Biodegradable polymers as non-viral carriers for plasmid DNA delivery

Altering amine basicities in biodegradable branched polycationic polymers for nonviral gene delivery

In this work, biodegradable branched polycationic polymers were synthesized by Michael addition polymerization from different amine monomers and the triacrylate monomer trimethylolpropane triacrylate. The polymers varied in the number of amines that dissociate in different pH ranges, which are considered to be beneficial to different parts of the gene delivery process. P-DED, a polymer synthesized from trimethylolpropane triacrylate and dimethylethylenediamine, had the highest number of protonated amines that are available for plasmid DNA (pDNA) complexation at pH 7.4 of all polymers synthesized. P-DED formed a positive polyplex (13.9 +/- 0.5 mV) at a polymer/pDNA weight ratio of 10:1 in contrast with the other polymers synthesized, which formed positive polyplexes only at higher weight ratios. Polyplexes formed with the synthesized polymers at the highest polymer/pDNA weight ratio tested (300:1) resulted in higher transfection with enhanced green fluorescent protein reporter gene (5.3 +/- 1.0 to 30.6 +/- 6.6%) compared with naked pDNA (0.8 +/- 0.4%), as quantified by flow cytometry. Polyplexes formed with P-DED (weight ratio of 300:1) also showed higher transfection (30.6 +/- 6.6%) as compared with polyplexes formed with branched polyethylenimine (weight ratio of 2:1, 25.5 +/- 2.7%). The results from this study demonstrated that polymers with amines that dissociate above pH 7.4, which are available as positively charged groups for pDNA complexation at pH 7.4, can be synthesized to produce stable polyplexes with increased zeta potential and decreased hydrodynamic size that efficiently transfect cells. This work indicated that polymers containing varying amine functionalities with different buffering capabilities can be synthesized by using different amine monomers and used as effective gene delivery vectors.

Poly(ethylene glycol) analogs grafted with low molecular weight poly(ethylene imine) as non-viral gene vectors

A novel class of non-viral gene vectors consisting of low molecular weight poly(ethylene imine) (PEI) (molecular weight 800 Da) grafted onto degradable linear poly(ethylene glycol) (PEG) analogs was synthesized. First, a Michael addition reaction between poly(ethylene glycol) diacrylates (PEGDA) (molecular weight 258 Da) and d,l-dithiothreitol (DTT) was carried out to generate a linear polymer (PEG-DTT) having a terminal thiol, methacrylate and pendant hydroxyl functional groups. Five PEG-DTT analogs were synthesized by varying the molar ratio of diacrylates to thiols from 1.2:1 to 1:1.2. Then PEI (800 Da) was grafted onto the main chain of the PEG-DTTs using 1,1'-carbonyldiimidazole as the linker. The above reaction gave rise to a new class of non-viral gene vectors, (PEG-DTT)-g-PEI copolymers, which can effectively complex DNA to form nanoparticles. The molecular weights and structures of the copolymers were characterized by gel permeation chromatography, (1)H nuclear magnetic resonance and Fourier transform infrared spectroscopy. The size of the nanoparticles was<200 nm and the surface charge of the nanoparticles, expressed as the zeta potential, was between+20 and+40 mV. Cytotoxicity assays showed that the copolymers exhibited much lower cytotoxicities than high molecular weight PEI (25 kDa). Transfection was performed in cultured HeLa, HepG2, MCF-7 and COS-7 cells. The copolymers showed higher transfection efficiencies than PEI (25 kDa) tested in four cell lines. The presence of serum (up to 30%) had no inhibitory effect on the transfection efficiency. These results indicate that this new class of non-viral gene vectors may be a promising gene carrier that is worth further investigation.

