A biodegradable poly(ester amine) based on polycaprolactone and polyethylenimine as a gene carrier

PEI-based functional materials: Fabrication techniques, properties, and biomedical applications

Cationic polymers have recently attracted considerable interest as research breakthroughs for various industrial and biomedical applications. They are particularly interesting due to their highly positive charges, acceptable physicochemical properties, and ability to undergo further modifications, making them attractive candidates for biomedical applications. Polyethyleneimines (PEIs), as the most extensively utilized polymers, are one of the valuable and prominent classes of polycations. Owing to their flexible polymeric chains, broad molecular weight (MW) distribution, and repetitive structural units, their customization for functional composites is more feasible. The specific beneficial attributes of PEIs could be introduced by purposeful functionalization or modification, long service life, biocompatibility, and distinct geometry. Therefore, PEIs have significant potential in biotechnology, medicine, and bioscience. In this review, we present the advances in PEI-based nanomaterials, their transfection efficiency, and their toxicity over the past few years. Furthermore, the potential and suitability of PEIs for various applications are highlighted and discussed in detail. This review aims to inspire readers to investigate innovative approaches for the design and development of next-generation PEI-based nanomaterials possessing cutting-edge functionalities and appealing characteristics.

Poly (beta-amino ester) as an in vivo nanocarrier for therapeutic nucleic acids

Therapeutic nucleic acids are an emerging class of therapy for treating various diseases through immunomodulation, protein replacement, gene editing, and genetic engineering. However, they need a vector to effectively and safely reach the target cells. Most gene and cell therapies rely on ex vivo gene delivery, which is laborious, time-consuming, and costly; therefore, devising a systematic vector for effective and safe in vivo delivery of therapeutic nucleic acids is required to target the cells of interest in an efficient manner. Synthetic nanoparticle vector poly beta amino ester (PBAE), a class of degradable polymer, is a promising candidate for in vivo gene delivery. PBAE is considered the most potent in vivo vector due to its excellent transfection performance and biodegradability. PBAE nanoparticles showed tunable charge density, diverse structural characteristics, excellent encapsulation capacity, high stability, stimuli-responsive release, site-specific delivery, potent binding to nucleic acids, flexible binding ability to various conjugates, and effective endosomal escape. These unique properties of PBAE are an essential contribution to in vivo gene delivery. The current review discusses each of the components used for PBAE synthesis and the impact of various environmental and physicochemical factors of the body on PBAE nanocarrier.

Amphiphilic chitosan-polyaminoxyls loaded with daunorubicin: Synthesis, antioxidant activity, and drug delivery capacity

The binding of aminoxyls to polymers extends their potential use as antioxidants and EPR-reporting groups and opens up new horizons for tailoring new smart materials. In this work, we synthesized and characterized non-sulfated and N-sulfated water-soluble amphiphilic chitosans with a critical micelle concentration of 0.02-0.05 mg/mL that contain 13-18% of aminoglycosides bound with various aminoxyls. Chitosan-polyaminoxyls (CPAs) formed micelles with hydrodynamic radii R_h of ca. 100 nm. The EPR spectra of CPAs were found to depend on the rigidity of the aminoxyl-polymer bond and structural changes caused by sulfation. CPAs demonstrated antioxidant capacity/activity in three tests against reactive oxygen species (ROS) of various nature. The charge of micelles and structure of aminoxyls significantly affected their antioxidant properties. CPAs were low toxic against tumor (HepG2, HeLa, A-172) and non-cancerous (Vero) cells (IC₅₀ > 0.8 mM of aminoglycosides). Sulfated CPAs showed better water solubility and the ability of binding and retaining the anti-tumor antibiotic daunorubicin (DAU). DAU-loaded micelles of CPAs (CPAs-DAU) demonstrated a 1.5-4-fold potentiation of DAU cytotoxicity against several cell lines. CPAs-DAU micelles were found to affect the cell cycle in a manner markedly different from that of free DAU. Our results demonstrated the ability of CPAs to act as bioactive drug delivery vehicles.

Highly Efficient Modular Construction of Functional Drug Delivery Platform Based on Amphiphilic Biodegradable Polymers via Click Chemistry

Amphiphilic copolymers with pendant functional groups in polyester segments are widely used in nanomedicine. These enriched functionalities are designed to form covalent conjugates with payloads or provide additional stabilization effects for encapsulated drugs. A general method is successfully developed for the efficient preparation of functional biodegradable PEG-polyester copolymers via click chemistry. Firstly, in the presence of mPEG as initiator, Sn(Oct)2-catalyzed ring-opening polymerization of the α-alkynyl functionalized lactone with D,L-lactide or ε-caprolactone afforded linear mPEG-polyesters bearing multiple pendant alkynyl groups. Kinetic studies indicated the formation of random copolymers. Through copper-catalyzed azide-alkyne cycloaddition reaction, various small azido molecules with different functionalities to polyester segments are efficiently grafted. The molecular weights, polydispersities and grafting efficiencies of azido molecules of these copolymers were investigated by NMR and GPC. Secondly, it is demonstrated that the resulting amphiphilic functional copolymers with low CMC values could self-assemble to form nanoparticles in aqueous media. In addition, the in vitro degradation study and cytotoxicity assays indicated the excellent biodegradability and low cytotoxicity of these copolymers. This work provides a general approach toward the preparation of functional PEG-polyester copolymers in a quite efficient way, which may further facilitate the application of functional PEG-polyesters as drug delivery materials.

