Polymer brush-stabilized polyplex for a siRNA carrier with long circulatory half-life

Targeted delivery systems of siRNA based on ionizable lipid nanoparticles and cationic polymer vectors

As an emerging therapeutic tool, small interfering RNA (siRNA) had the capability to down-regulate nearly all human mRNAs via sequence-specific gene silencing. Numerous studies have demonstrated the substantial potential of siRNA in the treatment of broad classes of diseases. With the discovery and development of various delivery systems and chemical modifications, six siRNA-based drugs have been approved by 2024. The utilization of siRNA-based therapeutics has significantly propelled efforts to combat a wide array of previously incurable diseases and advanced at a rapid pace, particularly with the help of potent targeted delivery systems. Despite encountering several extracellular and intracellular challenges, the efficiency of siRNA delivery has been gradually enhanced. Currently, targeted strategies aimed at improving potency and reducing toxicity played a crucial role in the druggability of siRNA. This review focused on recent advancements on ionizable lipid nanoparticles (LNPs) and cationic polymer (CP) vectors applied for targeted siRNA delivery. Based on various types of targeted modifications, we primarily described delivery systems modified with receptor ligands, peptides, antibodies, aptamers and amino acids. Finally, we discussed the challenges and opportunities associated with siRNA delivery systems based on ionizable LNPs and CPs vectors.

siRNA-based nanotherapeutic approaches for targeted delivery in rheumatoid arthritis

Rheumatoid arthritis (RA), characterized as a systemic autoimmune ailment, predominantly results in substantial joint and tissue damage, affecting millions of individuals globally. Modern treatment modalities are being explored as the traditional RA therapy with non-specific immunosuppressive drugs showcased potential side effects and variable responses. Research potential with small interfering RNA (siRNA) depicted potential in the treatment of RA. These siRNA-based therapies could include genes encoding pro-inflammatory cytokines like TNF-α, IL-1, and IL-6, as well as other molecular targets such as RANK, p38 MAPK, TGF-β, Wnt/Fz complex, and HIF. By downregulating the expression of these genes, siRNA-based nanoformulations can attenuate inflammation, inhibit immune system dysregulation, and prevent tissue damage associated with RA. Strategies of delivering siRNA molecules through nanocarriers could be targeted to treat RA effectively, where specific genes associated with this autoimmune disease pathology can be selectively silenced. Additionally, simultaneous targeting of multiple molecular pathways may offer synergistic therapeutic benefits, potentially leading to more effective and safer therapeutic strategies for RA patients. This review critically highlights the in-depth pathology of RA, RNA interference-mediated molecular targets, and nanocarrier-based siRNA delivery strategies, along with the challenges and opportunities to harbor future solutions.

Molecular Bottlebrushes as Emerging Nanocarriers: Material Design and Biomedical Application

As a unique unimolecular nanoobject, molecular bottlebrushes (MBBs) have attracted great interest from researchers in nanocarriers attributed to their defined structure, size, and shape. MBBs with various architectures have been proposed and constructed with well-defined domains for loading "cargos", including core, shell, and periphery functional groups. Compared with nanomaterials based on self-assembly, MBBs have lots of advantages, including facile synthesis, flexible compositions, favorable stability, and tunable size and shape, that make them a promising nanoplatform for various applications. This paper summarizes the recent progress during the past decade, with a focus on developments within the last five years in the synthesis of MBBs with different architectures, and uses them as nanocarriers in drug delivery, biological imaging, and other emerging applications.

The landscape of nanoparticle-based siRNA delivery and therapeutic development

Five small interfering RNA (siRNA)-based therapeutics have been approved by the Food and Drug Administration (FDA), namely patisiran, givosiran, lumasiran, inclisiran, and vutrisiran. Besides, siRNA delivery to the target site without toxicity is a big challenge for researchers, and naked-siRNA delivery possesses several challenges, including membrane impermeability, enzymatic degradation, mononuclear phagocyte system (MPS) entrapment, fast renal excretion, endosomal escape, and off-target effects. The siRNA therapeutics can silence any disease-specific gene, but their intracellular and extracellular barriers limit their clinical applications. For this purpose, several modifications have been employed to siRNA for better transfection efficiency. Still, there is a quest for better delivery systems for siRNA delivery to the target site. In recent years, nanoparticles have shown promising results in siRNA delivery with minimum toxicity and off-target effects. Patisiran is a lipid nanoparticle (LNP)-based siRNA formulation for treating hereditary transthyretin-mediated amyloidosis that ultimately warrants the use of nanoparticles from different classes, especially lipid-based nanoparticles. These nanoparticles may belong to different categories, including lipid-based, polymer-based, and inorganic nanoparticles. This review briefly discusses the lipid, polymer, and inorganic nanoparticles and their sub-types for siRNA delivery. Finally, several clinical trials related to siRNA therapeutics are addressed, followed by the future prospects and conclusions.

The emerging potential of siRNA nanotherapeutics in treatment of arthritis

RNA interference (RNAi) using small interfering RNA (siRNA) has shown potential as a therapeutic option for the treatment of arthritis by silencing specific genes. However, siRNA delivery faces several challenges, including stability, targeting, off-target effects, endosomal escape, immune response activation, intravascular degradation, and renal clearance. A variety of nanotherapeutics like lipidic nanoparticles, liposomes, polymeric nanoparticles, and solid lipid nanoparticles have been developed to improve siRNA cellular uptake, protect it from degradation, and enhance its therapeutic efficacy. Researchers are also investigating chemical modifications and bioconjugation to reduce its immunogenicity. This review discusses the potential of siRNA nanotherapeutics as a therapeutic option for various immune-mediated diseases, including rheumatoid arthritis, osteoarthritis, etc. siRNA nanotherapeutics have shown an upsurge of interest and the future looks promising for such interdisciplinary approach-based modalities that combine the principles of molecular biology, nanotechnology, and formulation sciences.

