Recent patents in cationic lipid carriers for delivery of nucleic acids

Gene therapy is a medical technique intended for treatment of disorders caused by defective, missing, or overexpressing genes. Efficient delivery vectors are necessary in order to transport genetic material to the target cells. Such vectors include viral and non-viral carriers. Viral vectors transfect cells efficiently, however risks associated with their use have limited their clinical applications. Nonviral delivery systems are safer, easier to prepare, more versatile and cost effective. However, their transfection efficiency still falls behind that of the viral vectors. Considerable research into nonviral gene delivery has been conducted in the last two decades on synthetic soft materials such as cationic lipids, polymers, surfactants, and dendrimers as prospective nucleotide carriers for gene delivery. So far, cationic lipids are the most widely used constituents of nonviral gene carriers, with multiple strategies employed to improve their in vitro and in vivo transfection. Efforts in synthesizing new cationic lipids were not fully successful in closing the gap between the efficiency of the viral vectors and that of binary cationic lipid/DNA complexes. Current efforts for improving lipofection efficiency are focused on the development of multicomponent carriers including cationic lipids as key constituents. This review summarizes the recent patents on new cationic lipids as well as on multicomponent formulations enhancing their efficiency as nucleotide carriers.     

Cationic polydiacetylene micelles for gene delivery

Cationic surfactants easily interact with plasmid DNA to form small lipoplexes. However, their detergent behavior and associated biological toxicity limit their use as gene delivery vectors. We have incorporated a diacetylene motif in the hydrophobic chain of cationic surfactants. By using UV irradiation, the small cationic micelles (9 nm) obtained with diacetylenic detergents were photopolymerized into 40 nm spheres. Electrostatic interactions with plasmid DNA led to the formation of 45 nm lipoplexes at N/P = 5 ratio. In vitro transfection of the pCMV-Luciferase plasmid resulted in gene expression (>10(10) RLU/mg protein) at the same ratio, comparable with the commercially available JetSi-ENDO gene delivery system. This new and versatile class of molecules could lead to a new generation of in vivo gene delivery vectors.     

Nature as a source of inspiration for cationic lipid synthesis

Synthetic gene delivery systems represent an attractive alternative to viral vectors for DNA transfection. Cationic lipids are one of the most widely used non-viral vectors for the delivery of DNA into cultured cells and are easily synthesized, leading to a large variety of well-characterized molecules. This review discusses strategies for the design of efficient cationic lipids that overcome the critical barriers of in vitro transfection. A particular focus is placed on natural hydrophilic headgroups and lipophilic tails that have been used to synthesize biocompatible and non-toxic cationic lipids. We also present chemical features that have been investigated to enhance the transfection efficiency of cationic lipids by promoting the escape of lipoplexes from the endosomal compartment and DNA release from DNA-liposome complexes. Transfection efficiency studies using these strategies are likely to improve the understanding of the mechanism of cationic lipid-mediated gene delivery and to help the rational design of novel cationic lipids.     

Efficient nucleic acid transduction with lipoplexes containing novel piperazine- and polyamine-conjugated cholesterol derivatives

To advance the use of cationic lipids for non-viral nucleic acid vector formulation, a panel of novel nitrogen heterocycle cholesteryl derivatives containing a biodegradable carbamate linker was synthesised. Optimally acting piperazine and cyclen compounds had nucleic acid-binding and lipoplex nanoparticle formation properties that were suitable for their use as non-viral vectors. It was found that the lipoplexes formed were capable of efficient non-toxic nucleic acid delivery to cells in culture. The chemical structure of individual cationic lipids, which is likely to influence lipoplex formation, affected efficiency of DNA or RNA transfection. The results indicated that the cyclen containing compound possessing two cholesteryl moieties resulted in efficient siRNA-mediated target gene silencing but was a poor reagent for DNA transfection.     

A pH-sensitive polymer that enhances cationic lipid-mediated gene transfer.

The efficient release of nonviral gene carriers from endosomes is an important step for the successful delivery of DNA into the cell nucleus. A synthetic pH-sensitive anionic polymer, poly(propylacrylic acid) (PPAA), was designed to aid in endosomal escape of nonviral vectors and improve the transfection efficiencies with these vectors. Transfection of NIH3T3 fibroblasts with ternary physical mixtures of the cationic lipid DOTAP, pCMVbeta plasmid DNA, and PPAA showed marked enhancement of both gene expression levels and fraction of cells transfected compared to binary control mixtures of DOTAP and DNA. PPAA also significantly improved the serum-stability of DOTAP/DNA vectors. The DOTAP/DNA/PPAA vectors maintained high levels of transfection in media containing up to 50% serum. The striking enhancement of transfection efficiency with cationic lipid/DNA/PPAA mixtures, along with the enhanced serum-stability, suggests that PPAA may provide significant improvements for the in vivo intracellular delivery of drugs such as DNA, oligonucleotides, proteins, and peptides.     

