Excess polycation mediates efficient chitosan-based gene transfer by promoting lysosomal release of the polyplexes

Poly(β-aminoester) Physicochemical Properties Govern the Delivery of siRNA from Electrostatically Assembled Coatings

Localized short interfering RNA (siRNA) therapy has the potential to drive high-specificity molecular-level treatment of a variety of disease states. Unfortunately, effective siRNA therapy suffers from several barriers to its intracellular delivery. Thus, drug delivery systems that package and control the release of therapeutic siRNAs are necessary to overcome these obstacles to clinical translation. Layer-by-layer (LbL) electrostatic assembly of thin film coatings containing siRNA and protonatable, hydrolyzable poly(β-aminoester) (PBAE) polymers is one such drug delivery strategy. However, the impact of PBAE physicochemical properties on the transfection efficacy of siRNA released from LbL thin film coatings has not been systematically characterized. In this study, we investigate the siRNA transfection efficacy of four structurally similar PBAEs in vitro. We demonstrate that small changes in structure yield large changes in physicochemical properties, such as hydrophobicity, pKa, and amine chemical structure, driving differences in the interactions between PBAEs and siRNA in polyplexes and in LbL thin film coatings for wound dressings. In our polymer set, Poly3 forms the most stable interactions with siRNA (Keff,w/w = 0.298) to slow release kinetics and enhance transfection of reporter cells in both colloidal and thin film coating approaches. This is due to its unique physiochemical properties: high hydrophobicity (clog P = 7.86), effective pKa closest to endosomal pH (pKa = 6.21), and high cooperativity in buffering (nhill = 7.2). These properties bestow Poly3 with enhanced endosomal buffering and escape properties. Taken together, this work elucidates the connections between small changes in polymer structure, emergent properties, and polyelectrolyte theory to better understand PBAE transfection efficacy.

Microencapsulated Multifunctionalized Graphene Oxide Equipped with Chloroquine for Efficient and Sustained siRNA Delivery

A multifunctionalized graphene oxide (GO)-based carrier with conjugation of aminated-polyethylene glycol (PEG-diamine), octaarginine (R8), and folic acid (FA), which also contains chloroquine (CQ), a lysosomotropic agent, is introduced. The cellular uptake mechanisms and intracellular targeting of FA-functionalized nanocarriers are examined. The localized releases of CQ and siRNA intracellular delivery are evaluated. Microencapsulation of the nanocarrier complexed with genes in layer-by-layer coating of alginate microbeads is also investigated. The covalently coconjugated FA with PEG and R8 provides a stable formulation with increased cellular uptake compared to FA-free carrier. The CQ-equipped nanocarrier shows a 95% release of CQ at lysosomal pH. The localized release of the drug inside the lysosomes is verified which accelerates the cargo discharge into cytoplasm.

Increased block copolymer length improves intracellular availability of protein cargo

Amphiphilic protein transduction domain mimics (PTDMs) of various lengths were used for protein delivery in Jurkat T cells. Although longer PTDMs facilitated greater cargo internalization, shorter PTDMs yielded greater cargo activity.

Chitosan Nanoparticles at the Biological Interface: Implications for Drug Delivery

The unique properties of chitosan make it a useful choice for various nanoparticulate drug delivery applications. Although chitosan is biocompatible and enables cellular uptake, its interactions at cellular and systemic levels need to be studied in more depth. This review focuses on the various physical and chemical properties of chitosan that affect its performance in biological systems. We aim to analyze recent research studying interactions of chitosan nanoparticles (NPs) upon their cellular uptake and their journey through the various compartments of the cell. The positive charge of chitosan enables it to efficiently attach to cells, increasing the probability of cellular uptake. Chitosan NPs are taken up by cells via different pathways and escape endosomal degradation due to the proton sponge effect. Furthermore, we have reviewed the interaction of chitosan NPs upon in vivo administration. Chitosan NPs are immediately surrounded by a serum protein corona in systemic circulation upon intravenous administration, and their biodistribution is mainly to the liver and spleen indicating RES uptake. However, the evasion of RES system as well as the targeting ability and bioavailability of chitosan NPs can be improved by utilizing specific routes of administration and covalent modifications of surface properties. Ongoing clinical trials of chitosan formulations for therapeutic applications are paving the way for the introduction of chitosan into the pharmaceutical market and for their toxicological evaluation. Chitosan provides specific biophysical properties for effective and tunable cellular uptake and systemic delivery for a wide range of applications.

