Synthetic, self-assembly ABCD nanoparticles; a structural paradigm for viable synthetic non-viral vectors

Elucidating the encapsulation of short interfering RNA in PEGylated cationic liposomes

Short interfering RNA (siRNA) holds great potential for the treatment of hard-to-cure diseases. One of the major challenges to translate siRNA into drugs is its efficient delivery to its site-of-action, namely the cytoplasm of the target cells. Cationic liposomes have been shown to do the trick, but their short circulation lifetime and potential aggregation in blood limit their applicability for intravenous administration. These hurdles might be overcome by attaching poly(ethylene glycol) (PEG) at the surface of the cationic liposomes through the use of PEGylated lipids. However, this paper reveals that the classical mixing of siRNA with preformed PEGylated cationic liposomes, as frequently done to load PEGylated liposomes with siRNA, prevents an efficient encapsulation of the siRNA in the liposomes. We show that only a minor fraction of the siRNA becomes encapsulated in the core of the PEGylated liposomes, whereas a major part of the siRNA becomes bound at the liposome's outer surface. In serum, the surface-bound siRNA is immediately released and becomes degraded by serum nucleases. By contrast, hydrating a lipid film (containing PEGylated and cationic lipids) directly with a concentrated solution of siRNA (so-called HYDRA protocol), instead of mixing the siRNA with preformed PEGylated liposomes, encapsulates almost 50% of the siRNA in the core of the PEGylated liposomes, which is the maximal encapsulation efficiency for this type of complexes. We show that the siRNA encapsulated in the core of the thus obtained "HYDRA siPLexes" remains fully encapsulated upon dispersing the PEGylated liposomes in human serum.

Targeting the urokinase plasminogen activator receptor with synthetic self-assembly nanoparticles

Targeting specific receptors is attracting growing interest in the fields of drug delivery and gene therapy for cancer treatment. The urokinase plasminogen activator receptor (uPAR) is overexpressed on many tumors,particularly that of prostate and breast cancers. The aim of this study is to design, prepare, and characterize a synthetic self-assembled nanoparticle that presents targeting ligands at a certain conformation and molar ratio onthe surface of the particles. Here, we describe the synthesis of a novel uPAR targeting ligand consisting of an 11-amino-acid sequence named U11 peptide modified with an alkyl chain to form an U11 peptide-lipid amphiphile.This peptide-lipid is inserted into the outer layer of a parent stealth liposome by post-modification to derive a U11 peptide-targeted nanoparticle. We demonstrate that the peptide moieties become separated into more singular conformations as they are inserted into a liposome membrane, rendering them to be sufficiently biologically active to observe specific receptor-mediated endocytosis (RME) and delivery of plasmid DNA to uPAR positive cells (DU145 cells). The U11 peptide targeted nanoparticle transfection of DU145 cells is essentially 10-fold higher compared to transfection achieved by nanoparticles having a scrambled peptide sequence on their surface.U11 peptide targeted nanoparticles also proved to be uPAR-specific, as they did not improve transfection levels on the uPAR-negative cell line, HEK293.

Designed multi-domain protein as a carrier of nucleic acids into cells

Protein-based nucleic acid carriers offer attractive possibilities to enhance in vitro and in vivo gene delivery to combat diseases. A multi-domain fusion protein, namely TAT-NLS-Mu, designated as TNM, has been designed, cloned, heterologously expressed in E. coli and purified to homogeneity by affinity chromatography. The recombinant chimera TNM harbors three epitopes, a cell-penetrating (TAT) domain, a nuclear localization domain comprising of three nuclear localization sequence (NLS) motifs in tandem and a DNA-binding (Mu) domain. Complexes prepared by combining plasmid DNA with TNM (DP) transfect MCF-7, COS, CHO and HepG2 cells. Ternary complexes prepared with DNA, protein and cationic lipid (DPL) resulted in ~5-7 fold enhancement in reporter gene expression over the DP alone. Treatment of cells with chloroquine during transfection, with DP complexes, resulted in remarkable increases in reporter gene expression suggesting the involvement of endosomal compartments in the uptake process. Interestingly, DPL prepared with Lipofectin or 1, 2-Dioleoyl-3-Trimethylammonium-Propane (DOTAP) exhibited enhanced transfection in the presence of serum in MCF-7 and HepG2 cells. Microinjection of DP complexes, with and without NLS sequence, into the cytoplasm and nucleus of smooth muscle cells (SMC) indicated that the presence of NLS sequence in protein carrier significantly enhanced transgene expression. Together the data suggest that modular design of proteins is a promising method to develop gene delivery carriers and also the role of NLS epitopes in mediating nuclear transfer of DNA complexes into various cell types.

