Lipoplex formulation of superior efficacy exhibits high surface activity and fusogenicity, and readily releases DNA

Looking Back, Moving Forward: Lipid Nanoparticles as a Promising Frontier in Gene Delivery

Lipid nanoparticles (LNPs) have shown remarkable success in delivering genetic materials like COVID-19 LNP vaccines, such as mRNA-1273/SpikeVax by Moderna and BNT162b2/Comirnaty by BioNTech/Pfizer, as well as siRNA for rare inherited diseases, such as Onpattro from Alnylam Pharmaceuticals. These LNPs are advantageous since they minimize side effects, target specific cells, and regulate payload delivery. There has been a surge of interest in these particles due to their success stories; however, we still do not know much about how they work. This perspective will recapitulate the evolution of lipid-based gene delivery, starting with Felgner's pioneering 1987 PNAS paper, which introduced the initial DNA-transfection method utilizing a synthetic cationic lipid. Our journey takes us to the early 2020s, a time when advancements in bionano interactions enabled us to create biomimetic lipoplexes characterized by a remarkable ability to evade capture by immune cells in vivo. Through this overview, we propose leveraging previous achievements to assist us in formulating improved research goals when optimizing LNPs for medical conditions such as infectious diseases, cancer, and heritable disorders.

Mechanistic Insights into the Superior DNA Delivery Efficiency of Multicomponent Lipid Nanoparticles: An In Vitro and In Vivo Study

Lipid nanoparticles (LNPs) are currently having an increasing impact on nanomedicines as delivery agents, among others, of RNA molecules (e.g., short interfering RNA for the treatment of hereditary diseases or messenger RNA for the development of COVID-19 vaccines). Despite this, the delivery of plasmid DNA (pDNA) by LNPs in preclinical studies is still unsatisfactory, mainly due to the lack of systematic structural and functional studies on DNA-loaded LNPs. To tackle this issue, we developed, characterized, and tested a library of 16 multicomponent DNA-loaded LNPs which were prepared by microfluidics and differed in lipid composition, surface functionalization, and manufacturing factors. 8 out of 16 formulations exhibited proper size and zeta potential and passed to the validation step, that is, the simultaneous quantification of transfection efficiency and cell viability in human embryonic kidney cells (HEK-293). The most efficient formulation (LNP15) was then successfully validated both in vitro, in an immortalized adult keratinocyte cell line (HaCaT) and in an epidermoid cervical cancer cell line (CaSki), and in vivo as a nanocarrier to deliver a cancer vaccine against the benchmark target tyrosine-kinase receptor HER2 in C57BL/6 mice. Finally, by a combination of confocal microscopy, transmission electron microscopy and synchrotron small-angle X-ray scattering, we were able to show that the superior efficiency of LNP15 can be linked to its disordered nanostructure consisting of small-size unoriented layers of pDNA sandwiched between closely apposed lipid membranes that undergo massive destabilization upon interaction with cellular lipids. Our results provide new insights into the structure-activity relationship of pDNA-loaded LNPs and pave the way to the clinical translation of this gene delivery technology.

Overcoming barriers in non-viral gene delivery for neurological applications

Gene therapy for neurological disorders has attracted significant interest as a way to reverse or stop various disease pathologies. Typical gene therapies involving the central and peripheral nervous system make use of adeno-associated viral vectors whose questionable safety and limitations in manufacturing has given rise to extensive research into non-viral vectors. While early research studies have demonstrated limited efficacy with these non-viral vectors, investigation into various vector materials and functionalization methods has provided insight into ways to optimize these non-viral vectors to improve desired characteristics such as improved blood-brain barrier transcytosis, improved perfusion in brain region, enhanced cellular uptake and endosomal escape in neural cells, and nuclear transport of genetic material post- intracellular delivery. Using a combination of various strategies to enhance non-viral vectors, research groups have designed multi-functional vectors that have been successfully used in a variety of pre-clinical applications for the treatment of Parkinson's disease, brain cancers, and cellular reprogramming for neuron replacement. While more work is needed in the design of these multi-functional non-viral vectors for neural applications, much of the groundwork has been done and is reviewed here.

