Temperature-Controlled Properties of DNA Complexes with Poly(ethylenimine)-graft-poly(N-isopropylacrylamide)

Magnetic thermo-responsive branched polymer for fast extraction and enrichment of phenolic acids in olive oil with tunable and enhanced performance

Magnetic thermo-responsive branched polymer (Fe₃O₄@poly(glycidyl methacrylate)@poly(N-isopropylacrylamide)) was fabricated for the first time and applied for microwave-assisted magnetic solid phase extraction of phenolic acids in olive oil samples followed by ultra-high performance liquid chromatography-tandem mass spectrometry analysis in multiple reaction monitoring mode. Owing to the controllable molecular weight of poly(glycidyl methacrylate) synthesized by atom transfer radical polymerization and the thermo-responsive characteristic of poly(N-isopropylacrylamide), extraction performance could be efficiently tuned and enhanced. The whole sample pretreatment process was accomplished within 1 min with the help of the microwave. The nanocomposites were characterized by transmission electron microscope, scanning electron microscope, Fourier transform infrared spectroscopy, thermogravimetric analysis, vibrating sample magnetometer, water contact angles and dynamic light scattering. The adsorption experimental data fitted well with the Freundlich isotherm model and followed the pseudo-second-order kinetic model. The factors affecting the extraction process including adsorbent amount, adsorption time, sample volume, desorption conditions and interferents were investigated and optimized. Under the most favorable conditions, the developed method showed good linearity (R² ≥ 97.98%) in the range of 0.2-30 μg L^-1, low limits of detection (0.005-0.030 μg L^-1) and limits of quantification (0.016-0.098 μg L^-1) as well as satisfactory precision (RSDs≤4.85%). Our proposed method was successfully used for determination of phenolic acids in olive oil samples and satisfactory recoveries at three spiked concentration levels were in the range of 84.6-108.1% with RSDs less than 9.20%. Coupled with principal component analysis, our developed method proved promising for fast and convenient differentiation between extra virgin olive oils and refined olive oils.

Regulation of oligonucleotide adsorption by a thermo and pH dual-responsive copolymer layer

Oligonucleotides hold great promise as therapeutic agents to specifically and selectively inhibit gene expression. In order to achieve better targeting efficiency and treatment efficacy, nanocarriers that are dual-responsive to both temperature and pH are more attractive and suitable due to the fact that certain malignancies can cause a slight increase of local temperature and a minor decrease in extracellular pH around the tumor site at the same time. Here, we systematically study oligonucleotide adsorption on the poly(ethyleneimine)-b-poly(N-isopropylacrylamide) (PEI-b-PNIPAm) copolymer layer grafted on a planar surface and nanoparticles with various radii, where the single effect of temperature or pH alone on oligonucleotide adsorption has been extensively investigated, but the combined effect of temperature and pH is less discussed. The theoretical results show that the surface density of the adsorbed oligonucleotides exhibits thermo and pH dual-responsive behavior, in which temperature and pH exhibit a combined effect on the loading capacity of the oligonucleotides. The underlying molecular mechanism of the dual-responsive behavior is revealed. Besides, the effect of important but coupled parameters in nanocarrier design such as polymer surface coverage and length, salt concentration as well as surface curvature (inverse nanoparticle radius) that may influence the dual-responsive behavior of oligonucleotide adsorption is further discussed, which is of great significance to direct the optimal design of PNIPAm/PEI-based nanocarriers to improve the transfection efficiency by achieving the maximal loading capacity of oligonucleotides at different temperatures and pH values.

Fabrication and Optimization of Linear PEI-Modified Crystal Nanocellulose as an Efficient Non-Viral Vector for In-Vitro Gene Delivery

BACKGROUND

One of the major challenges in gene therapy is producing gene carriers that possess high transfection efficiency and low cytotoxicity (1). To achieve this purpose, crystal nanocellulose (CNC) -based nanoparticles grafted with polyethylenimine (PEI) have been developed as an alternative to traditional viral vectors to eliminate potential toxicity and immunogenicity.

METHODS

In this study, CNC-PEI10kDa (CNCP) nanoparticles were synthetized and their transfection efficiency was evaluated and compared with linear cationic PEI10kDa (PEI) polymer in HEK293T (HEK) cells. Synthetized nanoparticles were characterized with AFM, FTIR, DLS, and gel retardation assays. In-vitro gene delivery efficiency by nano-complexes and their effects on cell viability were determined with fluorescent microscopy and flow cytometry.

