Vinyl Polymers as Non-Viral Gene Delivery Carriers: Current Status and Prospects

Poly(N,N-dimethylaminoethyl methacrylate) as a bioactive polyelectrolyte-production and properties

Poly(N,N-dimethylaminoethyl methacrylate) is a polyelectrolyte with many important chemical and physical properties and, above all, offers a wide range of interesting biological properties. Currently, research on this polymer is ongoing in several centres around the world. The process of polymerizing the monomer is not easy, as there are difficulties in obtaining a product with repeatable properties. This work collected and described most of the currently known and used polymerization methods of N,N-dimethylaminoethyl methacrylate, taking into account the type of method, the solvent used, the initiator, as well as the process temperature and the average molecular weight of the polymer obtained. The most important properties of the discussed polymer, such as solubility, bioactivity, hydrophilicity, cytotoxicity, conductivity, and thermal and hydrodynamic parameters, are discussed on the basis of the available scientific literature. This work aims, among other things, to increase the possibility of using poly(N,N-dimethylaminoethyl methacrylate) as a material in advanced practical applications. Therefore, various methods of applied use of the polymer in question have also been described so far. Copolymers of the N,N-dimethylaminoethyl methacrylate are now too large a collection to fit in a single publication. Therefore, only the most interesting examples were cited in this work.

PEGylated cationic nanoassemblies based on triblock copolymers to combine siRNA therapeutics with anticancer drugs

Nowadays, the clinical administration of siRNA therapeutics is still challenging due to the need of safe and efficient delivery carriers. In this context, biodegradable and amphiphilic triblock copolymers (ABC) containing amine-based cationic segments could be a powerful tool for siRNA delivery. Herein, we propose a range of poly(ethylene glycol) (PEG)-poly(2-dimethyl(aminoethyl) methacrylate) (pDMAEMA)-polycaprolactone (PCL) copolymers with different lengths of the blocks and hydrophilic/lipophilic balance to deliver siRNA alone or in association with a conventional anticancer drug. mPEG-pDMAEMA-PCL copolymers were synthesized by a combination of techniques and characterized by NMR analysis, Fourier transform infrared (FTIR) spectroscopy, gel permeation chromatography (GPC) and differential scanning calorimetry (DSC). Copolymers were then employed to prepare NPs through nanoprecipitation. NPs based on copolymers with long PCL chains (SSL-NPs and LLL-NPs) showed the best colloidal properties and a highly stable core-shell structure with a better orientation of the PEG fringe on the surface. Concerning siRNA delivery, SSL-NPs based on copolymers with short PEG and pDMAEMA chains showed optimized ability to complex and then deliver siRNA at the cell level. The strong interaction between the nucleic acid and the cationic pDMAEMA blocks of NPs was then confirmed by release studies that showed a sustained release of siRNA within 48 h. The transfection efficiency of NPs was assessed in human melanoma cells. NPs were complexed with a therapeutic siRNA against TUBB3 (TUB-siRNA). We observed the best results with SSL-NPs, probably due to the higher preserved buffer capacity of the pDMAEMA blocks. Finally, in order to give a proof of concept of a possible application in the combined chemo/gene-therapy of cancer, SSL-NPs complexed with TUB-siRNA were loaded with docetaxel (DTX) and then cytotoxicity was evaluated in the same cell line. The co-delivery of TUB-siRNA into NPs appeared to strongly potentiate the anti-proliferative activity of DTX, thus highlighting the combinatory activity of the NPs.

Nonviral DNA Delivery System with Supramolecular PEGylation Formed by Host-Guest Pseudo-Block Copolymers

