A Comparison of Thiolated and Disulfide-Crosslinked Polyethylenimine for Nonviral Gene Delivery

Elevating nucleic acid delivery via a stable anionic peptide-dextran ternary system

Nucleic acid-based therapies hold promise for treating previously intractable diseases but require effective delivery vectors to protect the therapeutic agents and ensure efficient transfection. Cationic polymeric vectors are particularly notable for their adaptability, high transfection efficiency, and low cost, but their positive charge often attracts blood proteins, causing aggregation and reduced transfection efficiency. Addressing this, we designed an anionic peptide-grafted dextran (Dex-LipE5H) to serve as a cross-linkable coating to bolster the stability of cationic polymer/nucleic acid complexes. The Dex-LipE5H was synthesized through a Michael addition reaction, combining an anionic peptide (LipE5H) with dextran modified by divinyl sulfone. We demonstrated Dex-lipE5H utility in a novel ternary nucleic acid delivery system, CDex-LipE5H/PEI/nucleic acid. CDex-LipE5H/PEI/nucleic acid demonstrated lower cytotoxicity and superior anti-protein absorption ability compared to PEI/pDNA and Dex-LipE5H/PEI/pDNA. Most notably, the crosslinked CDex-LipE5H/PEI/pDNA demonstrated remarkable transfection performance in HepG2 cells, which poses significant transfection challenges, even in a medium with 20% serum. This system's effective siRNA interference performance was further validated through a PCSK9 gene knockdown assay. This investigation provides novel insights and contributes to the design of cost-effective, next-generation nucleic acid delivery systems with enhanced blood stability and transfection efficiency.

Two-step fabricating micelle-like nanoparticles of cisplatin with the 'real' long circulation and high bioavailability for cancer therapy

Cisplatin is a widely used anticancer drug for various solid tumors. However, the serious adverse effects caused by systemic distribution limit its wide use. In this study, we intend to use biocompatible materials polyethyleneimine (PEI) and poly(L-glutamic acid)-g-methoxy poly(ethylene glycol) (PLG-g-PEG) to construct nanoparticles to enhance the efficacy of cisplatin and reduce its side effects. The micelle-like nanoparticles were fabricated by a simple two-step method, with a core consisting of PEI and cisplatin and a PLG-g-mPEG coating layer. The obtained nanoparticles have a small particle size (41.79 nm) and high drug loading (16.43%). The coated nanoparticles (NP-II) strengthened the structure of PEI and cisplatin complex (NP-I) and slowed the drug release for less than 20% at pH 7.4 PBS in 24 h. Therefore, it could effectively inhibit the binding of free drug and plasma proteins to achieve the long circulation, and the bioavailability could be increased to about 600% and 285% of cisplatin solution and NP-I respectively. Besides, the cellular uptake of NP-II was enhanced in the acidic tumor microenvironment due to the detachment of coating layer and the increase of positive zeta potential of nanoparticles, which was benefit to reduce the side effect of cisplatin to normal cells. In vivo pharmacodynamic experiments also showed that NP-II improved the efficacy and reduced side effects compared to the cisplatin solution. In conclusion, the two-step fabricating micelle-like nanoparticles with the improved therapeutic efficiency and reduced side effects show great potential for cancer chemotherapy.

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.

Mannosylated Cationic Copolymers for Gene Delivery to Macrophages

Macrophages are desirable targets for gene therapy of cancer and other diseases. Cationic diblock copolymers of polyethylene glycol (PEG) and poly-L-lysine (PLL) or poly{N-[N-(2-aminoethyl)-2-aminoethyl]aspartamide} (pAsp(DET)) are synthesized and used to form polyplexes with a plasmid DNA (pDNA) that are decorated with mannose moieties, serving as the targeting ligands for the C type lectin receptors displayed at the surface of macrophages. The PEG-b-PLL copolymers are known for its cytotoxicity, so PEG-b-PLL-based polyplexes are cross-linked using reducible reagent dithiobis(succinimidyl propionate) (DSP). The cross-linked polyplexes display low toxicity to both mouse embryonic fibroblasts NIH/3T3 cell line and mouse bone marrow-derived macrophages (BMMΦ). In macrophages mannose-decorated polyplexes demonstrate an ≈8 times higher transfection efficiency. The cross-linking of the polyplexes decrease the toxicity, but the transfection enhancement is moderate. The PEG-b-pAsp(DET) copolymers display low toxicity with respect to the IC-21 murine macrophage cell line and are used for the production of non-cross-linked pDNA-contained polyplexes. The obtained mannose modified polyplexes exhibit ca. 500-times greater transfection activity in IC-21 macrophages compared to the mannose-free polyplexes. This result greatly exceeds the targeting gene transfer effects previously described using mannose receptor targeted non-viral gene delivery systems. These results suggest that Man-PEG-b-pAsp(DET)/pDNA polyplex is a potential vector for immune cells-based gene therapy.

