Transfection properties of stabilized plasmid-lipid particles containing cationic PEG lipids

Lipid Nanoparticles Deliver mRNA to the Brain after an Intracerebral Injection

Neurological disorders are often debilitating conditions with no cure. The majority of current therapies are palliative rather than disease-modifying; therefore, new strategies for treating neurological disorders are greatly needed. mRNA-based therapeutics have great potential for treating such neurological disorders; however, challenges with delivery have limited their clinical potential. Lipid nanoparticles (LNPs) are a promising delivery vector for the brain, given their safer toxicity profile and higher efficacy. Despite this, very little is known about LNP-mediated delivery of mRNA into the brain. Here, we employ MC3-based LNPs and successfully deliver Cre mRNA and Cas9 mRNA/Ai9 sgRNA to the adult Ai9 mouse brain; greater than half of the entire striatum and hippocampus was found to be penetrated along the rostro-caudal axis by direct intracerebral injections of MC3 LNP mRNAs. MC3 LNP Cre mRNA successfully transfected cells in the striatum (∼52% efficiency) and hippocampus (∼49% efficiency). In addition, we demonstrate that MC3 LNP Cas9 mRNA/Ai9 sgRNA edited cells in the striatum (∼7% efficiency) and hippocampus (∼3% efficiency). Further analysis demonstrates that MC3 LNPs mediate mRNA delivery to multiple cell types including neurons, astrocytes, and microglia in the brain. Overall, LNP-based mRNA delivery is effective in brain tissue and shows great promise for treating complex neurological disorders.

GRP75-driven, cell-cycle-dependent macropinocytosis of Tat/pDNA-Ca2+ nanoparticles underlies distinct gene therapy effect in ovarian cancer

Practice of tumor-targeted suicide gene therapy is hampered by unsafe and low efficient delivery of plasmid DNA (pDNA). Using HIV-Tat-derived peptide (Tat) to non-covalently form Tat/pDNA complexes advances the delivery performance. However, this innovative approach is still limited by intracellular delivery efficiency and cell-cycle status. In this study, Tat/pDNA complexes were further condensed into smaller, nontoxic nanoparticles by Ca²⁺ addition. Formulated Tat/pDNA-Ca²⁺ nanoparticles mainly use macropinocytosis for intercellular delivery, and their macropinocytic uptake was persisted in mitosis (M-) phase and highly activated in DNA synthesis (S-) phase of cell-cycle. Over-expression or phosphorylation of a mitochondrial chaperone, 75-kDa glucose-regulated protein (GRP75), promoted monopolar spindle kinase 1 (MPS1)-controlled centrosome duplication and cell-cycle progress, but also driven cell-cycle-dependent macropinocytosis of Tat/pDNA-Ca²⁺ nanoparticles. Further in vivo molecular imaging based on DF (Fluc-eGFP)-TF (RFP-Rluc-HSV-ttk) system showed that Tat/pDNA-Ca²⁺ nanoparticles exhibited highly suicide gene therapy efficiency in mouse model xenografted with human ovarian cancer. Furthermore, arresting cell-cycle at S-phase markedly enhanced delivery performance of Tat/pDNA-Ca²⁺ nanoparticles, whereas targeting GRP75 reduced their macropinocytic delivery. More importantly, in vivo targeting GRP75 combined with cell-cycle or macropinocytosis inhibitors exhibited distinct suicide gene therapy efficiency. In summary, our data highlight that mitochondrial chaperone GRP75 moonlights as a biphasic driver underlying cell-cycle-dependent macropinocytosis of Tat/pDNA-Ca²⁺ nanoparticles in ovarian cancer.