Turning Toxic Nanomaterials into a Safe and Bioactive Nanocarrier for Co-delivery of DOX/pCRISPR

Hybrid bioactive inorganic-organic carbon-based nanocomposites of reduced graphene oxide (rGO) nanosheets enlarged with multi-walled carbon nanotubes (MWCNTs) were decorated to provide a suitable space for in situ growth of CoNi₂S₄ and green-synthesized ZnO nanoparticles. The ensuing nanocarrier supplied π-π interactions between the DOX drug and a stabilizing agent derived from leaf extracts on the surface of ZnO nanoparticles and hydrogen bonds; gene delivery of (p)CRISPR was also facilitated by chitosan and alginate renewable macromolecules. Also, these polymers can inhibit the potential interactions between the inorganic parts and cellular membranes to reduce the potential cytotoxicity. Nanocomposite/nanocarrier analyses and sustained DOX delivery (cytotoxicity analyses on HEK-293, PC12, HepG2, and HeLa cell lines after 24, 48, and 72 h) were indicative of an acceptable cell viability of up to 91.4 and 78.8% after 48 at low and high concentrations of 0.1 and 10 μg/mL, respectively. The MTT results indicate that by addition of DOX to the nanostructures, the relative cell viability increased after 72 h of treatment; since the inorganic compartments, specifically CoNi₂S₄, are toxic, this is a promising route to increase the bioavailability of the nanocarrier before reaching the targeted cells. Nanosystems were tagged with (p)CRISPR for co-transfer of the drug/genes, where confocal laser scanning microscopy (CLSM) pictures of the 4',6-diamidino-2-phenylindole (DAPI) were indicative of appropriate localization of DOX into the nanostructure with effective cell and drug delivery at varied pH. Also, the intrinsic toxicity of CoNi₂S₄ does not affect the morphology of the cells, which is a breakthrough. Furthermore, the CLSM images of the HEK-293 and HeLa cell displayed effective transport of (p)CRISPR into the cells with an enhanced green fluorescent protein (EGFP) of up to 8.3% for the HEK-293 cell line and 21.4% for the HeLa cell line, a record. Additionally, the specific morphology of the nanosystems before and after the drug/gene transport events, via images by TEM and FESEM, revealed an intact morphology for these biopolymers and their complete degradation after long-time usage.

Development of novel, biocompatible, polyester amines for microglia-targeting gene delivery

Recent progress in personalized medicine and gene delivery has created exciting opportunities in therapeutics for central nervous system (CNS) disorders. Despite the interest in gene-based therapies, successful delivery of nucleic acids for treatment of CNS disorders faces major challenges. Here we report the facile synthesis of a novel, biodegradable, microglia-targeting polyester amine (PEA) carrier based on hydrophilic triethylene glycol dimethacrylate (TG) and low-molecular weight polyethylenimine (LMW-PEI). This nanocarrier, TG-branched PEI (TGP), successfully condensed double-stranded DNA into a size smaller than 200 nm. TGP nanoplexes were nontoxic in primary mixed glial cells and showed elevated transfection efficiency compared with PEI-25K and lipofector-EZ. After intrathecal and intracranial administration, PEA nanoplexes delivered genes specifically to microglia in the spinal cord and brain, respectively, proposing TGP as a novel microglia-specific gene delivery nanocarrier. The microglia-specific targeting of the TGP nanocarrier offers a new therapeutic strategy to modulate CNS disorders involving aberrant microglia activation while minimizing off-target side effects.

A novel microglia-targeting polyester amine nanocarrier allows microglia-specific gene delivery for the treatment of CNS disorder involving microglia dysfunction.

Solvent and catalyst-free modification of hyperbranched polyethyleneimines by ring-opening-addition or ring-opening-polymerization of N-sulfonyl aziridines

Ring-opening (polymerization) of N-sulfonyl aziridines with PEI under solvent/catalyst-free conditions allows the atom-economic synthesis of amphiphilic alkylated PEIs and luminescent PEI-graft-polysulfonamide.

Mussel-inspired polydopamine-mediated surface modification of freeze-cast poly (ε-caprolactone) scaffolds for bone tissue engineering applications

There are many methods used to fabricate the scaffolds for tissue regeneration, among which freeze casting has attracted a great deal of attention due to the capability to create a unidirectional structure. In this study, polycaprolactone (PCL) scaffolds were fabricated by freeze-casting technology in order to create porous microstructure with oriented open-pore channels. To induce biomineralization, and to improve hydrophilicity and cell interactions, mussel-inspired polydopamine (PDA) was coated on the surface of the freeze-cast PCL constructs. Then, the synergistic effects of oriented microstructure and deposited layer on efficient reconstruction of injured bone were studied. Microscopic observations demonstrated that, the coated layer did not show any special change in lamellar microstructure of the scaffolds. Water-scaffold interactions were evaluated by contact angle measurements, and they demonstrated strong enhancement in the hydrophilicity of the polymeric scaffolds after PDA coating. Biodegradation ratio and water uptake evaluation confirmed an increase in the measured values after PDA precipitation. The biomineralization of the PDA-coated scaffolds was characterized by field-emission scanning electron microscopy (FE-SEM), energy dispersive X-ray (EDX) and X-ray diffraction (XRD). Obtained results confirmed biomineralization of the constructs after a 28-day immersion in a simulated body fluid (SBF) solution. Mechanical analysis demonstrated higher compressive strength after PDA coating. L929 fibroblast cell viability and attachment illustrated that PDA-coated PCL scaffolds are able to support cell adhesion and proliferation. The increased secretion of alkaline phosphatase (ALP) after culturing osteosarcoma cell lines (MG-63) revealed the initial capability of scaffolds to induce bone regeneration. Therefore, the PDA-coated scaffolds introduce a promising approach for bone tissue engineering application.