Ex vivo non-viral vector-mediated neurotrophin-3 gene transfer to olfactory ensheathing glia: effects on axonal regeneration and functional recovery after implantation in rats with spinal cord injury

OBJECTIVE

Combine olfactory ensheathing glia (OEG) implantation with ex vivo non-viral vector-based neurotrophin-3 (NT-3) gene therapy in attempting to enhance regeneration after thoracic spinal cord injury (SCI).

METHODS

Primary OEG were transfected with cationic liposome-mediated recombinant plasmid pcDNA3.1(+)-NT3 and subsequently implanted into adult Wistar rats directly after the thoracic spinal cord (T9) contusion by the New York University impactor. The animals in 3 different groups received 4x10(5) OEG transfected with pcDNA3.1(+)-NT3 or pcDNA3.1(+) plasmids, or the OEGs without any plasmid transfection, respectively; the fourth group was untreated group, in which no OEG was implanted.

RESULTS

NT-3 production was seen increased both ex vivo and in vivo in pcDNA3.1(+)-NT3 transfected OEGs. Three months after implantation of NT-3-transfected OEGs, behavioral analysis revealed that the hindlimb function of SCI rats was improved. All spinal cords were filled with regenerated neurofilament-positive axons. Retrograde tracing revealed enhanced regenerative axonal sprouting.

CONCLUSION

Non-viral vector-mediated genetic engineering of OEG was safe and more effective in producing NT-3 and promoting axonal outgrowth followed by enhancing SCI recovery in rats.

Biophysical properties of CDAN/DOPE-analogue lipoplexes account for enhanced gene delivery

Typically, cationic liposomes are formulated from the combination of a synthetic cationic lipid (cytofectin) and a neutral, biologically available co-lipid. However, the use of cationic liposome formulations to mediate gene delivery to cells is hampered by a paradox. Cationic lipids, such as N(1)-cholesteryloxycarbonyl-3-7-diazanonane-1,9-diamine (CDAN), are needed to ensure the formation of cationic liposome-DNA (lipoplex, LD) particles by plasmid DNA (pDNA) condensation, as well as for efficient cell binding of LD particles and intracellular trafficking of pDNA post-intracellular delivery by endocytosis. However, the same cationic lipids can exhibit toxicity, and also promote LD particle colloidal instability, leading to aggregation. This results from electrostatic interactions with anionic agents in biological fluids, particularly in vivo. One of the most commonly used neutral, bioavailable co-lipids, dioleoyl L-alpha-phosphatidylethanolamine (DOPE), has been incorporated into many cationic liposome formulations owing to its fusogenic characteristics that are associated with a preference for the inverted hexagonal (H(II)) phase-a phase typical of membrane-membrane fusion events. However, these same fusogenic characteristics also destabilize LD particles substantially with respect to aggregation, in vitro and especially in vivo. Therefore, there is a real need to engineer more stable cationic liposome systems with lower cellular toxicity. We hypothesize that one way to achieve this goal should be to find the means to reduce the mol fraction of cationic lipid in cationic liposomes without impairing the overall transfection efficiency, by replacing DOPE with an alternative co-lipid with fusogenic properties "tuned" with a greater preference for the more stable lamellar phases than DOPE is able to achieve. Herein, we document the syntheses of triple bond variants of DOPE, and their formulation into a range of low charge, low cationic lipid containing LD systems. The first indications are that our hypothesis is correct in vitro.

Clostridium neurotoxin fragments as potential targeting moieties for liposomal gene delivery to the CNS