Size-Dependency of the Surface Ligand Density of Liposomes Prepared by Post-insertion

In the active targeting of a drug delivery system (DDS), the density of the ligand on the functionalized liposome determines its affinity for binding to the target. To evaluate these densities on the surface of different sized liposomes, 4 liposomes with various diameters (188, 137, 70, 40 nm) were prepared and their surfaces were modified with fluorescently labeled ligand-lipid conjugates by the post-insertion method. Each liposomal mixture was fractionated into a series of fractions using size exclusion chromatography (SEC), and the resulting liposome fractions were precisely analyzed and the surface ligand densities calculated. The data collected using this methodology indicate that the density of the ligand on a particle is greatly dependent on the size of the liposome. This, in turn, indicates that smaller liposomes (75-40 nm) tend to possess higher densities. For developing active targeting systems, size and the density of the ligands are two important and independent factors that can affect the efficiency of a system as it relates to medical use.

Topology of Surface Ligands on Liposomes: Characterization Based on the Terms, Incorporation Ratio, Surface Anchor Density, and Reaction Yield

The surface topology of ligands on liposomes is an important factor in active targeting in drug delivery systems. Accurately evaluating the density of anchors and bioactive functional ligands on a liposomal surface is critical for ensuring the efficient delivery of liposomes. For evaluating surface ligand density, it is necessary to clarify that on the ligand-modified liposomal surfaces, some anchors are attached to ligands but some are not. To distinguish between these situations, a key parameter, surface anchor density, was introduced to specify amount of total anchors on the liposomal surface. Second, the parameter reaction yield was introduced to identify the amount of ligand-attached anchors among total anchors, since the conjugation efficiency is not always the same nor 100%. Combining these independent parameters, we derived: incorporation ratio=surface anchor density×reaction yield. The term incorporation ratio defines the surface ligand density. Since the surface anchor density represents the density of polyethylene glycol (PEG) on the surfaces in most cases, it also determines liposomal function. It is possible to accurately characterize various PEG and ligand densities and to define the surface topologies. In conclusion, this quantitative methodology can standardize the liposome preparation process and qualify the modified liposomal surfaces.

A Novel Terminator Primer and Enhancer Reagents for Direct Expression of PCR-Amplified Genes in Mammalian Cells

Escherichia coli plasmids are commonly used for gene expression experiments in mammalian cells, while PCR-amplified DNAs are rarely used even though PCR is a much faster and easier method to construct recombinant DNAs. One difficulty may be the limited amount of DNA produced by PCR. For direct utilization of PCR-amplified DNA in transfection experiments, efficient transfection with a smaller amount of DNA should be attained. For this purpose, we investigated two enhancer reagents, polyethylene glycol and tRNA, for a chemical transfection method. The addition of the enhancers to a commercial transfection reagent individually and synergistically exhibited higher transfection efficiency applicable for several mammalian cell culture lines in a 96-well plate. By taking advantage of a simple transfection procedure using PCR-amplified DNA, SV40 and rabbit β-globin terminator lengths were minimized. The terminator length is short enough to design in oligonucleotides; thus, terminator primers can be used for the construction and analysis of numerous mutations, deletions, insertions, and tag-fusions at the 3'-terminus of any gene. The PCR-mediated gene manipulation with the terminator primers will transform gene expression by allowing for extremely simple and high-throughput experiments with small-scale, multi-well, and mammalian cell cultures.

Critical considerations for developing nucleic acid macromolecule based drug products

Protein expression therapy using nucleic acid macromolecules (NAMs) as a new paradigm in medicine has recently gained immense therapeutic potential. With the advancement of nonviral delivery it has been possible to target NAMs against cancer, immunodeficiency and infectious diseases. Owing to the complex and fragile structure of NAMs, however, development of a suitable, stable formulation for a reasonable product shelf-life and efficacious delivery is indeed challenging to achieve. This review provides a synopsis of challenges in the formulation and stability of DNA/m-RNA based medicines and probable mitigation strategies including a brief summary of delivery options to the target cells. Nucleic acid based drugs at various stages of ongoing clinical trials are compiled.