RESULTS

Prepared CNC was oxidized with sodium periodate and its surface cationized with linear PEI. The new CNCP nano-complex showed different transfection efficiencies at different nanoparticle/plasmid ratios, which were greater than those of PEI polymer. CNPC and Lipofectamine were similar in their transfection efficiencies and effect on cell viability after transfection.

CONCLUSION

CNCP nanoparticles are appropriate candidates for gene delivery. This result highlights CNC as an attractive biomaterial and demonstrates how its different cationized forms may be applied in designing gene delivery systems.

Star-shaped poly(2-aminoethyl methacrylate)s as non-viral gene carriers: Exploring structure-function relationship

Gene therapy shows much promise in treating many inheritable and acquired diseases, but challenges remain in the design of gene vectors with low cytotoxicity and high transfection efficiency. Elucidating the structure-function relationship of non-viral polymer-based gene carriers is crucial for improving the design and performance of safe and effective gene therapy approaches. The cationic poly(2-aminoethyl methacrylate) (PAEM) containing primary amino side groups is an attractive carrier for gene delivery. This study focuses on four PAEM-based polycations with well-defined molecular weight and chain architecture. The polymers include three cyclodextrin (CD)-cored star-shaped PAEM polycations (s-PAEM), synthesized by atom transfer radical polymerization (ATRP), and a linear PAEM polycation (l-PAEM), synthesized via activators regenerated by electron transfer (ARGET) ATRP. All four polycations could condense plasmid DNA (pDNA) into spherical polyplexes with small sizes (<200 nm). The polyplexes showed excellent stability during storage and were able to resist electrostatic destabilization. The cytotoxicity of these polycations was depended on dose and target cell type and was influenced by molecular weight and chain architecture, yet the polyplexes showed little cytotoxicity regardless of the type of polymer used. The transfection efficiency of PAEM polycations was highly dependent upon molecular weight, molecular architecture (star versus linear) and target cell type. In most cases, polyplexes formed by high-molecular-weight s-PAEM performed the best. Moreover, at a specific N/P ratio, the transfection efficiency mediated by s-PAEM was higher in MCF-7 breast cancer cells than in COS-7 fibroblast-like cells, but such cell-type dependence was not obvious for l-PAEM. These findings indicate that the star-shaped PAEM polycations could be promising gene carriers for gene therapy applications.

Facile design and development of photoluminescent graphene quantum dots grafted dextran/glycol-polymeric hydrogel for thermoresponsive triggered delivery of buprenorphine on pain management in tissue implantation

A novel nano-formulations of biocompatible, biodegradable and thermo-responsive graphene quantum dots (GQDs) loaded dextran/poly(N-isopropylacrylamide) (Dex/PNIPAM) copolymeric matrix was synthesized and analyzed the materials characterization, sustained drug delivery system, tissue feasibility in the tissue implantation site. This research report was aimed to grafting and functionalizing thermo-responsive (Dex/PNIPAM) copolymeric composite with presence of graphene quantum dots to achieve thermal responsive drug delivery (TrDD) with no harm effect in the implantation site. The synthesized GQD by using ionic liquid were evaluated by spectroscopic (DLS, PL, XRD and Raman spectroscopy) and Transmission electron microscopic analysis (TEM). The ultra-small GQDs loaded Dex/PNIPAM and was appeared to be asymmetric and open uniform porous structure, which can be significantly favorable for cell uptake and greatly influenced to be an effective drug carrier into the cellular compartment with good fluid flow. The PNIPAM polymeric composite were exhibited sustained and enhanced drug release percentages with increasing temperature at above low critical solution temperature (LCST) is 39 °C comparable to the cumulative drug release profile of below LCST (32 °C), which demonstrated that thermo-responsive polymer was played a significant role in the delivery system. The treated group of GQDs-Dex/PNIPAM was observed that no inflammation and shows noteworthy stromal cell infiltration, demonstrating that the synthesized drug carriers did not harm to the nerves and tissues and only was responsible for the pain management.

