Poly(propylacrylic acid) enhances cationic lipid-mediated delivery of antisense oligonucleotides

Poly(2-Propylacrylic Acid) Increases In Vitro Bioactivity of Chitosan/mRNA Nanoparticles

Chitosan-based nanoparticles have been extensively studied for the delivery of nucleic acids. Previous results suggest that these nanoparticles have limited ability to escape the endosome, one of the main cellular barriers hindering nucleic acid delivery. Escape can be improved by the addition of endosomolytic agents during the formulation process or by developing delivery systems with intrinsic properties to disrupt endosomal membranes. In this study, Poly(2-Propylacrylic Acid) (PPAA), an anionic synthetic polymer with known membrane lytic activity was added to the binary chitosan/mRNA nanoparticles to improve bioactivity. The ionization behavior of PPAA was characterized to identify conditions in which PPAA is sufficiently charged to interact electrostatically with chitosan and thus form nanoparticles. The physicochemical characteristics (hydrodynamic diameter, polydispersity index, ζ-potential) and the in vitro transfection efficiency (bioactivity) of this new family of CS/mRNA/PPAA ternary nanoparticles were evaluated. The addition of PPAA to CS/mRNA nanoparticles was shown to be an efficient strategy to augment in vitro bioactivity. The optimal formulation reached an expression level  ~86% of the commercial lipid control at pH 6.5 without any signs of metabolic toxicity. In this paper, we report the effect of salt and pH on the ionization behavior of PPAA and demonstrate 1) successful incorporation of PPAA into/onto nanoparticles, 2) improved bioactivity with PPAA, and 3) that the kosmotropic effects of trehalose play a minimal role in the apparent increase in bioactivity in presence of trehalose.

pH-Responsive Amphiphilic Carboxylate Polymers: Design and Potential for Endosomal Escape

The intracellular delivery of emerging biomacromolecular therapeutics, such as genes, peptides, and proteins, remains a great challenge. Unlike small hydrophobic drugs, these biotherapeutics are impermeable to the cell membrane, thus relying on the endocytic pathways for cell entry. After endocytosis, they are entrapped in the endosomes and finally degraded in lysosomes. To overcome these barriers, many carriers have been developed to facilitate the endosomal escape of these biomacromolecules. This mini-review focuses on the development of anionic pH-responsive amphiphilic carboxylate polymers for endosomal escape applications, including the design and synthesis of these polymers, the mechanistic insights of their endosomal escape capability, the challenges in the field, and future opportunities.

An anionic, endosome-escaping polymer to potentiate intracellular delivery of cationic peptides, biomacromolecules, and nanoparticles

Peptides and biologics provide unique opportunities to modulate intracellular targets not druggable by conventional small molecules. Most peptides and biologics are fused with cationic uptake moieties or formulated into nanoparticles to facilitate delivery, but these systems typically lack potency due to low uptake and/or entrapment and degradation in endolysosomal compartments. Because most delivery reagents comprise cationic lipids or polymers, there is a lack of reagents specifically optimized to deliver cationic cargo. Herein, we demonstrate the utility of the cytocompatible polymer poly(propylacrylic acid) (PPAA) to potentiate intracellular delivery of cationic biomacromolecules and nano-formulations. This approach demonstrates superior efficacy over all marketed peptide delivery reagents and enhances delivery of nucleic acids and gene editing ribonucleoproteins (RNPs) formulated with both commercially-available and our own custom-synthesized cationic polymer delivery reagents. These results demonstrate the broad potential of PPAA to serve as a platform reagent for the intracellular delivery of cationic cargo.

Pestiviral E(rns) blocks TLR-3-dependent IFN synthesis by LL37 complexed RNA

The ribonuclease activity of the soluble glycoprotein E(rns) of pestiviruses represents a unique mechanism to circumvent the host's innate immune system by blocking interferon type-I synthesis in response to extracellularly added single- (ss) and double-stranded (ds) RNA. However, the reason why pestiviruses encode a ribonuclease in addition to the abundant serum RNases remained elusive. Here, we show that the 5' UTR and NS5B regions of various strains of the RNA genome of the pestivirus bovine viral diarrhea virus (BVDV) are resistant to serum RNases and are potent TLR-3 agonists. Inhibitory activity of E(rns) was restricted to cleavable RNA products, and did not extend to the synthetic TLR-7/8 agonist R-848. RNA complexed with the antimicrobial peptide LL37 was protected from degradation by E(rns)in vitro but was fully inhibited by E(rns) in its ability to induce IFN in cell cultures, suggesting that the viral protein is mainly active in cleaving RNA in an intracellular compartment. We propose that secreted E(rns) represents a potent IFN antagonist, which degrades viral RNA that is resistant to the ubiquitous host RNases in the extracellular space. Thus, the viral RNase prevents its own pathogen-associated molecular pattern (PAMP) to inadvertently activate the IFN response that might break innate immunotolerance required for persistent pestivirus infections.