Cell Biological and Biophysical Aspects of Lipid-mediated Gene Delivery

Cationic lipids are conceptually and methodologically simple tools to deliver nucleic acids into the cells. Strategies based on cationic lipids are viable alternatives to viral vectors and are becoming increasingly popular owing to their minimal toxicity. The first-generation cationic lipids were built around the quaternary nitrogen primarily for binding and condensing DNA. A large number of lipids with variations in the hydrophobic and hydrophilic region were generated with excellent transfection efficiencies in vitro. These cationic lipids had reduced efficiencies when tested for gene delivery in vivo. Efforts in the last decade delineated the cell biological basis of the cationic lipid gene delivery to a significant detail. The application of techniques such as small angle X-ray spectroscopy (SAXS) and fluorescence microscopy, helped in linking the physical properties of lipid:DNA complex (lipoplex) with its intracellular fate. This biological knowledge has been incorporated in the design of the second-generation cationic lipids. Lipid-peptide conjugates (peptoids) are effective strategies to overcome the various cellular barriers along with the lipoplex formulations methodologies. In this context, cationic lipid-mediated gene delivery is considerably benefited by the methodologies of liposome-mediated drug delivery. Lipid mediated gene delivery has an intrinsic advantage of being a biomimetic platform on which considerable variations could be built to develop efficient in vivo gene delivery protocols.     

Efficient Gene Delivery Using Anionic Liposome-Complexed Polyplexes (LPDII)

Synthetic gene transfer vectors based on polyplexes complexed to anionic liposomes (LPDII vectors) were characterized for their transfection efficiency in cultured mammalian cells. The effects of polycation to DNA ratio, lipid to DNA ratio, choice of polycation and lipid composition were systematically evaluated in human oral carcinoma KB cells, using a luciferase reporter gene. For LPDII formulations containing poly-L-lysine and dioeoylphosphatidylethanolamine/cholesteryl hemisuccinate (DOPE/CHEMS) anionic liposomes, at a constant lipid to DNA ratio, an increase in the polycation/DNA (N/P) ratio resulted in an increase in transfection activity. Meanwhile, the optimal lipid to DNA ratio for efficient gene delivery was influenced by the N/P ratio used, and was increased at higher N/P ratios. For the DNA condensing agent, poly-L-lysine could be replaced by polyethylenimine (PEI) as the DNA condensing agent in the formulations. For the lipidic components, CHEMS could be replaced by other anioniclipids including oleic acid, dicetylphosphate and phosphatidylserine, but DOPE, a fusogenic helper lipid, could not be replaced by dioleolyphosphatidylcholine. LPDII formulation showed significantly less cytotoxicity compared to the commonly used cationic lipsomes or PEI mediated transfection and several cell lines were transfected with high efficiency. LPDII vectors avoid the use of toxic cationic lipids and may have potential application in gene therapy.     

Synthesis and in vitro evaluation of glutamide-containing cationic lipids for gene delivery

A novel series of cationic amphiphiles based on dialkyl glutamides with cationic pyridinium head group were synthesized as potential gene delivery agents. Four cationic lipids with glutamide as linker and varying chain lengths were tested for their transfection efficiency in three cell lines. The DNA-lipid complexes were characterized for their ability to bind to DNA, protection from nuclease digestion, size, zeta-potential, and toxicity. All four lipids demonstrated efficient transfection in MCF-7, COS, and HeLa cells, and the reporter gene expression was much higher with DOPE as the helper lipid in the formulation when compared to cholesterol. Among these 14-carbon lipids, lipid 2 has shown the highest transfection efficiency, complete protection of DNA from nuclease digestion, and low toxicity. Interestingly, lipid 2 has also shown remarkable enhancement in transfection in the presence of serum.     

Cationic lipid-mediated nucleic acid delivery: beyond being cationic

Realization of the potential of nucleic acids as drugs is intricately linked to their in vivo delivery. Cationic lipids demonstrated tremendous potential as safe, efficient and scalable in vitro carriers of nucleic acids. For in vivo delivery of nucleic acids, the extant two component liposomal preparations consisting of cationic lipids and nucleic acids have been largely found to be insufficient. Being a soft matter, liposomes readily respond to many physiological variables leading to complex component and morphological changes, thus confounding the efforts in a priori identification of a “competent” formulation. In the recent past many chemical moieties that provide advantage in facing the challenges of barriers in vivo, were incorporated into cationic lipids to improve the transfection efficiency. The cationic lipids, essential for DNA condensation and protection, definitely require additional components to be efficient in vivo. In addition, formulations of cationic lipid carriers with non-lipidic components, mainly peptides, have demonstrated success in in vivo transfection. The present review describes some recent successes of in vivo nucleic acid delivery by cationic lipids.     