Toward an injectable continuous osmotic glucose sensor

BACKGROUND

The growing pandemic of diabetes mellitus places a stringent social and economic burden on the society. A tight glycemic control circumvents the detrimental effects, but the prerogative is the development of new more effective tools capable of longterm tracking of blood glucose (BG) in vivo. Such discontinuous sensor technologies will benefit from an unprecedented marked potential as well as reducing the current life expectancy gap of eight years as part of a therapeutic regime.

METHOD

A sensor technology based on osmotic pressure incorporates a reversible competitive affinity assay performing glucose-specific recognition. An absolute change in particles generates a pressure that is proportional to the glucose concentration. An integrated pressure transducer and components developed from the silicon micro- and nanofabrication industry translate this pressure into BG data.

RESULTS

An in vitro model based on a 3.6 x 8.7 mm large pill-shaped implant is equipped with a nanoporous membrane holding 4-6 nm large pores. The affinity assay offers a dynamic range of 36-720 mg/dl with a resolution of +/-16 mg/dl. An integrated 1 x 1 mm(2) large control chip samples the sensor signals for data processing and transmission back to the reader at a total power consumption of 76 microW.

CONCLUSIONS

Current studies have demonstrated the design, layout, and performance of a prototype osmotic sensor in vitro using an affinity assay solution for up to four weeks. The small physical size conforms to an injectable device, forming the basis of a conceptual monitor that offers a tight glycemic control of BG.

Anti-arthritis activity of cationic materials

Cationic materials exhibit remarkable anti-inflammatory activity in experimental arthritis models. Our aim was to confirm this character of cationic materials and investigate its possible mechanism. Adjuvant-induced arthritis (AIA) models were used to test cationic materials for their anti-inflammatory activity. Cationic dextran (C-dextran) with different cationic degrees was used to investigate the influence of the cationic elements of materials on their anti-inflammatory ability. Peritoneal macrophages and spleen cells were used to test the expression of cytokines stimulated by cationic materials. Interferon (IFN)-gamma receptor-deficient mice and macrophage-depleted rats were used to examine the possible mechanisms of the anti-inflammatory activity of cationic materials. In AIA models, different cationic materials shared similar anti-inflammatory characters. The anti-inflammatory activity of C-dextran increased with as the cationic degree increased. Cationic materials stimulated interleukin (IL)-12 expression in peritoneal macrophages, and strong stimulation of IFN-gamma secretion was subsequently observed in spleen cells. In vivo experiments revealed that circulating IL-12 and IFN-gamma were enhanced by the cationic materials. Using IFN-gamma receptor knockout mice and macrophage-depleted rats, we found that IFN-gamma and macrophages played key roles in the anti-inflammatory activity of the materials towards cells. We also found that neutrophil infiltration at inflammatory sites was reduced when AIA animals were treated with C-dextran. We propose that cationic signals act through an unknown receptor on macrophages to induce IL-12 secretion, and that IL-12 promotes the expression of IFN-gamma by natural killer cells (or T cells). The resulting elevated systemic levels of IFN-gamma inhibit arthritis development by preventing neutrophil recruitment to inflammatory sites.

Electrostatic surface modifications to improve gene delivery

IMPORTANCE OF THE FIELD

Gene therapy has the potential to treat a wide variety of diseases, including genetic diseases and cancer.

AREAS COVERED IN THIS REVIEW

This review introduces biomaterials used for gene delivery and then focuses on the use of electrostatic surface modifications to improve gene delivery materials. These modifications have been used to stabilize therapeutics in vivo, add cell-specific targeting ligands, and promote controlled release. Coatings of nanoparticles and microparticles as well as non-particulate surface coatings are covered in this review. Electrostatic principles are crucial for the development of multilayer delivery structures fabricated by the layer-by-layer method.

WHAT THE READER WILL GAIN

The reader will gain knowledge about the composition of biomaterials used for surface modifications and how these coatings and multilayers can be utilized to improve spatial control and efficiency of delivery. Examples are shown for the delivery of nucleic acids, including DNA and siRNA, to in vitro and in vivo systems.

