Novel Symmetric Amphiphilic Dendritic Poly(l-lysine)-b-Poly(l-lactide)-b-Dendritic Poly(l-lysine) with High Plasmid DNA Binding Affinity as a Biodegradable Gene Carrier

Safety Challenges and Application Strategies for the Use of Dendrimers in Medicine

Dendrimers are used for a variety of applications in medicine but, due to their host–guest and entrapment characteristics, are particularly used for the delivery of genes and drugs. However, dendrimers are intrinsically toxic, thus creating a major limitation for their use in biological systems. To reduce such toxicity, biocompatible dendrimers have been designed and synthesized, and surface engineering has been used to create advantageous changes at the periphery of dendrimers. Although dendrimers have been reviewed previously in the literature, there has yet to be a systematic and comprehensive review of the harmful effects of dendrimers. In this review, we describe the routes of dendrimer exposure and their distribution in vivo. Then, we discuss the toxicity of dendrimers at the organ, cellular, and sub-cellular levels. In this review, we also describe how technology can be used to reduce dendrimer toxicity, by changing their size and surface functionalization, how dendrimers can be combined with other materials to generate a composite formulation, and how dendrimers can be used for the diagnosis of disease. Finally, we discuss future challenges, developments, and research directions in developing biocompatible and safe dendrimers for medical purposes.

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.

Biodegradable nano-organosilica gene carrier for high-efficiency gene transfection

Finding and exploiting safe and high-efficiency gene carriers have always been critical tasks for gene therapy. In this work, novel GSH-triggered degradable organosilica nanoparticles grafted with guanidinated-fluorinated α-polylysine (o-SiNP-GF) are prepared to be studied as gene carriers. The organosilica matrix of o-SiNP-GF is synthesized through the hydrolysis and condensation of 1,2-bis(triethoxysilyl)ethane (BTSE) and bis[3-(triethoxysilyl)propyl]tetrasulfide (BTSPTS). The o-SiNP-GF nanoparticles have a size of about 20 nm. They possess a positive zeta potential of 42 mV in PBS (pH 7.4) and can be disintegrated in the presence of GSH. The cytotoxicity and DNA-binding ability of o-SiNP-GF, as well as in vitro gene transfection performance of DNA/o-SiNP-GF complexes, have been investigated using enhanced green fluorescent protein plasmid (pEGFP) as the DNA model. MTT assay shows that the cytotoxicity of o-SiNP-GF is very low even at a concentration up to 800 μg mL-1. The o-SiNP-GF nanoparticles can effectively bind to pEGFP through a complex coacervation method. The in vitro transfection efficiency of pEGFP/o-SiNP-GF complexes in 293T cells is up to 94.7% at the N/P ratio of 10, much higher than that of pEGFP/PEI complexes. Luciferase gene and fibroblast growth factor (FGF2) gene are also used as the DNA models to study the in vivo gene transfection performance of the o-SiNP-GF carrier by bioluminescence imaging and the evaluation of the healing rate of a mouse wound, respectively. Compared with naked DNA and DNA/PEI complexes, DNA/o-SiNP-GF complexes show much higher in vivo transfection efficiency. This work not only provides a way to prepare novel GSH-triggered degradable organosilica nanoparticles of size less than 50 nm, but also proves that the modification of guanidinated-fluorinated α-polylysine is an effective method to improve the efficiency of gene carriers.

Designer Peptide and Protein Dendrimers: A Cross-Sectional Analysis

Dendrimers have attracted immense interest in science and technology due to their unique chemical structure that offers a myriad of opportunities for researchers. Dendritic design allows us to present peptides in a branched three-dimensional fashion that eventually leads to a globular shape, thus mimicking globular proteins. Peptide dendrimers, unlike other classes of dendrimers, have immense applications in biomedical research due to their biological origin. The diversity of potential building blocks and innumerable possibilities for design, along with the fact that the area is relatively underexplored, make peptide dendrimers sought-after candidates for various applications. This review summarizes the stepwise evolution of peptidic dendrimers along with their multifaceted applications in various fields. Further, the introduction of biomacromolecules such as proteins to a dendritic scaffold, resulting in complex macromolecules with discrete molecular weights, is an altogether new addition to the area of organic chemistry. The synthesis of highly complex and fully folded biomacromolecules on a dendritic scaffold requires expertise in synthetic organic chemistry and biology. Presently, there are only a handful of examples of protein dendrimers; we believe that these limited examples will fuel further research in this area.