Research progress of siVEGF complex and their application in antiangiogenic therapy

Vascular endothelial growth factor (VEGF) is an important factor in the development of some diseases such as tumors, ocular neovascular disease and endometriosis. Inhibition of abnormal VEGF expression is one of the most effective means of treating these diseases. The resistance and side effects of currently used VEGF drugs limit their application. Herein, small interfering RNA for VEGF (siVEGF) are developed to inhibit VEGF expression at the genetic level by means of RNA interference. However, as a foreign substance entering the organism, siVEGF is prone to induce an immune response or mismatch, which adversely affects the organism. It is also subjected to enzymatic degradation and cell membrane blockage, which greatly reduces its therapeutic effect. Targeted siVEGF complexes are constructed by nanocarriers to avoid their clearance by the body and precisely target cells, exerting anti-vascular effects for the treatment of relevant diseases. In addition, some multifunctional complexes allow for the combination of siVEGF with other therapeutic tools to improve the treat efficiency of the disease. Therefore, this review describes the construction of the siVEGF complex, its mechanism of action, application in anti-blood therapy, and provides an outlook on its current problems and prospects.

Therapeutic application of sequence-specific binding molecules for novel genome editing tools

Genome editing has been expected to widely increase the available treatment options for various diseases and permit pharmaceutical interventions in previously untreatable conditions. The availability of genome editing tools was dramatically increased by the development of the CRISPR-Cas9 system. However, a number of issues limit the use of the CRISPR-Cas9 system and other gene-editing tools in the clinical treatment of diseases. This review summarized the history and types of genome editing tools and limitations of their use. In addition, the study addressed several next-generation technologies aiming to overcome the limitations of current gene therapy protocols in an effort to accelerate the clinical development of potential treatment options. This review has provided an extensive foundation of the current state of genome editing technology and its clinical development. This review also indicate that the study additionally highlighted the need for multidisciplinary approaches to overcome current bottlenecks in the development of genome editing.

Overcoming Barriers for siRNA Therapeutics: From Bench to Bedside

The RNA interference (RNAi) pathway possesses immense potential in silencing any gene in human cells. Small interfering RNA (siRNA) can efficiently trigger RNAi silencing of specific genes. FDA Approval of siRNA therapeutics in recent years garnered a new hope in siRNA therapeutics. However, their therapeutic use is limited by several challenges. siRNAs, being negatively charged, are membrane-impermeable and highly unstable in the systemic circulation. In this review, we have comprehensively discussed the extracellular barriers, including enzymatic degradation of siRNAs by serum endonucleases and RNAases, rapid renal clearance, membrane impermeability, and activation of the immune system. Besides, we have thoroughly described the intracellular barriers such as endosomal trap and off-target effects of siRNAs. Moreover, we have reported most of the strategies and techniques in overcoming these barriers, followed by critical comments in translating these molecules from bench to bedside.

Self-regenerating giant hyaluronan polymer brushes

Tailoring interfaces with polymer brushes is a commonly used strategy to create functional materials for numerous applications. Existing methods are limited in brush thickness, the ability to generate high-density brushes of biopolymers, and the potential for regeneration. Here we introduce a scheme to synthesize ultra-thick regenerating hyaluronan polymer brushes using hyaluronan synthase. The platform provides a dynamic interface with tunable brush heights that extend up to 20 microns - two orders of magnitude thicker than standard brushes. The brushes are easily sculpted into micropatterned landscapes by photo-deactivation of the enzyme. Further, they provide a continuous source of megadalton hyaluronan or they can be covalently-stabilized to the surface. Stabilized brushes exhibit superb resistance to biofilms, yet are locally digested by fibroblasts. This brush technology provides opportunities in a range of arenas including regenerating tailorable biointerfaces for implants, wound healing or lubrication as well as fundamental studies of the glycocalyx and polymer physics.

Cationic copolymer-chaperoned DNAzyme sensor for microRNA detection

Multi-component nucleic acid enzymes (MNAzymes) are allosteric deoxyribozymes that are activated upon binding of a specific nucleic acid effector. MNAzyme activity is limited due to an insufficient assembly of the MNAzyme and its turnover. In this work, we describe the successful improvement of MNAzyme reactivity and selectivity by addition of cationic copolymers, which exhibit nucleic acid chaperone-like activity. The copolymer allowed a 210-fold increase in signal activity and a 95-fold increase in the signal-to-background selectivity of MNAzymes constructed for microRNA (miRNA) detection. The selectivity of the MNAzyme for homologous miRNAs was demonstrated in a multiplex format in which isothermal reactions of two different MNAzymes were performed. In addition, the copolymer permitted miRNA detections even in the presence of a ribonuclease which is ubiquitous in environments, indicating the protective effect of the copolymer against ribonucleases.

Designing siRNA-conjugated plant oil-based nanoparticles for gene silencing and cancer therapy

In this study, the anticancer activities of two siRNA carriers were compared using a human lung adenocarcinoma epithelial cell line (A549). Firstly, poly(styrene)-graft-poly(linoleic acid) (PS-g-PLina) and poly(styrene)-graft-poly(linoleic acid)-graft-poly(ethylene glycol) (PS-g-PLina-g-PEG) graft copolymers were synthesized by free-radical polymerization. PS-PLina and PS-PLina-PEG nanoparticles (NPs) were prepared by solvent evaporation method and were then characterized. The size was found as 150 ± 10 nm for PS-PLina and 184 ± 6 nm for PS-PLina-PEG NPs. The NPs were functionalized with poly(l-lysine) (PLL) for c-myc siRNA conjugation. siRNA entrapment efficiencies were found in the range of 4-63% for PS-PLina-PLL and 6-42% for PS-PLina-PEG-PLL NPs. The short-term stability test was realised for 1 month. siRNA release profiles were also investigated. In vitro anticancer activity of siRNA-NPs was determined by MTT, flow cytometry, and fluorescence microscopy analyses. Obtained findings showed that both NPs systems were promising as siRNA delivery tool for lung cancer therapy.

Cationic micelle: A promising nanocarrier for gene delivery with high transfection efficiency

Micelles have demonstrated an excellent ability to deliver several different types of therapeutic agents, including chemotherapy drugs, proteins, small-interfering RNA and DNA, into tumor cells. Cationic micelles, comprising self-assemblies of amphiphilic cationic polymers, have exhibited tremendous promise with respect to the delivery of therapy genes and gene transfection. To date, research in the field has focused on achieving an enhanced stability of the micellar assembly, prolonged circulation times and controlled release of the gene. This review focuses on the micelles as a nanosized carrier system for gene delivery, the system-related modifications for cytoplasm release, stability and biocompatibility, and clinic trials. In accordance with the development of synthetic chemistry and self-assembly technology, the structures and functionalities of micelles can be precisely controlled, and hence the synthetic micelles not only efficiently condense DNA, but also facilitate DNA endocytosis, endosomal escape, DNA uptake and nuclear transport, resulting in a comparable gene transfection of virus.