Stabilization of a hyaluronate-associated gene delivery system using calcium ions

A "DPH" ternary complex consisting of plasmid DNA (pDNA), intracellularly degradable polyethyleneimine, and hyaluronic acid (HA) is a promising non-viral gene carrier with low toxicity and good gene transfection efficiency. HA plays a key role in providing an optimal balance between DNA protection and release, but it causes aggregation due to the entanglement of HA chains of neighbouring DPH particles. Here we report that the addition of an optimal level of Ca²⁺ successfully prevents particle aggregation and maintains a relatively small size. The Ca-stabilized DPH is comparable to DPH in cytotoxicity and gene transfection efficiency. MW monitoring and conductometric titration suggest that such size stabilization effect is partly mediated by the complexation between HA and Ca²⁺, which enables intra- and intermolecular interactions of HAs.

Calcium condensed LABL-TAT complexes effectively target gene delivery to ICAM-1 expressing cells

Targeted gene delivery using nonviral vectors is a highly touted scheme to reduce the potential for toxic or immunological side effects by reducing dose. In previous reports, TAT polyplexes with DNA have shown relatively poor gene delivery. The transfection efficiency has been enhanced by condensing TAT/DNA complexes to a small particle size using calcium. To explore the targetability of these condensed TAT complexes, LABL peptide targeting intercellular cell-adhesion molecule-1 (ICAM-1) was conjugated to TAT peptide using a polyethylene glycol (PEG) spacer. PEGylation reduced the transfection efficiency of TAT, but TAT complexes targeting ICAM-1 expressing cells regained much of the lost transfection efficiency. Targeted block peptides properly formulated with calcium offer promise for gene delivery to ICAM-1 expressing cells at sites of injury or inflammation.

Lipid-coated nano-calcium-phosphate (LNCP) for gene delivery

While calcium-phosphate has been used to deliver plasmid DNA (pDNA) for decades, the method is typically characterized by low and irreproducible transfection efficiency relative to the other non-viral approaches, such as liposomes and polymers. Here we report a novel gene transfer vector comprising lipid-coated nano-calcium-phosphate (LNCP) that provides consistently efficient and satisfactory pDNA delivery. It is based on core-shell nanoparticles comprising a calcium-phosphate core and a cationic lipid shell. This method, in contrast to the solution precipitation methods used in the past, yields colloidally stable calcium-phosphate nanoparticles inside the cationic liposomes. Our results indicate that the particle size and the size distribution of the LNCP remain virtually unchanged even after 21 days of storage. Atomic force microscopy measurements reveal that the LNCP have a 5-fold higher rigidity than common cationic liposomes. The LNCP transfected pDNA 24 times greater than the naked pDNA and 10-fold greater relative to the standard calcium-phosphate precipitation preparations, suggesting that the LNCP may have potential as a novel transfection agent for gene therapy.

Oligoarginine-PEG-lipid particles for gene delivery

Cell-penetrating peptides (CPPs) are small peptides that can facilitate the uptake of macromolecular drugs, such as proteins or nucleic acids, into mammalian cells. Cytosolic delivery of CPPs could be beneficial to bypass conventional endocytosis in order to avoid degradation in the lysosomes. Oligoarginine conjugates have characteristics similar to CPPs in terms of cell translocation and are used in the intracellular delivery of plasmid DNA. In these cases, oligoarginine length and/or charge are important factors in the cellular uptake of oligoarginine alone. The arginine moiety of oligoarginine-modified particles may also be a decisive factor for vectors to deliver plasmid DNA. Oligoarginine-PEG-lipids can form self-assembled particles and modify the surface of lipid- and polymer-based particles. This review focuses on the influence of: i) oligoarginine-modified particles such as micelles, liposomes and polymer-based particles; ii) the morphology of oligoarginine-PEG-lipid complexed with plasmid DNA by decreasing the charge ratio; and iii) the oligoarginine length in the complex on its cellular uptake, transfection efficiency and uptake mechanism. The oligoarginine length of oligoarginine-modified particle complexed with plasmid DNA governs the cellular uptake pathway that determines the destiny of intracellular trafficking and finally transfection efficiency. The new aspects of surface-functionalized particle vectors with oligoarginine are discussed.