Sugar alcohol-based polymeric gene carriers: Synthesis, properties and gene therapy applications

Advances in the field of nanomedicine have led to the development of various gene carriers with desirable cellular responses. However, unfavorable stability and physicochemical properties have hindered their applications in vivo. Therefore, multifunctional, smart nanocarriers with unique properties to overcome such drawbacks are needed. Among them, sugar alcohol-based nanoparticle with abundant surface chemistry, numerous hydroxyl groups, acceptable biocompatibility and biodegradable property are considered as the recent additions to the growing list of non-viral vectors. In this review, we present some of the major advances in our laboratory in developing sugar-based polymers as non-viral gene delivery vectors to treat various diseases. We also discuss some of the open questions in this field. STATEMENT OF SIGNIFICANCE: Recently, the development of sugar alcohol-based polymers conjugated with polyethylenimine (PEI) has attracted tremendous interest as gene delivery vectors. First, the natural backbone of polymers with their numerous hydroxyl groups display a wide range of hyperosmotic properties and can thereby enhance the cellular uptake of genetic materials via receptor-mediated endocytosis. Second, conjugation of a PEI backbone with sugar alcohols via Michael addition contributes to buffering capacity and thereby the proton sponge effect. Last, sugar alcohol based gene delivery systems improves therapeutic efficacy both in vitro and in vivo.

Synthesis and Properties of Low-Molecular-Weight PEI-Based Lipopolymers for Delivery of DNA

Rapid enzymatic degradation and fragmentation during DNA administration can result in limited gene expression, and consequently, poor efficacy. It is necessary to use novel vectors for DNA delivery. Herein, we aimed to design useful carriers for enhancing transfection efficiency (TE). These lipopolymers were prepared through Michael addition reactions from low-molecular-weight (LMW) polyethyleneimine (PEI) and linkers with three kinds of steroids. Agarose gel electrophoresis assay results displayed that the three lipopolymers could condense plasmid DNA well, and the formed polyplexes had appropriate sizes around 200⁻300 nm, and zeta potentials of about +25⁻40 mV. The results of in vitro experiments using HeLa, HEK293, and MCF-7 cells showed that these lipopolymers present higher TE than 25-kDa PEI, both in the absence and presence of 10% serum. Flow cytometry and confocal microscopy studies also demonstrated that these lipopolymer/DNA complexes present higher cellular uptake and intracellular distribution. The measurement of critical micelle concentration (CMC) revealed that these lipopolymers could form micelles, which are suited for drug delivery. All results suggest that the three materials may serve as hopeful candidates for gene and drug delivery in future in vivo applications.

Poly(β-amino ester)-co-poly(caprolactone) Terpolymers as Nonviral Vectors for mRNA Delivery In Vitro and In Vivo

The production of new proteins with messenger RNA (mRNA) has gained a broad interest due to its potential for addressing a wide range of diseases. Here, the design and characterization of novel ionizable poly(β-amino ester)-co-poly(caprolactone) terpolymers, synthesized via the combination of the ring opening polymerization and the Michael step-growth polymerization, are reported. The versatility of this method is demonstrated by varying the number of caprolactone units attached to each poly(β-amino ester) (PBAE) terpolymer. The ability of the novel poly-caprolactone (PCL)-based PBAE materials to deliver mRNA is shown to depend on the physiochemical characteristics of the material, such as lipophilicity, as well as the formulation method used to complex the polymer with the oligonucleotide. This latter variable represents a previously unstudied aspect of PBAE library screens that can play an important role in identifying true top candidates for nucleic acid delivery. The most stable terpolymer is injected intravenously (IV) in mice and shows a transfection efficacy several times higher than the polyethylenimine (PEI) which is focused in the spleen, opening the possibility to use these biodegradable carriers in the intravenous delivery of antigen-encoding mRNA for cancer immunotherapy and vaccination.

Impact of Cationic Charge Density and PEGylated Poly(amino acid) Tercopolymer Architecture on Their Use as Gene Delivery Vehicles. Part 1: Synthesis, Self-Assembly, and DNA Complexation

The interaction of PEGylated poly(amino acid)s with their biological targets depends on their chemical nature and spatial arrangement of their building blocks. The synthesis, self-assembly, and DNA complexation of ABC terblock copolymers consisting of poly(ethylene glycol), (PEG), poly(l-lysine), and poly(l-leucine), are reported. Block copolymers are produced by a metal-free, living ring-opening polymerization of respective amino acid N-carboxyanhydrides using amino-terminated PEG as macroinitiator: (PEG-b-p(l-Lys)_x -b-p(l-Leu)_y , PEG-b-p(l-Leu)_x -b-p(l-Lys)_y , and PEG-b-p((l-Lys)_x -co-p(l-Leu)_y ). Sizes of self-assembled nanoparticles depend on the formation method. The nanoprecipitation method proves useful for copolymers with the poly(l-lysine) block protected as trifluoroacetate, effective diameters range between 92 and 132 nm, while direct dissolution in distilled water is suitable for the deprotected copolymers, yielding effective diameters between 52 and 173 nm. Critical micelle concentration (CMC) analyses corroborate particle size analyses and show a distinct impact of the molecular architecture; the lowest CMC (8 µg mL^-1 ) is observed when the poly(l-leucine) segment forms the C-block and the hydrophilic, disassembly driving poly(l-lysine) segment is short. DNA complexation, evaluated by gel motility and RiboGreen analyses, depends strongly on the molecular architecture. A more efficient DNA complexation is observed when poly(l-lysine) and poly(l-leucine) form individual blocks as opposed to them forming a copolymer.