Glycopolymers/PEI complexes as serum-tolerant vectors for enhanced gene delivery to hepatocytes

Serum stability is a crucial factor for ideal polymeric gene vectors. In this work, a series of serum-tolerant and low-toxicity glycopolymers/poly(ethyleneimine) (PEI) complexes were designed for gene delivery. Atomic transfer radical polymerization (ATRP) was used to synthesize the comb-shaped random copolymers dextran-g-poly(2-dimethylaminoethyl methacrylate-co-2-lactobionamidoethyl methacrylate) (DDrL). Then DDrLs/PEI were investigated for their use as plasmid DNA (pDNA) vectors, which can completely condense the pDNA into nanoparticles. The DDrLs/PEI/pDNA complexes in serum-containing media showed better stability than PEI/pDNA complexes. in vitro gene transfection studies showed that DDrLs/PEI exhibited a remarkable transfection efficiency enhancement in the presence of serum compared to that in serum-free conditions. Moreover, the transfection level of DDrLs/PEI were two orders of magnitude higher than that of PEI alone in the presence of 30% serum. DDrLs/PEI complexes with galactose enhanced pDNA delivery to hepatocytes, with higher protein expression in ASGPr-presenting HepG2 than in HeLa cells, which lack the receptor. All of the DDrLs/PEI/pDNA complexes had lower cytotoxicity than PEI/pDNA.

Temperature- and Composition-Dependent DNA Condensation by Thermosensitive Block Copolymers

Successful intracellular delivery of genes requires an efficient carrier, as genes by themselves cannot diffuse across cell membranes. Because of the toxicity and immunogenicity of viral vectors, nonviral vectors are gaining tremendous interest in research. In this work, we have investigated the temperature-dependent DNA condensation efficiency of various compositions of a thermosensitive block copolymer viz., poly(N-isopropylacrylamide)-b-poly(2-(diethylamino)ethyl methacrylate) (PNIPA-b-PDMAEMA). Three different copolymer compositions of varying molecular weights were successfully synthesized via the RAFT polymerization technique. Steady-state fluorescence and circular dichroism (CD) spectroscopies, dynamic light scattering (DLS) and zeta potential measurements, agarose gel electrophoresis, and atomic force microscopy techniques were utilized to study the interaction of the copolymers with DNA at temperatures above and below the critical aggregation temperature (CAT). All these experiments revealed that, above the CAT, there was formation of highly stable and tight polymer-DNA complexes (polyplexes). The size of polyplexes was dependent on the temperature up to a certain charge ratio, as determined by the DLS results. The results obtained from temperature-dependent fluorescence spectroscopy, CD, and gel electrophoresis indicated that the DNA molecules were shielded more from aqueous exposure above the CAT because of the formation of relatively more compact complexes. The polyplexes also exhibited changes in the particle morphology below and above the CAT, with particles generated above CAT being more spherical in morphology. These results suggested at the possibility of modulating the complex formation by temperature modification. The present biophysical studies would provide new physical insight into the design of novel gene carriers.

Tunable PEGylation of branch-type PEI/DNA polyplexes with a compromise of low cytotoxicity and high transgene expression: in vitro and in vivo gene delivery

Although PEGylated polyplexes for gene delivery are widespread, there is a need for an in-depth investigation of the role of the PEGylation degree on the delivery efficiency of the systems. For this, a low-toxicity series of polymers for gene delivery were designed via Michael addition of poly(ethylene glycol)methyl ether methacrylate (PEGMA) onto branched polyethylenimine PEI. The goal was to finely tune the PEGylation degree in order to determine the system offering the best compromise between low cytotoxicity and high transfection efficiency under both in vitro and in vivo conditions. From dynamic light scattering tests, zeta potential measurements and gel retardation assay, it was found that nanoparticle assembly of PEI-g-PEGMA and DNA exhibited stable complex formation when the PEGylation degree was below 2.9%. In addition, complexes formed from polymers with a PEGylation degree of at least 1.67% (from PEI-g-PEGMA-6 to PEI-g-PEGMA-18) all showed very low hemolysis activity. Transfection efficiencies of the prepared complexes were determined using the pEGFP-C3 vector and β-galactosidase. Complexes made of PEI-g-PEGMA-6 and PEI-g-PEGMA-10 at a polymer nitrogen/DNA phosphorus weight ratio (W_n/W_p) of 5 led to the best transfection efficiencies. Moreover, PEGylation ensured low cytotoxicity of the complexes in particular at high W_n/W_p ratios. In vivo tests in a mouse model confirmed the in vitro results obtained for PEI-g-PEGMA-6-based complexes, at all W_n/W_p ratios tested, but also showed that a high PEGylation degree (5.2% for PEI-g-PEGMA-18), though inefficient in vitro could still lead to successful delivery in vivo, due to a prolonged contact time between the complex and the cells, and to the change in the biological environment. Overall, provided a fine tuning of the grafting density of PEGMA onto PEI and the polymer nitrogen/DNA phosphorus weight ratio, our results prove that PEI-g-PEGMA polymers constitute an efficient platform for successful in vitro and in vivo gene delivery, and ensure low cytotoxicity and prolonged cell viability.

