti-cancer drug to the desired site of action and prevent the interaction of encapsulated drug with the normal cells. Pluronic F127 (PF127) has been widely investigated for its broad-range of therodiagnostic applications in biomedical and pharmaceutical sciences, but rapid dissolution in the physiological fluids, short residence time, rapid clearance, and weak mechanical strength are the main shortcomings that are associated with PF127 and have recently been overcome by making various modifications in the structure of PF127 notably through preparation of PF127-based mixed polymeric micelles, PF127-conjugated nanoparticles and PF127-based hydrophobically modified thermogels. In this article, we have briefly discussed the recent studies that have been conducted on various anti-cancer drugs using PF127 as nano-carrier modified with other copolymers and/or conjugated with magnetic nanoparticles. The key findings of these studies demonstrated that the modified form of PF127 can significantly increase the stability of incorporated hydrophobic drugs with enhanced in vitro cytotoxicity and cellular uptake of anti-cancer drugs. Moreover, the modified form of PF127 has also shown its therapeutic potentials as therodiagnostics in various types of tumors and cancers. Hence, it can be concluded that the modified form of PF127 exhibits significant therodiagnostic effects with increased tumor-specific delivery of anti-cancer drugs having minimal toxic effects as compared to PF127 alone and/or other copolymers.

Histamine-functionalized copolymer micelles as a drug delivery system in 2D and 3D models of breast cancer

Histamine functionalized block copolymers based on poly(allyl glycidyl ether)-b-poly(ethylene oxide) (PAGE-b-PEO) were prepared with different ratios of histamine and octyl or benzyl groups using UV-initiated thiol-ene click chemistry. At neutral pH, the histamine units are uncharged and hydrophobic, while in acidic environments, such as in the endosome, lysosomes, or extracellular sites of tumours, the histamine groups are positively charged and hydrophilic. pH responsible polymer drug delivery systems is a promising route to site specific delivery of drugs and offers the potential to avoid side effects of systemic treatment. Our detailed in vitro experiments of the efficacy of drug delivery and the intracellular localization characteristics of this library of NPs in 2D and 3D cultures of breast cancer revealed that the 50% histamine-modified polymer loaded with DOX exhibited rapid accumulation in the nucleus of free DOX within 2 h. Confocal studies showed enhanced mitochondrial localization and lysosomal escape when compared to controls. From these combined studies, it was shown that by accurately tuning the structure of the initial block copolymers, the resulting self-assembled NPs can be designed to exploit histamine as an endosomal escape trigger and the octyl/benzyl units give rise to a hydrophobic core resulting in highly efficacious drug delivery systems (DDS) with control over intracellular localization. Optimization and rational control of the intracellular localization of both DDS and the parent drug can give nanomedicines a substantial increase in efficacy and should be explored in future studies.

Hydrogen-bonding dramatically modulates the gene transfection efficacy of surface-engineered dendrimers

Dendrimers have shown great promise in the design of efficient gene vectors. However, high transfection efficacy is usually associated with serious cytotoxicity for these cationic polymers. Here, we report a facile strategy to prepare surface-engineered dendrimers with a dramatic transfection efficacy and reduced cytotoxicity. Surface-engineered dendrimers with multiple hydrogen bonding ligands such as guanamine and nucleobase derivatives show superior efficacy and low cytotoxicity on commonly used cells as well as 3D tumor spheroids to representative transfection reagents such as Lipofectamine 2000. Complementary multiple hydrogen bonding interactions between the modified ligands and DNA nucleobases play essential roles in efficient gene transfection. The hydrogen-bond modulation strategy represents a promising tool in the design of highly efficient and less cytotoxic gene materials.