Immune Activities of Polycationic Vectors for Gene Delivery

Polycationic vectors are used widely in the field of gene delivery, while currently their immune activities in vivo are poorly understood. In this comprehensive review, we aim to present an overview of existing mechanisms of adverse immune responses induced by the polycation/gene complexes, which includes the polycations themselves, the gene sequences and the ROS produced by them. These causes can induce pro-inflammatory cytokines, hypersensitivity as well as the activation of toll-like receptors, and finally the immunostimulation occur. In addition, we introduce some different opinions and research results on the immunogenicity of classical polycations such as polylysine (PLL), polyethyleneimine (PEI), polyamidoamine dendrimers (PAMAM), chitosan and gelatin, most of which have immunogenicity and can induce immunoreactions in vivo. The methods now used to adjust their immunogenicity are shown in the final part of this review. Nowadays, there is still no accurate conclusion on immunogenicity of polycations, which confuses researchers seriously in in vivo test. We conclude that further research is needed in order to skillfully utilize or inhibit the immunogenicity of these polycationic vectors.

EGFR-Targeted Cationic Polymeric Mixed Micelles for Codelivery of Gemcitabine and miR-205 for Treating Advanced Pancreatic Cancer

Gemcitabine (GEM), a first-line chemotherapy for pancreatic cancer undergoes rapid metabolism and develops chemoresistance after repeated administration. We previously demonstrated that the combination of GEM and miR-205 provides an effective therapeutic strategy to sensitize GEM-resistant pancreatic cancer cells. Since epidermal growth factor receptor (EGFR) is overexpressed in pancreatic cancer cells, in this study, we aimed to deliver mixed micelles containing GEM and miR-205 decorated with EGFR-targeting cetuximab (C225) monoclonal antibody for targeted therapy. Cetuximab C225 was conjugated to malemido-poly(ethylene glycol)-block-poly(2-methyl-2-carboxyl-propylene carbonate-graft-dodecanol (C225-PEG-PCD) to prepare mixed micelles with mPEG-b-PCC-g-GEM-g-DC-g-TEPA for targeted codelivery of GEM and miR-205. This mixed micelle formulation showed a significant enhancement in EGFR-mediated cellular uptake in GEM-resistant MIA PaCa-2^R cells. Further, an enhanced tumor accumulation of C225-micelles conjugated with near-infrared fluorescent Cy7.5 dye and Dy677-labeled miR-205 in orthotopic pancreatic tumor bearing NSG mice was evident after systemic administration. In addition, inhibition of tumor growth was also observed with increased apoptosis and reduced EMT after treatment with C225-micelles containing GEM and miR-205. Therefore, we believe that the targeted delivery of GEM and miR-205 in combination could be a novel strategy for treating advanced pancreatic cancer.

Targeted delivery of in situ PCR-amplified Sleeping Beauty transposon genes to cancer cells with lipid-based nanoparticle-like protocells

A Sleeping Beauty (SB) transposon system is made of a transposon plasmid (containing gene encoding a desired functional or therapeutic protein) and a transposase plasmid (encoding an enzyme capable of cutting and pasting the gene into the host cell genome). It is a kind of natural, nonviral gene delivery vehicle, which can achieve efficient genomic insertion, providing long-term transgenic expression. However, before the SB transposon system could play a role in promoting gene expression, it has to be delivered efficiently first across cell membrane and then into cell nuclei. Towards this end, we used a nanoparticle-like lipid-based protocell, a closed bilayer of the neutral lipids with the DNA encapsulated inside, to deliver the SB transposon system to cancer cells. The SB transposon system was amplified in situ inside the protocells by a polymerase chain reaction (PCR) process, realizing more efficient loading and delivery of the target gene. To reach a high transfection efficiency, we introduced two targeting moieties, folic acid (FA) as a cancer cell-targeting motif and Dexamethasone (DEX) as a nuclear localization signaling molecule, into the protocells. As a result, the FA enabled the modified targeting protocells to deliver the DNA into the cancer cells with an increased efficiency and the DEX promoted the DNA to translocate to cell nuclei, eventually leading to the increased chromosome insertion efficiency of the SB transposon. In vivo study strongly suggested that the transfection efficiency of FA-modified protocells in the tumor tissue was much higher than that in other tissues, which was consistent with the in vitro results. Our studies implied that with the targeting ligand modification, the protocells could be utilized as an efficient targeting gene carrier. Since the protocells were made of neutral lipids without cationic charges, the cytotoxicity of protocells was significantly lower than that of traditional cationic gene carriers such as cationic liposomes and polyethylenimine, enabling the protocells to be employed in a wider dosage range in gene therapy. Our work shows that the protocells are a promising gene carrier for future clinical applications.