Delivery of antisense oligonucleotides using poly(alkylene oxide)-poly(propylacrylic acid) graft copolymers in conjunction with cationic liposomes

The clinical application of gene silencing is hindered by poor stability and low delivery efficiency of naked oligonucleotides. Here, we present the in vitro and in vivo behaviors of a rationally designed, ternary, self-assembled nanoparticle complex, consisting of an anionic copolymer, cationic DOTAP liposome, and antisense oligonucleotide (AON). The multifunctional copolymers are based on backbone poly(propylacrylic acid) (PPAA), a pH-sensitive hydrophobic polymer, with grafted poly(alkylene oxides) (PAOs) varying in extent of grafting and PAO chemistry. The nanoparticle complexes with PPAA-g-PAO copolymers enhance antisense gene silencing effects in A2780 human ovarian cancer cells. A greater amount of AON is delivered to ovarian tumor xenografts using the ternary copolymer-stabilized delivery system, compared to a binary DOTAP/AON complex, following intraperitoneal injection in mice. Further, intratumoral injection of the nanoparticle complexes containing 1 mol% grafted PAO reduced tumoral bcl-2 expression by up to 60%. The data for complexes across the set of PAO polymers support a strong role for the hydrophilic-lipophilic balance of the graft copolymer in achieving serum stability and cellular uptake. Based upon these results, we anticipate that this novel nanoparticle delivery system can be extended to the delivery of plasmid DNA, siRNA, or aptamers for preclinical and clinical development.

Recent trends of polymer mediated liposomal gene delivery system

Advancement in the gene delivery system have resulted in clinical successes in gene therapy for patients with several genetic diseases, such as immunodeficiency diseases, X-linked adrenoleukodystrophy (X-ALD) blindness, thalassemia, and many more. Among various delivery systems, liposomal mediated gene delivery route is offering great promises for gene therapy. This review is an attempt to depict a portrait about the polymer based liposomal gene delivery systems and their future applications. Herein, we have discussed in detail the characteristics of liposome, importance of polymer for liposome formulation, gene delivery, and future direction of liposome based gene delivery as a whole.

Surface modification of nonviral nanocarriers for enhanced gene delivery

Biomedical nanotechnology has given a new lease of life to gene therapy with the ever-developing and ever-diversifying nonviral gene delivery nanocarriers. These are designed to pass a series of barriers in order to bring their nucleic acid cargo to the right subcellular location of particular cells. For a given application, each barrier has its dedicated strategy, which translates into a physicochemical, biological and temporal identity of the nanocarrier surface. Different strategies have thus been explored to implement adequate surface identities on nanocarriers over time for systemic delivery. In that context, this review will mainly focus on organic nanocarriers, for which these strategies will be described and discussed.

Exploiting endocytosis for nanomedicines

In this article, we briefly review the endocytic pathways used by cells, pointing out their defining characteristics and highlighting physical limitations that may direct the internalization of nanoparticles to a subset of these pathways. A more detailed description of these pathways is presented in the literature. We then focus on the endocytosis of nanomedicines and present how various nanomaterial parameters impact these endocytic processes. This topic is an area of active research, motivated by the recognition that an improved understanding of how nanomaterials interact at the molecular, cellular, and whole-organism level will lead to the design of better nanomedicines in the future. Next, we briefly review some of the important nanomedicines already on the market or in clinical development that serve to exemplify how endocytosis can be exploited for medical benefit. Finally, we present some key unanswered questions and remaining challenges to be addressed by the field.

Multifunctional nanocarrier based on clay nanotubes for efficient intracellular siRNA delivery and gene silencing

