The role of the disulfide group in disulfide-based polymeric gene carriers

Polyamidoamine-Carbon Nanodot Conjugates with Bioreducible Building Blocks: Smart Theranostic Platforms for Targeted siRNA Delivery

This study focuses on designing hybrid theranostic nanosystems, utilizing gadolinium-doped carbon nanodots decorated with bioreducible amphoteric polyamidoamines (PAAs). The objective is to synergize the exceptional theranostic properties of gadolinium-doped carbon nanodots (CDs) with the siRNA complexation capabilities of PAAs. Linear copolymeric polyamidoamines, based on N,N'-bis(acryloyl)cystamine, arginine, and agmatine, were synthesized, resulting in three distinct amphoteric copolymers. Notably, sulfur bridges within the PAA repeating units confer pronounced susceptibility to glutathione-mediated degradation─a key attribute in the tumor microenvironment. This pathway enables controlled and stimuli-responsive siRNA release, theoretically providing precise spatiotemporal control over therapeutic interventions. The selected PAA, conjugated with CDs using the redox-sensitive spacer cystamine, formed the CDs-Cys-PAA conjugate with superior siRNA complexing capacity. Stable against polyanion exchange, the CDs-Cys-PAA/siRNA complex released siRNA in the presence of GSH. In vitro studies assessed cytocompatibility, internalization, and gene silencing efficacy on HeLa, MCF-7, and 16HBE cell lines.

Controllable Disulfide Exchange Polymerization of Polyguanidine for Effective Biomedical Applications by Thiol-Mediated Uptake

New preparation methods of vectors are the key to developing the next generation of biomacromolecule delivery systems. In this study, a controllable disulfide exchange polymerization was established to obtain low-toxicity and efficient bioreducible polyguanidines (mPEG₂₂₅ -b-PSS_n , n=13, 26, 39, 75, 105) by regulating the concentration of activated nucleophiles and reaction time under mild reaction conditions. The relationship between the degrees of polymerization and biocompatibility was studied to identify the optimal polyguanidine mPEG₂₂₅ -b-PSS₂₆ . Such polyguanidine exhibited good in vitro performance in delivering different functional nucleic acids. The impressive therapeutic effects of mPEG₂₂₅ -b-PSS₂₆ were further verified in the 4T1 tumor-bearing mice as well as the mice with full-thickness skin defects. Controllable disulfide exchange polymerization provides an attractive strategy for the construction of new biomacromolecule delivery systems.

Genetic and Covalent Protein Modification Strategies to Facilitate Intracellular Delivery

Protein-based therapeutics represent a rapidly growing segment of approved disease treatments. Successful intracellular delivery of proteins is an important precondition for expanded in vivo and in vitro applications of protein therapeutics. Direct modification of proteins and peptides for improved cytosolic translocation are a promising method of increasing delivery efficiency and expanding the viability of intracellular protein therapeutics. In this Review, we present recent advances in both synthetic and genetic protein modifications for intracellular delivery. Active endocytosis-based and passive internalization pathways are discussed, followed by a review of modification methods for improved cytosolic delivery. After establishing how proteins can be modified, general strategies for facilitating intracellular delivery, such as chemical supercharging or inclusion of cell-penetrating motifs, are covered. We then outline protein modifications that promote endosomal escape. We finally examine the delivery of two potential classes of therapeutic proteins, antibodies and associated antibody fragments, and gene editing proteins, such as cas9.

Poly(disulfide)s: From Synthesis to Drug Delivery

Bioresponsive polymers have been widely used in drug delivery because of their degradability. For example, poly(disulfide)s with repeating disulfide bonds in the main chain have attracted considerable research attention. The characteristics of the disulfide bonds, including their dynamic and reversible properties and their responsiveness to stimuli such as reductants, light, heat, and mechanical force, make them ideal platforms for on-demand drug delivery. This review introduces the synthesis methods and applications of poly(disulfide)s. Furthermore, the synthesis methods of poly(disulfide)s are classified on the basis of the monomers used: oxidative step-growth polymerization with dithiols, ring-opening polymerization with cyclic disulfides, and polymerization with linear disulfides. In addition, recent advances in poly(disulfide)s for the delivery of small-molecule or biomacromolecular drugs are discussed. Quantum-dot-loaded poly(disulfide) delivery systems for imaging are also included. This review provides an overview of the various design strategies employed in the construction of poly(disulfide) platforms to inspire new applications in the field of drug delivery.