Effect of substrate storage conditions on the stability of "Smart" films used for mammalian cell applications

When poly(N-isopropyl acrylamide) (pNIPAM) is tethered to a surface, it can induce the spontaneous release of a sheet of mammalian cells. The release of cells is a result of the reversible phase transition the polymer undergoes at its lower critical solution temperature (LCST). Many techniques are used for the deposition of pNIPAM onto cell culture substrates. Previously, we compared two methods of deposition (plasma polymerization, and co-deposition with a sol-gel). We proved that although both were technically appropriate for obtaining thermoresponsive pNIPAM films, the surfaces that were co-deposited with a sol-gel caused some disruption in cell activity. The variation of cell behavior could be due to the delamination of pNIPAM films leaching toxic chemicals into solution. In this work, we assessed the stability of these pNIPAM films by manipulating the storage conditions and analyzing the surface chemistry using X-ray photoelectron spectroscopy (XPS) and contact angle measurements over the amount of time required to obtain confluent cell sheets. From XPS, we demonstrated that ppNIPAM (plasma polymerized NIPAM) films remains stable across all storage conditions while sol-gel deposition show large deviations after 48 h of storage. Cell response of the deposited films was assessed by investigating the cytotoxicity and biocompatibility. The 37°C and high humidity storage affects sol-gel deposited films, inhibiting normal cell growth and proper thermoresponse of the film. Surface chemistry, thermoresponse and cell growth remained similar for all ppNIPAM surfaces, indicating these substrates are more appropriate for mammalian cell culture applications.

Thermo-Responsive Complexes of c-Myc Antisense Oligonucleotide with Block Copolymer of Poly(OEGMA) and Quaternized Poly(4-Vinylpyridine)

Solution behavior of thermo-responsive polymers and their complexes with biological macromolecules may be affected by environmental conditions, such as the concentration of macromolecular components, pH, ion concentration, etc. Therefore, a thermo-responsive polymer and its complexes should be characterized in detail to observe their responses against possible environments under physiological conditions before biological applications. To briefly indicate this important issue, thermo-responsive block copolymer of quaternized poly(4-vinylpyridine) and poly(oligoethyleneglycol methyl ether methacrylate) as a potential nonviral vector has been synthesized. Polyelectrolyte complexes of this copolymer with the antisense oligonucleotide of c-Myc oncogene are also thermo-responsive but, have lower LCST (lower critical solution temperature) values compared to individual copolymer. LCST values of complexes decrease with molar ratio of macromolecular components and presence of salt. Dilution of solutions also affects solution behavior of complexes and causes a significant decrease in size and an increase in LCST, which indicates possible effects of severe dilutions in the blood stream.

Carbohydrate-based amphiphilic nano delivery systems for cancer therapy

Nanoparticles (NPs) are novel drug delivery systems that have been attracting more and more attention in recent years, and have been used for the treatment of cancer, infection, inflammation and other diseases. Among the numerous classes of materials employed for constructing NPs, organic polymers are outstanding due to the flexibility of design and synthesis and the ease of modification and functionalization. In particular, NP based amphiphilic polymers make a great contribution to the delivery of poorly-water soluble drugs. For example, natural, biocompatible and biodegradable products like polysaccharides are widely used as building blocks for the preparation of such drug delivery vehicles. This review will detail carbohydrate based amphiphilic polymeric systems for cancer therapy. Specifically, it focuses on the nature of the polymer employed for the preparation of targeted nanocarriers, the synthetic methods, as well as strategies for the application and evaluation of biological activity. Applications of the amphiphilic polymer systems include drug delivery, gene delivery, photosensitizer delivery, diagnostic imaging and specific ligand-assisted cellular uptake. As a result, a thorough understanding of the relationship between chemical structure and biological properties facilitate the optimal design and rational clinical application of the resulting carbohydrate based nano delivery systems for cancer therapy.