A cationic supramolecular system based on host-guest pseudoblock copolymers was developed for nonviral DNA delivery. In this system, the macromolecular host was a cationic star-shaped polymer composed of a β-cyclodextrin (β-CD) core and multiple poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) chains grafted on the core, while the macromolecular guest was a linear adamantyl-ended poly(ethylene glycol) (mPEG-Ad). Pseudoblock copolymers were self-assembled from the polymeric host-guest pairs (typically, 1:1 molar ratio) in aqueous media through the inclusion of an adamantyl group at the end of guest polymer into the β-CD cavity of host polymers. Through such an approach, the resultant supramolecular system was integrated with not only a superior DNA condensing ability due to the host polymer but also an outstanding polyplex-stabilizing ability as well as biocompatibility due to the guest polymer. The cationic star-shaped host polymers alone were capable of condensing plasmid DNA efficiently into nanoparticles (70-100 nm) with positive surface charge. They showed obviously lower cytotoxicity than PEI 25K (commercial branched polyethylenimine with a molecular weight around 25 kDa) in cell lines of L929, MB231, and Hela under high dose. In serum-free or serum-containing culture conditions, these host polymers exhibited either higher or lower in vitro DNA transfection efficiency as compared with PEI 25K in the three cell lines under study, which was dependent on the N/P ratios and PDMAEMA arm length. Upon incorporation of the PEG block through host-guest complexation with mPEG-Ad (i.e., supramolecular PEGylation), the resulting host-guest supramolecular systems exhibited even lower cytotoxicity than the host polymers alone. The polyplexes between plasmid DNA (pDNA) and the host-guest systems showed significantly improved stability in BSA-PBS buffer solution (pH 7.4) and enhanced in vitro DNA transfection efficiency in the cases of higher N/P ratios or longer PDMAEMA arms in all tested cell lines under both serum-free and serum-containing culture conditions, as compared with the corresponding polyplexes without supramolecular PEGylation. Further, through forming pseudoblock copolymer, the DNA transfection ability of the supramolecular system can be easily modulated and optimized either by changing the ratio between the guest and host or by using different hosts with varied PDMAEMA arm lengths.

Non-viral Vectors in Gene Therapy: Recent Development, Challenges, and Prospects

Gene therapy has been experiencing a breakthrough in recent years, targeting various specific cell groups in numerous therapeutic areas. However, most recent clinical studies maintain the use of traditional viral vector systems, which are challenging to manufacture cost-effectively at a commercial scale. Non-viral vectors have been a fast-paced research topic in gene delivery, such as polymers, lipids, inorganic particles, and combinations of different types. Although non-viral vectors are low in their cytotoxicity, immunogenicity, and mutagenesis, attracting more and more researchers to explore the promising delivery system, they do not carry ideal characteristics and have faced critical challenges, including gene transfer efficiency, specificity, gene expression duration, and safety. This review covers the recent advancement in non-viral vectors research and formulation aspects, the challenges, and future perspectives.

Polymeric nanoparticles for RNA delivery

As exemplified by recent clinical approval of RNA drugs including the latest COVID-19 mRNA vaccines, RNA therapy has demonstrated great promise as an emerging medicine. Central to the success of RNA therapy is the delivery of RNA molecules into the right cells at the right location. While the clinical success of nanotechnology in RNA therapy has been limited to lipid-based nanoparticles currently, polymers, due to their tunability and robustness, have also evolved as a class of promising material for the delivery of various therapeutics including RNAs. This article overviews different types of polymers used in RNA delivery and the methods for the formulation of polymeric nanoparticles and highlights recent progress of polymeric nanoparticle-based RNA therapy.

Water-Soluble and Cytocompatible Phospholipid Polymers for Molecular Complexation to Enhance Biomolecule Transportation to Cells in Vitro

Water-soluble and cytocompatible polymers were investigated to enhance a transporting efficiency of biomolecules into cells in vitro. The polymers composed of a 2-methacryloyloxyethyl phosphorylcholine (MPC) unit, a hydrophobic monomer unit, and a cationic monomer unit bearing an amino group were synthesized for complexation with model biomolecules, siRNA. The cationic MPC polymer was shown to interact with both siRNA and the cell membrane and was successively transported siRNA into cells. When introducing 20–50 mol% hydrophobic units into the cationic MPC polymer, transport of siRNA into cells. The MPC units (10–20 mol%) in the cationic MPC polymer were able to impart cytocompatibility, while maintaining interaction with siRNA and the cell membrane. The level of gene suppression of the siRNA/MPC polymer complex was evaluated in vitro and it was as the same level as that of a conventional siRNA transfection reagent, whereas its cytotoxicity was significantly lower. We concluded that these cytocompatible MPC polymers may be promising complexation reagent for introducing biomolecules into cells, with the potential to contribute to future fields of biotechnology, such as in vitro evaluation of gene functionality, and the production of engineered cells with biological functions.