Biophysical characterization of anionic lipoplexes

Transfection efficiency of liposomal gene delivery vectors depends on an optimal balance in the electro-chemical and structural properties of the transfection-capable complexes. We have recently reported a novel anionic lipoplex DNA delivery system composed of a ternary complex of endogenous occurring non-toxic anionic lipids, physiological Ca²⁺ cations, and plasmid DNA encoding a gene of interest with high transfection efficiency and low toxicity. In this work, we investigate the electro-chemical and structural properties anionic lipoplexes and compare them with those of Ca²⁺-DNA complexes. Biophysical characterization is used to explain the transfection efficiency of anionic lipoplexes in mammalian CHO-K1 cells. Circular dichroism and fluorescence spectroscopy showed that the plasmid DNA underwent conformational transition from native B-DNA to Z-DNA due to compaction and condensation upon Ca²⁺-mediated complexation with anionic liposomes. Zeta potential measurements and gel electrophoresis studies demonstrated that Ca²⁺ interaction with plasmid DNA during the formation of lipoplexes also led to increased association of supercoiled plasmid DNA with the lipoplexes, leading to charge neutralization which is expected to facilitate transfection. However, even 10-fold higher concentrations of Ca²⁺ alone (in the absence of the anionic liposomes) were unable to induce these changes in plasmid DNA molecules. A model explaining the possible mechanism of anionic lipoplex formation and the correlation of high transfection efficiency to biophysical properties was proposed. These studies confirm the utility of biophysical studies to identify optimal formulation conditions to design efficient liposomal gene delivery vectors.     

Efficient in vivo gene delivery using modified Tat peptide with cationic lipids

A combination of modified HIV-1 Tat (mTat) peptide and cationic lipids, FuGENE HD (FH), dramatically enhanced transfection efficiency across a range of cell lines when compared to mTat or FH alone (Biomaterials 35:1705–1715 2014). The efficiency of this Tat peptide combination was significantly higher than many commercial non-viral vectors. In this present study, we tested the feasibility of this non-viral vector, mTat/FH, in vivo using plasmid DNA encoding a luciferase gene. The results of the in vivo studies showed that animals administered mTat/FH/DNA intramuscularly had significantly higher and longer luciferase expression (≈7 months) than those with mTat/DNA, FH/DNA, or DNA alone. Histological evaluation showed little immune response in the muscles, livers, and kidneys of mice administered with the mTat/FH. The combination of mTat with FH could significantly improve transfection efficiency, expanding the potential use of non-viral gene vectors in vivo.     

In vitro cationic lipid-mediated gene delivery with fluorinated glycerophosphoethanolamine helper lipids.

There is a need for the development of nonviral gene transfer systems with improved and original properties. "Fluorinated" lipoplexes are such candidates, as supported by the remarkably higher in vitro and in vivo transfection potency found for such fluorinated lipoplexes as compared with conventional ones or even with PEI-based polyplexes (Boussif, O., Gaucheron, J., Boulanger, C., Santaella, C., Kolbe, H. V. J., Vierling, P. (2001) Enhanced in vitro and in vivo cationic lipid-mediated gene delivery with a fluorinated glycerophosphoethanolamine helper lipid. J. Gene Med. 3, 109-114). Here, we describe the synthesis of fluorinated glycerophosphoethanolamines (F-PEs), close analogues of dioleoylphosphatidylethanolamine (DOPE), and report on their lipid helper properties vs that of DOPE, as in vitro gene transfer components of fluorinated lipoplexes based on pcTG90, DOGS (Transfectam), or DOTAP. To evaluate the contribution of the F-PEs to in vitro lipoplex-mediated gene transfer, we examined the effect of including the F-PEs in lipoplexes formulated with these cationic lipids (CL) for various CL:DOPE:F-PE molar ratios [1:(1 - x):x with x = 0, 0.5 and 1; 1:(2 - y):y with y = 0, 1, 1.5, and 2], and various N/P ratios (from 10 to 0.8, N = number of CL amines, P = number of DNA phosphates). Irrespective of the F-PE chemical structure, of the colipid F-PE:DOPE composition, and of the N/P ratio, comparable transfection levels to those of their respective control DOPE lipoplexes were most frequently obtained when using one of the F-PEs as colipid of DOGS, pcTG90, or DOTAP in place of part of or of all DOPE. However, a large proportion of DOGS-based lipoplexes were found to display a higher transfection efficiency when formulated with the F-PEs rather than with DOPE alone while the opposite tendency was evidenced for the DOTAP-based lipoplexes. The present work indicates that "fluorinated" lipoplexes formulated with fluorinated helper lipids and conventional cationic lipids are very attractive candidates for gene delivery. It confirms further that lipophobicity and restricted miscibility of the lipoplex lipids with the endogenous lipids does not preclude efficient gene transfer and expression. Their transfection potency is rather attributable to their unique lipophobic and hydrophobic character (resulting from the formulation of DNA with fluorinated lipids), thus preventing to some extent DNA from interactions with lipophilic and hydrophilic biocompounds, and from degradation.     

