Cross-linked small polyethylenimines: while still nontoxic, deliver DNA efficiently to mammalian cells in vitro and in vivo

Modulating efficacy and cytotoxicity of lipoamino fatty acid nucleic acid carriers using disulfide or hydrophobic spacers

Double pH-responsive xenopeptides comprising polar ionizable succinoyl tetraethylene pentamine (Stp) motifs and lipophilic ionizable lipoamino fatty acids (LAFs) were recently found to efficiently transfect mRNA and pDNA at low doses. However, potency was often accompanied with cytotoxicity at higher doses. Insertion of bioreducible disulfide building blocks (ssbb) or non-reducible hydrophobic spacers between polar and apolar ionizable domains of LAF-Stp carriers should mitigate toxicity of xenopeptides. Carriers showed stable nucleic acid complexation and endosomal pH-dependent lytic activities, both of which were abolished after reductive cleavage of ssbb-containing carriers. For pDNA, U-shaped carriers with one Stp and two LAF units or bundle carriers with two Stps and four LAFs displayed highest potency. For mRNA, best transfection was achieved with bundle carriers with one Stp and four LAFs. Both the ssbb and hydrophobic spacer containing analogs displayed improved metabolic activity, reduced membrane damage, and improved cell growth. The ssbb carriers were most beneficial regarding living cell count and low apoptosis rates. Mechanistically, inserted spacers decelerated the transfection kinetics and altered the requirement of endosomal protonation. Overall, mRNA and pDNA carriers with improved biocompatibility have been designed, with their high potency illustrated in transfection of various cell lines including low passage number colon carcinoma cells.

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.

Self-assembled redox-responsive BRD4 siRNA nanoparticles: fomulation and its in vitro delivery in gastric cancer cells

With the development of newer biomarkers in the diagnosis of gastric cancer (GC), therapeutic targets are emerging and molecular-targeted therapy is in progress RNA interference has emerged as a promising method of gene targeting therapy. However, naked small interfering RNA (siRNA) is unstable and susceptible to degradation, so employing vectors for siRNA delivery is the focus of our research. Therefore, we developed LMWP modified PEG-SS-PEI to deliver siRNA targeting BRD4 (L-NPs/siBRD4) for GC therapy. L-NPs/siBRD4 were prepared by electrostatic interaction and characterized by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The release characteristics, cellular uptake and intracellular localization were also investigated. The in vitro anticancer activity of the prepared nanoparticles was analysed by MTT, Transwell invasion and wound healing assay. Quantitative real time-polymerase chain reaction (qRT-PCR) and Western blot were used to detect the effect of gene silencing. The results showed that the optimal N/P was 30 and the prepared L-NPs/siBRD4 uniformly distributed in the system with a spherical and regular shape. L-NPs/siBRD4 exhibited an accelerated release in GSH-containing media from 12h to 24h. The uptake of L-NPs/siBRD4 was enhanced and mainly co-localized in the lysosomes. After 6h incubation, LMWP modified PEG-SS-PEI helped siRNA escape from the lysosomes and diffused into the cytoplasm. L-NPs/siBRD4 significantly inhibited the proliferation, migration and invasion of cells. This might be related with the silence of BRD4, then inhibition of PI3K/Akt and c-Myc. Our results demonstrate that L-NPs/siBRD4 are a novel delivery system with anticancer, which may provide a more effective strategy for GC treatment.

Polyethylenimine (PEI) in gene therapy: Current status and clinical applications

Polyethlyenimine (PEI) was introduced 1995 as a cationic polymer for nucleic acid delivery. PEI and its derivatives are extensively used in basic research and as reference formulations in the field of polymer-based gene delivery. Despite its widespread use, the number of clinical applications to date is limited. Thus, this review aims to consolidate the past applications of PEI in DNA delivery, elucidate the obstacles that hinder its transition to clinical use, and highlight potential prospects for novel iterations of PEI derivatives. The present review article is divided into three sections. The first section examines the mechanism of action employed by PEI, examining fundamental aspects of cellular delivery including uptake mechanisms, release from endosomes, and transport into the cell nucleus, along with potential strategies for enhancing these delivery phases. Moreover, an in-depth analysis is conducted concerning the mechanism underlying cellular toxicity, accompanied with approaches to overcome this major challenge. The second part is devoted to the in vivo performance of PEI and its application in various therapeutic indications. While systemic administration has proven to be challenging, alternative localized delivery routes hold promise, such as treatment of solid tumors, application as a vaccine, or serving as a therapeutic agent for pulmonary delivery. In the last section, the outcome of completed and ongoing clinical trials is summarized. Finally, an expert opinion is provided on the potential of PEI and its future applications. PEI-based formulations for nucleic acid delivery have a promising potential, it will be an important task for the years to come to introduce innovations that address PEI-associated shortcomings by introducing well-designed PEI formulations in combination with an appropriate route of administration.

Graphene-encapsulated iron nanoparticles as a non-viral vector for gene delivery into melanoma cells

The rapid progress of nanotechnology has led to use different nanomaterials for biomedical applications. Among them, graphene-encapsulated magnetic nanoparticles (GEMNS) are recognized as next generation carbon nanomaterials in translation cancer research. In this study, we utilized green fluorescence protein (GFP) expression plasmid DNA (pDNA) and GEMNS decorated with branched polyethyleneimine (PEI) to yield a novel transporter (GEMNS-PEI/pDNA) for gene delivery into melanoma cells (B16F10). The efficiency of transfection was examined using PCR and confocal microscopy. The studies show that the as-designed GEMNS-PEI construct is successfully used to transfect the melanoma cells with pDNA and it should be considered as a potent non-viral vector for introducing naked nucleic acids into eucaryotic cells.