Engineering Nanoparticles for Targeted Delivery of Nucleic Acid Therapeutics in Tumor

In the past 10 years, with the increase of investment in clinical nano-gene therapy, there are many trials that have been discontinued due to poor efficacy and serious side effects. Therefore, it is particularly important to design a suitable gene delivery system. In this paper, we introduce the application of liposomes, polymers, and inorganics in gene delivery; also, different modifications with some stimuli-responsive systems can effectively improve the efficiency of gene delivery and reduce cytotoxicity and other side effects. Besides, the co-delivery of chemotherapy drugs with a drug tolerance-related gene or oncogene provides a better theoretical basis for clinical cancer gene therapy.

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.

Poly(Ethylene Glycol)-Polylactide Micelles for Cancer Therapy

For the treatment of malignancy, many therapeutic agents, including small molecules, photosensitizers, immunomodulators, proteins and genes, and so forth, have been loaded into nanocarriers for controllable cancer therapy. Among these nanocarriers, polymeric micelles have been considered as one of the most promising nanocarriers, some of which have already been applied in different stages of clinical trials. The successful advantages of polymeric micelles from bench to bedside are due to their special core/shell structures, which can carry specific drugs in certain disease conditions. Particularly, poly(ethylene glycol)–polylactide (PEG–PLA) micelles have been considered as one of the most promising platforms for drug delivery. The PEG shell effectively prevents the adsorption of proteins and phagocytes, thereby evidently extending the blood circulation period. Meanwhile, the hydrophobic PLA core can effectively encapsulate many therapeutic agents. This review summarizes recent advances in PEG–PLA micelles for the treatment of malignancy. In addition, future perspectives for the development of PEG–PLA micelles as drug delivery systems are also presented.

Next-Generation Magnetic Nanocomposites: Cytotoxic and Genotoxic Effects of Coated and Uncoated Ferric Cobalt Boron (FeCoB) Nanoparticles In Vitro

Metal nanoparticles (NPs) have unique physicochemical properties and a widespread application scope depending on their composition and surface characteristics. Potential biomedical applications and the growing diversity of novel nanocomposites highlight the need for toxicological hazard assessment of next-generation magnetic nanomaterials. Our study aimed to evaluate the cytotoxic and genotoxic properties of coated and uncoated ferric cobalt boron (FeCoB) NPs (5-15 nm particle size) in cultured normal human dermal fibroblasts. Cell proliferation was assessed via ATP bioluminescence kit, and DNA breakage and chromosomal damage were measured by alkaline comet assay and micronucleus test. Polyacryl acid-coated FeCoB NPs [polyacrylic acid (PAA)-FeCoB NPs) and uncoated FeCoB NPs inhibited cell proliferation at 10 μg/ml. DNA strand breaks were significantly increased by PAA-coated FeCoB NPs, uncoated FeCoB NPs and l-cysteine-coated FeCoB NPs (Cys-FeCoB NPs), although high concentrations (10 μg/ml) of coated NPs (Cys- and PAA-FeCoB NPs) showed significantly more DNA breakage when compared to uncoated ones. Uncoated FeCoB NPs and coated NPs (PAA-FeCoB NPs) also induced the formation of micronuclei. Additionally, PAA-coated NPs and uncoated FeCoB NPs showed a negative correlation between cell proliferation and DNA strand breaks, suggesting a common pathomechanism, possibly by oxidation-induced DNA damage. We conclude that uncoated FeCoB NPs are cytotoxic and genotoxic at in vitro conditions. Surface coating of FeCoB NPs with Cys and PAA does not prevent but rather aggravates DNA damage. Further safety assessment and a well-considered choice of surface coating are needed prior to application of FeCoB nanocomposites in biomedicine.

Angiogenesis regulation by nanocarriers bearing RNA interference

Since the approval of bevacizumab as anti-angiogenic therapy in 2004 by the FDA, an array of angiogenesis inhibitors have been developed and approved. However, results were disappointing with regard to their therapeutic efficacy. RNA interference approaches offer the possibility of rational design with high specificity, lacking in many current drug treatments for various diseases including cancer. However, in vivo delivery issues still represent a significant obstacle for widespread clinical applications. In the current review, we summarize the advances in the last decade in the field of angiogenesis-targeted RNA interference approaches, with special emphasis on oncology applications. We present pro-angiogenic and anti-angiogenic factors as potential targets, experimental evidence and clinical trials data on angiogenesis regulation by RNA interference. Consequent challenges and opportunities are discussed.

Rational Design of Cancer Nanomedicine: Nanoproperty Integration and Synchronization

Current cancer nanomedicines can only mitigate adverse effects but fail to enhance therapeutic efficacies of anticancer drugs. Rational design of next-generation cancer nanomedicines should aim to enhance their therapeutic efficacies. Taking this into account, this review first analyzes the typical cancer-drug-delivery process of an intravenously administered nanomedicine and concludes that the delivery involves a five-step CAPIR cascade and that high efficiency at every step is critical to guarantee high overall therapeutic efficiency. Further analysis shows that the nanoproperties needed in each step for a nanomedicine to maximize its efficiency are different and even opposing in different steps, particularly what the authors call the PEG, surface-charge, size and stability dilemmas. To resolve those dilemmas in order to integrate all needed nanoproperties into one nanomedicine, stability, surface and size nanoproperty transitions (3S transitions for short) are proposed and the reported strategies to realize these transitions are comprehensively summarized. Examples of nanomedicines capable of the 3S transitions are discussed, as are future research directions to design high-performance cancer nanomedicines and their clinical translations.