Enhanced antitumor efficacies of multifunctional nanocomplexes through knocking down the barriers for siRNA delivery

Multifunctional nanocomplexes (NCs) consisting of urocanic acid-modified galactosylated trimethyl chitosan (UA-GT) conjugates as polymeric vectors, poly(allylamine hydrochloride)-citraconic anhydride (PAH-Cit) as charge-reversible crosslinkers, and vascular endothelial growth factor (VEGF) siRNA as therapeutic genes, were rationally designed to simultaneously overcome the extracellular, cellular, and intracellular barriers for siRNA delivery. The strong physical stability of UA-GT/PAH-Cit/siRNA NCs (UA-GT NCs) at pH 7.4 and 6.5 endowed protection from massive dilution, competitive ions, and ubiquitous nucleases in the blood and tumorous microenvironment. Their internalization into hepato-carcinoma cells was facilitated through the recognition of galactose receptors, followed by effective escape from endosomes/lysosomes owing to the strong buffering capacity of imidazole residues. At the meantime, the endosomal/lysosomal acidity triggered the charge reversal of PAH-Cit in UA-GT NCs, thus evoking their structural disassembly and subsequently accelerated release of siRNA in the cytosol. As a result, robust in vivo performance in terms of both gene silencing and tumor inhibition was achieved by UA-GT NCs at a low siRNA dose. Moreover, neither histological nor hematological toxicity was detected following repeated intravenous administration. Therefore, UA-GT NCs potentially served as an efficient and safe candidate in the treatment of hepatocellular carcinoma through knocking down the overall barriers for siRNA delivery.

Screening nylon-3 polymers, a new class of cationic amphiphiles, for siRNA delivery

Amphiphilic nucleic acid carriers have attracted strong interest. Three groups of nylon-3 copolymers (poly-β-peptides) possessing different cationic/hydrophobic content were evaluated as siRNA delivery agents in this study. Their ability to condense siRNA was determined in SYBR Gold assays. Their cytotoxicity was tested by MTT assays, their efficiency of delivering Alexa Fluor-488-labeled siRNA intracellularly in the presence and absence of uptake inhibitors was assessed by flow cytometry, and their transfection efficacies were studied by luciferase knockdown in a cell line stably expressing luciferase (H1299/Luc). Endosomal release was determined by confocal laser scanning microscopy and colocalization with lysotracker. All polymers efficiently condensed siRNA at nitrogen-to-phosphate (N/P) ratios of 5 or lower, as reflected in hydrodynamic diameters smaller than that at N/P 1. Although several formulations had negative zeta potentials at N/P 1, G2C and G2D polyplexes yielded >80% uptake in H1299/Luc cells, as determined by flow cytometry. Luciferase knockdown (20–65%) was observed after transfection with polyplexes made of the high molecular weight polymers that were the most hydrophobic. The ability of nylon-3 polymers to deliver siRNA intracellularly even at negative zeta potential implies that they mediate transport across cell membranes based on their amphiphilicity. The cellular uptake route was determined to strongly depend on the presence of cholesterol in the cell membrane. These polymers are, therefore, very promising for siRNA delivery at reduced surface charge and toxicity. Our study identified nylon-3 formulations at low N/P ratios for effective gene knockdown, indicating that nylon-3 polymers are a new, promising type of gene delivery agent.

The role of caveolin-1 and syndecan-4 in the internalization of PEGylated PAMAM dendrimer polyplexes into myoblast and hepatic cells