Cationic PLGA Nanoparticle Formulations as Biocompatible Immunoadjuvant for Serum Production and Immune Response against Bothrops jararaca Venom

Snakebite envenoming represents a worldwide public health issue. Suitable technologies have been investigated for encapsulated recombinant or native proteins capable of inducing an effective and long-lasting adaptive immune response. Nanoparticles are colloidal dispersions that have been used as drug delivery systems for bioactive biological compounds. Venom-loaded nanoparticles modulate the protein release and activate the immune response to produce specific antibodies. In this study, biocompatible cationic nanoparticles with Bothrops jararaca venom were prepared to be used as a novel immunoadjuvant that shows a similar or improved immune response in antibody production when compared to a conventional immunoadjuvant (aluminum hydroxide). We prepared stable, small-sized and spherical particles with high Bothrops jararaca venom protein association efficiency. The high protein loading efficiency, electrophoresis, and zeta potential results demonstrated that Bothrops jararaca venom is adsorbed on the particle surface, which remained as a stable colloidal dispersion over 6 weeks. The slow protein release occurred and followed parabolic diffusion release kinetics. The in vivo studies demonstrated that venom-loaded nanoparticles were able to produce an immune response similar to that of aluminum hydroxide. The cationic nanoparticles (CNp) as carriers of bioactive molecules, were successfully developed and demonstrated to be a promising immunoadjuvant.

Advancement of cell-penetrating peptides in combating triple-negative breast cancer

Extensive research efforts have been made and are still ongoing in the search for an ideal anti-cancer therapy. Almost all chemotherapeutics require a carrier or vehicle, a drug delivery system that can transport the drug specifically to the targeted cancer cells, sparing normal cells. Cell-penetrating peptides (CPPs) provide an effective and efficient pathway for the intra-cellular transportation of various bioactive molecules in several biomedical therapies. They are now well-recognized as facilitators of intracellular cargo delivery and have excellent potential for targeted anti-cancer therapy. In this review, we explain CPPs, recent progress in the development of new CPPs, and their utilization to transport cargoes such as imaging agents, chemotherapeutics, and short-interfering RNAs (siRNA) into tumor cells, contributing to the advancement of novel tumor-specific delivery systems.

Unmodified and tyrosine-modified polyethylenimines as potential carriers for siRNA: Biophysical characterization and toxicity

Polyethylenimines (PEIs) are being explored as efficient non-viral nanocarriers for nucleic acid delivery in vitro and in vivo. To address limitations regarding PEI efficacy and biocompatibility, modifications of the chemical structure of linear and branched PEIs have been introduced, including grafting with tyrosine. The aim has been to compare linear and branched polyethylenimines of a wider range of different molecular mass with their tyrosine-modified derivatives. To do so, physico-chemical and biological properties of the polymers were investigated. Even in the absence of a negatively charged nucleic acid counterpart, PEIs form particle structures with defined size and surface potential. Tyrosine modification of PEI led to significantly reduced toxicity, while simultaneously increasing interaction with cellular membranes. All the effects were also dependent on the PEI molecular weight and structure (i.e., linear vs. branched). Especially in the case of linear PEIs, the improved membrane interaction also translated into slightly enhanced hemolysis, whereas their genotoxic potential was essentially abolished. Due to the improvement of properties critical for nano-vector efficacy and biocompatibility, our data demonstrate that tyrosine-modified PEIs are very promising and safe nanocarriers for the delivery of small RNAs, like siRNAs and miRNAs.

Polymer-Conjugated Carbon Nanotubes for Biomolecule Loading

Nanomaterials have emerged as an invaluable tool for the delivery of biomolecules such as DNA and RNA, with various applications in genetic engineering and post-transcriptional genetic manipulation. Alongside this development, there has been an increasing use of polymer-based techniques, such as polyethylenimine (PEI), to electrostatically load polynucleotide cargoes onto nanomaterial carriers. However, there remains a need to assess nanomaterial properties, conjugation conditions, and biocompatibility of these nanomaterial-polymer constructs, particularly for use in plant systems. In this work, we develop mechanisms to optimize DNA loading on single-walled carbon nanotubes (SWNTs) with a library of polymer-SWNT constructs and assess DNA loading ability, polydispersity, and both chemical and colloidal stability. Counterintuitively, we demonstrate that polymer hydrolysis from nanomaterial surfaces can occur depending on polymer properties and attachment chemistries, and we describe mitigation strategies against construct degradation. Given the growing interest in delivery applications in plant systems, we also assess the stress response of plants to polymer-based nanomaterials and provide recommendations for future design of nanomaterial-based polynucleotide delivery strategies.