Novel zwitterionic vectors: Multi-functional delivery systems for therapeutic genes and drugs

Zwitterions consist of equal molar cationic and anionic moieties and thus exhibit overall electroneutrality. Zwitterionic materials include phosphorylcholine, sulfobetaine, carboxybetaine, zwitterionic amino acids/peptides, and other mix-charged zwitterions that could form dense and stable hydration shells through the strong ion-dipole interaction among water molecules and zwitterions. As a result of their remarkable hydration capability and low interfacial energy, zwitterionic materials have become ideal choices for designing therapeutic vectors to prevent undesired biosorption especially nonspecific biomacromolecules during circulation, which was termed antifouling capability. And along with their great biocompatibility, low cytotoxicity, negligible immunogenicity, systematic stability and long circulation time, zwitterionic materials have been widely utilized for the delivery of drugs and therapeutic genes. In this review, we first summarized the possible antifouling mechanism of zwitterions briefly, and separately introduced the features and advantages of each type of zwitterionic materials. Then we highlighted their applications in stimuli-responsive "intelligent" drug delivery systems as well as tumor-targeting carriers and stressed the multifunctional role they played in therapeutic gene delivery.

Encapsulation, Visualization and Expression of Genes with Biomimetically Mineralized Zeolitic Imidazolate Framework-8 (ZIF-8)

Recent work in biomolecule-metal-organic framework (MOF) composites has proven to be an effective strategy for the protection of proteins. However, for other biomacromolecules such as nucleic acids, the encapsulation into nano MOFs and the related characterizations are in their infancy. Herein, encapsulation of a complete gene-set in zeolitic imidazolate framework-8 (ZIF-8) MOFs and cellular expression of the gene delivered by the nano MOF composites are reported. Using a green fluorescent protein (GFP) plasmid (plGFP) as a proof-of-concept genetic macromolecule, successful transfection of mammalian cancer cells with plGFP for up to 4 days is shown. Cell transfection assays and soft X-ray cryo-tomography (cryo-SXT) demonstrate the feasibility of DNA@MOF biocomposites as intracellular gene delivery vehicles. Expression occurs over relatively prolonged time points where the cargo nucleic acid is released gradually in order to maintain sustained expression.

Influence of the degree of oligomerization of surfactants on the DNA/surfactant interaction

The interaction between calf thymus DNA, ctDNA, and a series of oligomeric surfactants derived from N-benzyl-N,N-dimethyl-N-(1-dodecyl)ammonium chloride is investigated. The influence of the surfactants' degree of oligomerization (2, 3 and 4) on the ctDNA/surfactant interaction is studied, as well as the effect of the structure of the spacer group linking the individual surfactant fragments. In particular, the effect of the distance between the positive charges and the hydrophobic chains within the oligomers on these interactions was examined, by using the three positional isomers (i.e., ortho-, meta-, and para-) with the rigid xylidene moiety as spacer. Results show that the dimeric ("gemini") surfactants are much more efficient in the inversion of the nucleic acid charge than the single-chained (monomeric) surfactant. Whereas the ortho - isomer causes a partial condensation, the meta - and para - isomers can completely condense ctDNA. The meta - and para - isomers of the trimeric surfactants can also completely condense the polynucleotide. In contrast, the tetrameric surfactant investigated does not change the morphology of the nucleic acid from an elongated coil into a compacted form, in spite of effectively inverting the nucleic acid's charge in their complex. Accordingly, the capacity for ctDNA compaction of oligomeric surfactants is not simply correlated to their degree of oligomerization, but depends on a complex balance of the number and relative distance of cationic charges and/or hydrophobic tails in the surfactants for effectively interacting with the nucleic acid to form the appropriate complex. This information will help to design more effective cationic surfactants as non-viral vectors for gene therapy.

Thiol redox-sensitive cationic polymers for dual delivery of drug and gene

Recently greater emphasis has been given to combination therapy for generating synergistic effects of treating cancer. Recent studies on thiol-sensitive nanocarriers for the delivery of drug or gene have shown promising results. In this review, we will examine the rationale and advantage in using nanocarriers for the combined delivery of different anticancer drugs and biologics. Here, we also discuss the role of nanocarriers, particularly redox-sensitive polymers in evading or inhibiting the efflux pump in cancer and how they modulate the sensitivity of cancer cells. The review aims to provide a good understanding of the new pattern of cancer treatment and key concerns for designing nanomedicine of synergistic combinations for cancer therapy.