Magnetic Cobalt and Cobalt Oxide Nanoparticles in Hyperbranched Polyester Polyol Matrix

A series of cobalt (Co) and its oxides based nanoparticles were synthesized by using hyperbranched polyester polyol Boltorn H20 as a platform and sodium borohydride as a reducing agent. UV, FT-IR, XRD, NTA, and TEM methods were employed to obtain physicochemical characteristics of the products. The average diameter of Co nanoparticles was approximately 8.2±3.4 nm. Their magnetic properties, including hysteresis loop, field-cooled, and zero field-cooled curves were investigated. The nanoparticles exhibit superparamagnetism at room temperature, accompanied by magnetic hysteresis below the blocking temperature.

ε-Caprolactone-Modified Polyethylenimine as Efficient Nanocarriers for siRNA Delivery in Vivo

RNA interference (RNAi) therapy is a promising treatment for various diseases. However, its application is still restricted by the lack of efficient and safe delivery systems. A novel siRNA delivery vehicle based on ε-caprolactone-modified polyethylenimine (PEI-CL) is presented here. The PEI-CL macromolecules with different grafting degrees were synthesized via a simple ring-opening reaction. This macromolecule strongly protects the siRNA from degradation in serum and promotes the cellular uptake and endosomal escape detected via chemical exchange saturation transfer magnetic resonance analysis and fluorescence imaging. The in vivo measurement was performed with HCT-116 colon tumor xenograft that stably expressed luciferase. The data showed that the PEI-CL/siRNA nanocomplexes elicited strong RNAi response. More interestingly, enhanced gene transfection efficiency was achieved by simultaneous cotransfection with siRNA and DNA plasmid via this novel nanosystem. Overall, our study suggests the PEI-CL macromolecule with great promise for siRNA delivery.

Synthesis of intracellular reduction-sensitive amphiphilic polyethyleneimine and poly(ε-caprolactone) graft copolymer for on-demand release of doxorubicin and p53 plasmid DNA

This study aims to present a new intelligent polymeric nano-system used for combining chemotherapy with non-viral gene therapy against human cancers. An amphiphilic copolymer synthesized through the conjugation of low molecular weight polyethyleneimine (LMw-PEI) and poly(ε-caprolactone) (PCL) via a bio-cleavable disulfide linkage was successfully employed for the simultaneous delivery of drug and gene molecules into target cells. Compared to the conventional PCL copolymerization pathway, this paper represents a straightforward and efficient reaction pathway including the activation of PCL-diol hydroxyl end groups, cystamine attachment and LMw-PEI conjugation which are successfully performed at mild conditions as confirmed by FTIR and (1)H NMR. Thermal, morphological characteristics as well as biocompatibility of the copolymer were investigated. The copolymer showed great tendency to form positively charged nanoparticles (∼163.1nm, +35.3mV) with hydrophobic core and hydrophilic shell compartments implicating its potential for encapsulation of anti-cancer drug and plasmid DNA, respectively. The gel retardation assay confirmed that the nanoparticles could successfully inhibit the migration of pDNA at ∼5 nanoparticle/pDNAw/w. The in vitro cytotoxicity tests and LDH assay revealed that the cationic amphiphilic copolymer was essentially non-toxic in different carcinoma cell lines in contrast to branched PEI 25K. Moreover, the presence of redox sensitive disulfide linkages provided smart nanoparticles with on-demand release behavior in response to reducing agents such as cytoplasmic glutathione (GSH). Importantly, confocal microscopy images revealed that in contrast to free Dox, the nanoparticles were capable of faster internalizing into the cells and accumulating in the perinuclear region or even in the nucleus. Finally, the co-delivery of Dox and p53-pDNA using the copolymer displayed greater cytotoxic effect compared with the Dox-loaded nanoparticle counterpart as revealed by cell viability and Caspase 3 expression assay. These results suggest the copolymer as a promising candidate for the development of smart delivery systems.

STATEMENT OF SIGNIFICANCE

We employed cystamine dihydrochloride as a disulfide linkage for the conjugation of PCL diol and low molecular weight PEI segments through a straightforward and efficient reaction pathway at mild conditions. The new copolymer was essentially non-toxic in different carcinoma cell lines and showed great tendency to form positively charged nanoparticles. Therefore, it can be utilized as a promising platform for simultaneous drug and gene delivery to aggressive cancers. The results of drug and gene co-delivery experiments confirmed the pivotal role of disulfide linkage on the controlled release of both drug and gene molecules in response to glutathione concentration gradient between extracellular and intracellular microenvironments. In addition, the co-delivery of doxorubicin and p53 plasmid DNA using the new copolymer displayed greater cytotoxic effect compared with single agent (i.e. Dox) loaded counterpart, which indicated the significance of rapid dissociation of therapeutic agents from the carrier for synergistic cytotoxic effects on cancer cells.

Low Molecular Weight PEI-Based Vectors via Acid-Labile Ortho Ester Linkage for Improved Gene Delivery

A series of novel pH-sensitive gene delivery vectors (POEI 1, 2, and 3) are synthesized through Michael addition from low molecular weight PEI (LMW PEI) via acid-labile ortho ester linkage with terminal acrylates (OEAc) by various feed molar ratios. The obtained POEI 1 and POEI 2 can efficiently condense plasmid DNA into nanoparticles with size range of 200-300 nm and zeta-potentials of about +15 mV while protecting DNA from enzymatic digestion compared with POEI 3. Significantly, ortho ester groups of POEI main-chains can make an instantaneous degradation-response to acidic endosomal pH (≈5.0), resulting in accelerated disruption of polyplexes and intracellular DNA release. MTT assay reveals that all POEIs exhibit much lower cytotoxicity in different cells than branched PEI (25 KDa). As expected, POEI 1 and POEI 2 perform improved gene transfection in vitro, suggesting that such polycations might be promising gene vectors based on overcoming toxicity-efficiency contradiction.