Scalable Purification of Plasmid DNA Nanoparticles by Tangential Flow Filtration for Systemic Delivery

Plasmid DNA (pDNA) nanoparticles synthesized by complexation with linear polyethylenimine (lPEI) are one of the most effective non-viral gene delivery vehicles. However, the lack of scalable and reproducible production methods and the high toxicity have hindered their clinical translation. Previously, we have developed a scalable flash nanocomplexation (FNC) technique to formulate pDNA/lPEI nanoparticles using a continuous flow process. Here, we report a tangential flow filtration (TFF)-based scalable purification method to reduce the uncomplexed lPEI concentration in the nanoparticle formulation and improve its biocompatibility. The optimized procedures achieved a 60% reduction of the uncomplexed lPEI with preservation of the nanoparticle size and morphology. Both in vitro and in vivo studies showed that the purified nanoparticles significantly reduced toxicity while maintaining transfection efficiency. TFF also allows for gradual exchange of solvents to isotonic solutions and further concentrating the nanoparticles for injection. Combining FNC production and TFF purification, we validated the purified pDNA/lPEI nanoparticles for future clinical translation of this gene nanomedicine.

Dose-Independent Transfection of Hydrophobized Polyplexes

Cationic polymers dynamically complex DNA into complexes (polyplexes). So, upon dilution, polyplexes easily dissociate and lose transfection ability, limiting their in vivo systemic gene delivery. Herein, it is found that polyplex's stability and endocytosis pathway determine its transfection dose-dependence. The polyplexes of hydrophilic polycations have dose-dependent integrity and lysosome-trafficking endocytosis; at low doses, most of these polyplexes dissociate, and the remaining few are internalized and trapped in lysosomes, abolishing their transfection ability. In contrast, the polyplexes of the polycations with optimal hydrophobicity remain integrated even at low concentrations and enter cells via macropinocytosis directly into the cytosol evading lysosomes, so each polyplex can accomplish its infection process, leading to dose-independent DNA transfection like viral vectors. Furthermore, the tuned hydrophobicity balancing the affinity of anionic poly(γ-glutamic acid) (γ-PGA) to the polyplex surface enables γ-PGA to stick on the polyplex surface as a shielding layer but peel off on the cell membrane to release the naked polyplexes for dose-independent transfection. These findings may provide guidelines for developing polyplexes that mimick a viral vector's dose-independent transfection for effective in vivo gene delivery.

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.

Construction of traceable cucurbit[7]uril-based virus-mimicking quaternary complexes with aggregation-induced emission for efficient gene transfection

Construction of an efficient cationic gene delivery system with low cytotoxicity, high transfection efficacy, as well as gene tracking function remains a major challenge in gene therapy. Fabrication of simple and reversible nanocomplexes based on host-guest interaction provides an opportunity to construct stimuli-responsive intelligent supramolecular systems. Inspired by the hierarchical structure of viruses, a novel virus-mimicking PG/CB/TPE/DNA gene delivery system is developed via a multistep noncovalent self-assembly process between pDNA and the preformed PG/CB/TPE complexes based on the host-guest interaction between cucurbit[7]uril (CB[7]) and the protonated diamine group in the poly(glycidyl methacrylate)s derivative (PG), as well as the electrostatic interaction between para-carboxyl functionalized tetraphenylethylene (TPE) and cationic PG. The developed efficient multifunctional gene delivery system exhibits stimuli responsive characteristics and aggregation-induced emission phenomena, thereby enabling gene delivery pH responsiveness and traceability. Moreover, the introduction of TPE and CB[7] endows the self-assembled PG/CB/TPE/DNA complexes with virus-mimicking architecture and properties such as low cytotoxicity, high stability, excellent endosomal escape, and efficient transfection, which are expected to be used as a promising gene delivery system.

Polyplexes for gene and nucleic acid delivery: Progress and bottlenecks

Gene and nucleic acid delivery constitute a huge biological challenge and several attempts have been made by research laboratories to address this issue. Cationic polymers and cationic lipids (positively charged carriers) can be utilized for the transport of these biomolecules. Polyplexes (PPs) are interpolyelectrolyte complexes which are spontaneously formed through the electrostatic condensation between nucleic acid and a cationic polymer. PPs are capable of high-density payload condensation leading to cell internalization and subsequent protection from enzymatic degradation. Most cationic polymers can cross extracellular barriers, but it is more challenging to overcome intracellular barriers (efficient disassembly and endosomal escape). In this review, the use of PPs for gene and nucleic acid delivery is discussed.

PEGylated gene carriers in serum under shear flow

The behaviour of drug/gene carriers in the blood stream under shear is still a puzzle. In this work, using the complexes formed by 21 bp DNA and poly(ethylene glycol)-b-poly(l-lysine) (PEG-PLL) of varying PEG lengths, we studied the dynamic behaviour of the complexes in the presence of fetal bovine serum (FBS) and under flow at different shear rates, a condition mimicking the internal physical environment of blood vessels. The PEG5k-PLL/DNA complex possesses a dense DNA/PLL core and a loose PEG5k protecting layer. The PEGylated DNA complexes exhibit multiple responses to external shear in the presence of FBS. The loose PEG5k layer is firstly disturbed at a shear rate below 30 s-1. The exposure of the charged core to the environment results in a secondary aggregation of the complex with FBS. The size of the aggregate is limited to a certain range as the shear rate increases to 50 s-1. The dense DNA/PLL core starts to withstand the shear force as the shear rate reaches 500 s-1. The reorganization of the core to accommodate more serum molecules leads to tertiary aggregation of the complexes. If PEG cannot form a valid layer around the complex, as in PEG2k-PLL/DNA, the complex forms an aggregate even without shear, and the first shear dependent region is missing. If the PEG layer is too stable around the complex, as in PEG10k-PLL/DNA, no tertiary aggregation occurs. The mechanism of shear on the behaviour of delivery particles in serum helps to design gene carriers with high efficacy.