Preparation of well-defined brush-like block copolymers for gene delivery applications under biorelevant reaction conditions

Well-defined oligo(ethylene glycol) methyl ether methacrylate (OEOMA) based block copolymers with cationic segments composed by N,N-(dimethylamino) ethyl methacrylate (DMAEMA) and/or 2-(diisopropylamino) ethyl methacrylate (DPA) were developed under biorelevant reaction conditions. These brush-type copolymers were synthesized through supplemental activator and reducing agent (SARA) atom transfer radical polymerization (ATRP) using sodium dithionite as SARA agent. The synthesis was carried out using an eco-friendly solvent mixture, very low copper catalyst concentration, and mild reaction conditions. The structure of the block copolymers was characterized by size exclusion chromatography (SEC) analysis and ¹H nuclear magnetic resonance (NMR) spectroscopy. The pH-dependent protonation of these copolymers enables the efficient complexation with plasmid DNA (pDNA), yielding polyplexes with sizes ranging from 200 up to 700 nm, depending on the molecular weight of the copolymers, composition and concentration used. Agarose gel electrophoresis confirmed the successful pDNA encapsulation. No cytotoxicity effect was observed, even for N/P ratios higher than 50, for human fibroblasts and cervical cancer cell lines cells. The in vitro cellular uptake experiments demonstrated that the pDNA-loaded block copolymers were efficiently delivered into nucleus of cervical cancer cells. The polymerization approach, the unique structure of the block copolymers and the efficient DNA encapsulation presented can open new avenues for development of efficient tailor made gene delivery systems under biorelevant conditions.

Polymeric Amines and Ampholytes Derived from Poly(acryloyl chloride): Synthesis, Influence on Silicic Acid Condensation and Interaction with Nucleic Acid

Polymeric amines are intensively studied due to various valuable properties. This study describes the synthesis of new polymeric amines and ampholytes by the reaction of poly(acryloyl chloride) with trimethylene-based polyamines containing one secondary and several (1⁻3) tertiary amine groups. The polymers contain polyamine side chains and carboxylic groups when the polyamine was in deficiency. These polymers differ in structure of side groups, but they are identical in polymerization degree and polydispersity, which facilitates the study of composition-properties relationships. The structure of the obtained polymers was confirmed with ¹³C nuclear magnetic resonance infrared spectroscopy, and acid-base properties were studied with potentiometry titration. Placement of the amine groups in the side chains influences their acid-base properties: protonation of the amine group exerts a larger impact on the amine in the same side chain than on the amines in the neighboring side chains. The obtained polymers are prone to aggregation in aqueous solutions tending to insolubility at definite pH values in the case of polyampholytes. Silicic acid condensation in the presence of new polymers results in soluble composite nanoparticles and composite materials which consist of ordered submicrometer particles according to dynamic light scattering and electron microscopy. Polymeric amines, ampholytes, and composite nanoparticles are capable of interacting with oligonucleotides, giving rise to complexes that hold promise for gene delivery applications.

Systematic Study of a Library of PDMAEMA-Based, Superparamagnetic Nano-Stars for the Transfection of CHO-K1 Cells

The introduction of the DNA into mammalian cells remains a challenge in gene delivery, particularly in vivo. Viral vectors are unmatched in their efficiency for gene delivery, but may trigger immune responses and cause severe side-reactions. Non-viral vectors are much less efficient. Recently, our group has suggested that a star-shaped structure improves and even transforms the gene delivery capability of synthetic polycations. In this contribution, this effect was systematically studied using a library of highly homogeneous, paramagnetic nano-star polycations with varied arm lengths and grafting densities. Gene delivery was conducted in CHO-K1 cells, using a plasmid encoding a green fluorescent reporter protein. Transfection efficiencies and cytotoxicities varied systematically with the nano-star architecture. The arm density was particularly important, with values of approximately 0.06 arms/nm² yielding the best results. In addition, a certain fraction of the cells became magnetic during transfection. The gene delivery potential of a nano-star and its ability to render the cells magnetic did not have any correlations. End-capping the polycation arms with di(ethylene glycol) methyl ether methacrylate (PDEGMA) significantly improved serum compatibility under transfection conditions; such nano-stars are potential candidates for future in vivo testing.