Rational Design of Programmable Monodisperse Semi-Synthetic Protein Nanomaterials Containing Engineered Disulfide Functionality*

The reversible nature of disulfide functionality has been exploited to design intelligent materials such as nanocapsules, micelles, vesicles, inorganic nanoparticles, peptide and nucleic acid nanodevices. Herein, we report a new chemical methodology for the construction redox-sensitive protein assemblies using monodisperse facially amphiphilic protein-dendron bioconjugates. The disulfide functionality is strategically placed between the dendron and protein domains. The custom designed bioconjugates self-assembled into nanoscopic objects of a defined size dictated by the nature of dendron domain. The stimuli-responsive behavior of the protein assemblies is demonstrated using a suitable redox trigger.

Thiol-Mediated Uptake

This Perspective focuses on thiol-mediated uptake, that is, the entry of substrates into cells enabled by oligochalcogenides or mimics, often disulfides, and inhibited by thiol-reactive agents. A short chronology from the initial observations in 1990 until today is followed by a summary of cell-penetrating poly(disulfide)s (CPDs) and cyclic oligochalcogenides (COCs) as privileged scaffolds in thiol-mediated uptake and inhibitors of thiol-mediated uptake as potential antivirals. In the spirit of a Perspective, the main part brings together topics that possibly could help to explain how thiol-mediated uptake really works. Extreme sulfur chemistry mostly related to COCs and their mimics, cyclic disulfides, thiosulfinates/-onates, diselenolanes, benzopolysulfanes, but also arsenics and Michael acceptors, is viewed in the context of acidity, ring tension, exchange cascades, adaptive networks, exchange affinity columns, molecular walkers, ring-opening polymerizations, and templated polymerizations. Micellar pores (or lipid ion channels) are considered, from cell-penetrating peptides and natural antibiotics to voltage sensors, and a concise gallery of membrane proteins, as possible targets of thiol-mediated uptake, is provided, including CLIC1, a thiol-reactive chloride channel; TMEM16F, a Ca-activated scramblase; EGFR, the epithelial growth factor receptor; and protein-disulfide isomerase, known from HIV entry or the transferrin receptor, a top hit in proteomics and recently identified in the cellular entry of SARS-CoV-2.

Disulfide Bridging Strategies in Viral and Nonviral Platforms for Nucleic Acid Delivery

Self-assembled nanostructures that are sensitive to environmental stimuli are promising nanomaterials for drug delivery. In this class, disulfide-containing redox-sensitive strategies have gained enormous attention because of their wide applicability and simplicity of nanoparticle design. In the context of nucleic acid delivery, numerous disulfide-based materials have been designed by relying on covalent or noncovalent interactions. In this review, we highlight major advances in the design of disulfide-containing materials for nucleic acid encapsulation, including covalent nucleic acid conjugates, viral vectors or virus-like particles, dendrimers, peptides, polymers, lipids, hydrogels, inorganic nanoparticles, and nucleic acid nanostructures. Our discussion will focus on the context of the design of materials and their impact on addressing the current shortcomings in the intracellular delivery of nucleic acids.

Silica Mesoporous Structures: Effective Nanocarriers in Drug Delivery and Nanocatalysts

The application of silica mesoporous structures in drug delivery and the removal of pollutants and organic compounds through catalytic reactions is increasing due to their unique characteristics, including high loading capacities, tunable pores, large surface areas, sustainability, and so on. This review focuses on very well-studied class of different construction mesoporous silica nano(particles), such as MCM-41, SBA-15, and SBA-16. We discuss the essential parameters involved in the synthesis of these materials with providing a diverse set of examples. In addition, the recent advances in silica mesoporous structures for drug delivery and catalytic applications are presented to fill the existing gap in the literature with providing some promising examples on this topic for the scientists in both industry and academia active in the field. Regarding the catalytic applications, mesoporous silica particles have shown some promises to remove the organic pollutants and to synthesize final products with high yields due to the ease with which their surfaces can be modified with various ligands to create appropriate interactions with target molecules. In the drug delivery process, as nanocarriers, they have also shown very good performance thanks to the easy surface functionalization but also adjustability of their porosities to providing in-vivo and in-vitro cargo delivery at the target site with appropriate rate.