TAKE HOME MESSAGE

The versatile and powerful approach of electrostatic coatings and multilayers will lead to the development of enhanced gene therapies.

NSAID drugs release from injectable microspheres produced by supercritical fluid emulsion extraction

Supercritical fluid emulsion extraction is an innovative technology that uses supercritical carbon dioxide (SC-CO(2)) to extract the dispersed oily phase of an emulsion. This technology was used to produce poly-lactic-co-glycolic acid (PLGA) microspheres charged with two common NSAIDs: piroxicam (PX) and diclophenac sodium (DF). Single (O/W) and double (W/O/W) emulsions were tested and a comparative study between the characteristics of the microspheres obtained by SC-CO(2) extraction and the ones produced by conventional solvent evaporation (SE) is proposed. Varying the droplet dimensions, microspheres with mean diameters (MDs) of 1, 2, and 3 microm were obtained; however, the microspheres produced by SC-CO(2) gave always a better reproduction of the MD of original droplets because aggregation phenomena often modify the mean size and distribution of the microparticles produced by SE. Moreover, very efficient drug loadings (88% w/w of DF in PLGA using W/O/W emulsion and 97% of PX w/w in PLGA starting from O/W emulsion) were measured in the products obtained by SC-CO(2), respectively; whereas, the SE produced a drug loading of 30% in the case of double emulsion and of 70% for single emulsion. Solvent residue of 10 ppm was also measured by SC-CO(2) technology against the 600 ppm of the SE products. The release profiles of the entrapped drugs were also monitored to check the structure of the microspheres produced by this new technology.

Well-defined block copolymers for gene delivery to dendritic cells: probing the effect of polycation chain-length

The development of safe and efficient polymer carriers for DNA vaccine delivery requires mechanistic understanding of structure-function relationship of the polymer carriers and their interaction with antigen-presenting cells. Here we have synthesized a series of diblock copolymers with well-defined chain-length using atom transfer radical polymerization and characterized the influence of polycation chain-length on the physico-chemical properties of the polymer/DNA complexes as well as the interaction with dendritic cells. The copolymers consist of a hydrophilic poly(ethylene glycol) block and a cationic poly(aminoethyl methacrylate) (PAEM) block. The average degree of polymerization (DP) of the PAEM block was varied among 19, 39, and 75, with nearly uniform distribution. With increasing PAEM chain-length, polyplexes formed by the diblock copolymers and plasmid DNA had smaller average particle size and showed higher stability against electrostatic destabilization by salt and heparin. The polymers were not toxic to mouse dendritic cells (DCs) and only displayed chain-length-dependent toxicity at a high concentration (1mg/mL). In vitro gene transfection efficiency and polyplex uptake in DCs were also found to correlate with chain-length of the PAEM block with the longer polymer chain favoring transfection and cellular uptake. The polyplexes induced a modest up-regulation of surface markers for DC maturation that was not significantly dependent on PAEM chain-length. Finally, the polyplex prepared from the longest PAEM block (DP of 75) achieved an average of 20% enhancement over non-condensed anionic dextran in terms of uptake by DCs in the draining lymph nodes 24h after subcutaneous injection into mice. Insights gained from studying such structurally well-defined polymer carriers and their interaction with dendritic cells may contribute to improved design of practically useful DNA vaccine delivery systems.

Recent trends in non-viral vector-mediated gene delivery

Nucleic acids-based next generation biopharmaceuticals (i.e., pDNA, oligonucleotides, short interfering RNA) are potential pioneering materials to cope with various incurable diseases. However, several biological barriers present a challenge for efficient gene delivery. On the other hand, developments in nanotechnology now offer numerous non-viral vectors that have been fabricated and found capable of transmitting the biopharmaceuticals into the cell and even into specific subcellular compartments like mitochondria. This overview illustrates cellular barriers and current status of non-viral gene vectors, i.e., lipoplexes, liposomes, polyplexes, and nanoparticles, to relocate therapeutic DNA-based nanomedicine into the target cell. Despite the awesome impact of physical methods (i.e., ultrasound, electroporation), chemical methods have been shown to accomplish high-level and safe transgene expression. Further comprehension of barriers and the mechanism of cellular uptake will facilitate development of nucleic acids-based nanotherapy for alleviation of various disorders.