A preliminary study of Parkinson's gene therapy via sono-magnetic sensing gene vector for conquering extra/intracellular barriers in mice

BACKGROUND

Non-virus genetic treatment for Parkinson's disease (PD) via plasmid glial cell-line derived neurotrophic factor (pGDNF) has shown potential for repairing damaged dopaminergic neurons. However, development of this gene therapy is largely hampered by the insufficient transfection efficiency as a result of the cell membrane, lysosome, and cytoskeleton meshwork.

METHODS

In this study, we propose the use of polyethylenimine (PEI)-superparamagnetic iron oxide-plasmid DNA (pDNA)-loaded microbubbles (PSp-MBs) in conjunction with focused ultrasound (FUS) and two-step magnetic navigation to provide cavitation, proton sponge effect and magnetic effects to increase the efficiency of gene delivery.

RESULTS

The gene transfection rate in the proposed system was 2.2-fold higher than that of the commercial agent (TransIT®-LT1). The transfection rate could be boosted ∼11%, ∼10%, and 6% by cavitation-magnetic hybrid enhanced cell membrane permeabilization, proton sponge effect, and magnetic-assisted cytoskeleton-reorganization, respectively. In vivo data suggested that effective gene delivery with this system results in a 3.2-fold increase in recovery of dopaminergic neurons and a 3.9-fold improvement in the motor behavior when compared to untreated genetic PD mice.

CONCLUSIONS

We proposed that this novel FUS-magnetic hybrid gene delivery platform could be integrated with a variety of therapeutic genes for treating neurodegenerative diseases in the future.

Efficiency of Chitosan/Hyaluronan-Based mRNA Delivery Systems In Vitro: Influence of Composition and Structure

Messenger RNA (mRNA)-containing nanoparticles were produced by electrostatic complexation with a library of pharmaceutical grade chitosans with different degrees of deacetylation and hyaluronic acids (HAs) (native vs. sulfated). Polymer length (Mn), HA degree of sulfation (DS), and amine to phosphate to carboxyl + sulfate (from HA) ratio (N:P:C) were controlled. In vitro transfections were performed in the presence/absence of trehalose and at different pH. Particle size and ζ-potential were correlated with transfection efficiency. Polymer length and charge densities (degree of deacetylation, degree of sulfation) of both HA and chitosan had a direct influence on transfection efficiency through modulation of avidity to mRNA. N:P:C ratio, trehalose, mixing concentration, and nucleic acid dose influenced transfection efficiency with optimized formulations reaching ∼60%-65% transfection efficiency relative to commercially available lipid control with no apparent toxicity for transfection at slightly acidic pH 6.5.

Dual carrier-cargo hydrophobization and charge ratio optimization improve the systemic circulation and safety of zwitterionic nano-polyplexes

While polymeric nano-formulations for RNAi therapeutics hold great promise for molecularly-targeted, personalized medicine, they possess significant systemic delivery challenges including rapid clearance from circulation and the potential for carrier-associated toxicity due to cationic polymer or lipid components. Herein, we evaluated the in vivo pharmacokinetic and safety impact of often-overlooked formulation parameters, including the ratio of carrier polymer to cargo siRNA and hydrophobic siRNA modification in combination with hydrophobic polymer components (dual hydrophobization). For these studies, we used nano-polyplexes (NPs) with well-shielded, zwitterionic coronas, resulting in various NP formulations of equivalent hydrodynamic size and neutral surface charge regardless of charge ratio. Doubling nano-polyplex charge ratio from 10 to 20 increased circulation half-life five-fold and pharmacokinetic area under the curve four-fold, but was also associated with increased liver enzymes, a marker of hepatic damage. Dual hydrophobization achieved by formulating NPs with palmitic acid-modified siRNA (siPA-NPs) both reduced the amount of carrier polymer required to achieve optimal pharmacokinetic profiles and abrogated liver toxicities. We also show that optimized zwitterionic siPA-NPs are well-tolerated upon long-term, repeated administration in mice and exhibit greater than two-fold increased uptake in orthotopic MDA-MB-231 xenografts compared to commercial transfection reagent, in vivo-jetPEI®. These data suggest that charge ratio optimization has important in vivo implications and that dual hydrophobization strategies can be used to maximize both NP circulation time and safety.