Polymer-Conjugated Carbon Nanotubes for Biomolecule Loading

Nanomaterials have emerged as an invaluable tool for the delivery of biomolecules such as DNA and RNA, with various applications in genetic engineering and post-transcriptional genetic manipulation. Alongside this development, there has been an increasing use of polymer-based techniques, such as polyethylenimine (PEI), to electrostatically load polynucleotide cargoes onto nanomaterial carriers. However, there remains a need to assess nanomaterial properties, conjugation conditions, and biocompatibility of these nanomaterial-polymer constructs, particularly for use in plant systems. In this work, we develop mechanisms to optimize DNA loading on single-walled carbon nanotubes (SWNTs) with a library of polymer-SWNT constructs and assess DNA loading ability, polydispersity, and both chemical and colloidal stability. Counterintuitively, we demonstrate that polymer hydrolysis from nanomaterial surfaces can occur depending on polymer properties and attachment chemistries, and we describe mitigation strategies against construct degradation. Given the growing interest in delivery applications in plant systems, we also assess the stress response of plants to polymer-based nanomaterials and provide recommendations for future design of nanomaterial-based polynucleotide delivery strategies.

Co-delivery of EGFR and BRD4 siRNA by cell-penetrating peptides-modified redox-responsive complex in triple negative breast cancer cells

AIMS

Triple negative breast cancer (TNBC) has drawn more and more attention due to its high mitotic indices, high metastatic rate and poor prognosis. Gene therapy, especially RNA interference (RNAi), has become a promising targeted therapy. However, improvement of transfection efficiency and discovery of target genes are major problems for the delivery of small interfering RNAs (siRNA).

MATERIALS AND METHODS

In the present study, we developed GALA- and CREKA-modified PEG-SS-PEI to deliver siRNAs targeting on EGFR and BRD4 for TNBC therapy. The PEG-SS-PEI/siRNA complexes were prepared by electrostatic interaction and characterized by dynamic light scattering (DLS) and transmission electron microscope (TEM). The release characteristic, stability, cellular uptake and intracellular localization of the complexes were also studied. The effect of the complexes on cell viability was measured in MDA-MB-231 and HUVEC cells. The in vitro anti-tumor activities of the complexes were analyzed by Transwell invasion assay and wound healing assay. The gene silencing effect was evaluated by quantitative real time-polymerase chain reaction (qRT-PCR) and western blot.

KEY FINDINGS

The results revealed that the GALA- and CREKA-modified PEG-SS-PEI/siRNA complexes showed excellent transfection efficiency with redox-sensitive release profile and good biological compatibility. The complexes protected siRNA from the degradation of RNA enzymes. The complexes significantly inhibited the proliferation, invasion and migration of MDA-MB-231 cells via the synergistic inhibition of EGFR/PI3K/Akt and BRD4/c-Myc pathways.

SIGNIFICANCE

Taken together, co-delivery of siEGFR and siBRD4 by GALA-PEG-SS-PEI and CREKA-PEG-SS-PEI may provide a more effective strategy for the treatment of TNBC.

A library of aminoglycoside-derived lipopolymer nanoparticles for delivery of small molecules and nucleic acids

Simultaneous delivery of small molecules and nucleic acids using a single vehicle can lead to novel combination treatments and multifunctional carriers for a variety of diseases. In this study, we report a novel library of aminoglycoside-derived lipopolymers nanoparticles (LPNs) for the simultaneous delivery of different molecular cargoes including nucleic acids and small-molecules. The LPN library was screened for transgene expression efficacy following delivery of plasmid DNA, and lead LPNs that showed high transgene expression efficacies were characterized using hydrodynamic size, zeta potential, 1H NMR and FT-IR spectroscopy, and transmission electron microscopy. LPNs demonstrated significantly higher efficacies for transgene expression than 25 kDa polyethyleneamine (PEI) and lipofectamine, including in presence of serum. Self-assembly of these cationic lipopolymers into nanoparticles also facilitated the delivery of small molecule drugs (e.g. doxorubicin) to cancer cells. LPNs were also employed for the simultaneous delivery of the small-molecule histone deacetylase (HDAC) inhibitor AR-42 together with plasmid DNA to cancer cells as a combination treatment approach for enhancing transgene expression. Taken together, our results indicate that aminoglycoside-derived LPNs are attractive vehicles for simultaneous delivery of imaging agents or chemotherapeutic drugs together with nucleic acids for different applications in medicine and biotechnology.

Dual pH- and GSH-Responsive Degradable PEGylated Graphene Quantum Dot-Based Nanoparticles for Enhanced HER2-Positive Breast Cancer Therapy

Dual stimuli-responsive degradable carbon-based nanoparticles (DS-CNPs) conjugated with Herceptin (HER) and polyethylene glycol (PEG) have been designed for the treatment of HER2-positive breast cancer. Each component has been linked through disulfide linkages that are sensitive to glutathione in a cancer microenvironment. β-cyclodextrin (β-CD) on the surface of DS-CNPs formed an inclusion complex (DL-CNPs) with doxorubicin (DOX) at a high loading capacity of 5.3 ± 0.4%. In response to a high level of glutathione (GSH) and low pH in a tumor environment, DL-CNPs were rapidly degraded and released DOX in a controlled manner via disruption of host-guest inclusion. These novel DL-CNPs exhibited high cellular uptake with low toxicity, which induced the efficient inhibition of antitumor activity both in vitro and in vivo. Cell viability, confocal laser scanning microscopy, and animal studies indicate that DL-CNPs are a great platform with a synergistically enhanced antitumor effect from the dual delivery of HER and DOX in DL-CNPs.

Non-viral transfection vectors: are hybrid materials the way forward?