Modular Synthesis of Bioreducible Gene Vectors through Polyaddition of N,N'-Dimethylcystamine and Diglycidyl Ethers

Bioreducible, cationic linear poly(amino ether)s (PAEs) were designed as promising gene vectors. These polymers were synthesized by the reaction of a disulfide-functional monomer, N,N'-dimethylcystamine (DMC), and several different diglycidyl ethers. The resulting PAEs displayed a substantial buffer capacity (up to 64%) in the endosomal acidification region of pH 7.4⁻5.1. The PAEs condense plasmid DNA into 80⁻200 nm sized polyplexes, and have surface charges ranging from +20 to +40 mV. The polyplexes readily release DNA upon exposure to reducing conditions (2.5 mM DTT) due to the cleavage of the disulfide groups that is present in the main chain of the polymers, as was demonstrated by agarose gel electrophoresis. Upon exposing COS-7 cells to polyplexes that were prepared at polymer/DNA w/w ratios below 48, cell viabilities between 80⁻100% were observed, even under serum-free conditions. These polyplexes show comparable or higher transfection efficiencies (up to 38%) compared to 25 kDa branched polyethylenimine (PEI) polyplexes (12% under serum-free conditions). Moreover, the PAE-based polyplexes yield transfection efficiencies as high as 32% in serum-containing medium, which makes these polymers interesting for gene delivery applications.

Disulfide bond based polymeric drug carriers for cancer chemotherapy and relevant redox environments in mammals

Increasing numbers of disulfide linkage-employing polymeric drug carriers that utilize the reversible peculiarity of this unique covalent bond have been reported. The reduction-sensitive disulfide bond is usually employed as a linkage between hydrophilic and hydrophobic polymers, polymers and drugs, or as cross-linkers in polymeric drug carriers. These polymeric drug carriers are designed to exploit the significant redox potential difference between the reducing intracellular environments and relatively oxidizing extracellular spaces. In addition, these drug carriers can release a considerable amount of anticancer drug in response to the reducing environment when they reach tumor tissues, effectively improving antitumor efficacy. This review focuses on various disulfide linkage-employing polymeric drug carriers. Important redox thiol pools, including GSH/GSSG, Cys/CySS, and Trx1, as well as redox environments in mammals, will be introduced.

Recent advances in smart biotechnology: Hydrogels and nanocarriers for tailored bioactive molecules depot

Over the past ten years, the global biopharmaceutical market has remarkably grown, with ten over the top twenty worldwide high performance medical treatment sales being biologics. Thus, biotech R&D (research and development) sector is becoming a key leading branch, with expanding revenues. Biotechnology offers considerable advantages compared to traditional therapeutic approaches, such as reducing side effects, specific treatments, higher patient compliance and therefore more effective treatments leading to lower healthcare costs. Within this sector, smart nanotechnology and colloidal self-assembling systems represent pivotal tools able to modulate the delivery of therapeutics. A comprehensive understanding of the processes involved in the self-assembly of the colloidal structures discussed therein is essential for the development of relevant biomedical applications. In this review we report the most promising and best performing platforms for specific classes of bioactive molecules and related target, spanning from siRNAs, gene/plasmids, proteins/growth factors, small synthetic therapeutics and bioimaging probes.

Bioreducible, hydrolytically degradable and targeting polymers for gene delivery

Recently, synthetic gene carriers have been intensively developed owing to their promising application in gene therapy and considered as a suitable alternative to viral vectors because of several benefits. But cationic polymers still face some problems like low transfection efficiency, cytotoxicity, and poor cell recognition and internalization. The emerging engineered and smart polymers can respond to some changes in the biological environment like pH change, ionic strength change and redox potential, which is beneficial for cellular uptake. Redox-sensitive disulfide based and hydrolytically degradable cationic polymers serve as gene carriers with excellent transfection efficiency and good biocompatibility owing to degradation in the cytoplasm. Additionally, biodegradable polymeric micelles with cell-targeting function are recently emerging gene carriers, especially for the transfection of endothelial cells. In this review, some strategies for gene carriers based on these bioreducible and hydrolytically degradable polymers will be illustrated.

Cellular uptake: lessons from supramolecular organic chemistry

The objective of this Feature Article is to reflect on the importance of established and emerging principles of supramolecular organic chemistry to address one of the most persistent problems in life sciences. The main topic is dynamic covalent chemistry on cell surfaces, particularly disulfide exchange for thiol-mediated uptake. Examples of boronate and hydrazone exchange are added for contrast, comparison and completion. Of equal importance are the discussions of proximity effects in polyions and counterion hopping, and more recent highlights on ring tension and ion pair-π interactions. These lessons from supramolecular organic chemistry apply to cell-penetrating peptides, particularly the origin of "arginine magic" and the "pyrenebutyrate trick," and the currently emerging complementary "disulfide magic" with cell-penetrating poly(disulfide)s. They further extend to the voltage gating of neuronal potassium channels, gene transfection, and the delivery of siRNA. The collected examples illustrate that the input from conceptually innovative chemistry is essential to address the true challenges in biology beyond incremental progress and random screening.