A hybrid siRNA delivery complex for enhanced brain penetration and precise amyloid plaque targeting in Alzheimer's disease mice

To realize the therapeutic potential of gene drugs for Alzheimer's disease (AD), non-invasive, tissue-specific and efficient delivery technologies must be developed. Here, a hybrid system for amyloid plaques targeted siRNA delivery was formed by PEGylated Poly(2-(N,N-dimethylamino) ethyl methacrylate) (PEG-PDMAEMA) conjugated with two d-peptides, a CGN for brain penetration and a QSH for β-amyloid binding. The hybrid complex CQ/siRNA, composed of 25% MPEG-PDMAEMA, 50% CGN-PEG-PDMAEMA and 25% QSH-PEG-PDMAEMA, showed negligible cytotoxicity and could protect siRNA from enzyme degradation. Being taken up by neuron cells, the complexes could escape from lysosomes, release siRNA in the cytoplasm and thus producing effective gene silence (down-regulated protein level to 18.5%). After intravenous injection, CQ/siRNA penetrated into the brain in an intact form and located around the plaques in transgenic AD mice. The precisely amyloid plaques delivery resulted in increased therapeutic activities, which was demonstrated by the strong mRNA (36.4%) knockdown of BACE1 (a therapeutic target of AD), the less yield of enzyme-digested products sAPPβ (-42.6%), as well as the better neurons protection than the single component complexes. In conclusion, the hybrid complex could efficiently and precisely deliver an siRNA to the AD lesion and might be a potential candidate for gene therapy for AD.

STATEMENT OF SIGNIFICANCE

The gene delivery system achieving high brain penetration and lesion region accumulation was first applied to treat AD, and the preparation exhibited a significantly better neuroprotective effect than that modified with a single ligand. The intracellular process of which the complexes escape from lysosomes and release the siRNA in cytoplasm was revealed. The brain targeting and amyloid plaque binding ability of the complex were systemic evaluated, and the in vivo co-location experiments provided a direct evidence of the precise delivery of the siRNA to the amyloid plaques. One of the targeting ligands, CGN, which was a retro-inverso modified peptide to achieve better affinity to the BBB, was first applied to the brain targeting system.

Amphiphilic polymers formed from ring-opening polymerization: a strategy for the enhancement of gene delivery

Ring-opening polymerization was found to be a promising strategy to improve the transfection efficiency and serum tolerance of cationic lipids.

Intracellular Delivery and Triggered Release of DNA Using Biodegradable Poly(2-hydroxypropylene imine)s Containing Cystamine Units

Poly(2-hydroxypropylene imine)s containing segments of cystamine (PHPI-CA) are synthesized by polycondensation of 1,3-dibromo-2-propanol with a mixture of 1,3-diamino-2-propanol and cystamine. High molecular weight fractions of these polymers are collected by ultrafiltration and characterized by chemical analysis, ¹ H and ¹³ C-NMR spectroscopy, size-exclusion chromatography with triple detection, and potentiometric titration, and are tested for DNA delivery in vitro. It is shown that PHPI-CA are highly branched polymers containing disulfide linkages. Transfection efficiency of PHPI-CA for DNA gives similar results to that of PHPI with GFP⁺ cell percent reaching 80-90%. Cytotoxicity levels for PHPI-CA are lower than that of PHPI. Novel polymers containing different amounts of disulfide linkages are able to disintegrate and release DNA following the treatment with reducing agent 1,4-dithiothreitol. Downstream application of PHPI-CA transfected cells for RNA purification shows that RNA yield is not affected even after the double transfection suggesting that these polymers could be great candidates for in vitro and in vivo transfection.