Cell-Targeting Cationic Gene Delivery System Based on a Modular Design Rationale

En route to target cells, a gene carrier faces multiple extra- and intracellular hurdles that would affect delivery efficacy. Although diverse strategies have been proposed to functionalize gene carriers for individually overcoming these barriers, it is challenging to generate a single multifunctional gene carrier capable of surmounting all these barriers. Aiming at this challenge, we have developed a supramolecular modular approach to fabricate a multifunctional cationic gene delivery system. It consists of two prefunctionalized modules: (1) a host module: a polymer (PCD-SS-PDMAEMA) composed of poly(β-cyclodextrin) backbone and disulfide-linked PDMAEMA arms, expectedly acting to compact DNA and release DNA upon cleavage of disulfide linkers in reductive microenvironment; and (2) a guest module: adamantyl and folate terminated PEG (Ad-PEG-FA), expectedly functioning to reduce nonspecific interactions, improve biocompatibility, and provide folate-mediated cellular targeting specificity. Through the host-guest interaction between β-cyclodextrin units of the "host" module and adamantyl groups of the "guest" module, the PCD-SS-PDMAEMA-1 (host) and Ad-PEG-FA (guest) self-assemble forming a supramolecular pseudocopolymer (PCD-SS-PDMAEMA-1/PEG-FA). Our comprehensive analyses demonstrate that the functions preassigned to the two building modules are well realized. The gene carrier effectively compacts DNA into stable nanosized polyplexes resistant to enzymatic digestion, triggers DNA release in reducing environment, possesses significantly improved hemocompatibility, and specifically targets folate-receptor positive cells. Most importantly, endowed with these predesigned functions, the PCD-SS-PDMAEMA-1/PEG-FA supramolecular gene carrier exhibits excellent transfection efficacy for both pDNA and siRNA. Thus, this work represents a proof-of-concept example showing the efficiency and convenience of an adaptable, modular approach for conferring multiple functions to a single supramolecular gene carrier toward effective in vivo delivery of therapeutic nucleic acids.

A nanogel with passive targeting function and adjustable polyplex surface properties for efficient anti-tumor gene therapy

A dual responsive nanogel with tuneable polyplex properties was finely prepared. Its highin vivo/vitrogene transfection ability and passive cellular targeting function strongly promoted intratumor accumulation and tumor inhibition.

A general strategy to prepare different types of polysaccharide-graft-poly(aspartic acid) as degradable gene carriers

Owing to their unique properties such as low cytotoxicity and excellent biocompatibility, poly(aspartic acid) (PAsp) and polysaccharides are good candidates for the development of new biomaterials. In order to construct better gene delivery systems by combining polysaccharides with PAsp, in this work, a general strategy is described for preparing series of polysaccharide-graft-PAsp (including cyclodextrin (CD), dextran (Dex) and chitosan (CS)) gene vectors. Such different polysaccharide-based vectors are compared systematically through a series of experiments including degradability, pDNA condensation capability, cytotoxicity and gene transfection ability. They possess good degradability, which would benefit the release of pDNA from the complexes. They exhibit significantly lower cytotoxicity than the control 'gold-standard' polyethylenimine (PEI, ∼25kDa). More importantly, the gene transfection efficiency of Dex- and CS-based vectors is 12-14-fold higher than CD-based ones. This present study indicates that properly grafting degradable PAsp from polysaccharide backbones is an effective means of producing a new class of degradable biomaterials.

Bioreducible POSS-cored star-shaped polycation for efficient gene delivery

The bioreducible star-shaped gene vector (POSS-(SS-PDMAEMA)8) with well-defined structure and relatively narrow molecular weight distribution was synthesized via atom transfer radical polymerization (ATRP) of (2-dimethylamino)ethyl methacrylate (DMAEMA) from a polyhedral oligomeric silsesquioxane (POSS) macroinitiator. POSS-(SS-PDMAEMA)8 was composed of a biocompatible POSS core and eight disulfide-linked PDMAEMA arms, wherein the PDMAEMA chain length could be adjusted by controlling polymerization time. POSS-(SS-PDMAEMA)8 can effectively bind pDNA into uniform nanocomplexes with appropriate particle size and zeta potential. The incorporation of disulfide bridges gave the POSS-(SS-PDMAEMA)8 material facile bioreducibility. In comparison with POSS-(PDMAEMA)8 without disulfide linkage, POSS-(SS-PDMAEMA)8 exhibited much lower cytotoxicity and substantially higher transfection efficiency. The present work would provide useful information for the design of new POSS-based drug/gene carriers.

