Physiochemical properties of low and high molecular weight poly(ethylene glycol)-grafted poly(ethylene imine) copolymers and their complexes with oligonucleotides

A Novel Family of Stable Polyelectrolyte Complexes Based on Mixed Olefins-Maleic Anhydride Copolymer

In the present study, the copolymer of mixed olefins included in unetherified gasoline and maleic anhydride (PUGM) was prepared by self-stabilized precipitation polymerization (2SP) and employed for the synthesis of a new family of stable polyelectrolyte complexes (PECs). Polyanionic saponified PUGM partially grafted with methoxy poly(ethylene glycol) (PUGMS-g-mPEG) and polycationic quaternized PUGM (PUGMQ) were both derived from PUGM via the facile modification of anhydride groups. The particle size, zeta potential, morphology, and stability of self-assembled PEC particles were investigated thoroughly. Strikingly, the introduction of long mPEG side chains (M_n = 4000) had a remarkable effect on the self-assembled particles, which displayed a constant particle size of ∼200 nm regardless of varying n+/n-. Moreover, it also enhanced the salt tolerance and long-term stability of PEC particles significantly. Our work not only provides an effective approach to PECs from petroleum resources with low cost but also deepens the understanding of the relationship between the chain structure of polyelectrolytes and the stability of PECs.

Microbubble–Nanoparticle Complexes for Ultrasound-Enhanced Cargo Delivery

Targeted delivery of therapeutics to specific tissues is critically important for reducing systemic toxicity and optimizing therapeutic efficacy, especially in the case of cytotoxic drugs. Many strategies currently exist for targeting systemically administered drugs, and ultrasound-controlled targeting is a rapidly advancing strategy for externally-stimulated drug delivery. In this non-invasive method, ultrasound waves penetrate through tissue and stimulate gas-filled microbubbles, resulting in bubble rupture and biophysical effects that power delivery of attached cargo to surrounding cells. Drug delivery capabilities from ultrasound-sensitive microbubbles are greatly expanded when nanocarrier particles are attached to the bubble surface, and cargo loading is determined by the physicochemical properties of the nanoparticles. This review serves to highlight and discuss current microbubble–nanoparticle complex component materials and designs for ultrasound-mediated drug delivery. Nanocarriers that have been complexed with microbubbles for drug delivery include lipid-based, polymeric, lipid–polymer hybrid, protein, and inorganic nanoparticles. Several schemes exist for linking nanoparticles to microbubbles for efficient nanoparticle delivery, including biotin–avidin bridging, electrostatic bonding, and covalent linkages. When compared to unstimulated delivery, ultrasound-mediated cargo delivery enables enhanced cell uptake and accumulation of cargo in target organs and can result in improved therapeutic outcomes. These ultrasound-responsive delivery complexes can also be designed to facilitate other methods of targeting, including bioactive targeting ligands and responsivity to light or magnetic fields, and multi-level targeting can enhance therapeutic efficacy. Microbubble–nanoparticle complexes present a versatile platform for controlled drug delivery via ultrasound, allowing for enhanced tissue penetration and minimally invasive therapy. Future perspectives for application of this platform are also discussed in this review.

Biomimetic cell membrane-coated DNA nanoparticles for gene delivery to glioblastoma

Gene therapy has been introduced as an alternative to radiation and chemical therapy for glioblastoma. Biomimetic nanoparticles coated with cell membranes (CM) have advantages such as high biocompatibility and prolong half-life. To apply CM coated nanoparticles to gene delivery, the polyethylenimine (PEI25k)/plasmid DNA (pDNA) complexes were coated with CM from C6 rat glioblastoma cells. With the CM covering, the PEI25k/pDNA complexes formed stable nanoparticles with negative surface charge. The PEI25k/pDNA/CM nanoparticles had high colloidal stability and could be stored for approximately 20 days without aggregation. The transfection efficiency of the PEI25k/pDNA/CM nanoparticles was higher than that of the PEI25k/pDNA complex in serum-containing medium. This suggests that serum does not interfere with transfection efficiency of the nanoparticles. Moreover, the PEI25k/pDNA/CM nanoparticles had lower toxicity than the PEI25k/DNA complex in vitro and in vivo. The PEI25k/pDNA/CM nanoparticles prepared with CMs of different types of cells were transfected into cells. The results showed that the PEI25k/pDNA/CM nanoparticles with the C6 CM had the highest transfection efficiency to C6 cells, suggesting the homotypic targeting effect. The therapeutic effects of the nanoparticles were evaluated in intracranial C6 transplanted glioblastoma animal models. The PEI25k/pDNA/CM nanoparticles were prepared with herpes simplex virus thymidine kinase plasmid (pHSVtk) and injected into the tumor locally. The results showed that the PEI25k/pHSVtk/CM nanoparticles induced higher HSVtk expression compared with the PEI25k/pHSVtk complex. Furthermore, tumor size was reduced more efficiently by the PEI25k/pHSVtk/CM nanoparticles than by the PEI25k/pHSVtk complex. Overall results indicate that PEI25k/pDNA/CM nanoparticles are suitable for pDNA delivery to glioblastoma.