Multifunctional cationic polyurethanes designed for non-viral cancer gene therapy

Nano-polyplexes from bioreducible cationic polymers have a massive promise for cancer gene therapy. However, the feasibility of cationic polyurethanes for non-viral gene therapy is so far not well studied. In this work, a linear cationic polyurethane containing disulfide bonds, urethane linkages and protonable tertiary amino groups was successfully generated by stepwise polycondensation reaction between 2,2'-dithiodiethanol bis(p-nitrophenyl carbonate) and 1,4-bis(3-aminopropyl)piperazine (BAP). We confirmed that the cationic polyurethane (denoted as PUBAP) displayed superior gene delivery properties to its cationic polyamide analogue, thus causing higher in vitro transfection efficiency in MCF-7 and SKOV-3 cells. Besides, further folate-PEGylation and hydrophobic deoxycholic acid (DCA) conjugation to amino-containing PUBAP can be conducted to afford multifunctional polyurethane gene delivery system. After optimization, folate-decorated nano-polyplexes from the PUBAP conjugated with 8 folate-PEG chains and 12 DCA residues exhibited superb colloidal stability under physiological conditions, and performed rapid uptake via folate receptor-mediated endocytosis, efficient intracellular gene release and nucleus translocation into SKOV-3 cells in vitro and in vivo. Importantly, PUBAP based polyplexes possess low cytotoxicity as a result of PUBAP biodegradability. Therefore, marked growth inhibition of SKOV-3 tumor xenografted in Balb/c nude mice was achieved with negligible side effects on the mouse health after intravenous administration of PUBAP based polyplexes with a therapeutic plasmid encoding for TNF-related apoptosis-inducing ligand. This work provides a new insight into biomedical application of bio-responsive polyurethanes for cancer therapy.

STATEMENT OF SIGNIFICANCE

In this study, we have confirmed that disulfide-based cationic polyurethane presents a new non-viral vector for gene transfer and cancer gene therapy. The significance of this work includes: (1) design and synthesis of a group of novel disulfide-based cationic polyurethane by non-isocyanate chemistry; (2) comparative study of transfection activity between cationic polyurethanes and cationic polyamides; (3) feasibility of bioreducible cationic polyurethanes for in vivo cancer gene therapy.

Bridging Small Molecules to Modified Bacterial Microparticles Using a Disulphide Linkage: MIS416 as a Cargo Delivery System

MIS416 is an intact minimal cell wall skeleton derived from Proprionibacterium acnes that is phagocytosed by antigen presenting cells, including dendritic cells (DCs). This property allows MIS416 to be exploited as a vehicle for the delivery of peptide antigens or other molecules (for example, nucleic acids) to DCs. We previously showed that covalent (non-cleavable) conjugation of OVA, a model antigen derived from ovalbumin, to MIS416 enhanced immune responses in DCs in vivo, compared to unconjugated MIS416 and OVA. Intracellular trafficking promotes the lysosomal degradation of MIS416, leading to the destruction of MIS416 plus the associated cargos conjugated to MIS416. However, lysosomal degradation of cargo may not be desired for some MIS416 conjugates. Here we have investigated whether a cleavable linkage could facilitate release of the cargo in the cytoplasm of DCs to avoid lysosomal degradation. DCs were treated in vitro with disulfide-containing conjugates, and as hypothesised faster release of SIINFEKL peptide in the cytoplasm of DCs was observed with the inclusion of a disulfide bond between MIS416 and cargo. The inclusion of a cleavable disulfide bond in the conjugates did not significantly alter the amount of SIINFEKL antigens presented on MHC I molecules on DCs as compared with conjugates without a disulfide bond. However, the conjugates containing disulfide-linkages performed either slightly better (p<0.05) than, or the same as conjugates without a disulfide bond with respect to in vitro OT-1 T-cell proliferation induced by the presentation of SIINFEKL antigens on DCs, or DC activation studies, respectively. However, disulfide-containing conjugates were less effective than conjugates without a disulfide bond in in vivo cytotoxicity assays. In conclusion, inclusion of a disulfide bond in MIS416-peptide conjugates was associated with efficient release of peptides in the cytoplasm of DCs, an important consideration for MIS416-mediated delivery of degradation-sensitive cargoes. However, treatment of DCs with disulfide-containing conjugates did not significantly alter the presentation of peptide antigens on MHC class I molecules to T-cells, or greatly enhance antigen-associated T-cell proliferation in vitro.