Transfection is a process by which oligonucleotides (DNA or RNA) are delivered into living cells. This allows the synthesis of target proteins as well as their inhibition (gene silencing). However, oligonucleotides cannot cross the plasma membrane by themselves; therefore, efficient carriers are needed for successful gene delivery. Recombinant viruses are among the earliest described vectors. Unfortunately, they have severe drawbacks such as toxicity and immunogenicity. In this regard, the development of non-viral transfection vectors has attracted increasing interests, and has become an important field of research. In the first part of this review we start with a tutorial introduction into the biological backgrounds of gene transfection followed by the classical non-viral vectors (cationic organic carriers and inorganic nanoparticles). In the second part we highlight selected recent reports, which demonstrate that hybrid vectors that combine key features of classical carriers are a remarkable strategy to address the current challenges in gene delivery.

Development of a Biocompatible Copolymer Nanocomplex to Deliver VEGF siRNA for Triple Negative Breast Cancer

Triple negative breast cancer (TNBC) is the most difficult breast cancer subtype to treat. TNBC patients have significantly higher expression of vascular endothelial growth factor (VEGF) in tumors compared to non-TNBC patients. VEGF not only exerts its pro-angiogenic effects on endothelial cells but also acts as a survival and autocrine growth factor for VEGF receptor (VEGFR) expressing cancer cells. Silencing the expression of VEGF is therefore a potential therapy for TNBC.

Methods: A novel biocompatible linear copolymer poly[bis(ε-Lys-PEI)Glut-PEG] (PLEGP) was developed to deliver VEGF siRNA for TNBC therapy. The copolymer is composed of lysine and glutaric acid, a natural metabolite of amino acids in the body. Low-molecular weight polyethyleneimine (PEI) was grafted to the copolymer to efficiently condense siRNA into nanocomplex without inducing cytotoxicity. Various in vitro studies were performed to evaluate the stability, cellular uptake, tumor penetration, and biological activities of the VEGF siRNA nanocomplex. The anti-tumor activities of the nanocomplex was also evaluated in an orthotopic TNBC mouse model.

Results: PEIs with different molecular weights were evaluated, and the copolymer PLEGP₁₈₀₀ was able to easily form a stable nanocomplex with siRNAs and protect them from serum degradation. The siRNA/PLEGP₁₈₀₀ nanocomplex exhibited negligible cytotoxicity but showed high cellular uptake, high transfection efficiency, and high tumor penetration. In vitro activity studies showed that the siRNA nanocomplex significantly inhibited migration and invasion of TNBC cells. Moreover, the VEGF siRNA nanocomplex efficiently inhibited tumor growth in an orthotopic TNBC mouse model and down-regulated VEGF expression in the tumor.

Conclusion: PLEGP₁₈₀₀ is a safe and efficient copolymer to deliver siRNAs for TNBC therapy. It could potentially be applied to other cancers by changing the cargo and incorporating tumor-specific ligands.

Addition of free poloxamer 407 to a new gene vector P407-PEI-K12 solution forms a sustained-release in situ hypergel that enhances cell transfection and extends gene expression

To address the concern around the efficiency/cytotoxicity ratio and the tumor-targeting effects of polyethylenimine (PEI), is a non-viral gene vector used for the delivery of the cancer therapy gene, poloxamer 407 (P407)-PEI-K12, was synthesized by cross-linking low-molecular weight PEI with P407 and further coupling a bifunctional peptide, K12, which is comprised of the tumor-targeting peptide tLyP-1 and the nuclear localization sequence. Furthermore, the addition of free P407 into the polymer/DNA complex solution produced a temperature-sensitive in situ gel-P407/P407-PEI-K12/DNA complex, which improved the effects of sustained-release gene delivery and transfection efficiency. The specificity, cytotoxicity and gene transfection efficiency of P407-PEI-K12 was investigated in Hela cells in vitro. The polymer efficiently prevented the degradation of plasmid DNA by DNase I and had a marked ability for serum tolerance. Agarose gel electrophoresis revealed that plasmid DNA was efficiently condensed and protected. The higher transfection efficiency of P407-PEI-K12h (the molar ratio of P407-PEI and K12 is 1:10) was achieved with a polymer and plasmid DNA ratio (w/w) of 20:1. The ability of free P407 to promote the transfection of the polymer/DNA complex was high (0.09%). The half-life of the P407/P407-PEI-K12-h/DNA gel complex was 228 min, and the transfection efficiency of the P407/P407-PEI-K12-h/DNA complex was markedly higher compared to that of the P407-PEI-K12-h/DNA complex at various release times.

Structure-function relationships of nonviral gene vectors: Lessons from antimicrobial polymers