Designing and Characterization of a Novel Delivery System for Improved Cellular Uptake by Brain Using Dendronised Apo-E-Derived Peptide

Neurodegenerative diseases (ND) are characterized by the progressive loss of neuronal structure or function mostly associated with neuronal death. The presence of the blood–brain barrier (BBB) is considered the main obstacle that prevents the penetration of almost all drugs rendering the diseases untreatable. Currently, one of the most promising approaches for drug delivery to the brain is by employing endogenous transcytosis to improve endothelial cell uptake. This study aimed to exploit this potential route of enhanced drug uptake through the design and characterization of low generations lysine dendrons with further functionalization of dendron with ApoE-derived peptide (AEP) ligand to improve cellular uptake and targeting of delivery to the brain. Dendrons and peptide were synthesized using solid phase peptide chemistry and the products were characterized by mass spectrometry and high performance liquid chromatography which confirmed the successful synthesis of dendrons and functionalization with the AEP. Cell viability and lactate dehydrogenase release were conducted to study the cytotoxicity of the materials against an immortalized brain endothelial cell line (bEnd.3) which demonstrated that no toxicity was seen at the concentration range used (up to 400 μM) for up to 48 h incubation. Cellular uptake of the synthesized molecules was examined using confocal microscopy and flow cytometer which clearly showed the cellular uptake of the dendronised carrier systems and that the highest percentage of cellular uptake was achieved with the AEP-functionalized dendron. This study has therefore demonstrated the successful synthesis of dendronised carrier systems with the potential to act as carriers for improved delivery and targeting the brain.

Intracellular plasmid DNA delivery by self-assembled nanoparticles of amphiphilic PHML-b-PLLA-b-PHML copolymers and the endocytosis pathway analysis

This work presents a new series of polycationic nanoparticles of (l-)-lysine conjugated amphiphilic triblock copolymer poly(hydroxyletheyl methacrylate-L-lysine)-b-poly(L-lactide)-b-poly(hydroxyletheyl methacrylate-L-lysine)s (PHML-b-PLLA-b-PHML) as potent low cytotoxic vectors for intracellular plasmid DNA delivery. First, the triblock PHML-b-PLLA-b-PHML copolymers were prepared via a combination of metal-free controlled ring opening polymerization and successive atom transfer radical polymerization. Then the cationic PHML-b-PLLA-b-PHML nanoparticles were further prepared by solution self-assembly. The particle size, zeta potential and morphology of as-prepared PHML-b-PLLA-b-PHML nanoparticles were characterized by dynamic light scattering and atomic force microscopy, respectively. The plasmid DNA binding affinities and polyplex stabilities were separately explored by agarose gel retardation and DNase I degradation assays. Then in vitro cytotoxicity and gene transfection efficiency of the PHML-b-PLLA-b-PHML nanoparticles vectors as well as relevant polyplex endocytosis pathway were investigated with H1299 cells. It was revealed that the PHML-b-PLLA-b-PHML nanoparticles exhibited low cytotoxicity, strong plasmid DNA binding affinity, high polyplex stability and efficient plasmid DNA transfection even under serum conditions (10% FBS). Moreover, the endocytosis analysis results disclosed that the PHML₃₀-b-PLLA-b-PHML₃₀ nanoparticle/plasmid DNA polyplexes were predominantly involved in lipid-raft-mediated endocytosis pathway, similar to that of SV40 virus-based vectors.