Fibrin-mediated lentivirus gene transfer: implications for lentivirus microarrays

We employed fibrin hydrogel as a bioactive matrix for lentivirus mediated gene transfer. Fibrin-mediated gene transfer was highly efficient and exhibited strong dependence on fibrinogen concentration. Efficient gene transfer was achieved with fibrinogen concentration between 3.75 and 7.5mg/ml. Lower fibrinogen concentrations resulted in diffusion of virus out of the gel while higher concentrations led to ineffective fibrin degradation by target cells. Addition of fibrinolytic inhibitors decreased gene transfer in a dose-dependent manner suggesting that fibrin degradation by target cells may be necessary for successful gene delivery. Under these conditions transduction may be limited only to cells interacting with the matrix thereby providing a method for spatially-localized gene delivery. Indeed, when lentivirus-containing fibrin microgels were spotted in an array format gene transfer was confined to virus-containing fibrin spots with minimal cross-contamination between neighboring sites. Collectively, our data suggest that fibrin may provide an effective matrix for spatially-localized gene delivery with potential applications in high-throughput lentiviral microarrays and in regenerative medicine.

Specific down regulation of 3T3-L1 adipocyte differentiation by cell-permeable antisense HIF1alpha-oligonucleotide

Hypoxia is a strong modulator of angiogenesis, accelerating adipose tissue expansion, suggesting that hypoxia inducible factor 1alpha (HIF1alpha) can be a novel target for anti-obesity. We conjugated antisense-HIF1alpha-oligonucleotide (ASO) with low molecular weight protamine (LMWP), a cell-penetrating peptide, to enhance its ability to block hypoxic-angiogenesis, thereby eliciting an anti-obesity effect. Nano-sized ASO-LMWP (AS-L) conjugates enhanced cellular uptake of ASO without yielding a cytotoxic effect and protected the ASO against enzymatic attack and chemical reduction. AS-L showed enhanced intra-cellular localization compared to naked ASO and the complex of ASO with lipofectamine during hypoxic-differentiation. Consequently AS-L induced significant down-regulation of leptin and VEGF gene expressions, thereby reducing fat accumulation in the cell. This proof-of-concept study shows that AS-L produces an inhibitory effect on adipogenesis and angiogenesis during differentiation, indicating LMWP mediated ASO delivery can potentially be a safe and promising treatment for obesity.

RNAi as a new therapeutic strategy against HCV

Hepatitis C virus is a major cause of liver associated diseases all over the world. Irrespective of the significant advances in the current therapy, drugs and vaccines are restricted with many factors such as toxicity, complexity, cost and resistance. New technologies particularly RNA interference (RNAi) mediated by small interfering RNA (siRNA) have become more and more interesting and effective therapeutic entities to silence pathogenic gene products associated with disease, including cancer, viral infections and autoimmune disorders. RNAi works at a posttranscriptional level by targeting mRNA as a mean for inhibiting the synthesis of the encoded protein. Several reports have indicated the efficiency and specificity of synthetic and vector based siRNAs inhibiting HCV replication. In the present review, we focused on the recent development in the potential use and issues regarding siRNA as a therapy for HCV.