Development of Non-Viral, Trophoblast-Specific Gene Delivery for Placental Therapy

Low birth weight is associated with both short term problems and the fetal programming of adult onset diseases, including an increased risk of obesity, diabetes and cardiovascular disease. Placental insufficiency leading to intrauterine growth restriction (IUGR) contributes to the prevalence of diseases with developmental origins. Currently there are no therapies for IUGR or placental insufficiency. To address this and move towards development of an in utero therapy, we employ a nanostructure delivery system complexed with the IGF-1 gene to treat the placenta. IGF-1 is a growth factor critical to achieving appropriate placental and fetal growth. Delivery of genes to a model of human trophoblast and mouse placenta was achieved using a diblock copolymer (pHPMA-b-pDMAEMA) complexed to hIGF-1 plasmid DNA under the control of trophoblast-specific promoters (Cyp19a or PLAC1). Transfection efficiency of pEGFP-C1-containing nanocarriers in BeWo cells and non-trophoblast cells was visually assessed via fluorescence microscopy. In vivo transfection and functionality was assessed by direct placental-injection into a mouse model of IUGR. Complexes formed using pHPMA-b-pDMAEMA and CYP19a-923 or PLAC1-modified plasmids induce trophoblast-selective transgene expression in vitro, and placental injection of PLAC1-hIGF-1 produces measurable RNA expression and alleviates IUGR in our mouse model, consequently representing innovative building blocks towards human placental gene therapies.

Photoreactive Polymers Bearing a Zwitterionic Phosphorylcholine Group for Surface Modification of Biomaterials

Photoreactive polymers bearing zwitterionic phosphorylcholine and benzophenone groups on the side chain were synthesized and used as surface modification reagents for biomaterials. A photoreactive methacrylate containing the benzophenone group, 3-methacryloyloxy-2-hydroxypropyl-4-oxybenzophenone (MHPBP), was synthesized via a ring-opening and addition reaction between glycidyl methacrylate and 4-hydroxybenzophenone. Then, water-soluble, amphiphilic polymers poly(2-methacryloyloxyethyl phosphorylcholine (MPC)-co-MHPBP) (PMH) and poly(MPC-co-n-butyl methacrylate-co-MHPBP), with different monomer unit compositions, were synthesized through radical polymerization. Ultraviolet-visible (UV/vis) absorption spectra of these polymer solutions showed that these polymers have maximum absorption peaks at 254 and 289 nm that can be attributed to the benzophenone unit. The intensity of UV adsorption at 289 nm was decreased with increased UV irradiation time, and it was saturated within a few minutes, indicating that the polymers are highly sensitive to UV irradiation. A commercial material (i.e., cyclic polyolefin) was simply modified by a UV irradiation for 1.0 min. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analysis results indicated that the stability of the polymer on the surface was dramatically enhanced because of the photochemical reaction of the benzophenone moiety. The air contact angles of PMH surfaces measured in water were up to 160°. Thus, highly hydrophilic surfaces were obtained. The critical surface tension of the PMH-modified surface was 45.7 mN/m. By evaluating the biological reactivity of the treated surface, protein adsorption and cell adhesion were completely inhibited on the surface, which was prepared using a photopatterning procedure using PMH. In conclusion, photoreactive MPC polymers with a benzophenone moiety could be used as a novel and effective surface modifier.

Ring-opening polymerization for hyperbranched polycationic gene delivery vectors with excellent serum tolerance

In order to improve the transfection efficiency (TE) and biocompatibility, we synthesized a series of hyperbranched cationic polymers by ring-opening polymerization between diepoxide and several polyamines. These materials can condense plasmid DNA efficiently into nanoparticles that have much lower cytotoxicity than those derived from bPEI. In vitro transfection experiments showed that polymers prepared from branched or cyclic polyamine (P1 and P5) exhibited TE several times higher than 25KDa bPEI. More significantly, serum seemed to have no negative effect on P1-P5 mediated transfection. On the contrary, the TE of P1 improved, even when the serum concentration reached 70%. Several assays demonstrated the excellent serum tolerance of such polycationic vectors: bovine serum albumin (BSA) adsorption assay revealed considerably lower protein adsorption of P1-P5 than PEI; P1 showed better DNA protection ability from degradation by DNase I than PEI; flow cytometry results suggested that any concentration of serum may not decrease the cellular uptake of P1/DNA polyplex; and confocal laser scanning microscopy also found that serum has little effect on the transfection. By using specific cellular uptake inhibitors, we found that the polyplexes enter the cells mainly via caveolae and microtubule-mediated pathways. We believe that this ring-opening polymerization may be an effective synthetic approach toward gene delivery materials with high biological activity.