A family of cationic polyamides for in vitro and in vivo gene transfection

The purpose of this study is to develop biodegradable cationic polyamides for non-viral gene delivery and elucidate their structural effects on gene transfection activity. To this end, a group of novel cationic polyamides were synthesized by polycondensation reaction between different di-p-nitrophenyl esters and tertiary amine-containing primary diamines. These linear polyamides have flexible alkylene group (ethylene or propylene), protonable amino group and bioreducible disulfide linkage in the polyamide main chain. The alkylene group and disulfide linkage in these polyamides have a distinct effect on their gene delivery properties including buffering capacity, gene binding ability and intracellular gene release profile. Those cationic polyamides containing disulfide linkage and 1,4-bis(3-aminopropyl)piperazine (BAP) residue exhibited high buffering capacity (endosomal escape ability), high gene binding ability, and intracellular gene release ability, thus inducing fast gene nucleus translocation and robust gene transfection in vitro against different cell lines and rat bone marrow mesenchymal stem cells. Moreover, the transfection efficiencies in vitro were comparable or higher than those of 25 kDa branched polyethylenimine and Lipofectamine 2000 transfection agent as positive controls. These cationic polyamides and their polyplexes were of low cytotoxicity when an optimal transfection efficacy was achieved. In vivo transfection tests showed that bioreducible BAP-based polyamides were applicable for intravenous gene delivery in a mouse model, leading to higher level of transgene expression in the liver as compared to 22 kDa linear polyethylenimine as a positive control. These cationic polyamides provide a useful platform to elucidate the relationship between chemical functionalities and gene transfection activity.

Multilayered Thin Films from Boronic Acid-Functional Poly(amido amine)s

PURPOSE

To investigate the properties of phenylboronic acid-functional poly(amido amine) polymers (BA-PAA) in forming multilayered thin films with poly(vinyl alcohol) (PVA) and chondroitin sulfate (ChS), and to evaluate their compatibility with COS-7 cells.

METHODS

Copolymers of phenylboronic acid-functional poly(amido amine)s, differing in the content of primary amine (DAB-BA-PAA) or alcohol (ABOL-BA-PAA) side groups, were synthesized and applied in the formation of multilayers with PVA and ChS. Biocompatibility of the resulting films was evaluated through cell culture experiments with COS-7 cells grown on the films.

RESULTS

PVA-based multilayers were thin, reaching ~100 nm at 10 bilayers, whereas ChS-based multilayers were thick, reaching ~600 nm at the same number of bilayers. All of the multilayers are stable under physiological conditions in vitro and are responsive to reducing agents, owing to the presence of disulfide bonds in the polymers. PVA-based films were demonstrated to be responsive to glucose at physiological pH at the investigated glucose concentrations (10-100 mM). The multilayered films displayed biocompatibility in cell culture experiments, promoting attachment and proliferation of COS-7 cells.

CONCLUSIONS

Responsive thin films based on boronic acid functional poly(amido amine)s are promising biocompatible materials for biomedical applications, such as drug releasing surfaces on stents or implants. Graphical Abstract Layer-by-Layer Assembly.

Strategies for oral delivery and mitochondrial targeting of CoQ10

Coenzyme Q10 (CoQ10), also known as ubiquinone or ubidecarenone, is a powerful, endogenously produced, intracellularly existing lipophilic antioxidant. It combats reactive oxygen species (ROS) known to be responsible for a variety of human pathological conditions. Its target site is the inner mitochondrial membrane (IMM) of each cell. In case of deficiency and/or aging, CoQ10 oral supplementation is warranted. However, CoQ10 has low oral bioavailability due to its lipophilic nature, large molecular weight, regional differences in its gastrointestinal permeability and involvement of multitransporters. Intracellular delivery and mitochondrial target ability issues pose additional hurdles. To maximize CoQ10 delivery to its biopharmaceutical target, numerous approaches have been undertaken. The review summaries the current research on CoQ10 bioavailability and highlights the headways to obtain a satisfactory intracellular and targeted mitochondrial delivery. Unresolved questions and research gaps were identified to bring this promising natural product to the forefront of therapeutic agents for treatment of different pathologies.

Cationic Polymers for Intracellular Delivery of Proteins

Many therapeutic proteins exert their pharmaceutical action inside the cytoplasm or onto individual organelles inside the cell. Intracellular protein delivery is considered to be the most direct, fastest and safest approach for curing gene-deficiency diseases, enhancing vaccination and triggering cell transdifferentiation processes, within other curative applications. However, several hurdles have to be overcome. For this purpose the use of polymers, with their ease of modification in physical and chemical properties, is attractive in protein drug carriers. They can protect their therapeutic protein cargo from degradation and enhance their bioavailability at targeted sites. In this chapter, potential and currently used polymers for fabrication of protein delivery systems and their applications for intracellular administration are discussed. Special attention is given to the use of cationic polymers for their ability to promote the cellular uptake of therapeutic proteins.