Combinatorial optimization of PEG architecture and hydrophobic content improves ternary siRNA polyplex stability, pharmacokinetics, and potency in vivo

A rationally-designed library of ternary siRNA polyplexes was developed and screened for gene silencing efficacy in vitro and in vivo with the goal of overcoming both cell-level and systemic delivery barriers. [2-(dimethylamino)ethyl methacrylate] (DMAEMA) was homopolymerized or copolymerized (50mol% each) with butyl methacrylate (BMA) from a reversible addition - fragmentation chain transfer (RAFT) chain transfer agent, with and without pre-conjugation to polyethylene glycol (PEG). Both single block polymers were tested as core-forming units, and both PEGylated, diblock polymers were screened as corona-forming units. Ternary siRNA polyplexes were assembled with varied amounts and ratios of core-forming polymers to PEGylated corona-forming polymers. The impact of polymer composition/ratio, hydrophobe (BMA) placement, and surface PEGylation density was correlated to important outcomes such as polyplex size, stability, pH-dependent membrane disruptive activity, biocompatibility, and gene silencing efficiency. The lead formulation, DB4-PDB12, was optimally PEGylated not only to ensure colloidal stability (no change in size by DLS between 0 and 24h) and neutral surface charge (0.139mV) but also to maintain higher cell uptake (>90% positive cells) than the most densely PEGylated particles. The DB4-PDB12 polyplexes also incorporated BMA in both the polyplex core- and corona-forming polymers, resulting in robust endosomolysis and in vitro siRNA silencing (~85% protein level knockdown) of the model gene luciferase across multiple cell types. Further, the DB4-PDB12 polyplexes exhibited greater stability, increased blood circulation time, reduced renal clearance, increased tumor biodistribution, and greater silencing of luciferase compared to our previously-optimized, binary parent formulation following intravenous (i.v.) delivery. This polyplex library approach enabled concomitant optimization of the composition and ratio of core- and corona-forming polymers (indirectly tuning PEGylation density) and identification of a ternary nanomedicine optimized to overcome important siRNA delivery barriers in vitro and in vivo.

Design Considerations for RNA Spherical Nucleic Acids (SNAs)

Ribonucleic acids (RNAs) are key components in many cellular processes such as cell division, differentiation, growth, aging, and death. RNA spherical nucleic acids (RNA-SNAs), which consist of dense shells of double-stranded RNA on nanoparticle surfaces, are powerful and promising therapeutic modalities because they confer advantages over linear RNA such as high cellular uptake and enhanced stability. Due to their three-dimensional shell of oligonucleotides, SNAs, in comparison to linear nucleic acids, interact with the biological environment in unique ways. Herein, the modularity of the RNA-SNA is used to systematically study structure-function relationships in order to understand how the oligonucleotide shell affects interactions with a specific type of biological environment, namely, one that contains serum nucleases. We use a combination of experiment and theory to determine the key architectural properties (i.e., sequence, density, spacer moiety, and backfill molecule) that affect how RNA-SNAs interact with serum nucleases. These data establish a set of design parameters for SNA architectures that are optimized in terms of stability.

Comparison of Modular PEG Incorporation Strategies for Stabilization of Peptide-siRNA Nanocomplexes

Nanoparticulate systems have shown great promise in overcoming the considerable trafficking barriers associated with systemic nucleic acid delivery, which must be addressed to unlock the full potential of technologies such as RNAi and gene editing in vivo. In addition to mediating the cytoplasmic delivery of nucleic cargo and shielding it from nuclease degradation and immunostimulation, nucleic-acid-containing nanomaterials delivered intravenously must also be stable in the bloodstream after administration to avoid toxicity and off-target delivery. To this end, the hydrophilic molecule polyethylene glycol (PEG) has been deployed in many different nanoparticle systems to prevent aggregation and recognition by the reticuloendothelial system. However, the optimal strategy for incorporating PEG into self-assembled nucleic acid delivery systems to obtain nanoparticle stability while retaining important functions such as receptor targeting and cargo activity remains unclear. In this work, we develop substantially improved formulations of tumor-penetrating nanocomplexes (TPNs), targeted self-assembled nanoparticles formulated with peptide carriers and siRNA that have been shown to mitigate tumor burden in an orthotopic model of ovarian cancer. We specifically sought to tailor TPNs for intravenous delivery by systematically comparing formulations with three different classes of modular PEG incorporation (namely PEG graft polymers, PEG lipids, and PEGylated peptide), each synthesized using straightforward bioconjugation techniques. We found that the addition of PEG lipids or PEGylated peptide carriers led to the formation of small and stable nanoparticles, but only nanoparticles formulated with PEGylated peptide carriers retained substantial activity in a gene silencing assay. In vivo, this formulation significantly decreased accumulation in off-target organs and improved initial availability in circulation compared to results from the original non-PEGylated particles. Thus, from among a set of candidate strategies, we identified TPNs with admixed PEGylated peptide carriers as the optimal formulation for systemic administration of siRNA on the basis of their performance in a battery of physicochemical and biological assays. Moreover, this optimized formulation confers pharmacologic advantages that may enable further translational development of tumor-penetrating nanocomplexes, highlighting the preclinical value of comparing formulation strategies and the relevance of this systematic approach for the development of other self-assembled nanomaterials.

Hydrophobic interactions between polymeric carrier and palmitic acid-conjugated siRNA improve PEGylated polyplex stability and enhance in vivo pharmacokinetics and tumor gene silencing

Formation of stable, long-circulating siRNA polyplexes is a significant challenge in translation of intravenously-delivered, polymeric RNAi cancer therapies. Here, we report that siRNA hydrophobization through conjugation to palmitic acid (siPA) improves stability, in vivo pharmacokinetics, and tumor gene silencing of PEGylated nanopolyplexes (siPA-NPs) with balanced cationic and hydrophobic content in the core relative to the analogous polyplexes formed with unmodified siRNA, si-NPs. Hydrophobized siPA loaded into the NPs at a lower charge ratio (N(+):P(-)) relative to unmodified siRNA, and siPA-NPs had superior resistance to siRNA cargo unpackaging in comparison to si-NPs upon exposure to the competing polyanion heparin and serum. In vitro, siPA-NPs increased uptake in MDA-MB-231 breast cancer cells (100% positive cells vs. 60% positive cells) but exhibited equivalent silencing of the model gene luciferase relative to si-NPs. In vivo in a murine model, the circulation half-life of intravenously-injected siPA-NPs was double that of si-NPs, resulting in a >2-fold increase in siRNA biodistribution to orthotopic MDA-MB-231 mammary tumors. The increased circulation half-life of siPA-NPs was dependent upon the hydrophobic interactions of the siRNA and the NP core component and not just siRNA hydrophobization, as siPA did not contribute to improved circulation time relative to unmodified siRNA when delivered using polyplexes with a fully cationic core. Intravenous delivery of siPA-NPs also achieved significant silencing of the model gene luciferase in vivo (∼40% at 24 h after one treatment and ∼60% at 48 h after two treatments) in the murine MDA-MB-231 tumor model, while si-NPs only produced a significant silencing effect after two treatments. These data suggest that stabilization of PEGylated siRNA polyplexes through a combination of hydrophobic and electrostatic interactions between siRNA cargo and the polymeric carrier improves in vivo pharmacokinetics and tumor gene silencing relative to conventional formulations that are stabilized solely by electrostatic interactions.