RNA interference-mediated gene silencing relating to disease has recently emerged as a powerful method in gene therapy. Despite the promises, effective transport of siRNA with minimal side effects remains a challenge. Halloysites are cheap and naturally available aluminosilicate clay nanotubes with high mechanical strength and biocompatibility. In this study, a novel multifunctional nanocarrier based on functionalized halloysite nanotubes (f-HNTs) has been developed via electrostatic layer-by-layer assembling approach for loading and intracellular delivery of therapeutic antisurvivin siRNA and simultaneously tracking their intracellular transport, in which PEI-modified HNTs are used as gene vector, antisurvivin siRNA as gene therapeutic agent, and mercaptoacetic acid-capped CdSe quantum dots as fluorescent labeling probes. The successful assembly of the f-HNTs-siRNA complexes was systematically characterized by transmission electron microscopy (TEM), UV-visible spectrophotometry, Zeta potential measurement, fluorescence spectrophotometry, and electrochemical impedance spectroscopy. Confocal microscopy, biological TEM, and flow cytometry studies revealed that the complexes enabled the efficient intracellular delivery of siRNA for cell-specific gene silencing. MTT assays exhibited that the complexes can enhance antitumor activity. Furthermore, Western blot analysis showed that f-HNTs-mediated siRNA delivery effectively knocked down gene expression of survivin and thereby decreased the levels of target proteins of PANC-1 cells. Therefore, this study suggested that the synthesized f-HNTs were a new effective drug delivery system for potential application in cancer gene therapy.

Delivery of siRNA silencing Runx2 using a multifunctional polymer-lipid nanoparticle inhibits osteogenesis in a cell culture model of heterotopic ossification

Heterotopic ossification (HO) associated with traumatic neurological or musculoskeletal injuries remains a major clinical challenge. One approach to understanding better and potentially treating this condition is to silence one or more genes believed to be responsible for osteogenesis by small interfering RNA (siRNA) post-injury. Improved methods of delivering siRNA to myoprogenitor cells as well as relevant cell culture models of HO are needed to advance this approach. We utilize a model of HO featuring C2C12 myoprogenitor cells stimulated to the osteogenic phenotype by addition of BMP-2. For siRNA delivery, we utilize a nanocomposite consisting of DOTAP-based cationic liposomes coated with a graft copolymer of poly(propylacrylic acid) grafted with polyetheramine (Jeffamine), as this system has been shown previously to deliver antisense oligonucleotides safely into cells and out of endosomes for gene silencing in vitro and in vivo. Delivery of siRNA targeting Runx2, a transcription factor downstream of BMP-2, to stimulated C2C12 cells produced greater than 60% down-regulation of the Runx2 gene. This level of gene silencing was sufficient to inhibit alkaline phosphatase activity over the course of several days and calcium phosphate deposition over the course of 2 weeks. These results show the utility of the BMP-2/C2C12 model for capturing the cellular cell-fate decision in HO. Further, they suggest DOTAP/PPAA-g-Jeffamine as a promising delivery system for siRNA-based therapy for HO.

Viral and nonviral delivery systems for gene delivery

Gene therapy is the process of introducing foreign genomic materials into host cells to elicit a therapeutic benefit. Although initially the main focus of gene therapy was on special genetic disorders, now diverse diseases with different patterns of inheritance and acquired diseases are targets of gene therapy. There are 2 major categories of gene therapy, including germline gene therapy and somatic gene therapy. Although germline gene therapy may have great potential, because it is currently ethically forbidden, it cannot be used; however, to date human gene therapy has been limited to somatic cells. Although numerous viral and nonviral gene delivery systems have been developed in the last 3 decades, no delivery system has been designed that can be applied in gene therapy of all kinds of cell types in vitro and in vivo with no limitation and side effects. In this review we explain about the history of gene therapy, all types of gene delivery systems for germline (nuclei, egg cells, embryonic stem cells, pronuclear, microinjection, sperm cells) and somatic cells by viral [retroviral, adenoviral, adeno association, helper-dependent adenoviral systems, hybrid adenoviral systems, herpes simplex, pox virus, lentivirus, Epstein-Barr virus)] and nonviral systems (physical: Naked DNA, DNA bombardant, electroporation, hydrodynamic, ultrasound, magnetofection) and (chemical: Cationic lipids, different cationic polymers, lipid polymers). In addition to the above-mentioned, advantages, disadvantages, and practical use of each system are discussed.

Endocytosis at the nanoscale

Endocytosis is a fundamental process in which eukaryotic cells internalise molecules and macromolecules via deformation of the membrane and generation of membrane-bound carriers. Functional aspects are not only limited to uptake of nutrients, but also play a primary role in evolutionary conserved processes such as the regulation of plasma membrane protein activity (i.e. signal-transducing receptors, small-molecule transporters and ion channels), cell motility and mitosis. The macromolecular nature of the material transported by endocytosis makes this route one of the most important targets for nanomedicine. Indeed, many nanoparticle formulations have been customised to enter cells through endocytosis and deliver the cargo within the cell. In this critical review, we present an overview of the biology of endocytosis and discuss its implications in cell internalisation of nanoparticles. We discuss how nanoparticle size, shape and surface chemistry can control this process effectively. Finally, we discuss different drug delivery strategies on how to evade lysosomal degradation to promote effective release of the cargo (376 references).