Chitosan-DNA polyelectrolyte complex: Influence of chitosan characteristics and mechanism of complex formation

Polyelectrolyte complexes formed between DNA and chitosan present different and interesting physicochemical properties combined with high biocompatibility; they are very useful for biomedical applications. DNA in its double helical structure is a semi-rigid polyelectrolyte chain. Chitosan, an abundant polysaccharide in nature, is considered as one of the most attractive vectors due to its biocompatibility and biodegradability. Here we study chitosan/DNA polyelectrolyte complex formation mechanism and the key factors of their stability. Compaction process of DNA with chitosan was monitored in terms of the ζ-potential and hydrodynamic radius variation as a function of charge ratios between chitosan and DNA. The influence of chitosan degree of acetylation (DA) and its molecular weight on the stoichiometry of chitosan/DNA complexes characteristics was also studied. It is shown that the isoelectric point of chitosan/DNA complexes, as well as their stability, is directly related to the degree of protonation of chitosan (depending on pH), to the DA and to the external salt concentration. It is demonstrated that DNA compaction process corresponds to an all or nothing like-process. Finally, since an important factor in cell travelling is the buffering effect of the vector used, we demonstrated the essential role of free chitosan on the proton-sponge effect.

Peptide-grafted dextran vectors for efficient and high-loading gene delivery

Among various polymeric gene delivery systems, peptide-based vectors demonstrate great potential owing to their unique structure and properties, including flexibility; however, there is insufficient molecular understanding of the role and properties of amino acids as building blocks in gene delivery.

Redox-responsive polymer inhibits macrophages uptake for effective intracellular gene delivery and enhanced cancer therapy

The development of advanced gene delivery carriers with stimuli-responsive release manner for tumor therapeutics is desirable, since they can exclusively release the therapeutic gene via their structural changes in response to the specific stimuli of the target site. Moreover, interactions between macrophages and drug delivery systems (DDSs) seriously impair the treatment efficiency of DDSs, thus macrophages uptake inhibition would to some extent improve the intracellular uptake of DDSs in tumor cells. Herein, a PEGylated redox-responsive gene delivery system was developed for effective cancer therapy. PEG modified glycolipid-like polymer (P-CSSO) was electrostatic interacted with p53 to form P-CSSO/p53 complexes, which exhibited an enhanced redox sensitivity in that the disulfide bond was degraded and the rate the plasmid released from P-CSSO was 2.29-fold that of nonresponsive platform (P-CSO-SA) in 10 mM levels of glutathione (GSH). PEGylation could significantly weaken macrophages uptake, while enhance the accumulation of P-CSSO in tumor cells both in vitro and in vivo. Compared with nonresponsive complexes (P-CSO-SA/p53) (59.2%) and Lipofectamine™ 2000/p53 complexes (52.0%), the tumor inhibition rate of P-CSSO/p53 complexes (77.1%) significantly increased, which was higher than CSSO/p53 complexes (69.9%). The present study indicates that tumor microenvironment sensitive and macrophages uptake suppressive P-CSSO/p53 is a powerful in vivo gene delivery system for enhanced anticancer therapy.

Diethylaminoethyl- chitosan as an efficient carrier for siRNA delivery: Improving the condensation process and the nanoparticles properties

Chitosan has been indicated as a promising carrier for the preparation of small interfering RNA (siRNA) delivery systems due to its remarkable properties. However, its weak interactions with siRNA molecules makes the condensation of siRNA molecules into nanoparticles difficult. In this work, a non-viral gene delivery system based on diethylaminoethyl chitosan (DEAE-CH) derivatives of varied Mw (25-230 kDa) having a low degree of substitution of 15% was investigated. The presence of secondary and tertiary amino groups strengthened the interaction of siRNA and DEAE-CH derivatives of higher Mw (130 kDa to 230 kDa) and provided the preparation of spherical nanoparticles at low charge ratios (N/P 2 to 3) with low polydispersities (0.15 to 0.2) in physiological ionic strength. Nanoparticles prepared with all derivatives exhibited remarkable silencing efficiencies (80% to 90%) on different cell lines (HeLa, MG-63, OV-3) by adjusting the charge ratios. A selected PEG-folic acid labeled derivative (FA-PEG-DEAE15-CH₂₃₀) was synthesized and its nanoparticles completely inhibited the mRNA expression level of TNF-α in RAW 264.7 macrophages. The study demonstrates that the insertion of DEAE groups provides improved physical properties to chitosan-siRNA nanoparticles and holds potential for in vivo applications.

Near-infrared AIEgen-functionalized and diselenide-linked oligo-ethylenimine with self-sufficing ROS to exert spatiotemporal responsibility for promoted gene delivery

We attempted to synthesize an oligo-ethyleneimine (OEI)-crosslinked polycation, characterized with self-sufficing ROS by virtue of a functional AIE component and an ROS-labile diselenide linkage.