Structural modifications in polymeric micelles to impart multifunctionality for improved drug delivery

Polymeric micelles are macromolecular nanoconstructs which are formed by self-assembly of synthetic amphiphilic block copolymers. These copolymers could be chemically modified to expand their functionality and hence obtain a multifunctional micelle which could serve several functions simultaneously, for example, long circulation time along with active targeting, smart polymeric micelles providing on-demand drug release for example, pH responsive micelles, redox- and light-sensitive micelles, charge-conversion micelles and core/shell cross-linked micelles. Additionally, micelles could be tailored to carry a contrast agent or siRNA/miRNA along with the drug for greater clinical benefit. The focus of the current commentary would be to highlight such chemical modifications which impart multifunctionality to a single carrier and discuss challenges involved in clinical translation of these multifunctional micelles.

Polyethylenimine analogs for improved gene delivery: effect of the type of amino groups

The 1°, 2° and 3° amine composition of PEI analogs could be easily adjusted by special synthetic method, and their effects on the gene transfection were studied.

Suppression of tumor growth in lung cancer xenograft model mice by poly(sorbitol-co-PEI)-mediated delivery of osteopontin siRNA

Small interfering RNA (siRNA)-mediated gene silencing represents a promising strategy for treating diseases such as cancer; however, specific gene silencing requires an effective delivery system to overcome the instability and low transfection efficiency of siRNAs. To address this issue, a polysorbitol-based transporter (PSOT) was prepared by low molecular weight branched polyethylenimine (bPEI) crosslinked with sorbitol diacrylate (SDA). Osteopontin (OPN) gene, which is highly associated with non-small cell lung cancer (NSCLC) was targeted by siRNA therapy using siRNA targeting OPN (siOPN). Characterization study confirmed that PSOT formed compact complexes with siOPN and protected siOPN against degradation by RNase. PSOT/siOPN complexes demonstrated low cytotoxicity and enhanced transfection efficiency in vitro, suggesting that this carrier may be suitable for gene silencing. In the A549 and H460 lung cancer cell lines, PSOT/siOPN complexes demonstrated significant silencing efficiency at both RNA and protein levels. To study in vivo tumor growth suppression, two lung cancer cell-xenograft mouse models were prepared and PSOT/siOPN complexes were delivered into the mice through intravenous injection. The siOPN-treated groups demonstrated significantly reduced OPN expression at both the RNA and protein levels as well as suppression of tumor volume and weight. Taken together, siOPN delivery using PSOT may present an effective and novel therapeutic system for lung cancer treatment.

Nanoparticles complexed with gene vectors to promote proliferation of human vascular endothelial cells

Amphiphilic block copolymers containing biodegradable hydrophobic segments of depsipeptide based copolymers have been synthesized and explored as gene carriers for enhancing proliferation of endothelial cells in vitro. These polymers form nanoparticles (NPs) with positive charges on their surface, which could condense recombinant plasmids of enhanced green fluorescent protein plasmid and ZNF580 gene (pEGFP-ZNF580) and protect them against DNase I. ZNF580 gene is efficiently transported into EA.hy926 cells to promote their proliferation, whereby the transfection efficiency of NPs/pEGFP-ZNF580 is approximately similar to that of Lipofectamine 2000. These results indicate that the NPs might have potential as a carrier for pEGFP-ZNF580, which could support endothelialization of cardiovascular implants.

Three-Layered Biodegradable Micelles Prepared by Two-Step Self-Assembly of PLA-PEI-PLA and PLA-PEG-PLA Triblock Copolymers as Efficient Gene Delivery System

"Three-layered micelles" (3LM) composed of two triblock copolymers, poly(L-lactide)-b-polyethyleneimine-b-poly(L-lactide) (PLLA-PEI-PLLA) and poly(L-lactide)-b-poly(ethylene glycol)-b-poly(L-lactide) (PLLA-PEG-PLLA) are designed to combine electrostatic interaction and solvent-induced condensation of DNA. The low molecular weight PLLA-PEI-PLLA is synthesized by a facile amine-protection/deprotection approach and employed as a gene vector, compacting DNA as a polyplex core in the organo-micelles. The individual organo-micelle is further encapsulated within a PLLA-PEG-PLLA amphiphilic micelle leading to an aqueous stable colloidal dispersion. The resulting spherical 3LM possess a hydrodynamic diameter of ca. 200 nm and zeta potential close to neutral and display excellent stability to competing polyanions such as dextran sulfate in neutral pH (7.4). Such high stability is attributed to the complete shielding of the PEI/DNA polyplex core with an impermeable hydrophobic intermediate layer. However, greater than 90% of the encapsulated DNA are released within 30 min when exposed to slightly acidic pH (4.5). Based on our findings, a new class of non-viral delivery system for nucleic acids with superb stability and stealth properties is identified.