Different types of degradable vectors from low-molecular-weight polycation-functionalized poly(aspartic acid) for efficient gene delivery

Poly(aspartic acid) (PAsp) has been employed as the potential backbone for the preparation of efficient gene carriers, due to its low cytotoxicity, good biodegradability and excellent biocompatibility. In this work, the degradable linear or star-shaped PBLA was first prepared via ring-opining polymerization of β-benzyl-L-aspartate N-carboxy anhydride (BLA-NCA) initiated by ethylenediamine (ED) or ED-functionalized cyclodextrin cores. Then, PBLA was functionalized via aminolysis reaction with low-molecular-weight poly(2-(dimethylamino)ethyl methacrylate) with one terminal primary amine group (PDMAEMA-NH2), followed by addition of excess ED or ethanolamine (EA) to complete the aminolysis process. The obtained different types of cationic PAsp-based vectors including linear or star PAsp-PDM-NH2 and PAsp-PDM-OH exhibited good condensation capability and degradability, benefiting gene delivery process. In comparison with gold standard polyethylenimine (PEI, ∼ 25 kDa), the cationic PAsp-based vectors, particularly star-shaped ones, exhibited much better transfection performances.

Assessment of cytotoxicity of (N-isopropyl acrylamide) and poly(N-isopropyl acrylamide)-coated surfaces

Poly(N-isopropyl acrylamide) (pNIPAM) is one of the most popular stimulus-responsive polymers for research. It is especially of great interest in the field of tissue engineering. While it is known that the NIPAM monomer is toxic, there is little conclusive research on the cytotoxicity of the polymer. In this work, the relative biocompatibility of the NIPAM monomer, pNIPAM, and pNIPAM-coated substrates prepared using different polymerization (free radical and plasma polymerization) and deposition (spin coating and plasma polymerization) techniques was evaluated using appropriate cytotoxicity tests (MTS, Live/Dead, plating efficiency). Four different mammalian cell types (endothelial, epithelial, smooth muscle, and fibroblasts) were used for the cytotoxicity testing. The pNIPAM-coated surfaces were evaluated for their thermoresponse and surface chemistry using X-ray photoelectron spectroscopy and goniometry. We found that while cell viability on pNIPAM surfaces decreases when compared to controls, the viability also seems to be deposition type dependent, with sol-gel based pNIPAM surfaces being the least biocompatible. Long term experiments proved that all pNIPAM-coated surfaces were not cytotoxic to the four cell types evaluated in a direct contact test. Plating efficiency experiments did not show cytotoxicity. Cellular sensitivity to pNIPAM and to the NIPAM monomer varied depending on cell type. Endothelial cells consistently showed decreased viability after 48 hours of exposure to pNIPAM extracts and were more sensitive than the other cell lines to impurities in the polymer.

Versatile functionalization of gene vectors via different types of zwitterionic betaine species for serum-tolerant transfection

For ideal polymeric gene vectors, their serum stability is of crucial importance. Polycation vectors usually suffer from colloidal aggregation, which makes them easily cleared from the bloodstream. Recently, we reported a comb-shaped vector (DPD) consisting of a dextran backbone and disulfide-linked cationic poly((2-dimethyl amino)ethyl methacrylate) side chains for efficient gene delivery. In this work, versatile functionalization of DPD (as a model gene vector) was proposed via the introduction of different types of zwitterionic carboxybetaine and sulfobetaine species for improving biophysical properties. The incorporation of zwitterionic betaine did not destroy the DNA condensation capability of vectors. All the zwitterionic betaine-functionalized DPD vectors exhibited lower cytotoxicities than the pristine DPD. The DPD-b-polycarboxybetaine block copolymer (DPDbPC) exhibited better gene delivery abilities than the corresponding DPD-r-polycarboxybetaine random copolymer (DPDrPC). Moreover, in the serum case with a high concentration (30%) of fetal bovine serum, the DPD-b-polysulfobetaine block copolymer (DPDbPS) produced much higher gene transfection efficiencies than DPDbPC. Cellular internalization results indicated that the incorporation of zwitterionic betaine could benefit serum stabilities of vectors and enhance cellular uptake. The present study demonstrated that proper incorporation of zwitterionic betaine into gene carriers was an effective method to produce serum-tolerant transfection vectors.