Exploring the role of peptides in polymer-based gene delivery

Polymers are widely studied as non-viral gene vectors because of their strong DNA binding ability, capacity to carry large payload, flexibility of chemical modifications, low immunogenicity, and facile processes for manufacturing. However, high cytotoxicity and low transfection efficiency substantially restrict their application in clinical trials. Incorporating functional peptides is a promising approach to address these issues. Peptides demonstrate various functions in polymer-based gene delivery systems, such as targeting to specific cells, breaching membrane barriers, facilitating DNA condensation and release, and lowering cytotoxicity. In this review, we systematically summarize the role of peptides in polymer-based gene delivery, and elaborate how to rationally design polymer-peptide based gene delivery vectors.

STATEMENT OF SIGNIFICANCE

Polymers are widely studied as non-viral gene vectors, but suffer from high cytotoxicity and low transfection efficiency. Incorporating short, bioactive peptides into polymer-based gene delivery systems can address this issue. Peptides demonstrate various functions in polymer-based gene delivery systems, such as targeting to specific cells, breaching membrane barriers, facilitating DNA condensation and release, and lowering cytotoxicity. In this review, we highlight the peptides' roles in polymer-based gene delivery, and elaborate how to utilize various functional peptides to enhance the transfection efficiency of polymers. The optimized peptide-polymer vectors should be able to alter their structures and functions according to biological microenvironments and utilize inherent intracellular pathways of cells, and consequently overcome the barriers during gene delivery to enhance transfection efficiency.

Peptide-Mediated Tumor Targeting by a Degradable Nano Gene Delivery Vector Based on Pluronic-Modified Polyethylenimine

Polyethylenimine (PEI) is considered to be a promising non-viral gene delivery vector. To solve the toxicity versus efficacy and tumor-targeting challenges of PEI used as gene delivery vector, we constructed a novel non-viral vector DR5-TAT-modified Pluronic-PEI (Pluronic-PEI-DR5-TAT), which was based on the attachment of low-molecular-weight polyethylenimine (LMW-PEI) to the amphiphilic polymer Pluronic to prepare Pluronic-modified LMW-PEI (Pluronic-PEI). This was then conjugated to a multifunctional peptide containing a cell-penetrating peptide (TAT) and a synthetic peptide that would bind to DR5-a receptor that is overexpressed in cancer cells. The vector showed controlled degradation, favorable DNA condensation and protection performance. The Pluronic-PEI-DR5-TAT/DNA complexes at an N/P ratio of 15:1 were spherical nanoparticles of 122 ± 11.6 nm and a zeta potential of about 22 ± 2.8 mV. In vitro biological characterization results indicated that Pluronic-PEI-DR5-TAT/DNA complexes had a higher specificity for the DR5 receptor and were taken up more efficiently by tumor cells than normal cells, compared to complexes formed with PEI 25 kDa or Pluronic-PEI. Thus, the novel complexes showed much lower cytotoxicity to normal cells and higher gene transfection efficiency in tumor cells than that exhibited by PEI 25 kDa and Pluronic-PEI. In summary, our novel, degradable non-viral tumor-targeting vector is a promising candidate for use in gene therapy.

Versatile nuclear localization signal-based oligopeptide as a gene vector

To develop a versatile nuclear-targeted gene vector, nuclear localization signal (NLS) oligopeptides combining cysteine (C), histidine (H), and stearic acid (STR) were investigated in this study. The original SV40 sequence (SV40: Pro-Lys-Lys-Lys-Arg-Lys-Val) was selected as the NLS sequence, and physical characterizations of various NLS-based oligopeptides (CSV40C, STR-CSV40C, and STR-CH2SV40H2C), including mean diameter, zeta-potential, complex condensation, and decondensation, were evaluated. In addition, cellular and nuclear uptake of plasmid DNA (pDNA) and gene expression in COS7 and dendritic cells (JAWS II) were determined. As a result, C and STR enhanced formation of a smaller and more stable nano-complex with pDNA based on ionic interactions, the disulfide linkage and hydrophobic interactions. STR-CSV40C and STR-CH2SV40H2C had significantly higher cellular uptake ability and transfection efficiency than SV40 and CSV40C. In particular, STR-CH2SV40H2C had higher nuclear uptake and gene expression efficiency than STR-CSV40C. Furthermore, STR-CH2SV40H2C could deliver pDNA to the nuclei and had high gene expression efficiency in dendritic cells. Our results indicate that STR-CH2SV40H2C is a promising gene delivery system in non- or slow-dividing cells.