Anionic pH sensitive lipoplexes

To provide long circulating nanoparticles which can carry a gene to tumors, we have designed anionic pegylated lipoplexes that are pH sensitive. Anionic pegylated lipoplexes have been prepared from the combined formulation of cationic lipoplexes and pegylated anionic liposomes. The neutralization of the particle surface charge as a function of the pH was monitored by light scattering, in order to determine the ratio between anionic and cationic lipids that would give pH sensitive complexes. This ratio has been optimized to form particles sensitive to pH change in the range 5.5-6.5. Compaction of DNA into these newly formed anionic complexes was checked by DNA accessibility to picogreen. The transfection efficiency and pH sensitive property of these formulations were shown in vitro using bafilomycin, a vacuolar H(+)-ATPase inhibitor.

Nanoparticle technologies for cancer therapy

Nanoparticles as drug delivery systems enable unique approaches for cancer treatment. Over the last two decades, a large number of nanoparticle delivery systems have been developed for cancer therapy, including organic and inorganic materials. Many liposomal, polymer-drug conjugates, and micellar formulations are part of the state of the art in the clinics, and an even greater number of nanoparticle platforms are currently in the preclinical stages of development. More recently developed nanoparticles are demonstrating the potential sophistication of these delivery systems by incorporating multifunctional capabilities and targeting strategies in an effort to increase the efficacy of these systems against the most difficult cancer challenges, including drug resistance and metastatic disease. In this chapter, we will review the available preclinical and clinical nanoparticle technology platforms and their impact for cancer therapy.

Biodegradable branched polycationic polymers with varying hydrophilic spacers for nonviral gene delivery

Biodegradable branched polycationic polymers with varying hydrophilic spacer lengths were synthesized from different triacrylate monomers and the amine monomer 1-(2-aminoethyl)piperazine by Michael addition polymerization. The hydrophilic spacers were varied by the number of ethyleneoxy groups in the triacrylate monomer (E/M) that ranged from 0 to 14. The polymer degradation depended on the spacer length and pH; the amount of ester degraded as determined by (1)H NMR after 14 days was 43.4 +/- 2.1% (pH 5.0) and 89.7 +/- 1.3% (pH 7.4) for the polymer with 0 E/M compared to 55.7 +/- 2.6% (pH 5.0) and 98.5 +/- 1.6% (pH 7.4) for the polymer with 14 E/M. Cell viability of rat fibroblasts after exposure to polymer solutions of concentrations up to 1000 microg/mL remained high (above 66.9 +/- 12.1% compared to below 7.6 +/- 1.1% for polyethylenimine at a concentration of 50 microg/mL or higher) and increased with the spacer length. The polyplexes made with all the synthesized polymers showed higher transfection efficiency (4.5 +/- 1.7% to 9.4 +/- 2.0%, dependent on the polymer/pDNA weight ratio) with an enhanced green fluorescent protein reporter gene compared to naked pDNA (0.8 +/- 0.4%) as quantified by flow cytometry. This study demonstrates that hydrophilic spacers can be incorporated into polycationic polymers to reduce their cytotoxicity and enhance their degradability for nonviral gene delivery.

Cationic poly(amidoamine) dendrimer induces lysosomal apoptotic pathway at therapeutically relevant concentrations

Poly(amidoamine) (PAMAM) dendrimers carrying different amounts of surface amino groups were synthesized and tested for their effects on cellular cytotoxicity, lysosomal pH, and mitochondria-dependent apoptosis. In KB cells, the PAMAM dendrimers were taken up into the lysosomal compartment, and they increased the lysosomal pH and cytotoxicity as a function of the number of surface amino groups on the dendrimer. PAMAM dendrimers that were surface-neutralized by acetylation of >80% of the surface amino groups failed to show any cytotoxicity. The positively charged, amine-terminated PAMAM dendrimer induced cellular apoptosis, as demonstrated by mitochondrial membrane potential changes and caspase activity measurements. These results suggest that PAMAM dendrimers are endocytosed into the KB cells through a lysosomal pathway, leading to lysosomal alkalinization and induction of mitochondria-mediated apoptosis.