In recent years, substantial advances have been achieved in the design and synthesis of nonviral gene vectors. However, lack of effective and biocompatible vectors still remains a major challenge that hinders their application in clinical settings. In the past decade, there has been a rapid expansion of cationic antimicrobial polymers, due to their potent, rapid, and broad-spectrum biocidal activity against resistant microbes, and biocompatible features. Given that antimicrobial polymers share common features with nonviral gene vectors in various aspects, such as membrane affinity, functional groups, physicochemical characteristics, and unique macromolecular architectures, these polymers may provide us with inspirations to overcome challenges in the design of novel vectors toward more safe and efficient gene delivery in clinic. Building off these observations, we provide here an overview of the structure-function relationships of polymers for both antimicrobial applications and gene delivery by elaborating some key structural parameters, including functional groups, charge density, hydrophobic/hydrophilic balance, MW, and macromolecular architectures. By borrowing a leaf from antimicrobial agents, great advancement in the development of newer nonviral gene vectors with high transfection efficiency and biocompatibility will be more promising. STATEMENT OF SIGNIFICANCE: The development of gene delivery is still in the preclinical stage for the lack of effective and biocompatible vectors. Given that antimicrobial polymers share common features with gene vectors in various aspects, such as membrane affinity, functional groups, physicochemical characteristics, and unique macromolecular architectures, these polymers may provide us with inspirations to overcome challenges in the design of novel vectors toward more safe and efficient gene delivery in clinic. In this review, we systematically summarized the structure-function relationships of antimicrobial polymers and gene vectors, with which the design of more advanced nonviral gene vectors is anticipated to be further boosted in the future.

Comparative analysis and optimization of protocols for producing recombinant lentivirus carrying the anti-Her2 chimeric antigen receptor gene

BACKGROUND

The production of anti-Her2 chimeric antigen receptor (CAR) T cells needs to be optimized to make it a reliable therapy.

METHODS

Three types of lentiviral vectors expressing anti-Her2 CAR together with packaging plasmids were co-transfected into 293 T-17 cells. The vector with the best packaging efficiency was selected, and the packaging cell culture system and packaging plasmid system were optimized. Centrifugation speed was optimized for the concentration of lentivirus stock. The various purification methods used included membrane filtration, centrifugation with a sucrose cushion and the novelly-designed instantaneous high-speed centrifugation. The recombinant lentiviruses were transduced into human peripheral T cells with an optimized multiplicity of infection (MOI). CAR expression levels by three vectors and the efficacy of CAR-T cells were compared.

RESULTS

When co-transfected, packaging cells in suspension were better than the commonly used adherent culture condition, with the packaging system psPAX2/pMD2.G being better than pCMV-dR8.91/pVSV-G. The optimal centrifugation speed for concentration was 20 000 g, rather than the generally used ultra-speed. Importantly, adding instantaneous centrifugation for purification significantly increased human peripheral T cell viability (from 13.25% to 62.80%), which is a technical breakthrough for CAR-T cell preparation. The best MOI value for transducing human peripheral T cells was 40. pLVX-EF1a-CAR-IRES-ZsGreen1 expressed the highest level of CAR in human peripheral T cells and the cytotoxicity of CAR-T cells reached 63.56%.

CONCLUSIONS

We optimized the preparation of recombinant lentivirus that can express third-generation anti-Her2 CAR in T cells, which should lay the foundation for improving the efficacy of CAR-T cells with respect to killing target cells.

Dual-responsive polyplexes with enhanced disassembly and endosomal escape for efficient delivery of siRNA

Despite the extracellular barriers for siRNA delivery have been overcome by utilizing advanced nanoparticle delivery systems, the key intracellular barriers after internalization including efficient disassembly of siRNA and endosomal escape still remains challenging. To address the issues, we developed a unique pH- and redox potential-responsive polyplex delivery system based on the copolymer of mPEG-b-PLA-PHis-ssPEI1.8 k, which is composed of a pH-responsive copolymer of PEG-b-PLA-PHis (Mw 5 k) and a branched PEI (Mw1.8 k) linked with redox cleavable disulfide bond. The copolymer showed excellent siRNA complexation and protection abilities against endogenous substances at the relatively low N/P ratio of 6. The siRNA release from the polyplexes (N/P 6) was markedly increased from 13.62% to 58.67% under conditions simulating the endosomal microenvironment. Fluorescence resonance energy transfer (FRET) test also indicated a higher disassembly extent of siRNA from the copolymer. The accelerated siRNA release from the polyplexes was markedly restrained when the N/P ratio was raised above 10 due to the increasing of electrostatic interactions. The efficient endosomal escape of siRNA after internalization was confirmed by confocal microscopy, which was attributed to the cleavaged PEI chains inducing membrane destabilization, the "proton sponge effect" of PHis and PEI as well as the relative small size of after disassembly. The enhanced disassembly and endosomal escape were elucidated as the leading cause for polyplexes (N/P 6) showed more efficient Bcl-2 silencing (85.45%) than those polyplexes with higher N/P ratios (N/P 10 and 15). In vivo results further demonstrated that polyplexes (N/P 6) delivery of siBcl-2 significantly inhibited the MCF-7 breast tumor growth as compared to its counterparts. The incorporation of convertible non-electrical interactions at a balance with electrostatic interactions in complexation siRNA has been demonstrated as an effective strategy to achieve efficient disassembly from stable polyplexes. Moreover, polyplexes equipped with the enhanced disassembly and endosomal escape provides a new potential way to tackle the intracellular delivery bottleneck for siRNA delivery.

Redox-triggered intracellular siRNA delivery

Stimuli-sensitive nanoformulation achieved successful intracellular siRNA delivery and GFP downregulation due to GSH-triggered disulfide bond breakage and PEG-de-shielding without toxicity.