PEGylation of Guanidinium and Indole Bearing Poly(methacrylamide)s - Biocompatible Terpolymers for pDNA Delivery

This study describes the first example for shielding of a high performing terpolymer that consists of N-(2-hydroxypropyl)methacrylamide (HPMA), N-(3-guanidinopropyl)methacrylamide (GPMA), and N-(2-indolethyl)methacrylamide monomers (IEMA) by block copolymerization of a polyethylene glycol derivative - poly(nona(ethylene glycol)methyl ether methacrylate) (P(MEO₉ MA)) via reversible addition-fragmentation chain transfer (RAFT) polymerization. The molecular weight of P(MEO₉ MA) is varied from 3 to 40 kg mol^-1 while the comonomer content of HPMA, GPMA, and IEMA is kept comparable. The influence of P(MEO₉ MA) block with various molecular weights is investigated over cytotoxicity, plasmid DNA (pDNA) binding, and transfection efficiency of the resulting polyplexes. Overall, the increase in molecular weight of P(MEO₉ MA) block demonstrates excellent biocompatibility with higher cell viability in L-929 cells and an efficient binding to pDNA at N/P ratio of 2. The significant transfection efficiency in CHO-K1 cells at N/P ratio 20 is obtained for block copolymers with molecular weight of P(MEO₉ MA) up to 10 kg mol^-1 . Moreover, a fluorescently labeled analogue of P(MEO₉ MA), bearing perylene monoimide methacrylamide (PMIM), is introduced as a comonomer in RAFT polymerization. Polyplexes consisting of labeled block copolymer with 20 kg mol^-1 of P(MEO₉ MA) and pDNA are incubated in Hela cells and investigated through structured illumination microscopy (SIM).

Polymeric Delivery of Therapeutic Nucleic Acids

The advent of genome editing has transformed the therapeutic landscape for several debilitating diseases, and the clinical outlook for gene therapeutics has never been more promising. The therapeutic potential of nucleic acids has been limited by a reliance on engineered viral vectors for delivery. Chemically defined polymers can remediate technological, regulatory, and clinical challenges associated with viral modes of gene delivery. Because of their scalability, versatility, and exquisite tunability, polymers are ideal biomaterial platforms for delivering nucleic acid payloads efficiently while minimizing immune response and cellular toxicity. While polymeric gene delivery has progressed significantly in the past four decades, clinical translation of polymeric vehicles faces several formidable challenges. The aim of our Account is to illustrate diverse concepts in designing polymeric vectors towards meeting therapeutic goals of in vivo and ex vivo gene therapy. Here, we highlight several classes of polymers employed in gene delivery and summarize the recent work on understanding the contributions of chemical and architectural design parameters. We touch upon characterization methods used to visualize and understand events transpiring at the interfaces between polymer, nucleic acids, and the physiological environment. We conclude that interdisciplinary approaches and methodologies motivated by fundamental questions are key to designing high-performing polymeric vehicles for gene therapy.

Development of Facile and Selective Fluorescent Probe for Physiological Phosphates based on Aggregation-induced Emission

In this work, two new fluorescence chemosensors 2-(4-(1,2,2-triphenylvinyl)phenoxy) acetic acid (TPE-COOH) and 2,2'-(((1,2-diphenylethane-1,2-diyl)bis(4,1-phenylene))bis(oxy))diacetic acid (TPE-(COOH)₂) were synthesized and applied for the facile detection of physiological phosphates. Due to the aggregation-induced emission (AIE) character, the emission can be turned on after label free interaction with polyethyleneimine (PEI). When the physiological phosphates were introduced to the system, the AIEgens/PEI complex was dissociated due to stronger electrostatic interaction between PEI and phosphates, which resulted in the significant fluorescence quenching of AIEgens. As the four kinds of phosphates cytidine-5'-diphosphate disodium salt (CDP), adenosine-5 (ADP), sodium pyrophosphate (PPi) and guanosine-5'-diphosphate disodium salt (GDP) had different interaction with PEI, also the TPE-COOH and TPE-(COOH)₂ had different interaction with PEI, the fluorescence quenching effect was distinct for four phosphates. The unique pattern of fluorescence variations was differentiated by chemometric methods including principal component analysis and linear discriminant analysis. The robustness of the sensor array was proved by discrimination of four kinds of phosphates in serum samples with different concentrations, and the discrimination capacity was not influenced in complicated samples Graphical abstract.

Polymeric siRNA gene delivery - transfection efficiency versus cytotoxicity

Within the field of gene therapy, there is a considerable need for the development of non-viral vectors that are able to compete with the efficiency obtained by viral vectors, while maintaining a good toxicity profile and not inducing an immune response within the body. While there have been many reports of possible polymeric delivery systems, few of these systems have been successful in the clinical setting due to toxicity, systemic instability or gene regulation inefficiency, predominantly due to poor endosomal escape and cytoplasmic release. The objective of this review is to provide an overview of previously published polymeric non-coding RNA and, to a lesser degree, oligo-DNA delivery systems with emphasis on their positive and negative attributes, in order to provide insight in the numerous hurdles that still limit the success of gene therapy.

Tunable Composition of Dynamic Non-Viral Vectors over the DNA Polyplex Formation and Nucleic Acid Transfection

Polyethylene glycol (PEG) functionalization of non-viral vectors represents a powerful tool through the formation of an overall surface charge shielding ability, which is fundamental for efficient nucleic acid delivery systems. The degree of non-viral vector PEGylation and the molecular weight of utilized PEG is crucial since the excessive use of PEG units may lead to a considerable reduction of the DNA-binding capacity and, subsequently, in a reduction of in vitro transfection efficiency. Herein, we report a detailed study on a series of dynamic combinatorial frameworks (DCFs) containing PEGylated squalene, poly-(ethyleneglycol)-bis(3-aminopropyl) of different lengths, and branched low molecular weight polyethylenimine components, reversibly connected in hyperbranched structures, as efficient dynamic non-viral vectors. The obtained frameworks were capable of forming distinct supramolecular amphiphilic architectures, shown by transmission electron microscopy (TEM) and dynamic light scattering (DLS), with sizes and stability depending on the length of PEG units. The interaction of PEGylated DCFs with nucleic acids was investigated by agarose gel retardation assay and atomic force microscopy (AFM), while their transfection efficiency (using pCS2+MT-Luc DNA as a reporter gene) and cytotoxicity were evaluated in HeLa cells. In addition, the data on the influence of the poly-(ethyleneglycol)-bis(3-aminopropyl) length in composition of designed frameworks over transfection efficiency and tolerance in human cells were analyzed and compared.