Targeting of stabilized plasmid lipid particles to hepatocytes in vivo by means of coupled lactoferrin

For non-viral gene delivery we prepared stabilized plasmid lipid particles (SPLPs), to which lactoferrin (LF) was coupled as a hepatocyte specific targeting ligand. LF-SPLPs and untargeted SPLPs labeled with [3H]cholesteryloleyl-ether were injected into rats. About 87% of the LF-SPLPs were eliminated from the blood within 5 min, while 80% of untargeted SPLPs were still circulating after 2 h. Fifty-two percent of the LF-SPLPs were taken up by hepatocytes, while non-parenchymal liver cells accounted for 16% of the uptake. Despite the efficient targeting of LF-SPLPs to hepatocytes and their capacity to transfect HepG2 and COS-7 cells in vitro, expression of a reporter gene was not detected in vivo. Overall, covalent coupling of LF to SPLPs leads to massive delivery in hepatocytes after systemic administration. However, these LF-SPLPs are not able to transfect these cells in vivo.

Importance of divalent cations in nanolipoplex gene delivery

Gene therapy is a promising therapeutic strategy to combat genetic or acquired diseases at their root cause rather than just treating symptoms. It is well recognised that there is an urgent need for non-toxic and efficient gene delivery vectors to fully exploit the current potential of gene therapy in molecular medicine. Cell-specific targeting of bioactive nucleotides is a prerequisite to attain the concentration of nucleic acids required for therapeutic efficacy in the target tissue. Many metal ions such as Mg2+, Mn2+, Ba2+ and, most importantly, Ca2+ have been demonstrated to have significant roles in gene delivery. These inorganic cations show low toxicity, good biocompatibility and promise for controlled delivery properties, thus presenting a new alternative to toxic and immunogenic carriers. Recently, inorganic nanoparticles alone, or in combination with a colloidal particulate system such as nanoliposome, an advanced approach to gene delivery, were found to exert a positive effect on gene transfer. In this report, the role of the divalent cations in nucleic acid delivery, particularly with respect to the potential improvement of transfection efficiency of nanolipoplexes, is reviewed.

Physico-chemical characterization and transfection efficacy of cationic liposomes containing the pEGFP plasmid

Cationic liposomes-DNA complexes (lipoplexes) are largely used in gene delivery. Deciphering specific chemical and physical properties of lipoplexes is a necessary step to unravel the mechanisms underlying transfection and to improve transfection efficacy in each experimental model. In the present paper we investigated the physico-chemical features of lipoplexes containing a plasmid encoding for the GFP protein, in order to correlate these results with transfection efficacy. Cationic unilamellar vesicles (mean diameter 100 nm) were prepared, from the cationic DC-Chol lipid and the zwitterionic phospholipid DOPE. The two components of the liposome bilayer were used at molar ratio close to unity. ESR spectra were recorded and zeta potential zeta was measured on liposomes complexed with the plasmid. One of the main points of interest in this paper resided in the fact that both kinds of measurements were carried out in the same conditions (i.e. lipid concentration, medium composition, and pH) employed for cell transfection experiments. Transfection was performed on CHO cells; the percentage of fluorescent cells was evaluated and compared with the above physico-chemical features. It emerged that the composition and pH of the medium, the lipoplex/cell ratio, as well as the amount of lipoplex added to the cell culture were critical parameters for transfection efficacy. Finally, lipoplex surface charge played a fundamental role to achieve a high transfection level.

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

Gene therapy research is still in trouble owing to a paucity of acceptable vector systems to deliver nucleic acids to patients for therapy. Viral vectors are efficient but may be too dangerous. Synthetic non-viral vectors are inherently safer but are currently not efficient enough to be clinically viable. The solution for gene therapy lies with improved synthetic non-viral vectors systems. This review is focused on synthetic cationic liposome/micelle-based non-viral vector systems and is a critical review written to illustrate the increasing importance of chemistry in gene therapy research. This review should be of primary interest to synthetic chemists and biomedical researchers keen to appreciate emerging technologies, but also to biological scientists who remain to be convinced about the relevance of chemistry to biology.