Sulfhydrylated graphene-encapsulated iron nanoparticles directly aminated with polyethylenimine: a novel magnetic nanoplatform for bioconjugation of gamma globulins and polyclonal antibodies

A graphene layer was directly aminated with polyethylenimine and a novel magnetic nanoplatform for bioconjugation of biologically active compounds was obtained.

Cationic Polymer Modified Mesoporous Silica Nanoparticles for Targeted SiRNA Delivery to HER2+ Breast Cancer

In vivo delivery of siRNAs designed to inhibit genes important in cancer and other diseases continues to be an important biomedical goal. We now describe a new nanoparticle construct that has been engineered for efficient delivery of siRNA to tumors. The construct is comprised of a 47-nm mesoporous silica nanoparticle (MSNP) core coated with a cross-linked PEI-PEG copolymer, carrying siRNA against the HER2 oncogene, and coupled to the anti-HER2 monoclonal antibody (trastuzumab). The construct has been engineered to increase siRNA blood half-life, enhance tumor-specific cellular uptake, and maximize siRNA knockdown efficacy. The optimized anti-HER2-nanoparticles produced apoptotic death in HER2 positive (HER2+) breast cancer cells grown in vitro, but not in HER2 negative (HER2-) cells. One dose of the siHER2-nanoparticles reduced HER2 protein levels by 60% in trastuzumab-resistant HCC1954 xenografts. Multiple doses administered intravenously over 3 weeks significantly inhibited tumor growth (p < 0.004). The siHER2-nanoparticles have an excellent safety profile in terms of blood compatibility and low cytokine induction, when exposed to human peripheral blood mononuclear cells. The construct can be produced with high batch-to-batch reproducibility and the production methods are suitable for large-scale production. These results suggest that this siHER2-nanoparticle is ready for clinical evaluation.

Unique Surface Modification of Silica Nanoparticles with Polyethylenimine (PEI) for siRNA Delivery Using Cerium Cation Coordination Chemistry

The discovery of RNA interference (RNAi) as a naturally occurring mechanism for gene knockdown has attracted considerable attention toward the use of small interfering RNAs (siRNAs) for therapeutic purposes. The main obstacles of harnessing siRNAs as drugs are their inefficient delivery to cells and off-target effect making clinical applications very challenging. The positively charged, branched 25 kDa polyethylenimine (b-PEI) polymer is widely regarded as one of the most efficient nonviral commercially available transfection agents. However, it has also been shown that 25 kDa b-PEI is highly cytotoxic and can readily lead to cell death. In this specific context, this study presents the preparation and characterization of innovative 25 kDa b-PEI-decorated polycationic silica nanoparticles (SiO2 NPs) for cellular siRNA delivery and subsequent gene silencing. A new method of b-PEI attachment onto the SiO2 NP surface has been developed that makes use of cerium(III) cations (Ce(3+)), a lanthanide group element, as an effective noncovalent inorganic linker between both polyNH2-SiO2 nanoparticle (SPA NPs) surface and polycationic 25 kDa b-PEI polymer. Two resulting novel SPA-Ce-PEI NPs consist of similar amounts of b-PEI, while possessing different amounts of Ce(3+). Various analytical techniques (TEM, DLS, ζ potential, ICP-AES, and TGA) have been used to deeply characterize NPs physicochemical qualities. The observed results of Ce(3+)-dependent gene silencing and cytotoxic activities led us to conclusions about the role of Ce(3+)-N bonding during the chemical attachment of the 25 kDa b-PEI shell onto the NP surface.

Thiomers--from bench to market

Thiolated polymers or designated thiomers are obtained by immobilization of sulhydryl bearing ligands on the polymeric backbone of well-established polymers such as poly(acrylates) or chitosans. This functionalization leads to significantly improved mucoadhesive properties compared to the corresponding unmodified polymers, as disulfide bonds between thiol groups of thiomers and cysteine-rich glycoproteins of the mucus gel layer are formed. Furthermore, enzyme- and efflux-pump inhibiting as well as improved permeation-enhancing properties are advantages of thiolization. By the covalent attachment of mercaptonicotinamide substructures via disulfide bonds to thiolated polymers these properties are even substantially further improved and stability towards oxidation even in aqueous media can be provided. Meanwhile, more than 50 research groups worldwide are working on thiolated polymers. For certain thiomers the scale up process for industrial production has already been done and GMP material is available. Furthermore, safety of thiolated poly(acrylic acid), thiolated chitosan and thiolated hyaluronic acid could be demonstrated via orientating studies in human volunteers and via various clinical trials. The first product (Lacrimera® eye drops, Croma-Pharma) containing a chitosan-N-acetylcysteine conjugate for treatment of dry eye syndrome will enter the European market this year. It is the only product providing a sustained protective effect on the ocular surface due to its comparatively much more prolonged residence time worldwide. Various further products utilizing, for instance, thiolated hyaluronic acid in ocular surgery are in the pipeline.