A pH and redox dual responsive 4-arm poly(ethylene glycol)-block-poly(disulfide histamine) copolymer for non-viral gene transfection in vitro and in vivo

A novel 4-arm poly(ethylene glycol)-b-poly(disulfide histamine) copolymer was synthesized by Michael addition reaction of poly(ethylene glycol) (PEG) vinyl sulfone and amine-capped poly(disulfide histamine) oligomer, being denoted as 4-arm PEG-SSPHIS. This copolymer was able to condense DNA into nanoscale polyplexes (<200 nm in average diameter) with almost neutral surface charge (+(5–10) mV). Besides, these polyplexes were colloidal stable within 4 h in HEPES buffer saline at pH 7.4 (physiological environment), but rapidly dissociated to liberate DNA in the presence of 10 mM glutathione (intracellular reducing environment). The polyplexes also revealed pH-responsive surface charges which markedly increased with reducing pH values from 7.4–6.3 (tumor microenvironment). In vitro transfection experiments showed that polyplexes of 4-arm PEG-SSPHIS were capable of exerting enhanced transfection efficacy in MCF-7 and HepG2 cancer cells under acidic conditions (pH 6.3–7.0). Moreover, intravenous administration of the polyplexes to nude mice bearing HepG2-tumor yielded high transgene expression largely in tumor rather other normal organs. Importantly, this copolymer and its polyplexes had low cytotoxicity against the cells in vitro and caused no death of the mice. The results of this study indicate that 4-arm PEG-SSPHIS has high potential as a dual responsive gene delivery vector for cancer gene therapy.

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

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

Comparison of lipoic and asparagusic acid for surface-initiated disulfide-exchange polymerization

Bring it on: Organic chemistry on surfaces and in solution is not the same; this study offers a perfect example that small changes (from 27 to 35°; see graphic) can result in big consequences. Strained cyclic disulfides from asparagusic, but not lipoic acid, are ideal for growing functional architectures directly on surfaces; for the substrate-initiated synthesis of cell-penetrating poly(disulfide)s in solution, exactly the contrary is true.

Design and physicochemical characterization of poly(amidoamine) nanoparticles and the toxicological evaluation in human endothelial cells: applications to peptide delivery to the brain

In this study, we investigated nanoparticles formulated by self-assembly of a biodegradable poly(amidoamine) (PAA) and a fluorescently labeled peptide, in their capacity to internalize in endothelial cells and deliver the peptide, with possible applications for brain drug delivery. The nanoparticles were characterized in terms of size, surface charge, and loading efficiency, and were applied on human cerebral microvascular endothelial cells (hCMEC/D3) and human umbilical vein endothelial cells (Huvec) cells. Cell-internalization and cytotoxicity experiments showed that the PAA-based nanocomplexes were essentially nontoxic, and the peptide was successfully internalized into cells. The results indicate that these PAAs have an excellent property as nontoxic carriers for intracellular protein and peptide delivery, and provide opportunities for novel applications in the delivery of peptides to endothelial cells of the brain.

Bioresponsive poly(amidoamine)s designed for intracellular protein delivery

Poly(amidoamine)s with bioreducible disulfide linkages in the main chain (SS-PAAs) and pH-responsive, negatively charged citraconate groups in the sidechain have been designed for effective intracellular delivery and release of proteins with a net positive charge at neutral pH. Using lysozyme as a cationic model protein these water soluble polymers efficiently self-assemble into nanocomplexes by charge attraction. At pH5 (the endosomal pH) the amide linkages connecting the citraconate groups in the sidechains of the SS-PAAs are hydrolyzed by intramolecular catalysis, resulting in expulsion of the negative citraconate groups and formation of protonated amine groups, resulting in charge reversal of the polymeric carrier from negative to positive. The concomitant endosomal buffering effect and increased polymer-endosomal membrane interactions are considered to lead to increased protein delivery into the cytosol. Besides destabilization of the polymer-protein nanoparticles by the charge reversal effect, intracellular cleavage of disulfide linkages in the polymer ensure further unpacking of the protein in the cytosol. Cellinternalization and cytotoxicity experiments with primary human umbilical vein endothelial cells (HUVEC) showed that the SS-PAA-based nanocomplexes were essentially non-toxic, and that lysozyme is successfully internalized into HUVEC. The results indicate that these charge reversal SS-PAAs have excellent properties as non-toxic intracellular delivery systems for cationic proteins.