Aminated poly(glycidyl methacrylate)s for constructing efficient gene carriers

Aminated poly(glycidyl methacrylate) (PGMA) vectors could efficiently mediate gene delivery. Recently, we reported that ethanolamine (EA)-functionalized PGMA could provide high transfection efficiency, while exhibiting very low toxicity. Herein, different amine species, including 1-amino-2-propanol (AP1), 3-amino-2-propanol (AP2), EA, and N,N,-dimethylethylenediamine (DED), and its quaternized DED, were proposed to aminate PGMA. The DNA condensation abilities, pH buffering capacities, cytotoxicities, and gene transfection efficiencies of the resultant aminated PGMA vectors were systematically compared. Compared with EA, AP1 (or AP2) contains an additional methyl (or methylene) group. EA-, AP1-, and AP2-functionalized PGMA vectors exhibited similar condensation abilities. The methyl (from AP1) and methylene (from AP2) species could benefit the gene delivery. The transfection performance mediated by AP1-functionalized PGMA is best. DED possesses a tertiary amine group, which could be quaternized to further enhance the DNA condensation ability of aminated PGMA. No obvious increase in cytotoxicity of quaternized DED-aminated PGMA was observed. But both DED- and its quaternized counterpart-functionalized PGMA vectors exhibited very low pH buffering capacities, making them exhibit poor gene transfection performances. The current study would provide useful information for constructing better PGMA-based delivery systems with good biophysical properties.

To aggregate, or not to aggregate? considerations in the design and application of polymeric thermally-responsive nanoparticles

The aim of this review is to highlight some of the challenges in designing thermally responsive nanoparticles, where the responsivity is endowed by a responsive polymeric corona. A review of the literature reveals many contradictory observations upon heating these particles through their transition temperature. Indeed, both an increase in size due to aggregation and particle shrinkage have been reported for apparently similar materials. Furthermore, careful review of the literature shows that responsive nanoparticles do not have the same transition temperature or properties as their constituent polymers. These observations raise serious questions as to how to achieve the rational design of a responsive particle with a predictable and reproducible response. Here we highlight specific cases where conflicting results have been observed for spherical particles and put these results into the context of flat-surface grafted polymer brushes to explain the behaviour in terms of grafting density, curvature, chain end effects and the role of the underlying substrate. A better understanding of these observations should lead to the improved design of nanoparticles with real function and applications.

New star-shaped carriers composed of β-cyclodextrin cores and disulfide-linked poly(glycidyl methacrylate) derivative arms with plentiful flanking secondary amine and hydroxyl groups for highly efficient gene delivery

The biocleavable star-shaped vectors (CD-SS-PGEAs) consisting of nonionic β-cyclodextrin (β-CD) cores and disulfide-linked low-molecular-weight poly(glycidyl methacrylate) (PGMA) derivative arms with plentiful flanking secondary amine and hydroxyl groups were successfully proposed for highly efficient gene delivery. A simple two-step method was first adopted to introduce reduction-sensitive disulfide-linked initiation sites of atom transfer radical polymerization (ATRP) onto β-CD cores. The disulfide-linked PGMA arms prepared subsequently via ATRP were functionalized via the ring-opening reaction with ethanolamine (EA) to produce the cationic EA-functionalized PGMA (PGEA) arms with plentiful secondary amine and nonionic hydroxyl units. The cationic PGEA arms can be readily cleavable from the β-CD cores under reducible conditions. Such biocleavable star-shaped CD-SS-PGEA vectors possessed the good pDNA condensation ability, low cytotoxicity, and efficient gene delivery ability.

Functional study of dextran-graft-poly((2-dimethyl amino)ethyl methacrylate) gene delivery vector for tumor therapy

The obstacle of gene therapy is the shortage of efficient delivery system. The development of the gene delivery system with high transfection efficiency and low toxicity appears to be crucial. Recently, we reported that the dextran-graft-poly((2-dimethyl amino)ethyl methacrylate) (DPD) can be potentially used as efficient gene vector. Herein, DPD was systematically studied for its potential in tumor gene therapy. DPD was synthesized and characterized by agarose gel electrophoresis, particle size and zeta potential. The particle size and zeta potential of the DPD/enhanced green fluorescent protein (pEGFP-C1) plasmid complexes at various N/P ratios were 130-150 nm and about 40 mV, respectively. The results showed that DPD exhibit a higher transfection effect compared with Lipofectamine 2K (Lipo 2K), a commercialized vector. The possibility of DPD in gene therapy was evaluated using p53, a gene that has been wildly applied in the research of cancer gene therapy. DPD/pEGFP-C1-p53 complex was found to be able to inhibit tumor cell proliferation through cell cycle arrest and apoptosis. Moreover, the tumor growth was found to be restrained when DPD/pEGFP-C1-p53 complex was used in a xenograft MCF7 tumor model in vivo. These observations indicated that DPD/pEGFP-C1-p53 complex may be considered to be an efficient delivery system for tumor gene therapy.