To improve gene delivery efficiency of PEGylated poly(amidoamine) dendrimers in livers and muscles, the roles of syndecan-4 receptor and caveolin-1 protein in the endocytosis of PEGylated generation 5 (G5-PEG) or 7 (G7-PEG) dendrimers and plasmid DNA polyplexes were explored in C2C12 and HepG2 cells. Expression levels of syndecan-4 for both cell lines were downregulated by transfection of the cells with syndecan-4 specific siRNA. Caveolin-1 was upregulated by infecting the cells with adenovirus vector expressed caveolin-1 (Ad-CAV-1). The impact of syndecan-4 and caveolin-1 on endocytosis of G5-PEG/DNA or G7-PEG/DNA polyplexes was then measured by flow cytometry. Our results demonstrate that downregulation of syndecan-4 and upregulation of caveolin-1 significantly improved internalization of PEG-PAMAM dendrimer polyplexes in HepG2 cells; however, in C2C12 cells, downregulation of syndecan-4 decreased the internalization of the polyplexes while upregulation of caveolin-1 had no effect on internalization. Gene expression results for G5-PEG/pGFP on the two cell lines exhibited the same trends for syndecan-4 and caveolin-1 as was observed for endocytosis of the polyplexes. This study gives a clue how to take strategies by up- or down-regulation of the expressions of syndecan-4 and caveolin-1 to improve in vivo gene delivery efficiency of the PEG-PAMAM dendrimers in clinical transgenic therapy.

Dilution-stable PAMAM G1-grafted polyrotaxane supermolecules deliver gene into cells through a caveolae-dependent pathway

Numerous preclinical studies have demonstrated that polycation mediated gene delivery systems successfully achieved efficient gene transfer into cells and animal models. However, results of their clinical trials to date have been disappointing. That self-assembled gene and polycation systems should be stable undergoing dilution in the body is one of the prerequisites to ensuring efficiency of gene transfer in clinical trials, but it was neglected in most preclinical studies. In this account, we developed the dilution-stable PAMAM G1-grafted polyrotaxane (PPG1) supermolecules in which PAMAM G1-grafted α-cyclodextrins are threaded onto a PEG chain capped with hydrophobic adamantanamine. The PPG1/pDNA polyplex (approximate 100 nm in diameter) was very stable and kept its initial particle size and a uniform size distribution at ultrahigh dilution, whereas DNA/PEI 25K polyplex was above three times bigger at a 16-fold dilution than the initial size and their particle size distribution indicated multiple peaks mainly due to forming loose and noncompacted aggregates. PPG1 supermolecules showed significantly superior transfection efficiencies compared to either PEI 25K or Lipofectamine 2000 in most cell lines tested including normal cells (HEK293A) and cancer cells (Bel7402, HepG2, and HeLa). Furthermore, we found that the PPG1 supermolecules delivered DNA into HEK293A through a caveolae-dependent pathway but not a clathrin-dependent pathway as PEI 25K did. These findings raised the intriguing possibility that the caveolae-dependent pathway of PPG1 supermolecule/pDNA polyplex avoiding lysosomal degradation was attributed to their high transfection efficiency. The dilution-stable PPG1 supermolecule polyplex facilitating caveolae-dependent internalization has potential applications to surmount the challenges of high dilutions in the body and lysosomal degradation faced by most gene therapy clinical trials.

Efficient gene delivery system mediated by cis-aconitate-modified chitosan-g-stearic acid micelles

Cis-aconitate-modified chitosan-g-stearic acid (CA-CSO-SA) micelles were synthesized in this study to improve the gene transfection efficiency of chitosan-g-stearic acid (CSO-SA). The CA-CSO-SA micelles had a similar size, critical micelle concentration, and morphology, but their zeta potential and cytotoxicity were reduced compared with CSO-SA micelles. After modification with cis-aconitate, the CA-CSO-SA micelles could also compact plasmid DNA (pDNA) to form nanocomplexes. However, the DNA binding ability of CA-CSO-SA was slightly reduced compared with that of CSO-SA. The transfection efficiency mediated by CA-CSO-SA/pDNA against HEK-293 cells reached up to 37%, and was much higher than that of CSO-SA/pDNA (16%). Although the cis-aconitate modification reduced cellular uptake kinetics in the initial stages, the total amount of cellular uptake tended to be the same after 24 hours of incubation. An endocytosis inhibition experiment showed that the internalization mechanism of CA-CSO-SA/pDNA in HEK-293 cells was mainly via clathrin-mediated endocytosis, as well as caveolae-mediated endocytosis and macropinocytosis. Observation of intracellular trafficking indicated that the CSO-SA/pDNA complexes were trapped in endolysosomes, but CA-CSO-SA/pDNA was more widely distributed in the cytosol. This study suggests that modification with cis-aconitate improves the transfection efficiency of CSO-SA/pDNA.