Silver nanoparticles-quercetin conjugation to siRNA against drug-resistant Bacillus subtilis for effective gene silencing: in vitro and in vivo

Quercetin (Qe) exhibited extremely low water solubility, and thus, it was modified using silver nanoparticles (AgNPs). We fabricated AgNPs combined with Qe (AgNPs-Qe). The modification suggested that the synergistic properties of Qe enhanced the antibacterial activity of AgNPs. However, AgNPs-Qe exerted no effect on many kinds of drug-resistant bacteria, including Pseudomonas aeruginosa and Bacillus subtilis. RNA interference has considerable therapeutic potential because of its high specificity and potential capability to evade drug resistance. Therefore, we stabilized AgNPs-Qe with a layer of molecules (siRNA). The newly fabricated nanoparticles exerted improved effect on many kinds of bacteria, including the most prominent drug-resistant species B. subtilis. Agarose gel electrophoresis showed that the highest critical nitrogen-to-phosphorus (N/P) ratio occurred at a vector/siRNA with a w/w ratio of 7:1. Characterization experiment indicated that the diameter of siRNA/AgNPs-Qe was approximately 40 nm (40 ± 10 nm). Moreover, AgNPs-Qe were stabilized with a layer of siRNA that was approximately 10nm thick. Results of the in vitro study suggested that siRNA/AgNPs-Qe could destroy the cell wall and inhibit bacterial propagation. Meanwhile, the in vivo experiment on the animal bacteremia model, as well as the optical imaging of nude mice and their isolated organs, demonstrated that bacteria accumulated in the blood, heart, liver, spleen, lungs, and kidneys after the intravenous injection of B. subtilis. The bacteria in the blood and organs, as well as the inflamed cells in the tissues, gradually decreased after the mice received intravenous tail injection of siRNA/AgNPs-Qe for treatment. Both the in vitro and the in vivo studies exhibit that siRNA/AgNPs-Qe can be a potential nanoscale drug delivery system for B. subtilis targeting bacterimia.

Hydrolytic charge-reversal of PEGylated polyplexes enhances intracellular un-packaging and activity of siRNA

Hydrolytically degrading nano-polyplexes (HDG-NPs) that reverse charge through conversion of tertiary amines to carboxylic acids were investigated to improve intracellular un-packaging of siRNA and target gene silencing compared to a non-degradable analog (non-HDG-NPs). Both NP types comprised reversible addition-fragmentation chain-transfer (RAFT) synthesized diblock copolymers of a poly(ethylene glycol) (PEG) corona-forming block and a cationic block for nucleic acid packaging that incorporated butyl methacrylate (BMA) and either dimethylaminoethyl methacrylate (DMAEMA, non-HDG-NPs) or dimethylaminoethyl acrylate (DMAEA, HDG-NPs). HDG-NPs decreased significantly in size and released significantly more siRNA (∼40%) than non-HDG-NPs after 24 h in aqueous solution. While both HDG-NPs and non-HDG-NPs had comparable uptake and cytotoxicity up to 150 nM siRNA doses, HDG-NPs achieved significantly higher target gene silencing of the model gene luciferase in vitro. High resolution FRET confocal microscopy was used to monitor the intracellular un-packaging of siRNA. Non-HDG-NPs had significantly higher FRET efficiency than HDG-NPs, indicating that siRNA delivered from HDG-NPs was more fully un-packaged and therefore had improved intracellular bioavailability.

One-pot RAFT and fast polymersomes assembly: a ‘beeline’ from monomers to drug-loaded nanovectors

A ‘fast RAFT’ strategy that allows the engineering of drug-containing polymer vesicles in only a few hours, starting from functional monomers.

Rational Design of Polymeric Hybrid Micelles with Highly Tunable Properties to Co‐Deliver MicroRNA‐34a and Vismodegib for Melanoma Therapy

A polymeric hybrid micelle (PHM) system with highly tunable properties is reported to co‐deliver small molecule and nucleic acid drugs for cancer therapy; this system is structurally simple and easy‐to‐fabricate. The PHM consists of two amphiphilic diblock copolymers, polycaprolactone‐polyethylenimine (PCL‐PEI) and polycaprolactone‐polyethyleneglycol (PCL‐PEG). PHMs are rationally designed with different physicochemical properties by simply adjusting the ratio of the two diblock copolymers and the near neutral PHM‐2 containing a low ratio of PCL‐PEI achieves the optimal balance between high tumor distribution and subsequent cellular uptake after intravenous injection. Encapsulating Hedgehog (Hh) pathway inhibitor vismodegib (VIS) and microRNA‐34a (miR‐34a) into PHM‐2 generates the VIS/PHM‐2/34a co‐delivery system. VIS/PHM‐2/34a shows synergistic anticancer efficacy in murine B16F10‐CD44+ cells, a highly metastatic tumor model of melanoma. VIS/PHM‐2/34a synergistically attenuates the expression of CD44, a vital receptor indicating the metastasis of melanoma. Intriguingly, inhibiting Hh pathway by VIS is accompanied by downregulation of CD44 expression, revealing that Hh signaling might be an upstream regulator of CD44 expression in melanoma. Thus, co‐delivery of miR‐34a and VIS demonstrates great potential in cancer therapy, and PHM offers a structurally simple and highly tunable platform for the co‐delivery of small molecule and nucleic acid drugs in tumor combination therapy.