Novel Oligo-Guanidyl-PEG Carrier Forming Rod-Shaped Polyplexes

A novel unconventional supramolecular oligo-cationic structure (Agm₆-M-PEG-OCH₃) has been synthesized to yield high efficiency therapeutic oligonucleotide (ON) delivery. Agm₆-M-PEG-OCH₃ was obtained by a multistep protocol that included the conjugation of agmatine (Agm) moieties to maltotriose (M), which was further derivatized with one poly(ethylene glycol) (PEG) chain. Gel electrophoresis analysis showed that the 19 base pairs dsDNA model ON completely associates with Agm₆-M-PEG-OCH₃ at 3 N/P molar ratio, which is in agreement with the in silico molecular predictions. Isothermal titration calorimetry (ITC) analyses showed that the Agm₆-M-PEG-OCH₃/ON association occurs through a combination of mechanisms depending on the N/P ratios resulting in different nanostructures. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) revealed that the Agm₆-M-PEG-OCH₃/ON polyplexes have rod-shape structure with a mean diameter of 50-75 nm and aspect ratio depending on the N/P ratio. The polyplexes were stable over time in buffer, while a slight size increase was observed in the presence of serum proteins. Cell culture studies showed that neither Agm₆-M-PEG-OCH₃ nor polyplexes displayed cytotoxic effects. Cellular uptake depended on the cell line and polyplex composition: cellular internalization was higher in the case of MCF-7 and KB cells compared to MC3T3-E1 cells and polyplexes with smaller aspect ratio were taken-up by cells more efficiently than polyplexes with higher aspect ratio. Finally, preliminary studies showed that our novel carrier efficiently delivered ONs into cells providing gene silencing.

pH-Responsive Natural Polymeric Gene Delivery Shielding System Based on Dynamic Covalent Chemistry

A novel pH-responsive system based on aldehyde-bearing dextran derivatives (ODEX or FDEX) was designed to use as gene carrier shielding. Through pH sensitive Schiff base bonds between amino groups of PEI (in PEI/DNA polyplex) and aldehyde groups of dextran derivatives, PEI/DNA polyplex could be shielded and further condensed to obtain an effectively decreasing ζ-potential with smaller size. Schiff base bonds were pH-responsive, which were relatively stable in neutral environment but were deformed in slightly acidic and acidic environments. Through use of this characteristic, the PEI/DNA polyplex was effectively shielded during circulation in the body, and upon arrival at the tumor, the slightly acid pH triggered the breaking of Schiff base bonds to expose the positive PEI/DNA polyplex, which further interacted with tumor cell membranes, achieving efficient gene expression. Use of such characteristics could effectively address the high transfection efficiency versus stability dilemma of gene carriers. FDEX/PEI/DNA nanoparticles not only mediate higher cellular uptake and transfection efficiency in vitro but also effectively accumulate in tumors with gene expression in vivo higher than that of the ODEX analogues. As a result, this pH-responsive system is a promising strategy for cancer therapy.

Suppression of chronic inflammation with engineered nanomaterials delivering nuclear factor κB transcription factor decoy oligodeoxynucleotides

As a prototypical pro-inflammatory transcription factor, constitutive activation of NF-κB signaling pathway has been reported in several chronic inflammatory disorders including inflammatory bowel disease, cystic fibrosis, rheumatoid arthritis and cancer. Application of decoy oligodeoxynucleotides (ODNs) against NF-κB, as an effective molecular therapy approach, has brought about several promising outcomes in treatment of chronic inflammatory disorders. However, systematic administration of these genetic constructs is mostly hampered due to their instability, rapid degradation by nucleases and poor cellular uptake. Both chemical modification and application of delivery systems have shown to effectively overcome some of these limitations. Among different administered delivery systems, nanomaterials have gained much attention for delivering NF-κB decoy ODNs owing to their high loading capacity, targeted delivery and ease of synthesis. In this review, we highlight some of the most recently developed nanomaterial-based delivery systems for overcoming limitations associated with clinical application of these genetic constructs.

Recent Advances in Nanomaterials for Gene Delivery-A Review

With the rapid development of nanotechnology in the recent decade, novel DNA and RNA delivery systems for gene therapy have become available that can be used instead of viral vectors. These non-viral vectors can be made of a variety of materials, including inorganic nanoparticles, carbon nanotubes, liposomes, protein and peptide-based nanoparticles, as well as nanoscale polymeric materials. They have as advantages over viral vectors a decreased immune response, and additionally offer flexibility in design, allowing them to be functionalized and targeted to specific sites in a biological system with low cytotoxicity. The focus of this review is to provide an overview of novel nanotechnology-based methods to deliver DNA and small interfering RNAs into biological systems.