Aromatic Modification of Low Molecular Weight PEI for Enhanced Gene Delivery

Low molecular weight polyethylenimine (1800 Da, also referred to as oligoethylenimines, OEI) was modified with amino acids, including two aromatic amino acids (tryptophan, phenylalanine) and an aliphatic amino acid (leucine). The substitution degree of amino acids could be controlled by adjusting the feeding mole ratio of the reactants. Fluorescence spectroscopy and circular dichroism experiments demonstrated that the indole ring of tryptophan may intercalate into the DNA base pairs and contribute to efficient DNA condensation. In vitro gene expression results revealed that the modified OEIs (OEI-AAs) may provide higher transfection efficiency even than high molecular weight polyethylenimine (25 kDa, PEI), especially the aromatic tryptophan substituted OEI. Moreover, OEI-AAs exhibited excellent serum tolerance, and up to 137 times higher transfection efficiency than PEI 25 kDa that was obtained in the presence of serum. The cytotoxicity of OEI-AAs is much lower than PEI 25 kDa. This study may afford a new method for the development of low molecular weight oligomeric non-viral gene vectors with both high efficiency and biocompatibility.

Preparation, characterization, and transfection efficiency of low molecular weight polyethylenimine-based nanoparticles for delivery of the plasmid encoding CD200 gene

Various strategies have been utilized to improve both gene transfer efficiency and cell-induced toxicity of polyethylenimine (PEI), the most extensively investigated cationic polymeric vector. In this study, we sought to enhance transfection efficiency of low molecular weight PEI (LMW PEI) while maintaining its low toxicity by cross-linking LMW PEI via succinic acid linker. These modifications were designed to improve the hydrophilic–hydrophobic balance of the polymer, by enhancing the buffering capacity and maintaining low cytotoxic effects of the final conjugate. Decreased expression of CD200 in the central nervous system has been considered as one of the proposed mechanisms associated with neuroinflammation in multiple sclerosis; therefore, we selected plasmid-encoding CD200 gene for transfection using the modified PEI derivatives. Dynamic light scattering experiments demonstrated that the modified PEIs were able to condense plasmid DNA and form polyplexes with a size of approximately 130 nm. The highest level of CD200 expression was achieved at a carrier to plasmid ratio of 8, where the expression level was increased by 1.5 fold in the SH-SY5Y cell line, an in vitro model of neurodegenerative disorders. Furthermore, the results of in vivo imaging of the LMW PEI-based nanoparticles in the mouse model of multiple sclerosis revealed that fluorescently labeled plasmid encoding CD200 was distributed from the injection site to various tissues and organs including lymph nodes, liver, brain, and finally, kidneys. The nanoparticles also showed the ability to cross the blood–brain barrier and enter the periventricular area.

A targeted drug delivery system based on folic acid-functionalized upconversion luminescent nanoparticles

In this paper, multifunctional upconversion luminescent NaYF₄:Yb,Er nanoparticles with excellent hollow mesoporous structure were first fabricated. The effects of various reaction conditions on the morphology and size of the as-prepared samples were investigated in detail and Ostwald ripening effect was adapted to explain the formation mechanism of the HMUCNPs. Then, folic acid, a well-known ligand for the selective targeting of drugs into tumor cells, was conjugated to the surface of the hollow mesoporous structured upconversion luminescent nanoparticles (HMUCNPs) via amide reaction for targeted delivery of anticancer drugs so as to enhance the therapeutic efficacy. The properties were extensively studied, which indicated the obtained samples showed a typical hollow mesoporous structure and excellent upconversion luminescence that were useful for cell imaging and drug delivery. Drug storage/release properties were demonstrated to be pH responsive, in which the drug release might be beneficial at the reduced pH in certain cancerous tissues for targeted release and controlled therapy at the pathological sites. Meanwhile, DOX-NaYF₄:Yb,Er-FA HMUCNPs exhibited greater cytotoxicity than free doxorubicin hydrochloride because folic acid-conjugated HMUCNPs can be specifically taken up by FR-positive KB cells via a receptor-mediated endocytosis. Therefore, the folic acid-functionalized nanoparticles combining upconversion luminescent property and hollow mesoporous structure have potential for simultaneous targeted anticancer drug delivery and cell imaging.

Transfection of bovine fetal fibroblast with polyethylenimine (PEI) nanoparticles: effect of particle size and presence of fetal bovine serum on transgene delivery and cytotoxicity

The development of efficient transfection protocols for livestock cells is crucial for implementation of cell-based transgenic methods to produce genetically modified animals. We synthetized fully deacylated linear 22, 87 and 217 kDa polyethylenimine (PEI) nanoparticles and compared their transfection efficiency and cytotoxicity to commercial branched 25 kDa PEI and linear 58 kDa poly(allylamine) hydrochloride. We studied the effect of PEI size and presence of serum on transfection efficiency on primary cultures of bovine fetal fibroblasts and established cells lines (HEK 293 and Hep G2). We found that transfection efficiency was affected mainly by polymer/pDNA ratio and DNA concentration and in less extent by PEI MW. In bovine fibroblast, preincubation of PEI nanoparticles with fetal bovine serum (FBS) greatly increased percentage of cells expressing the transgene (up to 82%) while significantly decreased the polymer cytotoxic effect. 87 and 217 kDa PEI rendered the highest transfection rates in HEK 293 and Hep G2 cell lines (>50% transfected cells) with minimal cell toxicity. In conclusion, our results indicate that fully deacylated PEI of 87 and 217 kDa are useful DNA vehicles for non-viral transfection of primary cultures of bovine fetal fibroblast and HEK 293 and Hep G2 cell lines.