Biodegradable hybrid recombinant block copolymers for non-viral gene transfection

Thermal targeting of therapeutic genes can enhance local gene concentration to maximize their efficacy. However, lack of safe and efficient carriers has impeded the development of this delivery option. Herein, we report the preparation and evaluation of a hybrid recombinant material, p[Asp(DET)](53)ELP(1-90), that possess a thermo-responsive elastin-like polypeptide (ELP) segment and a diethylenetriamine (DET) modified poly-L-aspartic acid segment. The term, hybrid, indicates that the material was prepared by genetic engineering and synthetic chemistry. In summary, the thermal phase transition behavior and cytotoxicity of the biodegradable copolymer were studied. The polyplexes formed by the copolymer and pGL4 plasmid were characterized by dynamic light scattering and ζ-potential measurements. The polyplexes retained the thermal phase transition behavior conferred by the copolymer; however, they exhibited a two-step transition process not seen with the copolymer. The polyplexes also showed appreciable transfection efficiency with low cytotoxicity.

Comparison of ethanolamine/ethylenediamine-functionalized poly(glycidyl methacrylate) for efficient gene delivery

Cationic polymers with low cytotoxicity and high transfection efficiency have attracted considerable attention as non-viral carriers for gene delivery. Recently we reported that ethanolamine (EA)-functionalized poly(glycidyl methacrylate) (PGMA) (termed PGEA) vectors can have excellent transfection efficiency, while exhibiting very low toxicity. Herein different EA- and ethylenediamine (ED)-functionalized PGMA (termed PGEAED) vectors, as well as ED-functionalized PGMA (termed PGED) vectors, are proposed and compared for efficient gene delivery. In addition to the cationic pendant secondary amine and hydroxyl groups of PGEA, PGEAED, and PGED also contain flanking primary amine groups. PGEAED and PGED exhibited a substantially enhanced ability to condense pDNA into complex nanoparticles at the 100 nm level with positive zeta potentials of about 30 mV at nitrogen/phosphate (N/P) ratios of 10 or higher. More interestingly, no obvious change in the cytotoxicity of PGEAED was observed with a substantial increase in ED content. Moreover, the flanking primary amine groups induced by ED could be readily functionalized by glycyrrhetinic acid or cholic acid to improve the biophysical properties of the gene vectors.

Synthesis of folate-functionalized RAFT polymers for targeted siRNA delivery

Receptor-mediated, cell-specific delivery of siRNA enables silencing of target genes in specific tissues, opening the door to powerful therapeutic options for a multitude of diseases. However, the development of delivery systems capable of targeted and effective siRNA delivery typically requires multiple steps and the use of sophisticated, orthogonal chemistries. Previously, we developed diblock copolymers consisting of dimethaminoethyl methacrylate-b-dimethylaminoethyl methacrylate-co-butyl methacrylate-co-propylacrylic acid as potent siRNA delivery systems that protect siRNA from enzymatic degradation and enable its cytosolic delivery through pH-responsive, endosomolytic behavior. (1, 2) These architectures were polymerized using a living radical polymerization method, specifically reversible addition-fragmentation chain transfer (RAFT) polymerization, which employs a chain transfer agent (CTA) to modulate the rate of reaction, resulting in polymers with low polydispersity and telechelic chain ends reflecting the chemistry of the CTA. Here we describe the straightforward, facile synthesis of a folate receptor-targeted diblock copolymer siRNA delivery system because the folate receptor is an attractive target for tumor-selective therapies as a result of its overexpression in a number of cancers. Specifically, we detail the de novo synthesis of a folate-functionalized CTA, use the folate-CTA for controlled polymerizations of diblock copolymers, and demonstrate efficient, specific cellular folate receptor interaction and in vitro gene knockdown using the folate-functionalized polymer.

DNA-nanoparticle micelles as supramolecular fluorogenic substrates enabling catalytic signal amplification and detection by DNAzyme probes

Catalytic DNA molecules have tremendous potential in propagating detection events via nucleic acid sequence selective signal amplification. However, they suffer from product inhibition limiting their widespread utility. Herein, this limitation is overcome utilizing a novel fluorogenic substrate design consisting of cooperatively assembled DNA-nanoparticle micelles.