Self-aggregating 1.8kDa polyethylenimines with dissolution switch at endosomal acidic pH are delivery carriers for plasmid DNA, mRNA, siRNA and exon-skipping oligonucleotides

Efficiency of polyethylenimine (PEI) for nucleic acid delivery is affected by the size of the carrier and length of the nucleic acids. For instance, PEIs with molecular weights between 10-30kDa provide optimal DNA delivery activity whereas PEIs with molecular weights below 1.8kDa are ineffective. The activity of PEI is also severely diminished by substitution of DNA for shorter nucleic acids such as mRNA or siRNA. Here, through chemical modification of the primary amines to aromatic domains we achieved nucleic acid delivery by the 1.8kDa polyethylenimine (PEI) particles. This modification did not affect the PEI buffering abilities but enhanced its pH-sensitive aggregation, enabling stabilization of the polyplex outside the cell while still allowing nucleic acid release following cellular entry. The aromatic PEIs were then evaluated for their gene, mRNA, siRNA and 2'O-methyl phosphorothioate oligonucleotide in vitro transfection abilities. The salicylamide-grafted PEI showed to be a reliable carrier for delivering nucleic acids with cytoplasmic activity such as the mRNA and siRNA or nuclear diffusible oligonucleotide. It was then further equipped with polyethyleneglycol (PEG) and the delivery efficiency of the copolymer was tested in vivo for regeneration of dystrophin in the muscle of mdx mouse through a 2'O-methyl phosphorothioate-mediated splicing modulation. Intramuscular administration of polyplexes resulted in dystrophin-positive fibers in a mouse model of Duchenne muscular dystrophy without apparent toxicity. These findings indicate that precise modifications of low molecular weight PEI improve its bio-responsiveness and yield delivery vehicles for nucleic acids of various types in vitro and in vivo.

A theranostic micelleplex co-delivering SN-38 and VEGF siRNA for colorectal cancer therapy

The development of an efficient colorectal cancer therapy is currently a public health priority. In the present work, we proposed a multifunctional theranostic micellar drug delivery system utilizing cationic PDMA-block-poly(ε-caprolactone) (PDMA-b-PCL) micelles as nanocarriers of SN-38 (7-ethyl-10-hydroxycamptothecin), ultra-small superparamagnetic iron oxide nanoparticles (USPIO), and small interfering RNA (siRNA) that targets human vascular endothelial growth factor (VEGF). The VEGF siRNA was conjugated to polyethylene glycol (PEG) (siRNA-PEG) before complexation with the micelles in order to improve the siRNA's stability and to prolong its retention time in the blood circulation. To further improve the in vivo biosafety, we prepared mixed micelles using mPEG-PCL together with PDMA-b-PCL copolymer. The SN-38/USPIO-loaded siRNA-PEG mixed micelleplexes passively targeted to tumor regions and synergistically facilitated VEGF silencing and chemotherapy, thus efficiently suppressing tumor growth via a multi-dose therapy regimen. Additionally, the SN-38/USPIO-loaded siRNA-PEG mixed micelleplexes acted as a negative magnetic resonance imaging (MRI) contrast agent in T2-weighted imaging, resulting in a powerful tool for the diagnosis and for tracking of the therapeutic outcomes. In summary, we established a theranostic micellar drug and gene delivery system that not only synergistically combined gene silencing and chemotherapy but also served as a negative MRI contrast agent, which reveal its potential as a novel colorectal cancer therapy.

Poly-L-Lysine-Poly[HPMA] Block Copolymers Obtained by RAFT Polymerization as Polyplex-Transfection Reagents with Minimal Toxicity

Herein we describe the synthesis of poly-L-lysine-b-poly[N-(2-hydroxypropyl)-metha-crylamide)] (poly[HPMA]) block copolymers by combination of solid phase peptide synthesis or polymerization of α-amino acid-N-carboxy-anhydrides (NCA-polymerization) with the reversible addition-fragmentation chain transfer polymerization (RAFT). In the presence of p-DNA, these polymers form polyplex micelles with a size of 100-200 nm in diameter (monitored by SDS-PAGE and FCS). Primary in vitro studies with HEK-293T cells reveal their cellular uptake (FACS studies and CLSM) and proof successful transfection with efficiencies depending on the length of polylysine. Moreover, these polyplexes display minimal toxicity (MTT-assay and FACS-measurements) featuring a p[HPMA] corona for efficient extracellular shielding and the potential ligation with antibodies.

Stability and toxicity of empty or gene-loaded lipopolysaccharide-amine nanopolymersomes

Successful in vivo gene delivery mediated by nonviral vectors requires efficient extracellular and intracellular gene delivery, but few studies have given attention to the former. That is why numerous gene delivery systems have succeeded in vitro, while the expected clinical success has not come about. To realize efficient extracellular gene delivery, the stability of vectors and/or their complexes with genes in body fluids is first required, which prevents loaded genes from premature unloading and degradation. Furthermore, the storage stability of vectors under common conditions is important for their widespread applications. Lipopolysaccharide-amine nanopolymersomes (NPs), a gene vector developed by our group recently, have higher than 95% in vitro transfection efficiency in mesenchymal stem cells when delivering pEGFP, and induce significant angiogenesis in zebrafish when delivering plasmid encoding vascular endothelial growth factor deoxyribonucleic acid (pVEGF). To reveal their extracellular delivery ability and storage stability, in this study their stability in various simulant physiological environments and storage conditions was systematically studied by monitoring their changes in disassembly, size, zeta potential, and transfection efficiency. Additionally, damage to the mitochondria of mesenchymal stem cells was evaluated. Results show that NPs and plasmid deoxyribonucleic acid (pDNA)-loaded NPs (pNPs) have acceptable stability against dilution, anions, salts, pH, enzyme, and serum, presumably assuring their efficient extracellular delivery in vivo. Moreover, both the lyophilized NPs at room temperature and NP/pNP solution at 4°C have high storage stability, and pNPs show low damage to the mitochondria. The acceptable stability of NPs combined with compatibility and efficient gene transfection highlight their huge potential in the clinic as a gene delivery vector.