3rd generation poly(ethylene imine)s for gene delivery

In this study, a series of high molar mass poly(2-oxazoline)-based copolymers was synthesized, introducing 2-ethyl-2-oxazoline, ethylene imine, and primary amine bearing monomer units representing a new generation of PEI.

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.

Alkyl cross-linked low molecular weight polypropyleneimine dendrimers as efficient gene delivery vectors

OBJECTIVES

In recent years, polypropyleneimine (PPI) dendrimers have attracted great interest as non-viral gene delivery systems because of their attractive features including highly branched architecture with number of reactive end groups. However, without being structurally modified, they are not efficient gene carriers. In the present study, generation 2 and 3 (G2 and G3) of PPI dendrimers were conjugated with alkylcarboxylate groups as linker to enhance the transfection efficiency while maintaining their low cell toxicity.

MATERIALS AND METHODS

First, 10-bromodecanoic acid was covalently attached to all available surface primary amines of PPI G2 and G3 to increase their lipophilicity. In the subsequent step, PPIs were conjugated to the alkylcarboxylate groups of alkylcarboxylate-PPI derivatives to increase the number of surface primary amines. Physicochemical properties of modified PPIs were determined. Transfection experiments (using both luciferase and green fluorescent protein (GFP)- expressing plasmids) and cytotoxicity assay were performed to evaluate the efficiency of the final derivatives.

RESULTS

Fabricated vectors condensed DNA effectively so that polyplexes with appropriate size (below 155 nm) and positive surface charge were constructed. Cross-linked low molecular weight PPIs (G2 or G3) with decanoate linkage increased transfection efficiency significantly while maintaining the low cytotoxicity. PPI G2 derivative exhibited increased buffering capacity which is believed to be responsible for better proton sponge mechanism leading to higher transfection efficiency.

CONCLUSION

Our results indicated that oligomerization of low molecular weight PPI (PPI G2-alkyl-PPI G2 conjugate) could be an approach to increase the transfection efficiency and to lower the cytotoxicity of low molecular weight polycations.

Recent advances in siRNA delivery

In the 1990s an unexpected gene-silencing phenomena in plants, the later called RNA interference (RNAi), perplexed scientists. Following the proof of activity in mammalian cells, small interfering RNAs (siRNAs) have quickly crept into biomedical research as a new powerful tool for the potential treatment of different human diseases based on altered gene expression. In the past decades, several promising data from ongoing clinical trials have been reported. However, despite surprising successes in many pre-clinical studies, concrete obstacles still need to be overcome to translate therapeutic siRNAs into clinical reality. Here, we provide an update on the recent advances of RNAi-based therapeutics and highlight novel synthetic platforms for the intracellular delivery of siRNAs.

Evaluation of a nanotechnology-based approach to induce gene-expression in human THP-1 macrophages under inflammatory conditions

Macrophages orchestrate the initiation and resolution of inflammation by producing pro- and anti-inflammatory products. An imbalance in these mediators may originate from a deficient or excessive immune response. Therefore, macrophages are valid therapeutic targets to restore homeostasis under inflammatory conditions. We hypothesize that a specific mannosylated nanoparticle effectively induces gene expression in human macrophages under inflammatory conditions without undesirable immunogenic responses. THP-1 macrophages were challenged with lipopolysaccharide (LPS, 5μg/mL). Polyethylenimine (PEI) nanoparticles grafted with a mannose receptor ligand (Man-PEI) were used as a gene delivery method. Nanoparticle toxicity, Man-PEI cellular uptake rate and gene induction efficiency (GFP, CD14 or CD68) were studied. Potential immunogenic responses were evaluated by measuring the production of tumor necrosis factor-alpha (TNF-α), Interleukin (IL)-6 and IL-10. Man-PEI did not produce cytotoxicity, and it was effectively up-taken by THP-1 macrophages (69%). This approach produced a significant expression of GFP (mRNA and protein), CD14 and CD68 (mRNA), and transiently and mildly reduced IL-6 and IL-10 levels in LPS-challenged macrophages. Our results indicate that Man-PEI is suitable for inducing an efficient gene overexpression in human macrophages under inflammatory conditions with limited immunogenic responses. Our promising results set the foundation to test this technology to induce functional anti-inflammatory genes.

Therapeutic nucleic acids: current clinical status

Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are simple linear polymers that have been the subject of considerable research in the last two decades and have now moved into the realm of being stand-alone therapeutic agents. Much of this has stemmed from the appreciation that they carry out myriad functions that go beyond mere storage of genetic information and protein synthesis. Therapy with nucleic acids either uses unmodified DNA or RNA or closely related compounds. From both a development and regulatory perspective, they fall somewhere between small molecules and biologics. Several of these compounds are in clinical development and many have received regulatory approval for human use. This review addresses therapeutic uses of DNA based on antisense oligonucleotides, DNA aptamers and gene therapy; and therapeutic uses of RNA including micro RNAs, short interfering RNAs, ribozymes, RNA decoys and circular RNAs. With their specificity, functional diversity and limited toxicity, therapeutic nucleic acids hold enormous promise. However, challenges that need to be addressed include targeted delivery, mass production at low cost, sustaining efficacy and minimizing off-target toxicity. Technological developments will hold the key to this and help accelerate drug approvals in the years to come.