Hydrophobic chain modified low molecular weight polyethylenimine for efficient antigen delivery

Developing new therapeutic vaccines to promote antigen cross-presentation in antigen-presenting cells, especially dendritic cells, is regarded as a promising approach to prime antigen-specific T cell responses against tumor cells.

Combination of positive charges and honeycomb pores to promote MC3T3-E1 cell behaviour

Symmetric poly(l-lactide) (PLLA)-based dendritic l-lysine copolymer, with the PLLA block as the core and the lysine dendrons in the two ends, was prepared through a divergent method. The honeycomb pores on this copolymer film significantly enhanced the MC3T3-E1 cell functions.

Glutamine-chitosan modified calcium phosphate nanoparticles for efficient siRNA delivery and osteogenic differentiation

RNA interference (RNAi)-based therapy using small interfering RNA (siRNA) exhibits great potential to treat diseases. Although calcium phosphate (CaP)-based systems are attractive options to deliver nucleic acids due to their good biocompatibility and high affinity with nucleic acids, they are limited by uncontrollable particle formation and inconsistent transfection efficiencies. In this study, we developed a stable CaP nanocarrier system with enhanced intracellular uptake by adding highly cationic, glutamine-conjugated oligochitosan (Gln-OChi). CaP nanoparticles coated with Gln-OChi (CaP/Gln-OChi) significantly enhanced gene transfection and knockdown efficiency in both immortalized cell line (HeLa) and primary mesenchymal stem cells (MSCs) with minimal cytotoxicity. The osteogenic bioactivity of siRNA-loaded CaP/Gln-OChi particles was further confirmed in three-dimensional environments by using photocrosslinkable chitosan hydrogels encapsulating MSCs and particles loaded with siRNA targeting noggin, a bone morphogenetic protein antagonist. These findings suggest that our CaP/Gln-OChi nanocarrier provides an efficient and safe gene delivery system for therapeutic applications.

Responsive linear-dendritic block copolymers

The combination of dendritic and linear polymeric structures in the same macromolecule opens up new possibilities for the design of block copolymers and for applications of functional polymers that have self-assembly properties. There are three main strategies for the synthesis of linear-dendritic block copolymers (LDBCs) and, in particular, the emergence of click chemistry has made the coupling of preformed blocks one of the most efficient ways of obtaining libraries of LDBCs. In these materials, the periphery of the dendron can be precisely functionalised to obtain functional LDBCs with self-assembly properties of interest in different technological areas. The incorporation of stimuli-responsive moieties gives rise to smart materials that are generally processed as self-assemblies of amphiphilic LDBCs with a morphology that can be controlled by an external stimulus. Particular emphasis is placed on light-responsive LDBCs. Furthermore, a brief review of the biomedical or materials science applications of LDBCs is presented.

Functional and biodegradable dendritic macromolecules with controlled architectures as nontoxic and efficient nanoscale gene vectors

Gene therapy has provided great potential to revolutionize the treatment of many diseases. This therapy is strongly relied on whether a delivery vector efficiently and safely directs the therapeutic genes into the target tissue/cells. Nonviral gene delivery vectors have been emerging as a realistic alternative to the use of viral analogs with the potential of a clinically relevant output. Dendritic polymers were employed as nonviral vectors due to their branched and layered architectures, globular shape and multivalent groups on their surface, showing promise in gene delivery. In the present review, we try to bring out the recent trend of studies on functional and biodegradable dendritic polymers as nontoxic and efficient gene delivery vectors. By regulating dendritic polymer design and preparation, together with recent progress in the design of biodegradable polymers, it is possible to precisely manipulate their architectures, molecular weight and chemical composition, resulting in predictable tuning of their biocompatibility as well as gene transfection activities. The multifunctional and biodegradable dendritic polymers possessing the desirable characteristics are expected to overcome extra- and intracellular obstacles, and as efficient and nontoxic gene delivery vectors to move into the clinical arena.