Cell transfection by DNA-lipid complexes — Lipoplexes

Nonviral vectors such as complexes of plasmid DNA with cationic lipids known as lipoplexes are considered as an attractive alternative to virus-based delivery systems. Unlike viruses, lipoplexes do not suffer from immunological and mutational hazards, though the efficiency of lipoplexes is often not sufficient for therapeutic purposes and require higher level of transfection than achieved until now. A number of critical steps responsible for transfection efficiency are discussed here. They include processes of lipoplexes formation, interaction with cell surface, their internalization into cell, and DNA release and delivery into the nucleus. All these processes should be thoroughly studied to be able to enhance the transfection efficacy.     

Lipid-mediated siRNA delivery down-regulates exogenous gene expression in the mouse brain at picomolar levels

BACKGROUND: Efficient in vivo vectors are needed to exploit the enormous potential of RNA interference (RNAi). Such methods require optimisation for specific delivery routes, tissues and usages. We tested the capacity of different non-viral vectors and formulation methods for inhibition of exogenous (luciferase) gene expression when used to introduce small interfering RNA (siRNA) into the mouse brain in vivo. METHODS: Polyethylenimine (PEI)-based polyplexes and JetSI (a mixture of cationic lipids)-based lipoplexes were used to vectorise plasmid DNA encoding the firefly Photinus pyralis luciferase gene and picomolar amounts of siRNA directed against this gene. Two controls were used, DNA encoding an unrelated luciferase from Renilla reniformis and a mutated siRNA sequence. RESULTS: First, we found that linear PEI, although efficient for delivering nucleic acids to cells, did not permit development of siRNA activity within the dose range tested (<0.5 pmol). Second, various combinations of cationic lipids were tried and the best formulation was found to be a combination of JetSI with the fusogenic lipid dioleoylphosphatidylethanolamine (DOPE). Efficient inhibition of target, firefly luciferase was obtained with exceedingly low amounts of siRNA: 78 +/- 6% inhibition at 24 h post-transfection with 0.2 pmol siRNA. This inhibition was dose-dependent and specific. No effect was seen on the control gene, co-transfected Renilla luciferase, and the control mutated siRNA sequence had no effect on the targeted firefly luciferase. CONCLUSIONS: We have optimised an efficient cationic lipoplex method for delivery of siRNA into the newborn mouse brain. Specific inhibition of exogenous target gene expression is obtained with picomolar amounts of siRNA.     

Fluorescence methods for lipoplex characterization

Since the first reported transfection studies using cationic liposomes in 1987, significant advances have been made on the understanding of the physical properties of DNA/cationic liposome complexes (lipoplexes) in order to improve their transfection efficiencies. In this review a critical survey of the biophysical techniques used in their characterization is presented, with an emphasis on fluorescence methodologies, namely FRET. It is shown that the use of FRET combined with state-of-the-art modeling and data analysis allows detailed structural information in conditions close to the in vivo utilization of these non-viral based vectors. We describe in detail the use of fluorescence-based methods in (i) the assessment of DNA-lipid interaction and kinetics of lipoplex formation; (ii) membrane mixing studies; (iii) characterization of lipoplex molecular structure through the determination of interlamellar distances; and (iv) qualitative and quantitative evaluation of DNA condensation by cationic liposomes. This review aims at providing a framework for future characterization studies of novel liposomal formulations as gene delivery carriers, taking advantage of more sensitive nucleic acid and lipid dyes concomitantly with increasingly sophisticated fluorescence techniques.     