Ratio of Polycation and Serum Is a Crucial Index for Determining the RNAi Efficiency of Polyplexes

We report that the mass ratio of the polycation to serum in the medium determines the (RNA interference) RNAi efficiency in vitro by using spermine-modified pullulan (Ps) and spermine-modified dextran (Ds) as polycation models. The high ratio of Ps to serum protein (Ps/Pr) mediated the formation of larger polyplexes, which led to the promoted cellular uptake, enhanced lysosomal escape, and elevated RNAi efficiency. In addition, the supplementary of free Ps also enhanced small interfering RNA transfection because of the elevation of Ps/Pr. Similar results were obtained with Ds. Compared with the adjustment of the nitrogen to phosphate (N/P) ratio in the polyplex, these findings revealed a more applicable strategy to tune the polycation-mediated RNAi efficiency in the serum-containing culture medium.

Significant role of cationic polymers in drug delivery systems

Cationic polymers are characterized as the macromolecules that possess positive charges, which can be either inherently in the polymer side chains and/or its backbone. Based on their origins, cationic polymers are divided in two category including natural and synthetic, in which the possessed positive charges are as result of primary, secondary or tertiary amine functional groups that could be protonated in particular situations. Cationic polymers have been employed commonly as drug delivery agents due to their superior encapsulation efficacy, enhanced bioavailability, low toxicity and improved release profile. In this paper, we focus on the most prominent examples of cationic polymers which have been revealed to be applicable in drug delivery systems and we also discuss their general synthesis and surface modification methods as well as their controlled release profile in drug delivery.

Lyophilisation and concentration of chitosan/siRNA polyplexes: Influence of buffer composition, oligonucleotide sequence, and hyaluronic acid coating

Chitosan (CS)/siRNA polyplexes have great therapeutic potential for treating multiple diseases by gene silencing. However, clinical application of this technology requires the development of concentrated, hemocompatible, pH neutral formulations for safe and efficient administration. In this study we evaluate physicochemical properties of chitosan polyplexes in various buffers at increasing ionic strengths, to identify conditions for freeze-drying and rehydration at higher doses of uncoated or hyaluronic acid (HA)-coated polyplexes while maintaining physiological compatibility. Optimized formulations are used to evaluate the impact of the siRNA/oligonucleotide sequence on polyplex physicochemical properties, and to measure their in vitro silencing efficiency, cytotoxicity, and hemocompatibility. Specific oligonucleotide sequences influence polyplex physical properties at low N:P ratios, as well as their stability during freeze-drying. Nanoparticles display greater stability for oligodeoxynucleotides ODN vs siRNA; AT-rich vs GC-rich; and overhangs vs blunt ends. Using this knowledge, various CS/siRNA polyplexes are prepared with and without HA coating, freeze-dried and rehydrated at increased concentrations using reduced rehydration volumes. These polyplexes are non-cytotoxic and preserve silencing activity even after rehydration to 20-fold their initial concentration, while HA-coated polyplexes at pH∼7 also displayed increased hemocompatibility. These concentrated formulations represent a critical step towards clinical development of chitosan-based oligonucleotide intravenous delivery systems.

Lysosomal rupture induced by structurally distinct chitosans either promotes a type 1 IFN response or activates the inflammasome in macrophages

Chitosan is a family of glucosamine and N-acetyl glucosamine polysaccharides with poorly understood immune modulating properties. Here, functional U937 macrophage responses were analyzed in response to a novel library of twenty chitosans with controlled degree of deacetylation (DDA, 60-98%), molecular weight (1 to >100 kDa), and acetylation pattern (block vs. random). Specific chitosan preparations (10 or 190 kDa 80% block DDA and 3, 5, or 10 kDa 98% DDA) either induced macrophages to release CXCL10 and IL-1ra at 5-50 μg/mL, or activated the inflammasome to release IL-1β and PGE₂ at 50-150 μg/mL. Chitosan induction of these factors required lysosomal acidification. CXCL10 production was preceded by lysosomal rupture as shown by time-dependent co-localization of galectin-3 and chitosan and slowed autophagy flux, and specifically depended on IFN-β paracrine activity and STAT-2 activation that could be suppressed by PGE₂. Chitosan induced a type I IFN paracrine response or inflammasome response depending on the extent of lysosomal rupture and cytosolic foreign body invasion. This study identifies the structural motifs that lead to chitosan-driven cytokine responses in macrophages and indicates that lysosomal rupture is a key mechanism that determines the endogenous release of either IL-1ra or IL-1β.