Preparation of functional water-soluble low-cytotoxic poly(methacrylate)s with pendant cationic L-lysines for efficient gene delivery

In this work, we present the preparation of water-soluble poly(methacrylate)s with pendant cationic L-lysines PHMLs(6-30 K). Plasmid DNA binding affinity as well as particle sizes and zeta potentials of the polyplexes were examined for these PHML vectors, and their cytotoxicities were assayed with HeLa cells by CCK-8 and lactate dehydrogenase kits. Gene transfection efficacy and intracellular uptake of the polyplexes by the PHML vectors were also studied with HeLa cells. As a result, it was revealed that the low cytotoxic PHMLs tended to exhibit gene transfection efficiencies significantly higher than those of the linear structural PLL (15-30 K) control, in particular the molecular weight of a PHML vector remarkably influenced its pDNA binding affinity, transfection efficacy and intracellular uptake of the polyplexes.

Honeycomb-structured films by multifunctional amphiphilic biodegradable copolymers: surface morphology control and biomedical application as scaffolds for cell growth

Recently, fabrication of functional porous polymer films with patterned surface structures at the scale from nanometer to micrometer has been attracting increasing interests in material science and nanobiotechnology. In this work, we present new preparation of two series of multifunctional amphiphilic copolymers and preparation of their microporous thin films on solid substrates. First, diblock dendritic poly(l-lysine)-b-poly(l-lactide)s and triblock dendritic poly(l-lysine)-b-poly(l-lactide)-b-dendritic poly(l-lysine)s (C1-C6) were synthesized through 4-dimethylaminopyridine (DMAP)-catalyzed living ring-opening polymerization of (l-)-lactide with (l-)-lysine dendron initiators, and their structures were characterized by nuclear magnetic resonance spectrometer (NMR), gel permeation chromatography (GPC) and matrix-assisted laser desorption/ionization Fourier-transformed mass spectra (MALDI-FTMS). Employing the breath-figure (BF) fabrication strategy, thin films of the synthesized amphiphiles (C1-C6) were drop-cast, and their surface topologies were examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM), and the effects of new amphiphile structure and drop-casting parameters of amphiphile concentration, humidity and temperature on self-assembly of ordered porous surface were studied. Furthermore, the influence of surface energy of drop-casting substrates was additionally investigated. With a human cervical epithelial carcinoma cell line (HeLa), cytotoxicity of the prepared honeycomb-structured films by new amphiphile C6 was evaluated by thiazoyl-blue-tetrazolium-bromide (MTT) assay, and HeLa cell growth behavior with microporous amphiphile films as the scaffolds was also examined. It was found that tunable micropore diameter sizes and well ordered surface topologies of BF films could be achieved for the new prepared amphiphiles, and utilization of the honeycomb-like microporous films as scaffolds indicated favorable enhancement in cell proliferation. Therefore, the honeycomb-structured films by these biocompatible multifunctional amphiphiles may provide new materials as 3D-scaffold materials for potential application in tissue engineering and regeneration.

Novel poly(glycidyl methacrylate-b-propylene oxide-b-glycidyl methacrylate) derivatives with low cytotoxicity and efficient gene delivery

Gene therapy has been developed for decades, but is still hampered for general clinical treatment by lack of gene delivery vectors with high transfection efficiency and low cytotoxicity. In this study, well-defined BAB triblock copolymer, poly(glycidyl methacrylate-b-propylene oxide-b-glycidyl methacrylate), P(GMA-b-PO-b-GMA), was prepared via atom transfer radical polymerization and modified by different ratios of ethylenediamine (EDA) and 1-(3-aminopropyl) imidazole (API) to obtain cationic amphiphilic polymers. The difference in the ratio of EDA and API had an influence on pDNA-binding capability, size, and zeta potential of P(GMA-b-PO-b-GMA) derivatives. All the cationic amphiphilic polymers exhibited low cytotoxicity and good transfection activity in comparison with 25 kDa polyethylenimine (PEI) due to their special architecture. The optimal polymer, with 89% API and 11% EDA, showed the highest transfection efficiency among these polymers. Its luciferase expression at N/P ratio of 30 was comparable to that of 25 kDa PEI in a serum-free medium and higher than that of 25 kDa PEI by roughly an order of magnitude in a medium with serum.