Advances in Development of mRNA-Based Therapeutics

Recently, mRNA-based therapeutics have been greatly boosted since the development of novel technologies of both mRNA synthesis and delivery system. Promising results were showed in both preclinical and clinical studies in the field of cancer vaccine, tumor immunotherapy, infectious disease prevention and protein replacement therapy. Recent advancements in clinical trials also encouraged scientists to attempt new applications of mRNA therapy such as gene editing and cell programming. These studies bring mRNA therapeutics closer to real-world application. Herein, we provide an overview of recent advances in mRNA-based therapeutics.

The Process of Binding and Releasing of Genetic Material from Lipoplexes Based on Trimeric Surfactants and Phospholipids

Nonviral vectors for gene therapy such as lipoplexes are characterized by low toxicity, high biocompatibility, and good transfection efficiency. Specifically, lipoplexes based on polymeric surfactants and phospholipids have great potential as gene carriers due to the increased ability to bind genetic material (multiplied positive electric charge) while lowering undesirable effects (the presence of lipids makes the system more like natural membranes). This study aimed to test the ability to bind and release genetic material by lipoplexes based on trimeric surfactants and lipid formulations of different compositions and to characterize formed complexes by circular dichroism (CD) spectroscopy and atomic force microscopy (AFM). The cytotoxicity of studied lipoplexes was tested on HeLa cells by the MTT cell viability assay and the dye exclusion test (trypan blue). The presence of lipids in the system lowered the surfactant concentration required for complexation (higher efficiency) and reduced the cytotoxicity of lipoplexes. Surfactant/lipids/DNA complexes were more stable than surfactant/DNA complexes. Surfactant molecules induced the genetic material condensation, but the presence of lipids significantly intensified this process. Systems based on trimeric surfactants and lipid formulations, particularly TRI_N and TRI_IMI systems, could be used as delivery carrier, and have proven to be highly effective, nontoxic, and universal for DNA of various lengths.

The influence of cationic lipoid - 1-palmitoyl-2-oleoyl-sn-glycero-3-ethylphosphocholine - on model lipid membranes

The triesters of phosphatidylcholine as the derivatives of natural phosphatidylcholines are less cytotoxic than the other cationic lipoids, therefore they can be applied in lipofection and in drug delivery. However, a successful and effective use of these compounds requires detailed information of their mechanism of action, which is probably highly complex and multi-stages. However, the first barrier in the way to cell and thus the first side of action of these compounds is the cellular membrane. The aim of this work was to investigate the effect of one cationic lipoid, namely 1-palmitoyl-2-oleoyl-sn-glycero-3-ethylphosphocholine (EPOPC) on model POPC/SM/Chol = 1:1:1 membranes. The experiments were performed on monolayer and bilayer systems and they involved the surface pressure measurements, Brewster angle microscopy studies, dynamic light scattering and zeta potential measurements and the experiments with the surfactant solution and steady-state fluorescence anisotropy of DPH and TMA-DPH. Moreover, to perform the studies systematically also the properties of the binary (POPC/EPOPC, SM/EPOPC, Chol/EPOPC) and ternary (POPC/Chol/EPOPC, SM/Chol/EPOPC) model systems were investigated. The obtained results indicated that even low concentration of EPOPC alters properties and organization of model membranes. Namely, EPOPC makes the interactions in model membrane weaker and increases fluidity and permeability of the lipid system. Finally, based on these data it can be proposed that the mechanism of action of EPOPC in lipofection/drug delivery involves the modifications in membrane organization, which facilitates the incorporation of drug or other material into the cell.