Substrate-initiated synthesis of cell-penetrating poly(disulfide)s

Lessons from surface-initiated polymerization are applied to grow cell-penetrating poly(disulfide)s directly on substrates of free choice. Reductive depolymerization after cellular uptake should then release the native substrates and minimize toxicity. In the presence of thiolated substrates, propagators containing a strained disulfide from asparagusic or, preferably, lipoic acid and a guanidinium cation polymerize into poly(disulfide)s in less than 5 min at room temperature at pH 7. Substrate-initiated polymerization of cationic poly(disulfide)s and their depolymerization with dithiothreitol causes the appearance and disappearance of transport activity in fluorogenic vesicles. The same process is further characterized by gel-permeation chromatography and fluorescence resonance energy transfer.

Monitoring the degradation of reduction-sensitive gene carriers with fluorescence spectroscopy and flow cytometry

Polycations like poly(ethylene imine) (PEI) or poly(L-lysine) (pLL) form nanometer-sized complexes with nucleic acids (polyplexes) which can be used for gene delivery. It is known that the properties of these -carriers can be greatly improved by introducing disulfide bridges on the polymers, thus making them reduction sensitive. However, little is known about how such modified carriers behave intracellularly. Here, we describe a method that uses the reduction-sensitive fluorescent dye BODIPY FL L-cystine to label PEI and pLL. Our probe is activated under reductive conditions leading to strongly increased fluorescence intensity. Subsequently, we show how the intracellular route of polyplexes made from these labeled polymers can be monitored by flow cytometry.

Design and Development of Degradable Polyethylenimines for Delivery of DNA and Small Interfering RNA: An Updated Review

Polyethylenimine (PEI), considered as the most potent and promising alternative carrier to viral vectors, has been studied as the “state of the art” among various polymers for nonviral gene delivery applications for many years. Although PEI-based carrier minimizes the bottlenecks associated with viral vectors such as unwanted immunogenicity and production problems, the toxic side effects of PEI prevent its rapid advancements due to nondegradable nature. In this regard, various degradable cross-linking and/or grafting agents have been linked to synthesize degradable PEIs in order to minimize the toxicity and improve the efficacy of PEI-mediated gene carriers. This paper describes an update on various cross-linkers and grafting agents in the design and development of degradable PEI derivatives and their potential applications for effective delivery of DNA in vitro and in vivo. The molecular weight (MW) of PEI and the structural relationship to its cellular toxicity and transfection ability were also discussed. Finally, the potential applications of various degradable PEIs for small interfering RNA (siRNA)-mediated gene silencing were also covered.

Crosslinked linear polyethylenimine enhances delivery of DNA to the cytoplasm

Crosslinked polyethylenimines (PEIs) have been frequently examined over the past decade since they can maintain the transfection efficiency of commercially available, 25k branched PEI, but exhibit less cytotoxicity. The argument is often made that the degradability of such polymers, generally synthesized with either disulfide or hydrolytically degradable crosslinkers, is critical to the high efficiency and low toxicity of the system. In this work, we present a crosslinked linear PEI (xLPEI) system in which either disulfide-responsive or non-degradable linkages are incorporated. As with previous systems, strong transfection efficiency in comparison with commercial standards was achieved with low cytotoxicity. However, these properties were shown to be present when either the degradable or non-degradable crosslinker was used. Uncomplexed polymer was demonstrated to be the critical factor determining transfection efficiency for these polymers, mediating efficient endosomal escape without signs of cell membrane damage. While several crosslinked PEI systems in the literature have demonstrated the effect of the disulfide moiety, this work demonstrates that disulfide-mediated unpackaging may not be as important as conventionally thought for some PEI systems.

Advances in polymeric and inorganic vectors for nonviral nucleic acid delivery

Nonviral systems for nucleic acid delivery offer a host of potential advantages compared with viruses, including reduced toxicity and immunogenicity, increased ease of production and less stringent vector size limitations, but remain far less efficient than their viral counterparts. In this article we review recent advances in the delivery of nucleic acids using polymeric and inorganic vectors. We discuss the wide range of materials being designed and evaluated for these purposes while considering the physical requirements and barriers to entry that these agents face and reviewing recent novel approaches towards improving delivery with respect to each of these barriers. Furthermore, we provide a brief overview of past and ongoing nonviral gene therapy clinical trials. We conclude with a discussion of multifunctional nucleic acid carriers and future directions.

