Quantitative aspects of endocytic activity in lipid-mediated transfections

Erythrocyte membrane based cationic polymer-mcDNA complexes as an efficient gene delivery system

An erythrocyte membrane based gene delivery system presents high transfection efficiency and negligible cytotoxicity.

Synthesis and transfection efficiency of cationic oligopeptide lipids: role of linker

In the design of new cationic lipids for gene transfection, the chemistry of linkers is widely investigated from the viewpoint of biodegradation and less from their contribution to the biophysical properties. We synthesized two dodecyl lipids with glutamide as the backbone and two lysines to provide the cationic headgroup. Lipid 1 differs from Lipid 2 by the presence of an amide linkage instead of an ester linkage that characterizes Lipid 2. The transfection efficiency of lipoplexes with cholesterol as colipid was found to be very high with Lipid 1 on Chinese Hamster Ovary (CHO) and HepG2 cell lines, whereas Lipid 2 has shown partial transfection efficiency on HepG2 cells. Lipid 1 was found to be stable in the presence of serum when tested in HepG2 and CHO cells albeit with lower activity. Fluorescence-based dye-binding and agarose gel-based assays indicated that Lipid 1 binds to DNA more efficiently than Lipid 2 at charge ratios of >1:1. The uptake of oligonucleotides with Lipid 1 was higher than Lipid 2 as revealed by confocal microscopy. Transmission electron microscopy (TEM) images reveal distinct formation of liposomes and lipoplexes with Lipid 1 but fragmented and unordered structures with Lipid 2. Fusion of Lipids 1 and 2 with anionic vesicles, with composition similar to plasma membrane, suggests that fusion of Lipid 2 was very rapid and unlike a fusion event, whereas the fusion kinetics of Lipid 1 vesicles was more defined. Differential scanning calorimetry (DSC) revealed a high T(m) for Lipid 1 (65.4 °C) while Lipid 2 had a T(m) of 23.5 °C. Surface area-pressure isotherms of Lipid 1 was less compressible compared to Lipid 2. However, microviscosity measured using 1,6-diphenyl-1,3,5-hexatriene (DPH) revealed identical values for vesicles made with either of the lipids. The presence of amide linker apparently resulted in stable vesicle formation, higher melting temperature, and low compressibility, while retaining the membrane fluid properties suggesting that the intermolecular hydrogen bonds of Lipid 1 yielded stable lipoplexes of high transfection efficiency.

Tailoring lipoplex composition to the lipid composition of plasma membrane: a Trojan horse for cell entry?

The first interaction between lipoplexes and cells is charge-mediated and not specific. Endocytosis is considered to be the main pathway for lipoplex entry. Upon interaction between lipoplexes and the plasma membrane, intermixing between lipoplex and membrane lipids is necessary for efficient endocytosis. Here we study the mechanism of the different endocytic pathways in lipid-mediated gene delivery. We show that DC-Chol-DOPE/DNA lipoplexes preferentially use a raft-mediated endocytosis, while DOTAP-DOPC/DNA systems are mainly internalized by not specific fluid phase macropinocitosys. On the other hand, most efficient multicomponent lipoplexes, incorporating different lipid species in their lipid bilayer, can use multiple endocytic pathways to enter cells. Our data demonstrate that efficiency of endocytosis is regulated by shape coupling between lipoplex and membrane lipids. We suggest that such a shape-dependent coupling regulates efficient formation of endocytic vesicles thus determining the success of internalization. Our results suggest that tailoring the lipoplex lipid composition to the patchwork-like plasma membrane profile could be a successful machinery of coordinating the endocytic pathway activities and the subsequent intracellular processing.

Cationic lipids: molecular structure/ transfection activity relationships and interactions with biomembranes

Abstract Synthetic cationic lipids, which form complexes (lipoplexes) with polyanionic DNA, are presently the most widely used constituents of nonviral gene carriers. A large number of cationic amphiphiles have been synthesized and tested in transfection studies. However, due to the complexity of the transfection pathway, no general schemes have emerged for correlating the cationic lipid chemistry with their transfection efficacy and the approaches for optimizing their molecular structures are still largely empirical. Here we summarize data on the relationships between transfection activity and cationic lipid molecular structure and demonstrate that the transfection activity depends in a systematic way on the lipid hydrocarbon chain structure. A number of examples, including a large series of cationic phosphatidylcholine derivatives, show that optimum transfection is displayed by lipids with chain length of approximately 14 carbon atoms and that the transfection efficiency strongly increases with increase of chain unsaturation, specifically upon replacement of saturated with monounsaturated chains.