Inter-polyelectrolyte nano-assembly induces folding and activation of functional peptides

Insufficient solubility, fragile folding structure and short half-life frequently hamper use of peptides as biological reagents or therapies. To enhance the peptide function, the effect of complexation of the peptides with ionic graft copolymers with water-soluble graft chains was tested in this study. Amphiphilic anionic peptide E5 acquires membrane disrupting activity at acidic pH due to folding from the random coil state to an ordered α-helical structure. Aggregation and imprecise folding of the peptide limited membrane disrupting activity of the peptide. In the presence of a cationic graft copolymer, E5 and its analogs adopted an ordered conformation without aggregation. The mixture of the peptides and the copolymer functioned more efficiently than peptide alone at not only acidic pH but also neutral pH at which the peptide alone had no activity. Similarly, a cationic peptide was successfully folded and activated by an anionic graft copolymer. Thus, our analysis indicated that spontaneous nano-assembly of ionic peptides with graft copolymers having opposite ionic charges triggers the folding of peptides without loss of solubility, leading to enhanced bioactivity.

Cationic Mucic Acid Polymer-Based siRNA Delivery Systems

Nanoparticle (NP) delivery systems for small interfering RNA (siRNA) that have good systemic circulation and high nucleic acid content are highly desired for translation into clinical use. Here, a family of cationic mucic acid-containing polymers is synthesized and shown to assemble with siRNA to form NPs. A cationic mucic acid polymer (cMAP) containing alternating mucic acid and charged monomers is synthesized. When combined with siRNA, cMAP forms NPs that require steric stabilization by poly(ethylene glycol) (PEG) that is attached to the NP surface via a 5-nitrophenylboronic acid linkage (5-nitrophenylboronic acid-PEGm (5-nPBA-PEGm)) to diols on mucic acid in the cMAP in order to inhibit aggregation in biological fluids. As an alternative, cMAP is covalently conjugated with PEG via two methods. First, a copolymer is prepared with alternating cMAP-PEG units that can form loops of PEG on the surface of the formulated siRNA-containing NPs. Second, an mPEG-cMAP-PEGm triblock polymer is synthesized that could lead to a PEG brush configuration on the surface of the formulated siRNA-containing NPs. The copolymer and triblock polymer are able to form stable siRNA-containing NPs without and with the addition of 5-nPBA-PEGm. Five formulations, (i) cMAP with 5-nPBA-PEGm, (ii) cMAP-PEG copolymer both (a) with and (b) without 5-nPBA-PEGm, and (iii) mPEG-cMAP-PEGm triblock polymer both (a) with and (b) without 5-nPBA-PEGm, are used to produce NPs in the 30-40 nm size range, and their circulation times are evaluated in mice using tail vein injections. The mPEG-cMAP-PEGm triblock polymer provides the siRNA-containing NP with the longest circulation time (5-10% of the formulation remains in circulation at 60 min postdosing), even when a portion of the excess cationic components used in the formulation is filtered away prior to injection. A NP formulation using the mPEG-cMAP-PEGm triblock polymer that is free of excess components could contain as much as ca. 30 wt % siRNA.

A novel nonviral gene delivery system: multifunctional envelope-type nano device

In this review we introduce a new concept for developing a nonviral gene delivery system which we call "Programmed Packaging." Based on this concept, we succeeded in developing a multifunctional envelope-type nano device (MEND), which exerts high transfection activities equivalent to those of an adenovirus in a dividing cell. The use of MEND has been extended to in vivo applications. PEG/peptide/DOPE ternary conjugate (PPD)-MEND, a new in vivo gene delivery system for the targeting of tumor cells that dissociates surface-modified PEG in tumor tissue by matrix metalloproteinase (MMP) and exerts significant transfection activities, was developed. In parallel with the development of MEND, a quantitative gene delivery system, Confocal Image-assisted 3-dimensionally integrated quantification (CIDIQ), also was developed. This method identified the rate-limiting step of the nonviral gene delivery system by comparing it with adenoviral-mediated gene delivery. The results of this analysis provide a new direction for the development of rational nonviral gene delivery systems.

Preparation and characterization of PEG-modified PCL nanoparticles for oxygen carrier: a new application of Fourier transform infrared spectroscopy for quantitative analysis of the hemoglobin in nanoparticles

The influence of polyethylene glycol (PEG) molar ratio on the nanoparticles (NPs) properties is described herein. Especially, a facile and nondestructive determination route has been raised to quantify the hemoglobin (Hb) amounts in NPs via an internal standard FTIR method. The subsequent results indicated that, briefly, the PEG molar ratio did negligible influence on the size distribution of NPs, however, it did have great effect on the NPs zeta potential and hydrophilicity as well as the Hb loading amount. These findings highlight that the PEG density on the surface is a key parameter affecting the NPs properties.

Addition of poly (propylene glycol) to multiblock copolymer to optimize siRNA delivery

Previous studies have examined different strategies for siRNA delivery with varying degrees of success. These include use of viral vectors, cationic liposomes, and polymers. Several copolymers were designed and synthesized based on blocks of poly(ethylene glycol) PEG, poly(propylene glycol) PPG, and poly(l-lysine). These were designated as P1, P2, and P3. We studied the copolymer self-assembly, siRNA binding, particle size, surface potential, architecture of the complexes, and siRNA delivery. Silencing of GFP using copolymer P3 to deliver GFP-specific siRNA to Neuro-2a cells expressing GFP was almost as effective as using Lipofectamine 2000, with minimal cytotoxicity. Thus, we have provided a new copolymer platform for siRNA delivery that we can continue to modify for improved delivery of siRNA in vitro and eventually in vivo.