Bioreducible polymer-delivered siRNA targeting human telomerase reverse transcriptase for human cancer gene therapy

The success of siRNA therapeutics for cancer therapy largely depends on the delivery carrier that can safely and efficiently escort siRNA from the extracellular environment into the targeted human cancer cells. Over the past few years, disulfide-containing (bioreducible) cationic polymers have been designed, prepared and successfully applied as nonviral carriers for powerful gene/siRNA transfer, meanwhile displaying lower cytotoxicity as compared with their counterparts lacking the disulfide linkage, in part due to the intracellular degradation of the disulfide linkage. We have recently developed bioreducible disulfide-based polyethylenimine (SSPEI) for potent in vitro and in vivo delivery of siRNA targeting human telomerase reverse transcriptase (hTERT). It was found that SSPEI-delivered hTERT siRNA induced significant growth inhibition of different human cancer cells in vitro and also tumor growth suppression in vivo. Importantly, the SSPEI, at an appropriate dose, revealed a negligible adverse effect on cellular metabolic activity in vitro and liver and kidney function in vivo.

Effects of branched or linear architecture of bioreducible poly(amido amine)s on their in vitro gene delivery properties

In this study, the gene delivery properties of new hyperbranched poly(amido amine)s (PAAs) with disulfide linkages in the main chain were investigated in comparison with their linear analogs. Eight different bioreducible PAAs were prepared by Michael addition of N,N'-bisacryloylpiperazine (BP) with cystamine (CYST) or N,N'-dimethylcystamine (DMC) and of N,N'-cystaminebisacrylamide (CBA) with N,N'-ethylenediamine (EDA) or N,N'-dimethylethylenediamine (DMEDA). In order to study the effect of terminal groups on the transfection efficiency, each polymer was terminated with 4-aminobutanol (ABOL) or with 2-aminoethanol (ETA). The hyperbranched and the linear PAAs generally formed polyplexes with plasmid DNA with sizes around 200nm and positive zeta potentials ranging from +10 to +22mV at polymer/DNA weight ratios equal or higher than 3/1. Remarkably low or no cytotoxicity was observed for both hyperbranched and linear PAAs. Hyperbranched CBA-containing PAAs showed higher gene expression in DNA transfection tests with COS-7 cells than their linear analogs and up to two times higher than linear PEI that was used as the reference polymer. Transfection efficiencies of the branched PAAs were generally enhanced by the presence of serum, which is a promising property for future in vivo studies with these hyperbranched PAAs. In this study the ease of synthetic modification of both linear and hyperbranched poly(amido amide)s and the versatility of hyperbranched PAAs in regulating DNA transfection and cytotoxicity are demonstrated. The results show the large possibilities for this class of polymers to provide polymeric vectors with controllable properties for gene therapy applications.

Ligand-decorated nanogels: fast one-pot synthesis and cellular targeting

Nanoscale vehicles for delivery have been of interest and extensively studied for two decades. However, the encapsulation stability of hydrophobic drug molecules in delivery vehicles and selective targeting these vehicles into disease cells are potential hurdles for efficient delivery systems. Here we demonstrate a simple and fast synthetic protocol of nanogels that shows high encapsulation stabilities. These nanogels can also be modified with various targeting ligands for active targeting. We show that the targeting nanogels (T-NGs), which are prepared within 2 h by a one-pot synthesis, exhibit very narrow size distributions and have the versatility of surface modification with cysteine-modified ligands including folic acid, cyclic arginine-glycine-aspartic acid (cRGD) peptide, and cell-penetrating peptide. T-NGs hold their payloads, undergo facilitated cell internalization by receptor-mediated uptake, and release their drug content inside cells due to the reducing intracellular environment. Selective cytotoxicity to cells, which have complementary receptors, is also demonstrated.

DEGRADABLE POLYETHYLENIMINE DERIVATIVES AS GENE CARRIERS

Gene therapy is a treatment for inborn and acquired diseases, although the development of safe and effective gene delivery system is a great challenge to make a gene therapy a success. Viral vectors have been used in a majority of clinics because of their high transfection efficiency in vitro and in vivo. However, their use has been limited because of several drawbacks, such as induction of immune response, recombination of wild-type viruses, limitation in the size of inserted gene, and difficulty in large-scale production. Nonviral vectors have been widely proposed safe alternatives to viral vectors because they have low immunogenicity, flexibility in the size of gene to be delivered, cell targetibility, and easy scalability of production, although they have low transfection efficiency compared to viral vectors. Among nonviral vectors, polyethylenimine (PEI) has been widely used as a standard gene carriers due to its high pH-buffering capacity for endosomal escape although high-molecular-weight PEI is too toxic owing to non-degradability. Recently, many types of degradable PEI have been studied due to high transfection efficiency with lower cytotoxicity. This review explains recent progress on the development of degradable PEIs as nonviral vectors. The present paper summarizes the transfection efficiency of DNA or silencing efficiency of small interfering RNA (siRNA) based on the kinds of degradable linkage between low PEI and crosslinkers. Degradable linkages, such as ester, disulfide, imines, carbamate, amide and ketal in the degradable PEIs are covered.