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

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

Evaluation of the effects of amphiphilic oligomers in PEI based ternary complexes on the improvement of pDNA delivery

(HEMA-b-NIPAM) was incorporated into PEI/P(HEMA-b-NIPAM)/pDNA ternary complexes through non-electrostatic assembly to enhance the interaction between complexes and cellular/endocellular membranes to improve gene transfection.

Balancing cationic and hydrophobic content of PEGylated siRNA polyplexes enhances endosome escape, stability, blood circulation time, and bioactivity in vivo

A family of pH-responsive diblock polymers composed of poly[(ethylene glycol)-b-[(2-(dimethylamino)ethyl methacrylate)-co-(butyl methacrylate)], PEG-(DMAEMA-co-BMA), was reversible addition-fragmentation chain transfer (RAFT) synthesized with 0-75 mol % BMA in the second polymer block. The relative mole % of DMAEMA and BMA was varied in order to identify a polymer that can be used to formulate PEGylated, siRNA-loaded polyplex nanoparticles (NPs) with an optimized balance of cationic and hydrophobic content in the NP core based on siRNA packaging, cytocompatibility, blood circulation half-life, endosomal escape, and in vivo bioactivity. The polymer with 50:50 mol % of DMAEMA:BMA (polymer "50 B") in the RAFT-polymerized block efficiently condensed siRNA into 100 nm NPs that displayed pH-dependent membrane disruptive behavior finely tuned for endosomal escape. In vitro delivery of siRNA with polymer 50 B produced up to 94% protein-level knockdown of the model gene luciferase. The PEG corona of the NPs blocked nonspecific interactions with constituents of human whole blood, and the relative hydrophobicity of polymer 50 B increased NP stability in the presence of human serum or the polyanion heparin. When injected intravenously, 50 B NPs enhanced blood circulation half-life 3-fold relative to more standard PEG-DMAEMA (0 B) NPs (p < 0.05), due to improved stability and a reduced rate of renal clearance. The 50 B NPs enhanced siRNA biodistribution to the liver and other organs and significantly increased gene silencing in the liver, kidneys, and spleen relative to the benchmark polymer 0 B (p < 0.05). These collective findings validate the functional significance of tuning the balance of cationic and hydrophobic content of polyplex NPs utilized for systemic siRNA delivery in vivo.

Poly(ethylene glycol)-block-cationic polylactide nanocomplexes of differing charge density for gene delivery

Representing a new type of biodegradable cationic block copolymer, well-defined poly(ethylene glycol)-block-cationic polylactides (PEG-b-CPLAs) with tertiary amine-based cationic groups were synthesized by thiol-ene functionalization of an allyl-functionalized diblock precursor. Subsequently the application of PEG-b-CPLAs as biodegradable vectors for the delivery of plasmid DNAs (pDNAs) was investigated. Via the formation of PEG-b-CPLA:pDNA nanocomplexes by spontaneous electrostatic interaction, pDNAs encoding luciferase or enhanced green fluorescent protein were successfully delivered to four physiologically distinct cell lines (including macrophage, fibroblast, epithelial, and stem cell). Formulated nanocomplexes demonstrated high levels of transfection with low levels of cytotoxicity and hemolysis when compared to a positive control. Biophysical characterization of charge densities of nanocomplexes at various polymer:pDNA weight ratios revealed a positive correlation between surface charge and gene delivery. Nanocomplexes with high surface charge densities were utilized in an in vitro serum gene delivery inhibition assay, and effective gene delivery was observed despite high levels of serum. Overall, these results help to elucidate the influence of charge, size, and PEGylation of nanocomplexes upon the delivery of nucleic acids in physiologically relevant conditions.

Design of polyethylene glycol-polyethylenimine nanocomplexes as non-viral carriers: mir-150 delivery to chronic myeloid leukemia cells

MicroRNAs (miRNAs) are acknowledged as indispensable regulators relevant in many biological processes, and they have been pioneered as therapeutic targets for curing disease. miRNAs are single-stranded, small (19-22 nt) regulatory non-coding RNAs whose deregulation of expression triggers human cancers, including leukemias, mainly through dysregulation of expression of leukemia genes. miRNAs can function as tumour suppressors (suppressing malignant potential) or oncogenes (activating malignant potential) like actors of complex diseases. To address the issue of overcoming instability and low transfection efficiency in vitro, the polyethylene glycol-polyethyleneimine (PEG-PEI) nanoparticle was used as non-viral vector carrier for miR-150 transfection, which is downregulated in chronic myeloid leukemia. PEG-PEI [PEG(550)3 -g-PEI(1800) ]/miRNA nanocomplexes were synthesised and characterised by particle size distribution (PSD), polydispersity index (PDI) and zeta potential, surface charge, their cytotoxicity, and transfection efficiency. Interaction with human leukemia cells (K-562 and KU812) and control cells NCI-BL2347 with them has been investigated. The transfection efficiency of PEG-PEI/miRNA at N/P 26 rose 6.7-fold above the control by qRT-PCR. The size of homogenous nanocomplexes (PBI < 0.5) was 160.8 ± 11 nm. The data indicate that PEG-PEI may be an encouraging non-viral carrier for altering miRNA expression in the treatment of chronic myeloid leukemia, with many advantages such as relatively high miRNA transfection efficiency and low cytotoxicity.