Multicomponent polymeric nanoparticles enhancing intracellular drug release in cancer cells

Three kinds of amphiphilic copolymer, that is, poly(ε-caprolactone)-SS-poly(ethylene glycol) (PCL-SS-PEG), poly(ε-caprolactone)-polyethylenimine (PCL-PEI), and poly(ε-caprolactone)-polyethylenimine-folate (PCL-PEI-Fol) were synthesized and self-assembled into surface engineered hybrid nanoparticles (NPs). Morphological studies elucidated the stable, spherical, and uniform sandwich structure of the NPs. PCL-PEI and PCL-SS-PEG segments have introduced pH and reduction responsive characteristics in these NPs, while PCL-PEI-FA copolymers could provide specific targeting capability to cancer cells. The stimuli responsive capabilities of these NPs were carried out. Negative-to-positive charge reversible property, in response to the pH change, was investigated by zeta potential and nuclear magnetic resonance (NMR) measurements. The structure cleavage, due to redox gradient, was studied by dynamic light scattering (DLS) and transmission electron microscopy (TEM). These NPs showed controlled degradation, better drug release, less toxicity, and effective uptake in MCF-7 breast cancer cells. These multifunctional NPs showed promising potential in the treatment of cancer.

Reducible cationic PAA-g-PEI polymeric micelle/DNA complexes for enhanced gene delivery

The design of unique vectors to overcome the cytotoxicity and increase the efficiency of gene transfection has enormous challenges. Polyethylenimine (PEI) is one of the most effective polymer-based gene carriers. However, the transfection efficiency and toxicity of PEI correlate strongly to its molecular weight (MW). In this study, novel reduction-sensitive amphiphilic poly[phenethylamido- N,N-bis(acryloyl) cystine]- g-polyethylenimine (PAA- g-PEI) copolymers were synthesized by grafting low-MW PEIs onto reducible poly[phenethylamido-N,N-bis(acryloyl) cystine] (PAA).

These copolymers self-assembled in aqueous solution into micelles with sizes <70 nm, as determined by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The PAA- g-PEI2000 micelles effectively condense with the plasmid DNA to form complex nanoparticles with diameters of ~100 nm at an N/P ratio of 4/1. The PAA- g-PEI2000 micelle/DNA complexes protected the DNA from degrading by nuclease and released DNA under reductive conditions by the cleavage of the disulfide bonds and the subsequent disassembly of the micelles. As determined by gene transfection experiments, the transfection efficiency of the PAA- g-PEI2000 micelle/DNA complexes was significantly greater than that of the PEI25K/DNA complexes, while the cytotoxicity of the copolymers was much lower than that for PEI25K.

Low molecular weight PEIs modified by hydrazone-based crosslinker and betaine as improved gene carriers

Low-molecular-weight polyethyleneimine (LMW PEI) exhibits poorer transfection efficiency but lower cytotoxicity compared to high-molecular-weight polyethyleneimine (such as PEI 25kDa). To enhance the gene transfection performance of LMW PEI, we herein demonstrate a new strategy for modifying LMW PEI. A crosslinker containing an acid-labile hydrazone bond (hydrazone-based crosslinker) was synthesized and used to crosslink PEI 1.8kDa and convert it into higher-molecular-weight polycations. And the crosslinked polycations were further modified by incorporating a betaine monomer [N,N-dimethyl(acrylamidopropyl)ammonium propane sulfonate, DMAAPS] onto their surfaces. The molar percentages of the incorporated betaine molecules to amino groups on the polycations were determined as 21.2%, 36.0% and 77.2%, respectively. Molecular weights of the modified polycations were measured using capillary viscometry at pH 7.4 and 5.0, respectively, and the degradation of the polymers in acidic solution was confirmed. The PEIs modified with hydrazone and betaine (PEI-Hdz-DMAAPS) exhibit much lower cytotoxicity than PEI 25K, and they also show no or little hemolytic effect with their hemolysis rates around 5%. PEI-Hdz-DMAAPS21.2%/DNA and PEI-Hdz-DMAAPS36.0%/DNA complexes exhibit high transfection efficiencies, which are comparable to or higher than that of PEI 25K/DNA complex in the absence or presence of 10% serum. With these improved gene delivery properties, the PEI-Hdz-DMAAPS samples have great potential for serving as efficient gene carriers. This strategy may provide some insights for constructing some other biocompatible materials.

Efficacy of gemcitabine conjugated and miRNA-205 complexed micelles for treatment of advanced pancreatic cancer

Clinical effectiveness of gemcitabine in pancreatic cancer is hindered due to its rapid plasma metabolism and development of chemo-resistance. We have previously delineated the significant role of miRNAs in mediating the growth and proliferation of cancer stem cells (CSCs) which in turn result in chemo-resistance, invasion and metastasis. Here, we designed self-assembling, gemcitabine conjugated cationic copolymers for co-delivery of a tumor suppressor miRNA-205 (miR-205) and evaluated their in vivo efficacy in a pancreatic cancer ectopic tumor model developed using gemcitabine resistant MIA PaCa-2(R) cells. Combination formulations showed mean a particle size of <100 nm and gemcitabine payload of >10% w/w, exhibited miRNA complexation at N/P ratio of 4/1, sustained release of gemcitabine for >10 days, transfection efficiency of >90%, extended miRNA and drug stability in serum. Functional assays in gemcitabine resistant MIA PaCa-2(R) and CAPAN-1(R) pancreatic cancer cells revealed that the combination formulations effectively reversed chemo-resistance, invasion and migration. In pancreatic tumor model, the combination formulation treated group showed significant inhibition of tumor growth. Immuno-hiostochemical analysis revealed decreased tumor cell proliferation with increased apoptosis in the animals treated with miR-205 and gemcitabine combination.