Multi-armed poly(L-glutamic acid)-graft-polypropyleneinime as effective and serum resistant gene delivery vectors

A new series of multi-armed MP-g-PPI dendrimers were synthesized by polymerization of BLG-NCA using G2.0PPI as macromolecular initiator and subsequent aminolysis with G1.0PPI or G2.0PPI. The chemical structure and composition of the MP-g-PPI dendrimers were characterized by Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance spectroscopy ((1)H NMR). The MP-g-PPI showed a great ability to combine with pDNA to form complexes, which protect the pDNA from nuclease degradation. Dynamic light scattering (DLS) measurement illustrated that the sizes of complexes were in range of 111-219 nm. The transmission electron microscope (TEM) and atomic force microscope (AFM) observation showed that the morphology of these complexes was spherical. The MTT assay demonstrated that cytotoxicity of the MP-g-PPI was lower than that of PEI 25K. The in vitro transfection test indicated that MP-g-PPI gene vectors displayed relative high transfection efficiency than that of PEI 25K and Lipofectamine 2000 in serum-containing medium. Furthermore, MP-g-PPI at the weight ratio of 7.5 displayed better serum-resistant capability than that of PEI 25K and Lipofectamine 2000. The above facts revealed that multi-armed MP-g-PPI dendrimers may be promising gene vectors with low cytotoxicity, high transfection efficiency and serum-resistant ability.

Surface-engineered dendrimers with a diaminododecane core achieve efficient gene transfection and low cytotoxicity

Cationic dendrimers are widely used as gene vectors; however, these materials are usually associated with unsatisfied transfection efficiency and biocompatibility. In this study, we used an aliphatic hydrocarbon-cored polyamidoamine (PAMAM) dendrimer as an alternative to traditional cationic PAMAM dendrimers in the design of efficient gene vectors. Diaminododecane-cored generation 4 (C12G4) PAMAM dendrimer showed dramatically higher efficacy in luciferase and EGFP gene transfection than diaminoethane-cored generation 4 (C2G4) and diaminohexane-cored generation 4 (C6G4) PAMAM dendrimers. The viability of cells incubated with C12G4 at transfection concentrations is above 90%. The significantly improved gene transfection efficacy of C12G4 is attributed to the hydrophobic core of C12G4 which increases the cellular uptake of dendrimer/DNA polyplexes. Further modification of C12G4 with functional ligands such as arginine, 2,4-diamino-1,3,5-triazine, and fluorine compounds significantly increase its transfection efficiency on several cell lines. These results suggest that diaminododecane-cored dendrimers can be developed as a versatile scaffold in the design of efficient gene vectors.

Current progress in gene delivery technology based on chemical methods and nano-carriers

Gene transfer methods are promising in the field of gene therapy. Current methods for gene transfer include three major groups: viral, physical and chemical methods. This review mainly summarizes development of several types of chemical methods for gene transfer in vitro and in vivo by means of nano-carriers like; calcium phosphates, lipids, and cationic polymers including chitosan, polyethylenimine, polyamidoamine dendrimers, and poly(lactide-co-glycolide). This review also briefly introduces applications of these chemical methods for gene delivery.