α-Amino acid containing degradable polymers as functional biomaterials: rational design, synthetic pathway, and biomedical applications

Currently, biomedical engineering is rapidly expanding, especially in the areas of drug delivery, gene transfer, tissue engineering, and regenerative medicine. A prerequisite for further development is the design and synthesis of novel multifunctional biomaterials that are biocompatible and biologically active, are biodegradable with a controlled degradation rate, and have tunable mechanical properties. In the past decades, different types of α-amino acid-containing degradable polymers have been actively developed with the aim to obtain biomimicking functional biomaterials. The use of α-amino acids as building units for degradable polymers may offer several advantages: (i) imparting chemical functionality, such as hydroxyl, amine, carboxyl, and thiol groups, which not only results in improved hydrophilicity and possible interactions with proteins and genes, but also facilitates further modification with bioactive molecules (e.g., drugs or biological cues); (ii) possibly improving materials biological properties, including cell-materials interactions (e.g., cell adhesion, migration) and degradability; (iii) enhancing thermal and mechanical properties; and (iv) providing metabolizable building units/blocks. In this paper, recent developments in the field of α-amino acid-containing degradable polymers are reviewed. First, synthetic approaches to prepare α-amino acid-containing degradable polymers will be discussed. Subsequently, the biomedical applications of these polymers in areas such as drug delivery, gene delivery and tissue engineering will be reviewed. Finally, the future perspectives of α-amino acid-containing degradable polymers will be evaluated.

Design of biocompatible dendrimers for cancer diagnosis and therapy: current status and future perspectives

In the past decade, nanomedicine with its promise of improved therapy and diagnostics has revolutionized conventional health care and medical technology. Dendrimers and dendrimer-based therapeutics are outstanding candidates in this exciting field as more and more biological systems have benefited from these starburst molecules. Anticancer agents can be either encapsulated in or conjugated to dendrimer and be delivered to the tumour via enhanced permeability and retention (EPR) effect of the nanoparticle and/or with the help of a targeting moiety such as antibody, peptides, vitamins, and hormones. Imaging agents including MRI contrast agents, radionuclide probes, computed tomography contrast agents, and fluorescent dyes are combined with the multifunctional nanomedicine for targeted therapy with simultaneous cancer diagnosis. However, an important question reported with dendrimer-based therapeutics as well as other nanomedicines to date is the long-term viability and biocompatibility of the nanotherapeutics. This critical review focuses on the design of biocompatible dendrimers for cancer diagnosis and therapy. The biocompatibility aspects of dendrimers such as nanotoxicity, long-term circulation, and degradation are discussed. The construction of novel dendrimers with biocompatible components, and the surface modification of commercially available dendrimers by PEGylation, acetylation, glycosylation, and amino acid functionalization have been proposed as available strategies to solve the safety problem of dendrimer-based nanotherapeutics. Also, exciting opportunities and challenges on the development of dendrimer-based nanoplatforms for targeted cancer diagnosis and therapy are reviewed (404 references).