Gene delivery via DNA incorporation within a biomimetic apatite coating

Integrating inductivity with conductivity in a material may advance tissue engineering. An organic/inorganic hybrid was developed by incorporating plasmid DNA encoding for the beta-gal gene complexed with Lipofectamine 2000 (DNA-Lipoplex) within apatite via coprecipitation. It was hypothesized that this system will result in enhanced transfection efficiency compared to DNA-Lipoplexes adsorbed to the mineral surface and DNA coprecipitated without Lipofectamine 2000. PLGA films were cast onto glass slips and apatite and DNA were coprecipitated in modified simulated body fluid (mSBF). DNA-Lipoplex presence in mineral, DNA-Lipoplex stability (vs. coprecipitation time), and transfection efficiency (determined with C3H10T1/2 cells) as a function of coprecipitation time, DNA-Lipoplex concentration, and DNA incorporation method were studied. DNA-Lipoplex presence and spatial distribution on apatite were confirmed through fluorescence. Transfection efficiency was highest for 6h of DNA-Lipoplex coprecipitation. Differences in transfection efficiency were found between the DNA concentrations, with the highest efficiency for coprecipitation being 40 microg/ml (p < or = 0.009 relative to other coprecipitation concentrations). Significant differences in transfection efficiency existed between incorporation methods (p < 0.05) with the highest efficiency for DNA-Lipoplex coprecipitation. This hybrid material system not only integrates inductivity provided by the DNA and conductivity provided by the apatite, but it also has significant implications in non-viral gene delivery due to its ability to increase transfection efficiency.

Lipid-based delivery of CpG oligonucleotides enhances immunotherapeutic efficacy

There has been significant interest in the potential of cytosine-guanine (CpG) containing oligodeoxynucleotides (ODN) as an immunotherapy for malignant, infectious and allergic diseases. While human trials have yielded promising results, clinical use of free CpG ODN still faces several challenges which limit their effectiveness. These include suboptimal in vivo stability, toxicity, unfavorable pharmacokinetic/biodistribution characteristics, lack of specificity for target cells and the requirement for intracellular uptake. To overcome these challenges, optimized lipid-based delivery systems have been developed to protect the CpG ODN payload, modify their circulation/distribution so as to enhance immune cell targeting and facilitate intracellular uptake. Ultimately, lipid-mediated delivery has the capacity to increase the immunopotency of CpG ODN and enhance their prophylactic or therapeutic efficacy in a range of diseases. Lipid-encapsulation provides a feasible strategy to optimize the immunostimulatory activity and immunotherapeutic efficacy of CpG ODN, thereby allowing their full clinical potential to be realized.

The effect of nocodazole on the transfection efficiency of lipid-bilayer coated gold nanoparticles

Nonviral vectors are safer than viral systems for gene therapy applications. However, the limited efficacy always prevents their being widely used in clinical practice. Aside from searching new gene nonviral vectors, many researchers focus on finding out new substances to improve the transfection efficiency of existent vectors. In this work, we found a transfection enhancer, nocodazole (NCZ), for dimethyldioctadecylammonium (DODAB, a cationic lipid) bilayer coated gold nanoparticles (AuNPs) mediated gene delivery. It was found that NCZ produces 3-fold transfection enhancement to HEK 293T cells assessed by flow cytometry (FCM). The result was further confirmed by luciferase assay, in which NCZ induced more than 5 times improvement in transfection efficiency after 48 h of transfection. The results from the inductively coupled plasma mass spectrometry (ICP-MS) and FCM showed that NCZ did not affect the internalization of DODAB-AuNPs/DNA complexes. The trafficking of the complexes by transmission electron microscopy (TEM) indicated that the interrupted transportation of the complexes to the lysosomes contributed greatly to the transfection enhancement. Therefore, NCZ can be used as a transfection enhancer in DODAB-AuNPs mediated transfection system. This work also gave an insight to improving the efficiency of lipid-mediated transfection: modifying lipid on gold nanoparticles and pre-treating cells by NCZ before the transfection.