Cationic polymers and their therapeutic potential

The last decade has witnessed enormous research focused on cationic polymers. Cationic polymers are the subject of intense research as non-viral gene delivery systems, due to their flexible properties, facile synthesis, robustness and proven gene delivery efficiency. Here, we review the most recent scientific advances in cationic polymers and their derivatives not only for gene delivery purposes but also for various alternative therapeutic applications. An overview of the synthesis and preparation of cationic polymers is provided along with their inherent bioactive and intrinsic therapeutic potential. In addition, cationic polymer based biomedical materials are covered. Major progress in the fields of drug and gene delivery as well as tissue engineering applications is summarized in the present review.

Effects of branched or linear architecture of bioreducible poly(amido amine)s on their in vitro gene delivery properties

In this study, the gene delivery properties of new hyperbranched poly(amido amine)s (PAAs) with disulfide linkages in the main chain were investigated in comparison with their linear analogs. Eight different bioreducible PAAs were prepared by Michael addition of N,N'-bisacryloylpiperazine (BP) with cystamine (CYST) or N,N'-dimethylcystamine (DMC) and of N,N'-cystaminebisacrylamide (CBA) with N,N'-ethylenediamine (EDA) or N,N'-dimethylethylenediamine (DMEDA). In order to study the effect of terminal groups on the transfection efficiency, each polymer was terminated with 4-aminobutanol (ABOL) or with 2-aminoethanol (ETA). The hyperbranched and the linear PAAs generally formed polyplexes with plasmid DNA with sizes around 200nm and positive zeta potentials ranging from +10 to +22mV at polymer/DNA weight ratios equal or higher than 3/1. Remarkably low or no cytotoxicity was observed for both hyperbranched and linear PAAs. Hyperbranched CBA-containing PAAs showed higher gene expression in DNA transfection tests with COS-7 cells than their linear analogs and up to two times higher than linear PEI that was used as the reference polymer. Transfection efficiencies of the branched PAAs were generally enhanced by the presence of serum, which is a promising property for future in vivo studies with these hyperbranched PAAs. In this study the ease of synthetic modification of both linear and hyperbranched poly(amido amide)s and the versatility of hyperbranched PAAs in regulating DNA transfection and cytotoxicity are demonstrated. The results show the large possibilities for this class of polymers to provide polymeric vectors with controllable properties for gene therapy applications.

Preparation of a Nanoscaled Poly(vinyl alcohol)/Hydroxyapatite/DNA Complex Using High Hydrostatic Pressure Technology for In Vitro and In Vivo Gene Delivery

Our previous research showed that poly(vinyl alcohol) (PVA) nanoparticles incorporating DNA with hydrogen bonds obtained by high hydrostatic pressurization are able to deliver DNA without any significant cytotoxicity. To enhance transfection efficiency of PVA/DNA nanoparticles, we describe a novel method to prepare PVA/DNA nanoparticles encapsulating nanoscaled hydroxyapatites (HAps) prepared by high hydrostatic pressurization (980 MPa), which is designed to facilitate endosomal escape induced by dissolving HAps in an endosome. Scanning electron microscopic observation and dynamic light scattering measurement revealed that HAps were significantly encapsulated in PVA/HAp/DNA nanoparticles. The cytotoxicity, cellular uptake, and transgene expression of PVA/HAp/DNA nanoparticles were investigated using COS-7 cells. It was found that, in contrast to PVA/DNA nanoparticles, their internalization and transgene expression increased without cytotoxicity occurring. Furthermore, a similar level of transgene expression between plasmid DNA and PVA/HAp/DNA nanoparticles was achieved using in vivo hydrodynamic injection. Our results show a novel method of preparing PVA/DNA nanoparticles encapsulating HAp nano-crystals by using high hydrostatic pressure technology and the potential use of HAps as an enhancer of the transfection efficiency of PVA/DNA nanoparticles without significant cytotoxicity.