Artificially lipid-anchored proteins can elicit clustering-induced intracellular signaling events in Jurkat T-lymphocytes independent of lipid raft association

We have incorporated artificial lipid-anchored streptavidin conjugates with fully saturated or polyunsaturated lipid anchors into the plasma membranes of Jurkat T-lymphocytes to assess previous conclusions that the activation of signaling processes induced in these cells by clustering of endogenous glycosylphosphatidylinositol-anchored proteins or ganglioside GM1 depends specifically on the association of these membrane components with lipid rafts. Lipid-anchored streptavidin conjugates could be incorporated into Jurkat or other mammalian cell surfaces by inserting biotinylated phosphatidylethanolamine-polyethyleneglycols (PE-PEGs) and subsequently binding streptavidin to the cell-incorporated PE-PEGs. Saturated dipalmitoyl-PE-PEG-streptavidin conjugates prepared in this manner partitioned substantially into the detergent-insoluble membrane fraction isolated from Jurkat or fibroblast cells, whereas polyunsaturated dilinoleoyl-PE-PEG-anchored conjugates were wholly excluded from this fraction, consistent with the differences in the affinities of the two types of lipid anchors for liquid-ordered membrane domains. Remarkably, however, antibody-mediated cross-linking of either dipalmitoyl- or dilinoleoyl-PE-PEG-anchored streptavidin conjugates in Jurkat cells induced elevation of cytoplasmic calcium levels and tyrosine phosphorylation of the scaf-folding protein linker of T-cell activation in a manner similar to that observed upon cross-linking of endogenous CD59 or ganglioside GM1. The amplitude of the cross-linking-stimulated elevation of cytoplasmic calcium moreover showed an essentially identical dependence on the level of incorporated streptavidin conjugate for either type of lipid anchor. Confocal fluorescence microscopy revealed that PE-PEG-streptavidin conjugates with saturated versus polyunsaturated anchors showed very similar surface distributions vis à vis GM1 or CD59 under conditions where one or both species were cross-linked. These results indicate that cross-linking of diverse proteins anchored only to the outer leaflet of the plasma membrane can induce activation of Jurkat T-cell-signaling responses, but they appear to contradict previous suggestions that this phenomenon rests specifically on the association of such species with lipid rafts.

Distal cationic poly(ethylene glycol) lipid conjugates in large unilamellar vesicles prepared by extrusion enhance liposomal cellular uptake

Cationic poly(ethylene glycol)-lipid conjugates (CPLs), a class of lipid designed to enhance the interaction of liposomes with cells, possess the following architectural features: 1) a hydrophobic lipid anchor of distearoylphosphatidylethanolamine (DSPE); 2) a hydrophilic spacer of poly(ethylene glycol); and 3) a cationic head group prepared with 0, 1, 3, or 7 lysine residues located at the distal end of the PEG chain, giving rise to CPL possessing 1, 2, 4, or 8 positive charges, respectively (CPL1 to CPL8). Previously we have described the synthesis of CPL, have characterized the postinsertion of CPL into PEG-containing LUVs and SPLP (stabilized plasmid-lipid particles), have shown significant increases in the binding of CPL-LUV to cells, and have observed dramatically enhanced transfection (up to a million-fold) of cells with CPL-SPLP in the presence of calcium [Chen et al. (2000) Bioconjugate Chem. 11, 433-437; Fenske et al. (2001) Biochim. Biophys. Acta 1512, 259-272; Palmer et al. (2003) Biochim. Biophys. Acta 1611, 204-216]. In the present study, we examine a variety of CPL properties (such as polarity and CMC) and characterize CPL-vesicular systems formed by extrusion and examine their interaction with cells. While CPL polarity was observed to increase dramatically with increasing charge number, CMC values were all found to be low, in the range of other PEGylated lipids, and exhibited only a small increase, going from CPL1 (1.3 microM) to CPL8 (2 microM). The CPLs were almost quantitatively incorporated into large unilamellar vesicles (LUVs) prepared by the extrusion method and were evenly distributed across the lipid bilayer. Lower levels of incorporation were obtained when CPLs were incubated with preformed liposomes (DSPC/Chol, 55:45) at 60 degrees C. The binding of CPL-LUVs to BHK cells in vitro was found to be dependent on the distal charge density of the CPL rather than total surface charge. Liposomes possessing CPL4 or CPL8 were observed to bind efficiently to cell surfaces and enhance cellular uptake in BHK cells (as observed with both lipid and aqueous content markers), whereas those possessing CPL1 or CPL2 exhibited little or no binding. These results suggest new directions for the design of liposomal systems capable of in vivo delivery of both conventional and genetic (plasmid and antisense) drugs.