Dendrimer toxicity: Let's meet the challenge

Dendrimers are well-defined, versatile polymeric architecture with properties resembling biomolecules. Dendritic polymers emerged as outstanding carrier in modern medicine system because of its derivatisable branched architecture and flexibility in modifying it in numerous ways. Dendritic scaffold has been found to be suitable carrier for a variety of drugs including anticancer, anti-viral, anti-bacterial, antitubercular etc., with capacity to improve solubility and bioavailability of poorly soluble drugs. In spite of extensive applicability in pharmaceutical field, the use of dendrimers in biological system is constrained because of inherent toxicity associated with them. This toxicity is attributed to the interaction of surface cationic charge of dendrimers with negatively charged biological membranes in vivo. Interaction of dendrimers with biological membranes results in membrane disruption via nanohole formation, membrane thinning and erosion. Dendrimer toxicity in biological system is generally characterized by hemolytic toxicity, cytotoxicity and hematological toxicity. To minimize this toxicity two strategies have been utilized; first, designing and synthesis of biocompatible dendrimers; and second, masking of peripheral charge of dendrimers by surface engineering. Biocompatible dendrimers can be synthesized by employing biodegradable core and branching units or utilizing intermediates of various metabolic pathways. Dendrimer biocompatibility has been evaluated in vitro and in vivo for efficient presentation of biological performance. Surface engineering masks the cationic charge of dendrimer surface either by neutralization of charge, for example PEGylation, acetylation, carbohydrate and peptide conjugation; or by introducing negative charge such as half generation dendrimers. Neutral and negatively charged dendrimers do not interact with biological environment and hence are compatible for clinical applications as elucidated by various studies examined in this review. Chemical modification of the surface is an important strategy to overcome the toxicity problems associated with the dendrimers. The present review emphasizes on the approaches available to overcome the cationic toxicity inherently associated with the dendrimers.

Dendritic poly(L-lysine)-b-Poly(L-lactide)-b-dendritic poly(L-lysine) amphiphilic gene delivery vectors: roles of PLL dendritic generation and enhanced transgene efficacies via termini modification

As an effort to prepare new efficient gene delivery vectors, we have recently developed and reported an amphiphilic dendritic poly(L-lysine)-b-poly(L-lactide)-b-dendritic poly(L-lysine) D(2)-PLLA-D(2) with two-generation PLL dendrons and a PLLA block. In this work, we continued to explore the roles of dendritic PLL generation in DNA binding and intracellular delivery of gene, and a new series of amphiphilic dendritic poly(L-lysine)-b-poly(L-lactide)-b-dendritic poly(L-lysine)s D(n)-PLLA-D(n) (n = 3-5) were synthesized and were structurally characterized. Furthermore, plasmid DNA binding affinity for these cationic amphiphiles was examined by agarose gel electrophoresis and fluorescence titration assay in pure water and PBS buffer solution containing 150 mM NaCl (pH = 7.4), respectively. By dynamic light scattering (DLS) and transmission electronic microscopy (TEM), the interaction and complexation in between were investigated, concerning the DNA/vector polyplex particle morphologies and zeta potentials. Utilizing a human hepatocellular carcinoma cell-line SMMC-7721, cell toxicity, and gene transfection in vitro were explored. To further improve transgene efficiency for these synthetic cationic amphiphiles as gene delivery vectors, new structural DE(n)-PLLA-DE(n) (n = 2-3) were prepared through an amino termini modification of the D(n)-PLLA-D(n) (n = 2-3) with less toxic 4,7,10,13-tetraazatridecanoic acids, and gene transfection with these DE(n)-PLLA-DE(n) (n = 2-3) was examined with an alternative human gastric carcinoma cell-line HGC-27. As a result, the high plasmid DNA binding affinity, low cytotoxicity, and much enhanced transgene efficacy suggest a new possible clue to design effective synthetic gene delivery vectors with amphiphilic skeleton and less toxic polyamine building blocks.