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

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

Corrosion protection and improved cytocompatibility of biodegradable polymeric layer-by-layer coatings on AZ31 magnesium alloys

Composite coatings of electrostatically assembled layer-by-layer anionic and cationic polymers combined with an Mg(OH)2 surface treatment serve to provide a protective coating on AZ31 magnesium alloy substrates. These ceramic conversion coating and layer-by-layer polymeric coating combinations reduced the initial and long-term corrosion progression of the AZ31 alloy. X-ray diffraction and Fourier transform infrared spectroscopy confirmed the successful application of coatings. Potentiostatic polarization tests indicate improved initial corrosion resistance. Hydrogen evolution measurements over a 2 week period and magnesium ion levels over a 1 week period indicate longer range corrosion protection and retention of the Mg(OH)2 passivation layer in comparison to the uncoated substrates. Live/dead staining and DNA quantification were used as measures of biocompatibility and proliferation while actin staining and scanning electron microscopy were used to observe the cellular morphology and integration with the coated substrates. The coatings simultaneously provided improved biocompatibility, cellular adhesion and proliferation in comparison to the uncoated alloy surface utilizing both murine pre-osteoblast MC3T3 cells and human mesenchymal stem cells. The implementation of such coatings on magnesium alloy implants could serve to improve the corrosion resistance and cellular integration of these implants with the native tissue while delivering vital drugs or biological elements to the site of implantation.

Cell penetrating peptide conjugated polymeric micelles as a high performance versatile nonviral gene carrier

The major goal of this study is to design, synthesize, and evaluate linoleic acid and penetratin dual-functionalized chitosan (CS-Lin-Pen) as a nonviral gene carrier. The amphiphilic CS-Lin-Pen self-assembles to form cationic micelles in an aqueous environment. These polymeric micelles exhibited excellent hemocompatibility and cell viability, as evaluated by in vitro hemolysis and MTT assay, respectively. When CS-Lin-Pen micelles were added to plasmid DNA (pDNA) solution, the electrostatic interaction between the cationic micelles and anionic pDNA led to the formation of stable CS-Lin-Pen/pDNA polyplexes with ~100 nm in size. The resultant polyplexes demonstrated ~5-fold higher cellular uptake as compared to unmodified chitosan. Furthermore, CS-Lin-Pen micelles showed efficient protection of pDNA from DNase I attack and exhibited ~34-40-fold higher transfection in comparison with unmodified chitosan in HEK 293, CHO, and HeLa cells. These findings illustrate that the CS-Lin-Pen micelles could be exploited as a potential nonviral vector for efficient gene therapy.

Multi-armed poly(aspartate-g-OEI) copolymers as versatile carriers of pDNA/siRNA

To search for potential non-viral nucleic acids carriers, a series of novel cationic polymers, multi-armed poly(aspartate-graft-oligoethylenimine) (MP-g-OEI) copolymers were designed and synthesized by grafting different types of oligoethylenimine (OEI) to a multi-armed poly(l-aspartic acid) backbone. The as-synthesized MP-g-OEI copolymers were characterized by Fourier transform infrared spectroscopy, nuclear magnetic resonance and gel permeation chromatography. These MP-g-OEI copolymers (MP423, MP600 and MP1800) exhibited good capacity in condensing nucleic acids (pDNA or siRNA) into nanosized particles (90-150nm) with positive surface charges. Gene transfection activity of the MP-g-OEI copolymers (especially MP1800) showed improved performance compared with PEI25k in both HeLa and CHO cell lines. The silencing efficiency of MP600/siRNA and MP1800/siRNA complexes showed a superior knockdown effect in CT26 and Huh-7 cell lines. Moreover, the MP-g-OEI copolymers exhibited much lower cytotoxicity than PEI25k. Flow cytometric analysis showed that MP-g-OEI copolymers could efficiently mediate the entry of nucleic acids into cells. These results suggest that MP-g-OEI copolymers may be potential non-viral gene carriers for the delivery of nucleic acids in future gene therapy.

2-diethylaminoethyl-dextran methyl methacrylate copolymer nonviral vector: still a long way toward the safety of aerosol gene therapy

Revealing the lung tumor genome has directed the current treatment strategies toward targeted therapy. First line treatments targeting the genome of lung tumor cells have been approved and are on the market. However, they are limited by the small number of patients with the current investigated genetic mutations. Novel treatment administration modalities have been also investigated in an effort to increase the local drug deposition and disease control. In the current study, we investigated the safety of the new nonviral vector 2-diethylaminoethyl-dextran methyl methacrylate copolymer (DDMC; Ryujyu Science), which belongs to the 2-diethylaminoethyl-dextran family by aerosol administration. Thirty male BALBC mice, 2 month old, were included and divided into three groups. However, pathological findings indicated severe emphysema within three aerosol sessions. In addition, the CytoViva technique was applied for the first time to display the nonviral particles within the pulmonary tissue and emphysema lesions, and a spectral library of the nonviral vector was also established. Although our results in BALBC mice prevented us from further investigation of the DDMC nonviral vector as a vehicle for gene therapy, further investigation in animals with larger airways is warranted to properly evaluate the safety of the vector.