Targeted transfection of the CNS with synthetic, nonviral vectors represents a huge technical challenge. The approach explored here attempts to combine self-assembly ABCD nanoparticles (Kostarelos and Miller, Chem. Soc. Rev. 2005, 34, 970), with the potential of Clostridium neurotoxin fragments to effect receptor-mediated transfection of neuronal cells. Cationic liposome-plasmid DNA complexes were first modified with a PEG stealth layer, before the addition of C-terminal fragments of tetanus toxin (TH(C)), botulinum toxin (BH(C)) or the truncated C-terminal domain of TH(C) as biological "targeting" ligands. First-generation nanoparticles were identified for the transfection of two neuronal cell lines (human SH-5YSY and rat/mouse hybrid N18-RE105); control studies were also performed with HeLa cells. ABCD nanoparticle transfections of the neuronal cell lines were up to 30-fold higher than corresponding control transfections with nanoparticles that lacked the protein ligand. We also demonstrate apparent receptor-mediated uptake by means of competition-binding and real-time confocal experiments. By contrast, nanoparticle transfection of HeLa cells appeared to involve alternative nonspecific enhanced cellular uptake mechanism(s). Receptor-mediated and nonspecific mechanisms appear to be in competition, potentially harming the capacity of receptor-mediated delivery to effect proper targeted delivery of nucleic acids to cells ex vivo and in vivo.

Bimodal paramagnetic and fluorescent liposomes for cellular and tumor magnetic resonance imaging

A novel bimodal fluorescent and paramagnetic liposome is described for cellular labeling. In this study, we show the synthesis of a novel gadolinium lipid, Gd.DOTA.DSA, designed for liposomal cell labeling and tumor imaging. Liposome formulations consisting of this lipid were optimized in order to allow for maximum cellular entry, and the optimized formulation was used to label HeLa cells in vitro. The efficiency of this novel bimodal Gd-liposome formulation for cell labeling was demonstrated using both fluorescence microscopy and magnetic resonance imaging (MRI). The uptake of Gd-liposomes into cells induced a marked reduction in their MRI T 1 relaxation times. Fluorescence microscopy provided concomitant proof of uptake and revealed liposome internalization into the cell cytosol. The optimized formulation was also found to exhibit minimal cytotoxicity and was shown to have capacity for plasmid DNA (pDNA) transfection. A further second novel neutral bimodal Gd-liposome is described for the labeling of xenograft tumors in vivo utilizing the enhanced permeation and retention effect (EPR). Balb/c nude mice were inoculated with IGROV-1 cells, and the resulting tumor was imaged by MRI using these in vivo Gd-liposomes formulated with low charge and a poly(ethylene glycol) (PEG) calyx for long systemic circulation. These Gd-liposomes which were less than 100 nm in size were shown to accumulate in tumor tissue by MRI, and this was also verified by fluorescence microscopy of histology samples. Our in vivo tumor imaging results demonstrate the effectiveness of MRI to observe passive targeting of long-term circulating liposomes to tumors in real time, and allow for MRI directed therapy, wherein the delivery of therapeutic genes and drugs to tumor sites can be monitored while therapeutic effects on tumor mass and/or size may be simultaneously observed, quantitated, and correlated.

Recombinant fusion proteins TAT-Mu, Mu and Mu-Mu mediate efficient non-viral gene delivery

BACKGROUND

The inherent ability of certain peptides or proteins of viral, prokaryotic and eukaryotic origin to bind DNA was used to generate novel peptide-based DNA delivery protocols. We have developed a recombinant approach to make fusion proteins with motifs for DNA-binding ability, Mu and membrane transduction domains, TAT, and tested them for their DNA-binding, uptake and transfection efficiencies. In one of the constructs, the recombinant plasmid was designed to encode the Mu moiety of sequence MRRAHHRRRRASHRRMRGG in-frame with TAT of sequence YGRKKRRQRRR to generate TAT-Mu, while the other two constructs, Mu and Mu-Mu, harbor a single copy or two copies of the Mu moiety.

METHODS

Recombinant his-tag fusion proteins TAT-Mu, Mu and Mu-Mu were purified by overexpression of plasmid constructs using cobalt-based affinity resins. The peptides were characterized for their size and interaction with DNA, complexed with plasmid pCMVbeta-gal, and shown to transfect MCF-7, COS and CHOK-1 cells efficiently.

RESULTS

Recombinant fusion proteins TAT-Mu, Mu and Mu-Mu were cloned and overexpressed in BL21(DE3)pLysS with greater than 95% purity. The molecular weight of TAT-Mu was determined by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) to be 11.34 kDa while those of Mu and Mu-Mu were 7.78 and 9.83 kDa, respectively. Live uptake analysis of TAT-Mu, Mu and Mu-Mu as DP (DNA+peptide) or DPL (DNA+peptide+lipid) complexes into MCF-7 cells, followed by immunostaining and laser scanning confocal microscopy, demonstrated that the complexes are internalized very efficiently and localized in the nucleus. DNA:peptide complexes (DP) transfect MCF-7, COS and CHOK-1 cells. The addition of cationic liposomes enhances the uptake of the ternary complexes (DPL) further and also brings about 3-7-fold enhancement in reporter gene expression compared to DP alone.