A guanidinylated bioreducible polymer with high nuclear localization ability for gene delivery systems

Guanidinylated bioreducible polymer (GBP) was developed for gene delivery systems utilizing cellular penetrating ability of guanidine groups. GBP could retard pDNA from a weight ratio of 5 completely in agarose gel electrophoresis but pDNA was released from GBP polyplexes even at a weight ratio of 20 in reducing condition (2.5mm DTT) due to their biodegradation. GBP also could construct 200 nm-sized and positively charged (approximately 30 mV) polyplex nanoparticles with pDNA. The cytotoxicity of GBP was found to be minimal and GBP showed about 8 folds improved transfection efficiency than a scaffold polymer, poly(cystaminebisacrylamide-diaminohexane) (poly(CBA-DAH)) and even higher transfection efficiency than PEI25k in mammalian cell lines. Its high cellular uptake efficiency (96.1%) and strong nuclear localization ability for pDNA delivery due to the structural advantage of bioreducible polymer and guanidine groups were also identified, suggesting GBP is a promising candidate for efficient gene delivery systems.

Preparation and characterization of poly(DL-lactide-co-glycolide) nanoparticles for siRNA delivery

Synthetic short interfering RNA (siRNA) is promising for specific and efficient knockdown of disease-related genes. However, in vivo application of siRNA requires an effective delivery system. Commonly used siRNA carriers are based on polycations, which form electrostatic complexes with siRNA. Such poly- or lipoplexes are of limited use in vivo due to severe problems associated with toxicity, serum instability and non-specific immune-responses. The aim of the present study was to prepare uniformly sized nanoparticles (NPs) with a high load of siRNA by use of the safe and biodegradable poly-(DL-lactide-co-glycolide) (PLGA) polymer without including polycations. The siRNA was encapsulated in the core of NPs by the double emulsion solvent evaporation method. To optimize the NP formulation, the effects of important formulation and processing parameters were investigated systematically. Generally, spherical siRNA-loaded NPs (<300 nm, PDI<0.2, zeta potential -40 mV) were obtained. An encapsulation efficiency of up to 57% was achieved by adjusting the inner water phase volume, the PLGA concentration, the first emulsification sonication time, and stabilization of the water-oil interface with serum albumin. The integrity of siRNA was preserved during the preparation. Preparation of core-loaded siRNA-NPs based on PLGA and no cationic excipient seems possible and promising for delivery of siRNA.

Vectors for pulmonary gene therapy

The success of gene transfer in preclinical animal models and proof of principle clinical studies has made gene therapy an attractive concept for disease treatment. A variety of diseases affecting the lung are candidates for gene therapy. Delivery of genes to the lungs seems to be straightforward, because of the easy accessibility of epithelial cells via the airways. However, efficient delivery and expression of the therapeutic transgene at levels sufficient to result in phenotypic correction of the diseased state have proven elusive. This review presents a brief summary about current status and future prospects in the development of viral and non-viral strategies for pulmonary gene therapy.

Specific transgene expression in HIV-infected cells using protease-cleavable transcription regulator

Gene therapy is a promising strategy for the treatment of HIV infection, but cell specificity remains an issue. Recently we have developed a new concept for a drug or gene delivery system responding to cellular signals (D-RECS) to achieve cell-specific transgene expression using a non-viral polymer-based vehicle. According to this concept, intracellular signaling enzymes, which are activated specifically in target cells, are used to trigger transgene expression. We previously applied this concept to HIV-1 protease and showed that the recombinant protease could act as a suitable signal. Here we further developed this system to achieve highly specific transgene expression in HIV-infected cells. We prepared a polymeric gene regulator grafted with a cationic peptide containing the HIV-Tat peptide via a specific substrate for HIV-1 protease. The regulator formed a stable polyplex with the transgene, suppressing its transcription. HIV-1 protease cleaved the peptide and released the transgene, which was consequently expressed specifically in activated HIV-infected cells, but remained unreleased and inactive in uninfected cells. The validity of this approach was further confirmed by applying it to the CVB1 2A protease of coxsackievirus (Picornaviridae family). This strategy should be widely applicable for specific expression of a variety of therapeutic genes in virus-infected cells.