End functionalized polymeric system derived from pyrrolidine provide high transfection efficiency

Chemical architecture and functionality play an important role in the physico-chemical properties of cationic polymers with applications as gene vectors. In this study, linear homopolymers of N-ethyl pyrrolidine methacrylamide (EPA), copolymers of EPA with N,N-dimethylacrylamide (DMA) and oligomers of EPA were synthesized, and the resulting structures were evaluated for their transfection efficiency as non-viral gene vectors. Specifically, polymer species with high and low molecular weights (120-2.6 kDa) and different functionalities (tertiary amines as side chains and primary amine as chain end) were prepared as non-crosslinked, linear homopolymers, copolymers and oligomers, respectively. Polymer/DNA complexes (polyplexes) formation was evaluated by agarose gel electrophoresis, showing that all systems complexed with DNA in all P/N ratios with the exception of the EPA homopolymer. Furthermore, light scattering measurements and transmission electronic microscopy (TEM) showed different size (50-450 nm) and morphology depending on the composition and concentration of the polyplex systems. Cell viability and proliferation after contact with polymer and polyplexes were studied using 3T3 fibroblasts, and the systems showed an excellent biocompatibility at 2 and 4 days. Transfection studies were performed with plasmid Gaussian luciferase kit and were found that the highest transfection efficiency in serum free was obtained with oligomers from the P/N ratio of 1/6 to 1/10. Transfection values of the functionalized oligomers with respect to the control linear poly (dimethylaminoethyl methacrylate) [poly (DMAEMA)] are very interesting in the presence of serum. Haemolysis for these polymers values below 1%, which provide attractive potential applications in gene therapy with these non-toxic readsorbable polymers.

Controlled delivery of antisense oligonucleotides: a brief review of current strategies

Antisense therapy has been investigated extensively over the past two decades, either experimentally for gene functional research or clinically as therapeutic agents owing to the conceptual simplicity, ease of design and low cost. The concept of this therapeutic approach is promising because short antisense oligonucleotides (ASOs) can be delivered into target cells for specific hybridisation with target mRNA, resulting in the inhibition of the expression of pathogenic genes. However, the efficient delivery of the ASO molecules into target cells remains challenging; this bottleneck together with several other technical hurdles need to be overcome before this approach becomes effective and widely adopted. A variety of vectors such as lipids, polymers, peptides and nanoparticles have been explored. This review outlines the recent advances of the non-viral ASO delivery strategies. Several recent scientific studies, including authors' contributions, have been selected to highlight the technical aspects of ASO delivery.

Novel graft copolymers enhance in vitro delivery of antisense oligonucleotides in the presence of serum

Antisense technology holds tremendous potential in the research and clinical settings. However, successful delivery of antisense oligodeoxynucleotides (ODNs) to the intracellular site of action requires the passage of many barriers, including survival against extracellular serum nucleases and escape from endolysosomal degradation. Previous work has shown that the effectiveness of antisense delivery by the cationic liposome, dioleoyl-3-trimethylammonium-propane (DOTAP), is enhanced substantially by the incorporation of a pH-sensitive polymer, poly (propylacrylic acid) (PPAA), in serum-free media. To improve this system for application in serum-containing media conditions, PPAA was modified in this work by grafting onto it either poly(ethylene oxide) (PEO) or a more hydrophobic analog, poly (oxyalkylene amine), known as Jeffamine. The ternary formulation of DOTAP/ODN/PPAA-g-Jeffamine resulted in 8-fold increased uptake of fluorescently-labeled ODNs compared to DOTAP/ODN/PPAA and ~80% silencing of green fluorescent protein (GFP) expression in CHO-d1EGFP cells treated in the presence of 10% FBS-containing media. In contrast, the carrier systems that contained PPAA or PPAA-g-PEO failed to display any significant antisense activity in the presence of serum, even though all of the delivery systems displayed moderate to high levels of antisense activity in serum-free conditions. The results reveal that the carrier system with the Jeffamine graft copolymer effectively mediates specific gene silencing in the presence of serum, while the system with the PEO graft copolymer fails to do so. While the pH-dependent lytic functionality of PPAA was found to be lost upon grafting with PEO or Jeffamine, the hydrophobicity of the latter was sufficient to mediate cellular internalization and endosomal escape. Thus, the PPAA-g-Jeffamine copolymers hold substantial promise as agents for controlled therapeutic delivery of antisense oligonucleotides.