Influence of hydroxyl groups on the biological properties of cationic polymethacrylates as gene vectors

In this study poly(aminoethyl methacrylate) (PAEMA), poly(3-amino-2-hydroxypropyl methacrylate) (PAHPMA), poly(2-(2-aminoethylamino)ethyl methacrylate) (PAEAEMA) and poly(3-(2-aminoethylamino) 2-hydroxypropyl methacrylate) (PAEAHPMA) were synthesized using atom transfer radical polymerization to evaluate the effect of hydroxyl groups on the relative properties of cationic polymeric gene vectors. The results of heparin displacement assays showed that PAHPMA possessed a stronger binding capacity than PAEMA. PAHPMA/DNA complexes and PAEAHPMA/DNA complexes had lower zeta potentials than those of PAEMA and PAEAEMA. MTT assay results indicated that PAHPMA and PAEAHPMA exhibited obviously lower cytotoxicities than PAEMA and PAEAEMA. Subsequently, in vitro gene transfection studies in 293T cells without serum showed that PAHPMA exhibited a lower transfection efficiency than PAEMA and PAEAHPMA/DNA complexes possessed a similar transfection efficiency to PAEAEMA/DNA complexes. Moreover, PAHPMA and PAEAHPMA retained similar transfection efficiencies in DMEM with 10% serum, but PAEMA and PAEAEMA showed slightly lower transfection efficiencies than in the absence of serum. The reason for these phenomena might be attributed to the introduction of hydroxyl groups into PAHPMA and PAEAHPMA, i.e. the existence of hydroxyl groups might increase the binding capacity to DNA and at the same time decrease the surface charge of the polymer/DNA complexes due to the formation of hydrogen bonds between the polymers and DNA. Therefore, a lower zeta potential and stronger binding ability may result in a lower gene transfection efficiency. This effect of hydroxyl groups decreased with increasing amino group density on the polymer.

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.

Polyplex formation between four-arm poly(ethylene oxide)-b-poly(2-(diethylamino)ethyl methacrylate) and plasmid DNA in gene delivery

Amphiphilic polyelectrolytes comprising cationic and uncharged hydrophilic segments condensed negatively charged DNA to form a core-shell structure stabilized by a layer of hydrophilic corona chains. At physiological pH, four-arm star-shaped poly(ethylene oxide)-b-poly(2-(diethylamino)ethyl methacrylate) (four-arm PEO-b-PDEAEMA) block copolymer possessed positively charged amine groups that interacted with negatively charged plasmid DNA to form polymer/DNA complexes. The mechanism and physicochemical properties of the complex formation were investigated at varying molar ratio of amine groups on polymer chains and phosphate group on plasmid DNA segments (N/P ratio). The capability of the star block copolymer to condense DNA was demonstrated through gel electrophoresis and ethidium bromide exclusion assay. In the absence of salt, the hydrodynamic radius of polyplexes was about 94 nm at low polymer/DNA ratio, and it decreased to about 34 nm at large N/P ratios, forming a compact spherical structure with a weighted average molecular weight of 4.39 +/- 0.22 x 10(6) g/mol. Approximately 15 polymeric chains were required to condense a plasmid DNA. The addition of monovalent salt to the polyplexes significantly altered the size of the complexes, which would have an impact on cell transfection. Because of the electrostatic interaction induced by the diffusion of small ions, the polyplex increased in size to about 53 nm with a less compact structure. In vitro cytotoxicty of polymer and polymer/pDNA complexes were evaluated, and the polyplexes exhibited low toxicity at low N/P ratios. At N/P ratio of 4.5, the four-arm PEO-b-PDEAEMA showed the highest level of transfection in Neuro-2A cells. These observations showed that the star-shaped multi-arm polymers offers interesting properties in self-association and condensation ability for plasmid DNA and can serve as a nonviral DNA delivery system.

Synthetic polycation: polynucleotide interactions determined using liquid chromatography with short monolithic columns

LC on short monolithic columns (Convective Interaction Medium Disks) was applied to investigate several specially synthesized water soluble polycations of different charge type (primary, tertiary, quaternary amine), as well as a copolymer of neutral saccharide and cationic monomers, regarding their ability to form reversible complexes with DNA. For this purpose, two separation modes were used, namely, pseudo-affinity and cation-exchange chromatography. Synthetic polynucleotides, namely, polyriboadenylic acid (poly(rA)) and polyribocytidylic acid (poly(rC)), were used as approximate structural analogues of DNA. In first case, the hypothetical specific binding between dissolved polymers and polynucleotide (poly(rA) or poly(rC)), covalently attached to epoxy-bearing monolithic sorbent, has been studied and compared to the results obtained using cation exchange chromatography. Quantitative parameters of interactions between macromolecules were established using frontal elution method.