On the nature of biomaterials

The situations in which biomaterials are currently used are vastly different to those of just a decade ago. Although implantable medical devices are still immensely important, medical technologies now encompass a range of drug and gene delivery systems, tissue engineering and cell therapies, organ printing and cell patterning, nanotechnology based imaging and diagnostic systems and microelectronic devices. These technologies still encompass metals, ceramics and synthetic polymers, but also biopolymers, self assembled systems, nanoparticles, carbon nanotubes and quantum dots. These changes imply that our original concepts of biomaterials and our expectations of their performance also have to change. This Leading Opinion Paper addresses these issues. It concludes that many substances which hitherto we may not have thought of as biomaterials should now be considered as such so that, alongside the traditional structural biomaterials, we have substances that have been engineered to perform functions within health care where their performance is directly controlled by interactions with tissues and tissue components. These include engineered tissues, cells, organs and even viruses. This essay develops the arguments for a radically different definition of a biomaterial.

siRNA vs. shRNA: similarities and differences

RNA interference (RNAi) is a natural process through which expression of a targeted gene can be knocked down with high specificity and selectivity. Using available technology and bioinformatics investigators will soon be able to identify relevant bio molecular tumor network hubs as potential key targets for knockdown approaches. Methods of mediating the RNAi effect involve small interfering RNA (siRNA), short hairpin RNA (shRNA) and bi-functional shRNA. The simplicity of siRNA manufacturing and transient nature of the effect per dose are optimally suited for certain medical disorders (i.e. viral injections). However, using the endogenous processing machinery, optimized shRNA constructs allow for high potency and sustainable effects using low copy numbers resulting in less off-target effects, particularly if embedded in a miRNA scaffold. Bi-functional design may further enhance potency and safety of RNAi-based therapeutics. Remaining challenges include tumor selective delivery vehicles and more complete evaluation of the scope and scale of off-target effects. This review will compare siRNA, shRNA and bi-functional shRNA.

Bioengineered silk protein-based gene delivery systems

Silk proteins self-assemble into mechanically robust material structures that are also biodegradable and non-cytotoxic, suggesting utility for gene delivery. Since silk proteins can also be tailored in terms of chemistry, molecular weight and other design features via genetic engineering, further control of this system for gene delivery can be considered. In the present study, silk-based block copolymers were bioengineered with poly(L-lysine) domains for gene delivery. Ionic complexes of these silk-polylysine based block copolymers with plasmid DNA (pDNA) were prepared for gene delivery to human embryonic kidney (HEK) cells. The material systems were characterized by agarose gel electrophoresis, atomic force microscopy, and dynamic light scattering. The polymers self-assembled in solution and complexed plasmid DNA through ionic interactions. The pDNA complexes with 30 lysine residues prepared at a polymer/nucleotide ratio of 10 and with a solution diameter of 380 nm showed the highest efficiency for transfection. The pDNA complexes were also immobilized on silk films and demonstrated direct cell transfection from these surfaces. The results demonstrate the potential of bioengineered silk proteins as a new family of highly tailored gene delivery systems.

Polyethylenimine-grafted polycarbonates as biodegradable polycations for gene delivery