Chitosan derivatives for gene transfer: effect of phosphorylcholine and diethylaminoethyl grafts on the in vitro transfection efficiency

The purpose of this work was to improve the functional properties of chitosan for gene transfer by inserting phosphorylcholine (PC) and diethylaminoethyl (DEAE) groups into the main chain. A series of derivatives containing increasing contents of DEAE and a fixed content of PC groups were synthesized and characterized, aiming to evaluate the effect of these groups on the nanoparticles' properties and the in vitro transfection efficiency. The derivatives were soluble at physiological pH levels and all derivatives were less cytotoxic than the control, the lipid lipofectamine. The obtained derivatives complexed pDNA into nanoparticles with smaller sizes and higher zeta potentials than plain chitosan. The in vitro transfection was performed with nanoparticles prepared at pH 6.3 and 7.4 and the results showed that nanoparticles prepared with derivatives containing 20% of PC groups (PC18-CH) and high degrees of substitution by DEAE (PC20-CH-DEAE100, CH-DEAE80, CH-DEAE100) displayed the better transfection efficiencies in HeLa cells, reaching relative values comparable to lipofectamine. The most effective derivative, PC18CH, was selected for complexation with siRNA and its complexes demonstrated an in vitro knockdown efficiency highly dependent on the N/P ratio. Our combined results indicated that, by means of controlled modifications, the limitations of chitosan can be overcome to obtain more effective carriers based on chitosan, and the derivatives here studied hold potential for in vivo studies.

Chitosan DNA nanoparticles for oral gene delivery

Gene therapy is a promising technology with potential applications in the treatment of medical conditions, both congenital and acquired. Despite its label as breakthrough technology for the 21^st century, the simple concept of gene therapy - the introduction of a functional copy of desired genes in affected individuals - is proving to be more challenging than expected. Oral gene delivery has shown intriguing results and warrants further exploration. In particular, oral administration of chitosan DNA nanoparticles, one the most commonly used formulations of therapeutic DNA, has repeatedly demonstrated successful in vitro and in vivo gene transfection. While oral gene therapy has shown immense promise as treatment options in a variety of diseases, there are still significant barriers to overcome before it can be considered for clinical applications. In this review we provide an overview of the physiologic challenges facing the use of chitosan DNA nanoparticles for oral gene delivery at both the extracellular and intracellular level. From administration at the oral cavity, chitosan nanoparticles must traverse the gastrointestinal tract and protect its DNA contents from significant jumps in pH levels, various intestinal digestive enzymes, thick mucus layers with high turnover, and a proteinaceous glycocalyx meshwork. Once these extracellular barriers are overcome, chitosan DNA nanoparticles must enter intestinal cells, escape endolysosomes, and disassociate from genetic material at the appropriate time allowing transport of genetic material into the nucleus to deliver a therapeutic effect. The properties of chitosan nanoparticles and modified nanoparticles are discussed in this review. An understanding of the barriers to oral gene delivery and how to overcome them would be invaluable for future gene therapy development.

Delivery of Splice Switching Oligonucleotides by Amphiphilic Chitosan-Based Nanoparticles

Splice switching oligonucleotides (SSOs) are a class of single-stranded antisense oligonucleotides (ssONs) being used as gene therapeutics and demonstrating great therapeutic potential. The availability of biodegradable and biocompatible delivery vectors that could improve delivery efficiencies, reduce dosage, and, in parallel, reduce toxicity concerns could be advantageous for clinical translation. In this work we explored the use of quaternized amphiphilic chitosan-based vectors in nanocomplex formation and delivery of splice switching oligonucleotides (SSO) into cells, while providing insights regarding cellular uptake of such complexes. Results show that the chitosan amphiphilic character is important when dealing with SSOs, greatly improving colloidal stability under serum conditions, as analyzed by dynamic light scattering, and enhancing cellular association. Nanocomplexes were found to follow an endolysosomal route with a long lysosome residence time. Conjugation of a hydrophobic moiety, stearic acid, to quaternized chitosan was a necessary condition to achieve transfection, as an unmodified quaternary chitosan was completely ineffective. We thus demonstrate that amphiphilic quaternized chitosan is a biomaterial that holds promise and warrants further development as a platform for SSO delivery strategies.

Light-mediated activation of siRNA Release in diblock copolymer assemblies for controlled gene silencing

Controllable release is particularly important for the delivery of small interfering RNA (siRNA), as siRNAs have a high susceptibility to enzymatic degradation if release is premature, yet lack silencing activity if they remain inaccessible within the cytoplasm. To overcome these hurdles, novel and tailorable mPEG-b-poly(5-(3-(amino)propoxy)-2-nitrobenzyl methacrylate) (mPEG-b-P(APNBMA)) diblock copolymers containing light-sensitive o-nitrobenzyl moieties and pendant amines are employed to provide both efficient siRNA binding, via electrostatic and hydrophobic interactions, as well as triggered charge reversal and nucleic acid release. In particular, siRNA/mPEG-b-P(APNBMA)23.6 polyplexes show minimal aggregation in physiological salt and serum, and enhanced resistance to polyanion-induced unpackaging compared to polyethylenimine preparations. Cellular delivery of siRNA/mPEG-b-P(APNBMA)23.6 polyplexes reveals greater than 80% cellular transfection, as well as rapid and widespread cytoplasmic distribution. Additionally, UV irradiation indicates ≈70% reduction in targeted gene expression following siRNA/mPEG-b-P(APNBMA)23.6 polyplex treatment, as compared to 0% reduction in polyplex-treated cells without UV irradiation, and only ≈30% reduction for Lipofectamine-treated cells. The results here highlight the potential of these light-sensitive copolymers with a well-defined on/off switch for applications including cellular patterning for guided cell growth and extension, and cellular microarrays for exploring protein and drug interactions that require enhanced spatiotemporal control of gene activation.