The effect of N/P ratio on the in vitro and in vivo interaction properties of PEGylated poly[2-(dimethylamino)ethyl methacrylate]-based siRNA complexes

PEG-PnBA-PDMAEMA triblock and PEG-PDMAEMA diblock copolymers are used as model systems for studying the role of N/P ratio on the in vivo behavior of PEGylated siRNA carriers in mice. The presence of a free/uncomplexed polymer population coexisting with siRNA complexes is established. A change in the N/P ratio exerts no significant influence on the in vivo biodistribution and ex vivo blood chemistry properties of the respective systems. Histological analysis of major organs indicates that the presence of uncomplexed polymer elicits toxicity to the organ that is associated with the clearance of the siRNA complexes from the circulation system. This effect can be eliminated by working at N/P ratios near the charge-neutralization point of the complexes.

Self-assembled magnetic theranostic nanoparticles for highly sensitive MRI of minicircle DNA delivery

As a versatile gene vector, minicircle DNA (mcDNA) has a great potential for gene therapy. However, some serious challenges remain, such as to effectively deliver mcDNA into targeted cells/tissues and to non-invasively monitor the delivery of the mcDNA. Superparamagnetic iron oxide (SPIO) nanoparticles have been extensively used for both drug/gene delivery and diagnosis. In this study, an MRI visible gene delivery system was developed with a core of SPIO nanocrystals and a shell of biodegradable stearic acid-modified low molecular weight polyethyleneimine (Stearic-LWPEI) via self-assembly. The Stearic-LWPEI-SPIO nanoparticles possess a controlled clustering structure, narrow size distribution and ultrasensitive imaging capacity. Furthermore, the nanoparticle can effectively bind with mcDNA and protect it from enzymatic degradation. In conclusion, the nanoparticle shows synergistic advantages in the effective transfection of mcDNA and non-invasive MRI of gene delivery.

A combinatorial library of unsaturated lipidoids for efficient intracellular gene delivery

A combinatorial library of unsaturated lipidoids was synthesized through the Michael addition of amines to oleyl acrylamide. Their capability in facilitating in vitro gene delivery was evaluated by transfecting HeLa cells with EGFP-encoding plasmid DNA and mRNA. The preliminary screening results indicated that lipidoids with unsaturated oleyl tails are superior transfection agents compared to saturated lipidoids with n-octadecyl tails under the same conditions. The different transfection abilities of the unsaturated and saturated lipidioids were ascribed to the large, tightly packed lipoplexes of saturated lipidoids. The potential applications of the library of lipidoids were further expanded by looking at their ability to transfect fibroblasts as well as different cancerous cell lines.

Synaptotagmin-1 promotes the formation of axonal filopodia and branches along the developing axons of forebrain neurons

Synaptotagmin-1 (syt1) is a Ca(2+)-binding protein that functions in regulation of synaptic vesicle exocytosis at the synapse. Syt1 is expressed in many types of neurons well before synaptogenesis begins both in vivo and in vitro. To determine if expression of syt1 has a functional role in neuronal development before synapse formation, we examined the effects of syt1 overexpression and knockdown on the growth and branching of the axons of cultured primary embryonic day 8 chicken forebrain neurons. In vivo these neurons express syt1, and most have not yet extended axons. We present evidence that syt1 plays a role in regulating axon branching, while not regulating overall axon length. To study the effects of overexpression of syt1, we used adenovirus-mediated infection to introduce a syt1-YFP construct, or control GFP construct, into neurons. Syt1 levels were reduced using RNA interference. Overexpression of syt1 increased the formation of axonal filopodia and branches. Conversely, knockdown of syt1 decreased the number of axonal filopodia and branches. Time-lapse analysis of filopodial dynamics in syt1-overexpressing cells demonstrated that elevation of syt1 levels increased both the frequency of filopodial initiation and their lifespan. Taken together these data indicate that syt1 regulates the formation of axonal filopodia and branches before engaging in its conventional functions at the synapse.

Charge shielding effects on gene delivery of polyethylenimine/DNA complexes: PEGylation and phospholipid coating

Polyethylenimine (PEI) is an efficient cationic polymer for gene delivery, but defective in biocompatibility. In this study, we developed two different strategies to shield the positively charged PEI/DNA complexes: PEGylation and lipid coating. The physicochemical properties, cytotoxicity and transfection efficiency of the two gene delivery systems were investigated. Both PEGylation and lipid coating succeeded in reducing the zeta-potential of the complexes. Lipid-coated PEI/DNA complexes (LPD complexes) and PEI/DNA complexes exhibited similar cytotoxicity, whereas PEG-PEI/DNA complexes showed lower cytotoxicity, especially at high N/P ratios. LPD complexes were less efficient in transfection compared to PEG-PEI/DNA complexes. The transfection efficiency was influenced remarkably by cytotoxicity and surface charge of the complexes. Intracellular processes studies revealed that endosomal release might be one of the rate-limiting steps in cell transfection with PEI as a gene delivery carrier.

Metal ion-enriched polyelectrolyte complexes and their utilization in multilayer assembly and catalytic nanocomposite films

The mixing of Ag ion-doped poly(ethyleneimine) (PEI) and poly(acrylic acid) (PAA) produced Ag ion-doped polyelectrolyte complex particles (PECs) in solution. Positively charged Ag ion-doped PECs (Ag ion PECs) with a spherical shape were deposited alternatively with PAA to form a multilayer assembly. The multilayered film containing Ag ion PECs was reduced to generate a composite nanostructure. Metal nanoparticle (NP)-enriched nanocomposite films were formed by an additional process of the postadsorption of precursors on PECs within the nanocomposite films, which resulted in the enhancement of the catalytic and electrical properties of the composite films. Because the films contain PECs that are responsive to changes in pH and most of the NPs are embedded in the PECs, interesting catalytic properties, which are unexpected in a particle-type catalyst, were observed upon pH changes. As a result of the reversible structural changes of the films and the immobilization of the NPs within the films, the film-type catalysts showed enhanced performance and stability during catalytic reactions under various pH conditions, compared to particle-type catalysts.