Dual targeting of a thermosensitive nanogel conjugated with transferrin and RGD-containing peptide for effective cell uptake and drug release

In this paper, both arginine-glycine-aspartic acid (RGD)-containing peptide and transferrin (Tf) were conjugated to the thermosensitive poly(N-isopropylacrylamide-co-propyl acrylic acid) (poly(NIPAAm-co-PAAc)) nanogel to prepare a dual-targeting drug carrier. The obtained nanogel was characterized in terms of fluorescence spectroscopy, UV-vis spectroscopy, dynamic light scattering (DLS) and transmission electron microscopy (TEM). In order to track the dual-ligand conjugated nanogel, fluorescein isothiocyanate (FITC) was further conjugated to the nanogel. A cell internalization experiment showed that the dual-ligand conjugated nanogel exhibited obviously enhanced endocytosis by HeLa cells as compared with non-tumorous cells (COS-7 cells). The drug-loaded dual-ligand conjugated nanogel could be transported efficiently into the target tumor cells and the anti-tumor effect was enhanced significantly, suggesting that the dual-ligand conjugated nanogel has great potential as a tumor targeting drug carrier.

Progress toward liver-based gene therapy

The liver is involved in the synthesis of serum proteins, regulation of metabolism and maintenance of homeostasis and provides a variety of opportunities for gene therapy. The enriched vasculature and blood circulation, fenestrated endothelium, abundant receptors on the plasma membranes of the liver cells, and effective transcription and translation machineries in the hepatocytes are some unique features that have been explored for delivery, and functional analysis, of genetic sequences in the liver. Both viral and non-viral methods have been developed for effective gene delivery and liver-based gene therapy. This review describes the fundamentals of gene delivery, and the preclinical and clinical progress that has been made toward gene therapy using the liver as a target.

Thermosensitive P(NIPAAm-co-PAAc-co-HEMA) nanogels conjugated with transferrin for tumor cell targeting delivery

Multifunctional and thermosensitive poly(N-isopropylacrylamide-co-propyl acrylic acid-co-hydroxyethyl methacrylate) (P(NIPAAm-co-PAAc-co-HEMA)) nanogels were prepared by miniemulsion polymerization. The mean sizes of the nanogels measured by dynamic light scattering (DLS) varied from 120 to 400 nm with an increase in temperature. Transmission electron microscopy (TEM) showed that the nanogels displayed well-dispersed spherical morphology. The nanogels were conjugated by human transferrin (Tf) and the coupling of transferrin molecules with nanogels was verified by UV-vis spectroscopy. The cytotoxicity study indicated that the nanogels did not exhibit apparent cytotoxicity. Fluorescence spectroscopy analysis as well as confocal laser scanning microscopy (CLSM) was used to confirm that the Tf-conjugated nanogels could specifically bind to A549 tumor cells. In addition, the Tf-conjugated nanogels loaded with Doxorubicin (Dox) could efficiently release the drug inside the cell, suggesting that the Tf-conjugated nanogels are useful drug carriers for tumor cell targeting.

Interplay of polyethyleneimine molecular weight and oligonucleotide backbone chemistry in the dynamics of antisense activity

The widespread utilization of gene silencing techniques, such as antisense, is impeded by the poor cellular delivery of oligonucleotides (ONs). Rational design of carriers for enhanced ON delivery demands a better understanding of the role of the vector on the extent and time course of antisense effects. The aim of this study is to understand the effects of polymer molecular weight (MW) and ON backbone chemistry on antisense activity. Complexes were prepared between branched polyethyleneimine (PEI) of various MWs and ONs of phosphodiester and phosphorothioate chemistries. We measured their physico-chemical properties and evaluated their ability to deliver ONs to cells, leading to an antisense response. Our key finding is that the antisense activity is not determined solely by PEI MW or by ON chemistry, but rather by the interplay of both factors. While the extent of target mRNA down-regulation was determined primarily by the polymer MW, dynamics were determined principally by the ON chemistry. Of particular importance is the strength of interactions between the carrier and the ON, which determines the rate at which the ONs are delivered intracellularly. We also present a mathematical model of the antisense process to highlight the importance of ON delivery to antisense down-regulation.

Nonviral gene delivery: what we know and what is next

Gene delivery using nonviral approaches has been extensively studied as a basic tool for intracellular gene transfer and gene therapy. In the past, the primary focus has been on application of physical, chemical, and biological principles to development of a safe and efficient method that delivers a transgene into target cells for appropriate expression. This review summarizes the current status of the most commonly used nonviral methods, with an emphasis on their mechanism of action for gene delivery, and their advantages and limitations for gene therapy applications. The technical aspects of each delivery system are also reviewed, with a focus on how to achieve optimal delivery efficiency. A brief discussion of future development and further improvement of the current systems is intended to stimulate new ideas and encourage rapid advancement in this new and promising field.