Mucus barrier-triggered disassembly of siRNA nanocarriers

The mucus overlying mucosal epithelial surfaces presents not only a biological barrier to the penetration of potential pathogens, but also therapeutic modalities including RNAi-based nanocarriers. Movement of nanomedicines across the mucus barriers of the gastrointestinal mucosa is modulated by interactions of the nanomedicine carriers with mucin glycoproteins inside the mucus, potentiated by the large surface area of the nanocarrier. We have developed a fluorescence activation-based reporter system showing that the interaction between polyanionic mucins and the cationic chitosan/small interfering RNA (siRNA) nanocarriers (polyplexes) results in the disassembly and consequent triggered release of fluorescent siRNA. The quantity of release was found to be dependent on the molar ratio between chitosan amino groups and siRNA phosphate groups (NP ratio) of the polyplexes with a maximal estimated 48.6% release of siRNA over 30 min at NP 60. Furthermore, a microfluidic in vitro model of the gastrointestinal mucus barrier was used to visualize the dynamic interaction between chitosan/siRNA nanocarriers and native purified porcine stomach mucins. We observed strong interactions and aggregations at the mucin-liquid interface, followed by an NP ratio dependent release and consequent diffusion of siRNA across the mucin barrier. This work describes a new model of interaction at the nanocarrier-mucin interface and has important implications for the design and development of nucleic acid-based nanocarrier therapeutics for mucosal disease treatments and also provides insights into nanoscale pathogenic processes.

Targeted delivery of miRNA therapeutics for cardiovascular diseases: opportunities and challenges

Dysregulation of miRNA expression has been associated with many cardiovascular diseases in animal models, as well as in patients. In the present review, we summarize recent findings on the role of miRNAs in cardiovascular diseases and discuss the opportunities, possibilities and challenges of using miRNAs as future therapeutic targets. Furthermore, we focus on the different approaches that can be used to deliver these newly developed miRNA therapeutics to their sites of action. Since siRNAs are structurally homologous with the miRNA therapeutics, important lessons learned from siRNA delivery strategies are discussed that might be applicable to targeted delivery of miRNA therapeutics, thereby reducing costs and potential side effects, and improving efficacy.

Elucidating the role of free polycationic chains in polycation gene carriers by free chains of polyethylenimine or N,N,N-trimethyl chitosan plus a certain polyplex

Polycations as gene carriers have attracted considerable attention over the past decade. Generally, polyplexes between polycations and deoxyribonucleic acid (DNA) are formed at low N/P ratios (the ratios of the numbers of nitrogen atoms in a polycation to the numbers of phosphorus atoms in DNA), but high transfection efficiency can only be obtained at much higher N/P ratios. Thus, many polycationic chains are still free in solution. In this study, we investigated the detailed functions of free polyethylenimine chains (PEI-F) and free N,N,N-trimethyl chitosan chains (TMC-F) using the same polyplex, ie, TMC polyplex (TMC-P), which has high stability in Dulbecco’s Modified Eagle’s Medium (DMEM). Meanwhile, PEI polyplex (PEI-P)/PEI-F was also evaluated rather than PEI-P/TMC-F because the stability of PEI-P is low in DMEM and, in the latter case, the TMC-F may replace the bound PEI chain in PEI-P to form TMC-P. The transfection results show that both TMC-F and PEI-F can significantly increase the transfection efficiency of TMC-P; however, PEI-F can upregulate the gene expression of TMC-P more efficiently than TMC-F. Further investigations on the endocytosis and intracellular trafficking show that PEI-P/PEI-F, TMC-P/PEI-F, and TMC-P/TMC-F exhibit similar cellular uptake efficiency. However, by shutting down the clathrin-mediated endocytosis or vacuolar proton pump, the transfection efficiency decreases in the order of PEI-P/PEI-F > TMC-P/PEI-F > TMC-P/TMC-F. These findings indicate that PEI-F and TMC-F may promote the transfection efficiency of the polyplex by affecting its cellular uptake pathway and intracellular trafficking.