Thiocholesterol-based lipids for ordered assembly of bioresponsive gene carriers

A series of thiocholesterol-based cationic lipids (TCL) has been designed and synthesized by the attachment of thiocholesterol to a cationic amine via a disulfide bond. TCL can be incorporated into liposomes and used to package DNA into a lipoplex, thereby protecting it from DNase digestion. DNA is rapidly released from the complex in the presence of low concentrations of reducing agents. The lipoplex mediated efficient transfection activity and had low cytotoxicity. To improve the biocompatibility of the cationic lipoplex, TCL were used as a component in the assembly of a nanolipoparticle (NLP). The particle surface was subsequently modified by disulfide exchange to replace the cationic group with a negatively charged (glutathione) or zwitterionic (cysteine) reducing agent. A cell-binding ligand (TAT peptide, sequence GRKKRRQRRRGYG) was then incorporated onto the particle surface to enhance the particle-cell recognition. The sequentially assembled cell-binding NLP with a zwitterionic surface gave a larger transfection yield than the cationic NLP at all concentrations tested. At low DNA concentrations, the enhancement was 80-fold. The disulfide cationic lipids and the sequential assembly strategy enable one to tailor the surface charge, hydrophilicity, and recognition elements of a nanosized gene carrier. This results in increased gene transfer activity in a biocompatible particle.

“Diffusible‐PEG‐Lipid Stabilized Plasmid Lipid Particles”

Many viral and non-viral gene transfer systems suffer from common pharmacological issues that limit their utility in a systemic context. By application of the liposomal drug delivery paradigm, many of the limitations of the first generation non-viral delivery systems can be overcome. Encapsulation in small, long-circulating particles called stabilized plasmid lipid particles (SPLP) results in enhanced accumulation at disease sites and selective protein expression. This work compares the detergent dialysis method of SPLP manufacture with an alternative method, spontaneous vesicle formation by ethanol dilution. The pharmacology of SPLP, as determined by monitoring lipid label and quantitative real time PCR, is also presented.

What Role Can Chemistry Play in Cationic Liposome‐Based Gene Therapy Research Today?

Gene therapy research is still in trouble owing to a paucity of acceptable vector systems to deliver nucleic acids to patients for therapy. Viral vectors are efficient but may be too dangerous for routine clinical use. Synthetic non-viral vectors are inherently much safer but are currently not efficient enough to be clinically viable. The solution for gene therapy lies with improved synthetic non-viral vectors based upon well-found platform technologies and a thorough understanding of the barriers to efficient gene delivery and expression (transfection) relevant to clinical applications of interest. Here we introduce and interpret synthetic non-viral vector systems through the ABCD nanoparticle structural paradigm that represents, in our view, an appropriate lens through which to view all synthetic, non-viral vector systems applicable to in vitro use or in vivo applications and gene therapy. Our intention in introducing this paradigm is to shift the focus of organic and physical chemists away from the design of yet another cytofectin, and instead encourage them to appreciate the wider challenges presented by the need to produce tool kits of meaningful chemical components from which to assemble viable, tailor-made nanoparticles for in vivo applications and gene therapy, both now and in the future.