Poly(ester amine) constructed from polyethylenimine and pluronic for gene delivery in vitro and in vivo

A series of poly (ester amines) (PEAs) constructed from low molecular weight polyethyleneimine (LPEI, Mw: 0.8k, 1.2k Da) and Pluronic (different molecular weight (Mw) and hydrophilic-lipophilic-balance (HLB)) components were synthesized, and evaluated in vitro and in vivo as gene delivery carriers. Most PEA polymers were able to bind and condense plasmid DNA effectively into particles of approximately 150 nm in solution at the polymer/DNA ratio of 5 and above. Transfection efficiency of the PEA polymers depends on particle size of the polymer/DNA complex, molecular weight and HLB of the Pluronics and the size of PEI within PEA composition, as well as the cell type. Significant improvement in gene delivery efficacy was achieved with PEA01/04/05 composed of Pluronic size (Mw: 3000-5000 Da), and HLB (12-18) in CHO, C2C12 and HSkM cell lines; and the effective transfection was reflected with PEA 01/04/07 composed of Pluronics with size (2000-5000 Da) and HLB (12-23) in mdx mice. The best formulation for pDNA delivery was obtained with PEA 01 producing transgene expression efficiency 5, 19-folds of that of PEI 25k in vitro and in vivo, respectively. These results potent some of these PEA polymers as attractive vehicles for gene or oligonucleotide delivery.

Facile carbohydrate-mimetic modifications of poly(ethylene imine) carriers for gene delivery applications

PEI was chemically-modified with carbohydrates and carbohydrate-mimetics to improve biocompatibility.

Screening PEGylated polyethylenimine derivatives for safe and efficient delivery of gene materials

PEG–Et 1 : 1 was screened out for the safe and efficient gene delivery by precise design of PEGylated polymeric nanomaterials.

Antisense precision polymer micelles require less poly(ethylenimine) for efficient gene knockdown

Therapeutic nucleic acids are powerful molecules for shutting down protein expression. However, their cellular uptake is poor and requires transport vectors, such as cationic polymers. Of these, poly(ethylenimine) (PEI) has been shown to be an efficient vehicle for nucleic acid transport into cells. However, cytotoxicity has been a major hurdle in the development of PEI-DNA complexes as clinically viable therapeutics. We have synthesized antisense-polymer conjugates, where the polymeric block is completely monodisperse and sequence-controlled. Depending on the polymer sequence, these can self-assemble to produce micelles of very low polydispersity. The introduction of linear poly(ethylenimine) to these micelles leads to aggregation into size-defined PEI-mediated superstructures. Subsequently, both cellular uptake and gene silencing are greatly enhanced over extended periods compared to antisense alone, while at the same time cellular cytotoxicity remains very low. In contrast, gene silencing is not enhanced with antisense polymer conjugates that are not able to self-assemble into micelles. Thus, using antisense precision micelles, we are able to achieve significant transfection and knockdown with minimal cytotoxicity at much lower concentrations of linear PEI then previously reported. Consequently, a conceptual solution to the problem of antisense or siRNA delivery is to self-assemble these molecules into 'gene-like' micelles with high local charge and increased stability, thus reducing the amount of transfection agent needed for effective gene silencing.

Synthesis and evaluation of a glutamic acid-modified hPAMAM complex as a promising versatile gene carrier

Hyperbranched poly(amidoamine) (HPAMAM), structurally analogous to polyamidoamine dendrimer (PAMAM) dendrimers, has been suggested to be an effective carrier for gene delivery. In the present study, glutamic acid-modified hPAMAM was developed as a novel non-viral gene carrier for the first time. The hPAMAM was synthesized by using a modified one-pot method. DNA was found to be bound to hPAMAM at different weight ratios (WhPAMAM/WDNA). The resulting HPAMAM-Glu20 was able to efficiently protect the encapsulated-DNA against degradation for over 2 h. In addition to low cytotoxicity, the transfection efficiency of hPAMAM-Glu20 represented much higher (p < 0.05) than that of Lipofectamine 2000 in both MCF7 and MDA-MB231 cells. Cellular uptake of the hPAMAM-Glu20 in MDA-MB231 cells, 173.56 ± 1.37%, was significantly higher than that of MCF7 cells, 65.00 ± 1.73% (p < 0.05). The results indicated that hPAMAM-Glu20-mediated gene delivery to breast cancer cells is a feasible and effective strategy that may provide a new therapeutic avenue as a non-viral gene delivery carrier. In addition, it was found that hPAMAM-glutamic amino acid (Glu)-based gene delivery is an economical, effective and biocompatible method.

Lipid nanoparticles for short interfering RNA delivery

The discovery of RNA interference (RNAi) in mammalian cells has created a new class of therapeutics based on the reversible silencing of specific disease-causing genes. This therapeutic potential depends on the ability to deliver inducers of RNAi, such as short-interfering RNA (siRNA) and micro-RNA (miRNA), to cells of target tissues. This chapter reviews various challenges and delivery strategies for siRNA, with a particular focus on the development of lipid nanoparticle (LNP) delivery technologies. Currently, LNP delivery systems are the most advanced technology for systemic delivery of siRNA, with numerous formulations under various stages of clinical trials. We also discuss methods to improve gene silencing potency of LNP-siRNA, as well as application of LNP technologies beyond siRNA to the encapsulation of other nucleic acids such as mRNA and clustered regularly interspaced short palindromic repeats (CRISPR).