CONCLUSIONS

Recombinant proteins that are heterologous fusions, having DNA-binding domains and nuclear localization epitopes, generated in this study have considerable potential to facilitate DNA delivery and enhance transfection. The domains in these fusion proteins would be promising in the development of non-viral gene delivery vectors particularly in cells that do not divide.

Covalent attachment of multifunctional chimeric terminal proteins to 5' DNA ends: A potential new strategy for assembly of synthetic therapeutic gene vectors

The generation of synthetic therapeutic gene vectors requires the coupling of DNA to transfer-promoting peptides including cellular receptor ligands, protein transduction domains, hydrophobic peptides for attachment to lipid membranes, nuclear localisation signals, cytoskeleton attachment motifs, nuclear matrix association elements and immune evasion moieties. Existing methods of peptide-DNA joining often interfere with transgene expression and, therefore, are inadequate for production of effective therapeutic vector complexes, particularly destined for gene delivery in the challenging environment in vivo. However, there is a natural mechanism for rigid coupling of polypeptides with DNA. Some bacterial and eukaryotic linear plasmids, adenoviruses and a number of bacteriophages including phi29 of Bacillus subtilis and PRD1 of Escherichia coli use terminal proteins covalently bound to 5' DNA ends to prime replication. Inverted terminal DNA repeats, normally short DNA sequences, contain all the sequences required in cis for the covalent coupling reaction. The complex of the terminal protein, DNA polymerase and some known auxiliary proteins supplies sufficient trans-functions, thus enabling simple linking of the terminal proteins to DNA in vitro. We hypothesise that chimeric fusion proteins, constructed on the basis of terminal proteins of adenoviruses, linear plasmids or bacteriophages with protein-primed replication, can on the one hand retain the ability to bind covalently 5' DNA termini in conditions established previously for protein-primed replication in vitro, and on the other hand confer gene transfer facilitating properties and enhanced longevity of efficient transgene expression. Terminal localisation of the chimeric proteins can ensure that they do not interfere with transgene transcription. At the same time a covalent bond between polypeptide and DNA can provide rigid coupling ensuring their stable association en route to nuclei. Bound to 5'-ends of the delivered DNA, terminal protein-based chimeras could also protect the vector DNA from 5'-3' and possibly 3'-5' exonuclease attack, thus limiting its intracellular degradation and increasing longevity of transgene expression. Our hypothesis can be tested by measuring the gene transfer efficiency of the novel complexes containing linear DNA fragments with covalently linked multifunctional chimeric terminal proteins, using previously described synthetic gene vectors as standards.

Lipophilic Pyrylium Salts in the Synthesis of Efficient Pyridinium-Based Cationic Lipids, Gemini Surfactants, and Lipophilic Oligomers for Gene Delivery

Several new classes of pyridinium cationic lipids were synthesized and tested as gene delivery agents. They were obtained through a procedure that generates simultaneously the heterocyclic ring and the positively charged nitrogen atom, using lipophilic pyrylium salts as key intermediates that react with primary amines, yielding pyridinium salts. The choice of the appropriately substituted primary amine, diamine or polyamine, allows the design of the shape of the final lipids, gemini surfactants, or lipophilic polycations. We report also a comprehensive structure-activity relationship study that identified the most efficient structural variables at the levels of the hydrophobic anchor, linker, and counterion for these classes of pyridinium cationic lipids. This study was also aimed at finding the best liposomal formulation for the new transfection agents.

Imparting size, shape, and composition control of materials for nanomedicine

This tutorial review presents an overview of strategies for the synthesis and fabrication of organic nanomaterials, specifically those with potential for use in medical applications. Examples include liposomes, micelles, polymer-drug conjugates and dendrimers. Methods of driving shape via"bottom-up" synthetic approaches and thermodynamics and kinetics are discussed. Furthermore, methods of driving shape via"top-down" physical and engineering techniques are also explored. Finally, a novel method (referred to as PRINT) used to produce nanoparticles that are shape-specific, can contain any cargo, and can be easily modified is examined along with its potential future role in nanomedicine.