Balancing cationic and hydrophobic content of PEGylated siRNA polyplexes enhances endosome escape, stability, blood circulation time, and bioactivity in vivo

A family of pH-responsive diblock polymers composed of poly[(ethylene glycol)-b-[(2-(dimethylamino)ethyl methacrylate)-co-(butyl methacrylate)], PEG-(DMAEMA-co-BMA), was reversible addition-fragmentation chain transfer (RAFT) synthesized with 0-75 mol % BMA in the second polymer block. The relative mole % of DMAEMA and BMA was varied in order to identify a polymer that can be used to formulate PEGylated, siRNA-loaded polyplex nanoparticles (NPs) with an optimized balance of cationic and hydrophobic content in the NP core based on siRNA packaging, cytocompatibility, blood circulation half-life, endosomal escape, and in vivo bioactivity. The polymer with 50:50 mol % of DMAEMA:BMA (polymer "50 B") in the RAFT-polymerized block efficiently condensed siRNA into 100 nm NPs that displayed pH-dependent membrane disruptive behavior finely tuned for endosomal escape. In vitro delivery of siRNA with polymer 50 B produced up to 94% protein-level knockdown of the model gene luciferase. The PEG corona of the NPs blocked nonspecific interactions with constituents of human whole blood, and the relative hydrophobicity of polymer 50 B increased NP stability in the presence of human serum or the polyanion heparin. When injected intravenously, 50 B NPs enhanced blood circulation half-life 3-fold relative to more standard PEG-DMAEMA (0 B) NPs (p < 0.05), due to improved stability and a reduced rate of renal clearance. The 50 B NPs enhanced siRNA biodistribution to the liver and other organs and significantly increased gene silencing in the liver, kidneys, and spleen relative to the benchmark polymer 0 B (p < 0.05). These collective findings validate the functional significance of tuning the balance of cationic and hydrophobic content of polyplex NPs utilized for systemic siRNA delivery in vivo.

Multifunctional receptor-targeted nanocomplexes for the delivery of therapeutic nucleic acids to the brain

Convection enhanced delivery (CED) is a method of direct injection to the brain that can achieve widespread dispersal of therapeutics, including gene therapies, from a single dose. Non-viral, nanocomplexes are of interest as vectors for gene therapy in the brain, but it is essential that administration should achieve maximal dispersal to minimise the number of injections required. We hypothesised that anionic nanocomplexes administered by CED should disperse more widely in rat brains than cationics of similar size, which bind electrostatically to cell-surface anionic moieties such as proteoglycans, limiting their spread. Anionic, receptor-targeted nanocomplexes (RTN) containing a neurotensin-targeting peptide were prepared with plasmid DNA and compared with cationic RTNs for dispersal and transfection efficiency. Both RTNs were labelled with gadolinium for localisation in the brain by MRI and in brain sections by LA-ICP-MS, as well as with rhodamine fluorophore for detection by fluorescence microscopy. MRI distribution studies confirmed that the anionic RTNs dispersed more widely than cationic RTNs, particularly in the corpus callosum. Gene expression levels from anionic formulations were similar to those of cationic RTNs. Thus, anionic RTN formulations can achieve both widespread dispersal and effective gene expression in brains after administration of a single dose by CED.

Tumor delivery of Photofrin® by PLL-g-PEG for photodynamic therapy

Photofrin® (porfimer sodium) is a photosensitive reagent used for photodynamic therapy (PDT) of tumors and dysplasias. Because only photo-irradiated sites are damaged, PDT is less invasive than systemic treatments. However, a photosensitive reaction is a major side effect of systemically delivered Photofrin. To enhance localization of Photofrin to tumors, we have formulated Photofrin with the tumor-localizing graft copolymer poly(ethylene glycol)-grafted poly(l-lysine), PLL-g-PEG. We demonstrate that Photofrin preferentially interacts with PLL-g-PEG through both ionic and hydrophobic interactions. The serum competitive study showed that the highly PEG-grafted PLL is better for preventing serum binding to the Photofrin/PLL-g-PEG complex. In tumor-bearing mice, formulation of Photofrin with PLL-g-PEG enhanced tumor localization of Photofrin as twice as Photofrin alone and concomitantly suppressed the photosensitivity reaction drastically.

Surface-modified HK:siRNA nanoplexes with enhanced pharmacokinetics and tumor growth inhibition

We characterized in this study the pharmacokinetics and antitumor efficacy of histidine-lysine (HK):siRNA nanoplexes modified with PEG and a cyclic RGD (cRGD) ligand targeting αvβ3 and αvβ5 integrins. With noninvasive imaging, systemically administered surface-modified HK:siRNA nanoplexes showed nearly 4-fold greater blood levels, 40% higher accumulation in tumor tissue, and 60% lower luciferase activity than unmodified HK:siRNA nanoplexes. We then determined whether the surface-modified HK:siRNA nanoplex carrier was more effective in reducing MDA-MB-435 tumor growth with an siRNA targeting Raf-1. Repeated systemic administration of the selected surface modified HK:siRNA nanoplexes targeting Raf-1 showed 35% greater inhibition of tumor growth than unmodified HK:siRNA nanoplexes and 60% greater inhibition of tumor growth than untreated mice. The improved blood pharmacokinetic results and tumor localization observed with the integrin-targeting surface modification of HK:siRNA nanoplexes correlated with greater tumor growth inhibition. This investigation reveals that through control of targeting ligand surface display in association with a steric PEG layer, modified HK: siRNA nanoplexes show promise to advance RNAi therapeutics in oncology and potentially other critical diseases.

N-acetylgalactosamine functionalized mixed micellar nanoparticles for targeted delivery of siRNA to liver

Due to its efficient and specific gene silencing ability, RNA interference has shown great potential in the treatment of liver diseases. However, achieving in vivo delivery of siRNA to critical liver cells remains the biggest obstacle for this technique to be a real clinic therapeutic modality. Here, we describe a promising liver targeting siRNA delivery system based on N-acetylgalactosamine functionalized mixed micellar nanoparticles (Gal-MNP), which can efficiently deliver siRNA to hepatocytes and silence the target gene expression after systemic administration. The Gal-MNP were assembled in aqueous solution from mixed N-acetylgalactosamine functionalized poly(ethylene glycol)-b-poly(ε-caprolactone) and cationic poly(ε-caprolactone)-b-poly(2-aminoethyl ethylene phosphate) (PCL-b-PPEEA); the properties of nanoparticles, including particle size, zeta potential and the density of poly(ethylene glycol) could be easily regulated. The hepatocyte-targeting effect of Gal-MNP was demonstrated by significant enriching of fluorescent siRNA in primary hepatocytes in vitro and in vivo. Successful down-regulation of liver-specific apolipoprotein B (apoB) expression was achieved in mouse liver, at both the transcriptional and protein level, following intravenous injection of Gal-MNP/siapoB to BALB/c mice. Systemic delivery of Gal-MNP/siRNA did not induce the innate immune response or positive hepatotoxicity. The results of this study suggested therapeutic potential for the Gal-MNP/siRNA system in liver disease.