Chitosan-graft-branched polyethylenimine copolymers: influence of degree of grafting on transfection behavior

Background

Successful non-viral gene delivery currently requires compromises to achieve useful transfection levels while minimizing toxicity. Despite high molecular weight (MW) branched polyethylenimine (bPEI) is considered the gold standard polymeric transfectant, it suffers from high cytotoxicity. Inversely, its low MW counterpart is less toxic and effective in transfection. Moreover, chitosan is a highly biocompatible and biodegradable polymer but characterized by very low transfection efficiency. In this scenario, a straightforward approach widely exploited to develop effective transfectants relies on the synthesis of chitosan-graft-low MW bPEIs (Chi-g-bPEI_x) but, despite the vast amount of work that has been done in developing promising polymeric assemblies, the possible influence of the degree of grafting on the overall behavior of copolymers for gene delivery has been largely overlooked.

Methodology/Principal Findings

With the aim of providing a comprehensive evaluation of the pivotal role of the degree of grafting in modulating the overall transfection effectiveness of copolymeric vectors, we have synthesized seven Chi-g-bPEI_x derivatives with a variable amount of bPEI grafts (minimum: 0.6%; maximum: 8.8%). Along the Chi-g-bPEI_x series, the higher the degree of grafting, the greater the ζ-potential and the cytotoxicity of the resulting polyplexes. Most important, in all cell lines tested the intermediate degree of grafting of 2.7% conferred low cytotoxicity and higher transfection efficiency compared to other Chi-g-bPEI_x copolymers. We emphasize that, in transfection experiments carried out in primary articular chondrocytes, Chi-g-bPEI_2.7% was as effective as and less cytotoxic than the gold standard 25 kDa bPEI.

Conclusions/Significance

This work underlines for the first time the pivotal role of the degree of grafting in modulating the overall transfection effectiveness of Chi-g-bPEI_x copolymers. Crucially, we have demonstrated that, along the copolymer series, the fine tuning of the degree of grafting directly affected the overall charge of polyplexes and, altogether, had a direct effect on cytotoxicity.

Nucleic-acid based gene therapeutics: delivery challenges and modular design of nonviral gene carriers and expression cassettes to overcome intracellular barriers for sustained targeted expression

The delivery of nucleic acid molecules into cells to alter physiological functions at the genetic level is a powerful approach to treat a wide range of inherited and acquired disorders. Biocompatible materials such as cationic polymers, lipids, and peptides are being explored as safer alternatives to viral gene carriers. However, the comparatively low efficiency of nonviral carriers currently hampers their translation into clinical settings. Controlling the size and stability of carrier/nucleic acid complexes is one of the primary hurdles as the physicochemical properties of the complexes can define the uptake pathways, which dictate intracellular routing, endosomal processing, and nucleocytoplasmic transport. In addition to nuclear import, subnuclear trafficking, posttranscriptional events, and immune responses can further limit transfection efficiency. Chemical moieties, reactive linkers or signal peptide have been conjugated to carriers to prevent aggregation, induce membrane destabilization and localize to subcellular compartments. Genetic elements can be inserted into the expression cassette to facilitate nuclear targeting, delimit expression to targeted tissue, and modulate transgene expression. The modular option afforded by both gene carriers and expression cassettes provides a two-tier multicomponent delivery system that can be optimized for targeted gene delivery in a variety of settings.

Polyplex-microbubble hybrids for ultrasound-guided plasmid DNA delivery to solid tumors

Microbubble ultrasound contrast agents are being developed as image-guided gene carriers for targeted delivery in vivo. In this study, novel polyplex-microbubbles were synthesized, characterized and evaluated for systemic circulation and tumor transfection. Branched polyethylenimine (PEI; 25 kDa) was modified with polyethylene glycol (PEG; 5 kDa), thiolated and covalently attached to maleimide groups on lipid-coated microbubbles. The PEI-microbubbles demonstrated increasingly positive surface charge and DNA loading capacity with increasing maleimide content. The in vivo ultrasound contrast persistence of PEI-microbubbles was measured in the healthy mouse kidney, and a two-compartment pharmacokinetic model accounting for free and adherent microbubbles was developed to describe the anomalous time-intensity curves. The model suggested that PEI loading dramatically reduced free circulation and increased nonspecific adhesion to the vasculature. However, DNA loading to form polyplex-microbubbles increased circulation in the bloodstream and decreased nonspecific adhesion. PEI-microbubbles coupled to a luciferase bioluminescence reporter plasmid DNA were shown to transfect tumors implanted in the mouse kidney. Site-specific delivery was achieved using ultrasound applied over the tumor area following bolus injection of the DNA/PEI-microbubbles. In vivo imaging showed over 10-fold higher bioluminescence from the tumor region compared to untreated tissue. Ex vivo analysis of excised tumors showed greater than 40-fold higher expression in tumor tissue than non-sonicated control (heart) tissue. These results suggest that the polyplex-microbubble platform offers improved control of DNA loading and packaging suitable for ultrasound-guided tissue transfection.

Physicochemical and biological evaluation of siRNA polyplexes based on PEGylated Poly(amido amine)s

PURPOSE

Use of RNA interference as novel therapeutic strategy is hampered by inefficient delivery of its mediator, siRNA, to target cells. Cationic polymers have been thoroughly investigated for this purpose but often display unfavorable characteristics for systemic administration, such as interactions with serum and/or toxicity.