Lipophilic peptides for gene delivery

DNA transfections are widely performed in research laboratories and in vivo gene delivery holds the promise for curing many diseases. The synthetic carriers or vectors for DNA are typically cationic lipids. However, in biology, the recognition of nucleic acids by proteins involves both electrostatic and stacking contributions. As such we have prepared a series of new lipophilic peptide vectors that possess lysine and tryptophan amino acids for evaluation. These lipophilic peptides show minimal cytotoxicity and enhanced in vitro gene transfection activity.     

Design,synthesis, and evaluation of gadolinium cationic lipids as tools for biodistribution studies of gene delivery complexes

Gadolinium-chelating cationic lipids have been synthesized to obtain lipoplexes with MRI contrast properties. These compounds were designed to follow the biodistribution of synthetic DNA for gene delivery by nuclear magnetic resonance imaging. The lipid MCO-I-68 was synthesized, and chelate complexes with gadolinium were formed and characterized in terms of physicochemical and DNA binding properties. The transfection activity of MCO-I-68-Gd/DNA complexes was assayed in vitro on NIH 3T3. Different formulations of the product were tested. When up to 5% of the gadolinium lipid complexes were co-formulated with the cationic lipid RPR120535 used as a reference, the transfection levels were maintained as compared to RPR120535 alone. To date, only a liposomal formulation of a gadolinium-cationic lipid chelate without DNA had been observed using magnetic resonance imaging. In vivo intratumoral administration of MCO-I-68-Gd/DNA lipoplexes to tumor model led to an important increase of the NMR signal. It was demonstrated that the new complexes also acted as transfection carriers when they were formulated from liposomes.     

Evaluation of cationic assemblies constructed with amino acid based lipids for plasmid DNA delivery

We synthesized cationic lipids bearing lysine, histidine, or arginine as a cationic headgroup for use in gene transfer studies. The cationic assemblies formed from lysine- or arginine-type lipids gave unilamellar vesicles (approximately 100 nm diameter), whereas the morphology of the histidine-type lipids was tube-like. The competences of the cationic assemblies were sufficient to form lipoplexes, and the resulting lipoplexes were evaluated in terms of gene expression efficiencies with COS-7 cells. The lysine- or arginine-type lipids exhibited higher gene expression efficiencies than that of Lipofectamine2000, a conventional transgenic reagent, indicating that stable lipoplexes could be prepared between spherical cationic assemblies and plasmid DNA. The gene expression efficiency in relation to the cationic headgroup of the lipids was as follows: lysine > or = arginine > histidine. In addition, gene expression efficiency was enhanced by decreasing the length of the alkyl chain of the hydrophobic moiety. Unlike Lipofectamine2000, no reduction in transfection efficiency in the presence of fetal bovine serum was observed for the lipoplexes formed using synthetic cationic lipids. Moreover, the synthetic cationic lipids revealed remarkably low cytotoxicity compared with Lipofectamine2000. In conclusion, cationic assemblies formed from 1,5-ditetradecyl-N-lysyl-L-glutamate or 1,5-ditetradecyl-N-arginyl-L-glutamate can be used as an effective plasmid DNA delivery system.     

Biodegradable poly(vinyl alcohol)-polyethylenimine nanocomposites for enhanced gene expression in vitro and in vivo

Use of cationic polymers as nonviral gene vectors has several limitations such as low transfection efficiency, high toxicity, and inactivation by serum. In this study, varying amounts of low molecular weight branched polyethylenimine 1.8 kDa (bPEI 1.8) were introduced on to a neutral polymer, poly(vinyl alcohol) (PVA), to bring in cationic charge on the resulting PVA-PEI (PP) nanocomposites. We rationalized that by introducing bPEI 1.8, buffering and condensation properties of the proposed nanocomposites would result in improved gene transfer capability. A series of PVA-PEI (PP) nanocomposites was synthesized using well-established epoxide chemistry and characterized by IR and NMR. Particle size of the PP/DNA complexes ranged between 120 to 135 nm, as determined by dynamic light scattering (DLS), and DNA retardation assay revealed efficient binding capability of PP nanocomposites to negatively charged nucleic acids. In vitro transfection of PP/DNA complexes in HEK293, HeLa, and CHO cells revealed that the best working formulation in the synthesized series, PP-3/DNA complex, displayed ~2-50-fold higher transfection efficiency than bPEIs (1.8 and 25 kDa) and commercial transfection reagents. More importantly, the PP/DNA complexes were stable over a period of time, along with their superior transfection efficiency in the presence of serum compared to serum-free conditions, retaining the nontoxic property of low molecular weight bPEI. The in vivo administration of PP-3/DNA complex in Balb/c mice showed maximum gene expression in their spleen. The study demonstrates the potential of PP nanocomposites as promising nonviral gene vectors for in vivo applications.