Exploring the efficiency of gallic acid-based dendrimers and their block copolymers with PEG as gene carriers

The synthesis of a new family of amino-functionalized gallic acid-triethylene glycol (GATG) dendrimers and their block copolymers with polyethylene glycol (PEG) has recently being disclosed. In addition, these dendrimers have shown potential for gene delivery applications, as they efficiently complex nucleic acids and form small and homogeneous dendriplexes. On this basis, the present study aimed to explore the interaction of the engineered dendriplexes with blood components, as well as their stability, cytotoxicity and ability to enter and transfect mammalian cells. Results show that GATG dendrimers can form stable dendriplexes, protect the associated pDNA from degradation, and are biocompatible with HEK-293T cells and erythrocytes. More importantly, dendriplexes are effectively internalized by HEK-293T cells, which are successfully transfected. Besides, PEGylation has a marked influence on the properties of the resulting dendriplexes. While PEGylated GATG dendrimers have improved biocompatibility, the long PEG chains limit their uptake by HEK-293T cells, and thus, their ability to transfect them. As a consequence, the degree of PEGylation in dendriplexes containing dendrimer/block copolymer mixtures emerges as an important parameter to be modulated in order to obtain an optimized stealth formulation able to effectively induce the expression of the encoded protein.

Original submitted 29 November 2011; Revised submitted 8 March 2012; Published online 20 July 2012

Self-assembly nanomicelles based on cationic mPEG-PLA-b-Polyarginine(R15) triblock copolymer for siRNA delivery

Due to the absence of safe and effective carriers for in vivo delivery, the applications of small interference RNA (siRNA) in clinic for therapeutic purposes have been limited. In this study, a biodegradable amphiphilic tri-block copolymer (mPEG(2000)-PLA(3000)-b-R(15)) composed of monomethoxy poly(ethylene glycol), poly(d,l-lactide) and polyarginine was synthesized and further self-assembled to cationic polymeric nanomicelles for in vivo siRNA delivery, with an average diameter of 54.30 ± 3.48 nm and a zeta potential of approximately 34.8 ± 1.77 mV. The chemical structures of the copolymers were well characterized by (1)H NMR spectroscopy and FT-IR spectra. In vitro cytotoxicity and hemolysis assays demonstrated that the polymeric nanomicelles showed greater cell viability and haemocompatibility than those of polyethyleneimine (PEI) or R(15) peptide. In vitro experiments demonstrated that EGFR targeted siRNA formulated in micelleplexes exhibited approximately 65% inhibition of EGFR expression on MCF-7 cells in a sequence-specific manner, which was comparable to Lipofectamine™ 2000. The results of intravenous administration showed Micelleplex/EGFR-siRNA significantly inhibited tumor growth in nude mice xenografted MCF-7 tumors, with a remarkable inhibition of EGFR expression. Furthermore, no positive activation of the innate immune responses and no significant body weight loss was observed during treatment suggested that this polymeric micelle delivery system is non-toxic. In conclusion, the present nanomicelles based on cationic mPEG(2000)-PLA(3000)-b-R(15) copolymer would be a safe and efficient nanocarrier for in vivo delivery of therapeutic siRNA.

Enhancing in vivo circulation and siRNA delivery with biodegradable polyethylenimine-graft-polycaprolactone-block-poly(ethylene glycol) copolymers

The purpose of this study was to enhance the in vivo blood circulation time and siRNA delivery efficiency of biodegradable copolymers polyethylenimine-graft-polycaprolactone-block-poly(ethylene glycol) (hy-PEI-g-PCL-b-PEG) by introducing high graft densities of PCL-PEG chains. SYBR(®) Gold and heparin assays indicated improved stability of siRNA/copolymer-complexes with a graft density of 5. At N/P 1, only 40% siRNA condensation was achieved with non-grafted polymer, but 95% siRNA was condensed with copolymer PEI25k-(PCL570-PEG5k)(5). Intracellular uptake studies with confocal laser scanning microscopy and flow cytometry showed that the cellular uptake was increased with graft density, and copolymer PEI25k-(PCL570-PEG5k)(5) was able to deliver siRNA much more efficiently into the cytosol than into the nucleus. The in vitro knockdown effect of siRNA/hyPEI-g-PCL-b-PEG was also significantly improved with increasing graft density, and the most potent copolymer PEI25k-(PCL570-PEG5k)(5) knocked down 84.43% of the GAPDH expression. Complexes of both the copolymers with graft density 3 and 5 circulated much longer than unmodified PEI25 kDa and free siRNA, leading to a longer elimination half-life, a slower clearance and a three- or fourfold increase of the AUC compared to free siRNA, respectively. We demonstrated that the graft density of the amphiphilic chains can enhance the siRNA delivery efficiency and blood circulation, which highlights the development of safe and efficient non-viral polymeric siRNA nanocarriers that are especially stable and provide longer circulation in vivo.

Magnetic DNA vector constructed from PDMAEMA polycation and PEGylated brush-type polyanion with cross-linkable shell

A novel magnetic-responsive complex composed of polycation, DNA, and polyanion has been constructed via electrostatic interaction. The magnetic nanoparticles (MNPs) were first coated with a polycation, poly[2-(dimethylamino)ethyl methacrylate] end-capped with cholesterol moiety (Chol-PDMAEMA(30)), and then binded with DNA through electrostatic interaction; the complexes were further interacted with the brush-type polyanion, namely poly[poly(ethylene glycol)methyl ether methacrylate]-block-poly[methacrylic acid carrying partial mercapto groups] (PPEGMA-b-PMAA(SH)). The resulting magnetic particle/DNA/polyion complexes could be stabilized by oxidizing the mercapto groups to form cross-linking shell with bridging disulfide (S-S) between PPEGMA-b-PMAA(SH) molecular chains. The interactions among DNA, Chol-PDMAEMA coated MNPs, and PPEGMA-b-PMAA(SH) were studied by agarose gel retardation assay. The complexes were fully characterized by means of zeta potential, transmission electron microscopy (TEM), dynamic light scattering (DLS) measurements, cytotoxicity assay, antinonspecific protein adsorption, and in vitro transfection tests. All these results indicate that this kind of magnetic-responsive complex has potential applications for gene vector.