Structure-transfection activity studies of novel cationic cholesterol-based amphiphiles

Inclusion of DOPE in lipoplex formulations has hampered the establishment of a correlation between cationic lipid structure, biological specificity, and transfection activity, simply because the presence of a helper lipid not only alters the physicochemical properties of the lipoplex but also modifies cell surface specific interactions during the process of transfection. To this end, four cationic cholesterol-based derivatives were synthesized by systematically varying the methylation of the polar headgroup, after which the physicochemical properties, in the absence of DOPE and serum, were correlated with their transfection activity and interaction with cell membranes. It was found that only the primary and secondary amine derivatives, AC-Chol and MC-Chol, respectively, are able to mediate in vitro cell transfection. These results were consistent with fusion experiments and cell internalization studies which illustrated that although cell surface binding occurs for all of the cationic lipids, only the active analogues were able to gain entry into the cytosol. Given the minute differences in the physical properties of these cationic derivatives, we speculate that the biological specificity of the active cationic derivatives either triggers endocytotic pathways leading to eventual endosomal fusion allowing cytoplasmic access to the packaged DNA or other endocytotic pathways that avoid lysosomal degradation.

Anchoring Cationic Amphiphiles for Nucleotide Delivery Significance of DNA Release from Cationic Liposomes for Transfection

We have designed and synthesized lithocholic acid-based cationic amphiphile molecules as components of cationic liposomes for gene transfection (lipofection). To study the relationship between the molecular structures of those amphiphilic molecules, particularly the extended hydrophobic appendant (anchor) at the 3-hydroxyl group, and transfection efficiency, we synthesized several lithocholic and isolithocholic acid derivatives, and examined their transfection efficiency. We also compared the physico-chemical properties of cationic liposomes prepared from these derivatives. We found that isolithocholic acid derivatives exhibit higher transfection efficiency than the corresponding lithocholic acid derivatives. This result indicates that the orientation and extension of hydrophobic regions influence the gene transfection process. Isolithocholic acid derivatives showed a high ability to encapsulate DNA in a compact liposome-DNA complex and to protect it from enzymatic degradation. Isolithocholic acid derivatives also facilitated the release of DNA from the liposome-DNA complex, which is a crucial step for DNA entry into the nucleus. Our results show that the transfection efficiency is directly influenced by the ability of the liposome complex to release DNA, rather than by the DNA-encapsulating ability. Molecular modeling revealed that isolithocholic acid derivatives take relatively extended conformations, while the lithocholic acid derivatives take folded structures. Thus, the efficiency of release of DNA from cationic liposomes in the cytoplasm, which contributes to high transfection efficiency, appears to be dependent upon the molecular shape of the cationic amphiphiles.

Cellular delivery of small interfering RNA by a non-covalently attached cell-penetrating peptide: quantitative analysis of uptake and biological effect

Cell-penetrating peptides (CPPs) have evolved as promising new tools to deliver nucleic acids into cells. So far, the majority of these delivery systems require a covalent linkage between carrier and cargo. To exploit the higher flexibility of a non-covalent strategy, we focused on the characterisation of a novel carrier peptide termed MPGα, which spontaneously forms complexes with nucleic acids. Using a luciferase-targeted small interfering RNA (siRNA) as cargo, we optimised the conditions for MPGα-mediated transfection of mammalian cells. In this system, reporter gene activity could be inhibited up to 90% with an IC₅₀ value in the sub-nanomolar range. As a key issue, we addressed the cellular uptake mechanism of MPGα/siRNA complexes applying various approaches. First, transfection of HeLa cells with MPGα/siRNA complexes in the presence of several inhibitors of endocytosis showed a significant reduction of the RNA interference (RNAi) effect. Second, confocal laser microscopy revealed a punctual intracellular pattern rather than a diffuse distribution of fluorescently labelled RNA-cargo. These data provide strong evidence of an endocytotic pathway contributing significantly to the uptake of MPGα/siRNA complexes. Finally, we quantified the intracellular number of siRNA molecules after MPGα-mediated transfection. The amount of siRNA required to induce half maximal RNAi was 10 000 molecules per cell. Together, the combination of methods provided allows for a detailed side by side quantitative analysis of cargo internalisation and related biological effects. Thus, the overall efficiency of a given delivery technique as well as the mechanism of uptake can be assessed.

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.

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.