Serum-resistant complex nanoparticles functionalized with imidazole-rich polypeptide for gene delivery to pulmonary metastatic melanoma

To enhance serum-resistance and overcome the lysosomal barrier are effective and feasible strategies to increase the transfection efficiency of non-viral gene delivery system. For the systemic delivery of therapeutic gene, we previously developed self-assemble carboxymethyl poly(l-histidine) (CM-PLH)/poly(β-amino ester) (PbAE)/pDNA ternary complex nanoparticles based on electrostatic coating as an effective pDNA carrier. Recharging cationic PbAE/pDNA polyplexes with CM-PLH was a promising method to reduce the cytotoxicity and enhance the stability in vivo of positive charged polyplexes. In the present study, the transfection activities of ternary complex nanoparticles were further evaluated in vitro and in vivo. The transfection efficiency of ternary complex nanoparticles showed significant serum-resistance (CM-PLH-containing (51.9±4.35)% in 50% FBS>CM-PLH-free (14.7±5.66)% in 50% FBS), cell line dependent (HEK293>MCF-7>COS7>B16F10>A549>Hela>SPC-A1>CHO>SKOV3) and incubation period dependent (24 h, 20 h, 16 h>12 h>8 h>4 h>2 h>1 h>0.5 h). After transfected with ternary complex nanoparticles loading pGV240-MDA-7/IL-24, the B16F10 cells exhibited significant apoptosis and proliferation inhibition due to the expression of IL-24. Moreover, in the pulmonary metastatic melanoma model, ternary complex nanoparticles loading pGV240-MDA-7/IL-24 showed significant antitumor therapeutic efficacy in vivo. These results suggested that CM-PLH/PbAE/pDNA ternary complex nanoparticles were promising and challenging gene vector for practical application.

Enhancement of all-trans retinoic acid-induced differentiation by pH-sensitive nanoparticles for solid tumor cells

Cancer differentiation therapy is an attractive concept and has been clinically used to treat leukemia. However, it is limited to date for solid tumors. In this study, the pH-sensitive nanoparticles based on poly(amidoamine) (PAMAM) dendrimers are synthesized by coupling 3,4,5,6-tetrahydrophthalic anhydride with the first generation PAMAM. The modified dendrimers can self-assemble in aqueous solution to form nanoparticles with a diameter of 125-435 nm. The nanoparticles are relatively stable at physiological pH (pH 7.4) but dissociated in acidic environments (pH 5.0 or 6.0). The present studies show that the proliferation inhibition and albumin secretion of hepatoma carcinoma cells are enhanced with all-trans retinoic acid (ATRA) encapsulated in the nanoparticles. The enhancement of induced differentiation is due to the high internalization of ATRA in the cells by the nanoparticles. These experimental results demonstrate that pH-sensitive nanoparticles may be efficient for improving the differentiation therapy for solid tumor.

Pentablock copolymers of pluronic F127 and modified poly(2-dimethyl amino)ethyl methacrylate for internalization mechanism and gene transfection studies

Cationic polymers are one of the major nonviral gene delivery vectors investigated in the past decade. In this study, we synthesized several cationic copolymers using atom transfer radical polymerization (ATRP) for gene delivery vectors: pluronic F127-poly(dimethylaminoethyl methacrylate) (PF127-pDMAEMA), pluronic F127-poly (dimethylaminoethyl methacrylate-tert-butyl acrylate) (PF127-p(DMAEMA-tBA)), and pluronic F127-poly(dimethylaminoethyl methacrylate-acrylic acid) (PF127-p(DMAEMA-AA)). The copolymers showed high buffering capacity and efficiently complexed with plasmid deoxyribonucleic acid (pDNA) to form nanoparticles 80–180 nm in diameter and with positive zeta potentials. In the absence of 10% fetal bovine serum, PF127-p(DMAEMA-AA) showed the highest gene expression and the lowest cytotoxicity in 293T cells. After acrylic acid groups had been linked with a fluorescent dye, the confocal laser scanning microscopic image showed that PF127-p(DMAEMA-AA)/pDNA could efficiently enter the cells. Both clathrin-mediated and caveolae-mediated endocytosis mechanisms were involved. Our results showed that PF127-p(DMAEMA-AA) has great potential to be a gene delivery vector.