Polycations as one of non-viral vectors have gained increasing attentions. In this paper, polyethylenimine(PEI)-grafted polycarbonates (PMAC-g-PEIx) were synthesized as a kind of biodegradable polycations for gene delivery. Backbone polymer, poly(5-methyl-5-allyloxycarbonyl-trimethylene carbonate) (PMAC), was synthesized in bulk catalyzed by immobilized porcine pancreas lipase (IPPL). Then, PMAC-O, the allyl epoxidation product of PMAC, was further modified by PEIx with low molecular weight (x = 423, 800 and 1800). The MWs of PMAC-g-PEIx, measured by GPC-MALLS, were 81,900, 179,900 and 200,600 g/mol with polydispersities of 1.2, 1.4 and 1.7, respectively. PMAC-g-PEIx could form positively charged nano-sized particles (30-90 nm) with pDNA, and all the three PAMC-g-PEIx/DNA polyplexes had similar buffer capabilities. In vitro experiments demonstrated that the PAMC-g-PEIx showed much low cytotoxicity and enhanced transfection efficiency could be found in comparison with PEI25K in 293T cells. Furthermore, pre-incubation of PMAC-g-PEI1800 showed a weakening binding capacity with DNA. The biodegradability of PMAC-g-PEIx can facilitate the efficient release of pDNA from polyplexes and reduce cell cytotoxicity. These results suggested that PMAC-g-PEIx would be a promising non-viral biodegradable vector for gene delivery system.

Preparation and Characterization of Cationic PLA-PEG Nanoparticles for Delivery of Plasmid DNA

The purpose of the present work was to formulate and evaluate cationic poly(lactic acid)-poly(ethylene glycol) (PLA-PEG) nanoparticles as novel non-viral gene delivery nano-device. Cationic PLA-PEG nanoparticles were prepared by nanoprecipitation method. The gene loaded nanoparticles were obtained by incubating the report gene pEGFP with cationic PLA-PEG nanoparticles. The physicochemical properties (e.g., morphology, particle size, surface charge, DNA binding efficiency) and biological properties (e.g., integrity of the released DNA, protection from nuclease degradation, plasma stability, in vitro cytotoxicity, and in vitro transfection ability in Hela cells) of the gene loaded PLA-PEG nanoparticles were evaluated, respectively. The obtained cationic PLA-PEG nanoparticles and gene loaded nanoparticles were both spherical in shape with average particle size of 89.7 and 128.9 nm, polydispersity index of 0.185 and 0.161, zeta potentials of +28.9 and +16.8 mV, respectively. The obtained cationic PLA-PEG nanoparticles with high binding efficiency (>95%) could protect the loaded DNA from the degradation by nuclease and plasma. The nanoparticles displayed sustained-release properties in vitro and the released DNA maintained its structural and functional integrity. It also showed lower cytotoxicity than Lipofectamine 2000 and could successfully transfect gene into Hela cells even in presence of serum. It could be concluded that the established gene loaded cationic PLA-PEG nanoparticles with excellent properties were promising non-viral nano-device, which had potential to make cancer gene therapy achievable.

Brain-targeting gene delivery and cellular internalization mechanisms for modified rabies virus glycoprotein RVG29 nanoparticles

A 29 amino-acid peptide derived from the rabies virus glycoprotein (RVG29) was exploited as a ligand for efficient brain-targeting gene delivery. RVG29 was modified on polyamidoamine dendrimers (PAMAM) through bifunctional PEG, then complexed with DNA, yielding PAMAM-PEG-RVG29/DNA nanoparticles (NPs). The NPs were observed to be uptaken by brain capillary endothelial cells (BCECs) through a clathrin and caveolae mediated energy-depending endocytosis. The specific cellular uptake can be inhibited by free RVG29 and GABA but not by nicotinic acetylcholine receptor (nAchR) agonists/antagonists, indicating RVG29 probably relates to the GABA(B) receptor besides nAchR reported previously. PAMAM-PEG-RVG29/DNA NPs showed higher blood-brain barrier (BBB)-crossing efficiency than PAMAM/DNA NPs in an in vitro BBB model. In vivo imaging showed that the NPs were preferably accumulated in brain. The report gene expression of the PAMAM-PEG-RVG29/DNA NPs was observed in brain, and significantly higher than unmodified NPs. Thus, PAMAM-PEG-RVG29 provides a safe and noninvasive approach for the gene delivery across the BBB.