Versatile strategy for the synthesis of dendronlike polypeptide/linear poly(epsilon-caprolactone) block copolymers via click chemistry

A new class of dendron-like polypeptide/linear poly(epsilon-caprolactone) block copolymers with asymmetrical topology (i.e., dendron-like poly(gamma-benzyl-l-glutamate)/linear PCL copolymers having 2(m) PBLG branches, m = 0, 1, 2, and 3; denoted as PCL-Dm-PBLG) was for the first time synthesized via the combination of controlled ring-opening polymerization (ROP) of epsilon-caprolactone, click chemistry, and the ROP of gamma-benzyl-l-glutamate N-carboxyanhydride (BLG-NCA). The linear hydroxyl-terminated PCL (PCL-OH) was synthesized by controlled ROP of epsilon-caprolactone and then transformed into clickable azide-terminated PCL (PCL-N(3)). The PCL-N(3) precursor was further click conjugated with propargyl focal point PAMAM-typed dendrons (i.e., Dm having 2(m) primary amine groups) to generate PCL-dendrons (PCL-Dm) using CuBr/PMDETA as catalyst in dimethylformamide solution at 35 degrees C. Finally, PCL-Dm was used as macroinitiator for the ROP of BLG-NCA monomer to produce the targeted PCL-Dm-PBLG block copolymers. Their molecular structures and physical properties were characterized in detail by FT-IR, NMR, matrix assisted laser desorption ionization time-of-flight mass spectrometry, gel permeation chromatography, differential scanning calorimetry, and wide-angle X-ray diffraction. To the best of our knowledge, this is the first report that describes the synthesis of dendron-like polypeptide/linear PCL block copolymers with asymmetrical topology via the combination of ROP and click chemistry. Consequently, this provides a versatile strategy for the synthesis of biodegradable and biomimetic dendron-like polypeptide-based biohybrids.

Facile approach for DNA encapsulation in functional polyion complex for triggered intracellular gene delivery: design, synthesis, and mechanism

A facile route for DNA encapsulation in triggered intracellular degradable polymer microcapsules has been achieved via electrostatic interaction, using a polycation, that is, poly[(dimethylamino)ethyl methacrylate] end-capped with cholesterol moiety (Chol-PDMAEMA(30)), along with a polyanion named MePEG2000-block-poly(methacrylic acid) carring partial thiol groups (MePEG2000-b-PMAA(SH)). The encapsulation procedure involves three steps: (i) DNA was first complexed with the polycation (Chol-PDMAEMA(30)); (ii) the complex was then further set into interaction with the anion-containing MePEG2000-b-PMAA(SH); and (iii) the compound carrier was subsequently obtained by cross-linking the thiol groups of the MePEG2000-b-PMAA(SH) to form disulfide linkages. The interactions between every pair among calf thymus DNA, Chol-PDMAEMA(30), and MePEG2000-b-PMAA(SH) were studied by agarose gel retardation assay and ethidium bromide displacement assay. The results indicate that the prepared microcapsules may remain stable during systemic circulation, but degrade and release the carried DNA in a cellular reducing environment. Furthermore, the biophysical properties of the microcapsule have been investigated by zeta-potential, laser light scattering, and transmission electron microscopy (TEM) measurements.

The decrease of PAMAM dendrimer-induced cytotoxicity by PEGylation via attenuation of oxidative stress

Due to their unique structure, poly(amidoamine) (PAMAM) dendrimers have been widely used in medical applications. However, PAMAM dendrimers bearing amino terminals show certain cytotoxicity. In order to improve their biocompatibility, we modified Generation-5 PAMAM dendrimers by conjugating them with poly(ethylene glycol) (PEG) of two different molecular weights and different number of chains. The IC(50) values of PEGylated dendrimers were 12-105 fold higher than those of PAMAM dendrimers. To investigate the influence of PEGylation on PAMAM-induced cytotoxicity, the intracellular responses, reactive oxygen species (ROS) content, mitochondrial membrane potential (MMP), and apoptosis were examined. The results indicated that conjugation with PEG could effectively reduce the PAMAM-induced cell apoptosis by attenuating the ROS production and inhibiting PAMAM-induced MMP collapse. Meanwhile, dendrimers conjugated with less PEG of lower molecular weight did not significantly change the endocytic properties. Dendrimers conjugated with more PEG of higher molecular weight were much less cytotoxic. This study provided a novel insight into the effects of PEGylation on the decrease of cytotoxicity at the molecular level.