METHODS

We report the synthesis of a new PEGylated polymer based on biodegradable poly(amido amine)s with disulfide linkages in the backbone. Various amounts of PEGylated polymers were mixed with their unPEGylated counterparts prior to polyplex formation to alter PEG content in the final complex.

RESULTS

PEGylation effectively decreased polyplex surface charge, salt- or serum-induced aggregation and interaction with erythrocytes. Increasing amount of PEG in formulation also reduced its stability against heparin displacement, cellular uptake and subsequent silencing efficiency. Yet, for polyplexes with high PEG content, significant gene silencing efficacy was found, which was combined with almost no toxicity.

CONCLUSIONS

PEGylated poly(amido amine)s are promising carriers for systemic siRNA delivery in vivo.

Influence of nano-carrier architecture on in vitro siRNA delivery performance and in vivo biodistribution: polyplexes vs micelleplexes

Micelle-based siRNA carriers ("micelleplexes") were prepared from the A-B-C triblock copolymer poly(ethylene glycol)-poly(n-butyl acrylate)-poly(2-(dimethylamino)ethyl methacrylate) (PEG-PnBA-PDMAEMA), and their in vitro performance and in vivo biodistribution properties were compared with the benchmark PEGylated and basic polycation systems PEG-PDMAEMA and PDMAEMA, respectively. The micelle architecture, incorporating increased PEG shielding and a larger particle size (∼50 nm) than polycation-based complexes (polyplexes; ∼10 nm), enhances siRNA delivery performance in two important aspects: in vitro gene silencing efficiency and in vivo tumor accumulation. The in vitro gene silencing efficiency of the micelleplexes (24% in HeLa cells) was significantly better than the statistically insignificant levels observed for PDMAEMA and PEG-PDMAEMA polyplexes under identical conditions. This enhancement is linked to the different mechanisms by which micelleplexes are internalized (i.e., caveolar, etc.) compared to PDMAEMA and PEG-PDMAEMA polyplexes. Folate-functionalization significantly improved micelleplex uptake but had negligible influence on gene-silencing efficiency, suggesting that this parameter is not limited by cellular internalization. In vivo biodistribution analysis revealed that siRNA delivered by micelleplexes was more effectively accumulated and retained in tumor tissues than that delivered by PEGylated polyplexes. Overall, the micelle particle size and architecture appear to improve in vitro and in vivo delivery characteristics without significantly changing other properties, such as cytotoxicity and resistance to enzymes and dissociation. The self-assembled nature of micelleplexes is expected to enable incorporation of imaging modalities inside the hydrophobic micelle core, thus combining therapeutic and diagnostic capabilities. The findings from the present study suggest that the micelleplex-type carrier architecture is a useful platform for potential theranostic and tumor-targeting applications.

Oligonucleotide delivery in cancer therapy

IMPORTANCE OF THE FIELD

Cancer is frequently caused by altered protein expression. Oligonucleotides (ONs) are short synthetic nucleic acid fragments, able to selectively correct protein expression into cells by different mechanisms. However, biological barriers hamper the therapeutic use of ONs without suitable delivery strategies.

AREAS COVERED IN THIS REVIEW

This review summarizes the most meaningful non-viral strategies for ON delivery, including the chemical modifications of the ON backbone and non-viral delivery systems.

WHAT THE READER WILL GAIN

The reader will gain an update of the main strategies for ON delivery in cancer. Advantages and limits of each approach are underlined. Emphasis is given to the delivery strategies that contributed to bringing ONs into clinical trials.

TAKE HOME MESSAGE

In the long story of ONs for cancer therapy, the development of delivery strategies has led, in the last few years, to different opportunities to use the high therapeutic potential of these molecules in humans.

Comparative in vivo study of poly(ethylene imine)/siRNA complexes for pulmonary delivery in mice

Pulmonary siRNA delivery offers a new way to treat various lung diseases. Poly(ethylene imines) (PEIs) are promising cationic nanocarriers and various modifications are still under investigations to improve their cytotoxicity and efficacy for siRNA delivery. In this study, we analyzed two different types of PEI-based nanocomplexes in mice after intratracheal administration regarding their toxicity and efficacy in the lungs. Ubiquitously enhanced green fluorescent protein (EGFP) expressing transgenic and BALB/c mice were intratracheally instilled with 35μg siRNA complexed with the different types of PEI nanocarriers. Lung toxicity and inflammation were investigated after 24h, 3d and 7d treatment and knockdown of EGFP expression was analyzed by flow cytometry and fluorescence microscopy five days post instillation. Three different polyplexes caused more than 60% knockdown of EGFP expression, but only the fatty acid modified low molecular weight PEI 8.3kDa (C16-C18-EO25)1.4 specifically reduced EGFP expression in CD45+ leucocytes (25±12%) and CD11b-/CD11c+ lung macrophages (36±14%). Hydrophobic and hydrophilic PEG modifications on PEI caused severe inflammatory response and elevated levels of IgM in broncho-alveolar fluid (BALF). Thus, the PEG modification reduced cytotoxicity, but elevated the immune response and proinflammatory effects. Further investigations of the proinflammatory and immunomodulatory effects of the PEI-modified carriers are necessary to clarify the highly unspecific knockdown effects in the lung in more detail. Nevertheless, the more hydrophobic modification of PEI based non-viral vector system appeared to be a promising approach for improved siRNA therapeutics offering successful pulmonary siRNA delivery.