Ultrasound treatment increases transfection efficiency of low molecular weight chitosan in fibroblasts but not in KB cells

The aim of this study was to optimize transfection efficiency (TE) of the depolymerized low molecular weight (LW) chitosan with molecular weight (Mw) at 16 kDa and 54% degree of deacetylation (DDA) on three primary cells of fibroblast (F), dental pulp (P), and periodontal ligament (PDL). The effect of low frequency ultrasound treatment on the chitosan-DNA complexes prior transfection on TE was also evaluated. This LW chitosan required high N/P ratio (>34) to bind DNA completely. An N/P ratio above 56 tended to improve TE in most primary cells nearly at the level of Lipofectamine. Ultrasonication can reduce the aggregation and sizes of the chitosan-DNA microparticles. It increased TE of F cells at an N/P ratio above 34, which was higher than Lipofectamine. However, this ultrasound treatment caused loss of TE in KB cells. MTT assay of these chitosan-DNA complexes revealed no significant cytotoxicity to both KB and F cells. This LW chitosan has potential for further development into a safer alternative to gene delivery systems in various cells of interest; however the optimal conditions have to be adjusted, depending on each cell source.

Combined analysis of polycation/ODN polyplexes by analytical ultracentrifugation and dynamic light scattering reveals their size, refractive index increment, stoichiometry, porosity, and molecular weight

Analytical ultracentrifugation (AUC) and dynamic light scattering (DLS) were combined to characterize polyplexes formed with 10 kDa chitosan or 10 kDa PEI and oligodeoxynucleotides (ODN). Combined analysis revealed that both polyplexes were highly porous (over 80%) and that their weight average hydrodynamic diameters were of 46 and 55 nm for chitosan/ODN and PEI/ODN complexes, respectively. Transformation of the sedimentation coefficient distribution to a size and molecular weight distribution gave an average molecular weight of 19 and 29 MDa for chitosan and PEI polyplexes, respectively. Data from AUC also allowed for the calculation of the actual dn/dc and N/P ratios of each polyplex. Additional data from scanning electron microscopy and static light scattering confirmed the conclusions that were initially derived from AUC and DLS, thus validating that the combination of AUC and DLS is a powerful approach to characterize polyplexes in terms of refractive index increment, size, and molecular weight distributions, as well as porosity.

Epidermal stem cells cultured on collagen-modified chitin membrane induce in situ tissue regeneration of full-thickness skin defects in mice

A Large scale of full-thickness skin defects is lack of auto-grafts and which requires the engineered skin substitutes for repair and regeneration. One major obstacle in skin tissue engineering is to expand epidermal stem cells (ESCs) and develop functional substitutes. The other one is the scaffold of the ESCs. Here, we applied type I collagen-modified chitin membrane to form collagen-chitin biomimetic membrane (C-CBM), which has been proved to have a great biocompatibility and degraded totally when it was subcutaneously transplanted into rat skin. ESCs were cultured, and the resulting biofilm was used to cover full-thickness skin defects in nude mice. The transplantation of ESCs- collagen- chitn biomimetic membrane (ESCs-C-CBM) has achieved in situ skin regeneration. In nude mice, compared to controls with collagen-chitin biomimetic membrane (C-CBM) only, the ESCs-C-CBM group had significantly more dermatoglyphs on the skin wound 10 w after surgery, and the new skin was relatively thick, red and elastic. In vivo experiments showed obvious hair follicle cell proliferation in the full-thickness skin defect. Stem cell markers examination showed active ESCs in repair and regeneration of skin. The results indicate that the collagen-modified chitin membrane carry with ESCs has successfully regenerated the whole skin with all the skin appendages and function.

Advancing polymeric delivery systems amidst a nucleic acid therapy renaissance

Nucleic acid therapeutics are attracting renewed interest due to recent clinical advances and product approvals. Most leading programs use chemical conjugates, or viral vectors in the case of gene therapy, while several use no delivery system at all. Polymer systems, which have been at the periphery of this renaissance, often involve greater molecular complexity than competing approaches, which must be justified by their advantages. Advanced analytical methods, along with biological tools for characterizing biotransformation and intracellular trafficking, are increasingly being applied to nucleic acid delivery systems including those based on polymers. These frontiers of investigation create the opportunity for an era where highly defined polymer compositions are optimized based on mechanistic insights in a way that has not been previously possible, offering the prospect of greater differentiation from alternatives. This will require integrated collaboration between polymer scientists and those from other disciplines.

Chitosans for delivery of nucleic acids

Alternatives to efficient viral vectors in gene therapy are desired because of their poor safety profiles. Chitosan is a promising non-viral nucleotide delivery vector because of its biocompatibility, biodegradability, low immunogenicity and ease of manufacturing. Since the transfection efficiency of chitosan polyplexes is relatively low compared to viral counterparts, there is an impetus to gain a better understanding of the structure-performance relationship. Recent progress in preparation and characterisation has enabled coupling analysis of chitosans structural parameters that has led to increased TE by tailoring of chitosan's structure. In this review, we summarize the recent advances that have lead to a more rational design of chitosan polyplexes. We present an integrated review of all major areas of chitosan-based transfection, including preparation, chitosan and polyplexes physicochemical characterisation, in vitro and in vivo assessment. In each, we present the obstacles to efficient transfection and the strategies adopted over time to surmount these impediments.