Preparation of cationic proteoliposomes using cell-free membrane protein synthesis: the chaperoning effect of cationic liposomes

Membrane protein reconstituted cationic liposomes are constructed using cell-free membrane protein synthesis in the presence of cationic liposomes. The chaperon effect of cationic liposomal membrane assists in folding the functional conformation of membrane protein. This preparation method enables the provision of the usage of proteoliposomes for drug delivery.

The preparation method of cationic proteoliposomes is established using a cell-free membrane protein synthesis in the presence of cationic liposomes.

pH-Sensitive N,N-Dimethylalkane-1-amine N-Oxides in DNA Delivery: From Structure to Transfection Efficiency

pH-sensitive liposomes composed of homologues of series of N,N-dimethylalkane-1-amine N-oxides (CnNO, n = 8-18, where n is the number of carbon atoms in the alkyl substituent) and neutral phospholipid dioleoylphosphatidylethanolamine (DOPE) were prepared at two molar ratios (CnNO/DOPE = 0.4:1 and 1:1) and tested for their in vitro transfection activity. Several techniques (SAXS/WAXS, UV-vis, zeta potential measurements, confocal microscopy) were applied to characterize the system in an effort to unravel the relationship among the transfection efficiency, structure, and composition of the lipoplexes. The transfection efficiency of CnNO/DOPE for plasmid DNA in U2OS cells follows a quasi-parabolic dependence on CnNO's alkyl substituent length with a maximum at n = 16. The transfection efficiency of CnNO/DOPE (n = 12-18) lipoplexes was found to be higher than that of commercially available Lipofectamine 2000. C16NO/DOPE also positively transfected HEK 293T and HeLa cells. Small-angle X-ray scattering (SAXS) shows large structural diversity depending on the complex's composition and pH. Transfection efficiencies mediated by two structures, either a condensed lamellar (L_α^c) or epitaxially connected L_α^c and a condensed inverted hexagonal (H_II^c) phase (L_α^c & H_II^c), were found to be very similar. The change in pH from acidic to neutral induces phase transition L_α^c & H_II^c → Q_II + L_α, with cubic phase Q_II of the Pn3m space group. Q_II detected in lipoplexes of most efficient composition CnNO/DOPE (n = 16 and 18) facilitates DNA release and promotes its internalization in the cell.

Effect of white mange mixture in a murine model of psoriasis

Psoriasis is an autoimmune disease with periods of remission or aggravation. Until now, no effective treatment has been developed. The aim of this study was to assess the effect of the traditional Chinese medicine white mange mixture in a murine model of vaginal psoriasis. Female mice (n=70) were randomly divided into seven groups as follows: negative control group, positive control group, acitretin group, Xiaoying granule group, high-dose white mange mixture group, medium-dose white mange mixture group, and low-dose white mange mixture group. After vaginal psoriasis mouse model design, the inhibition of keratinocyte (KC) cell proliferating cell nuclear antigen (PCNA) was achieved by SP immunohistochemical method, spleen T lymphocyte apoptosis detection was assessed by using electron microscopy and granulocyte colony stimulating factor (GM-CSF) levels were detected by ELISA method. According to our results, T lymphocyte nucleus appearance in the negative control group was normal whereas in all the doses of white mange mixture the nucleus significantly showed apoptotic trend. Compared with the negative control group, the amount of GM-CSF in the serum of the model was significantly increased (P<0.01) while administration of white mange mixture in different doses decreased the GM-CSF content significantly (P<0.01). White mange mixture can significantly inhibit vaginal psoriasis in a mouse model by decreasing the amount of epithelium KC cell PCNA and production of the inflammatory cytokines GM-CSF in serum.

Endosomal Escape and Cytosolic Penetration of Macromolecules Mediated by Synthetic Delivery Agents

Cell delivery reagents often exploit the endocytic pathway as a route of cell entry. Once endocytosed, these reagents must overcome endosomal entrapment to ensure the release of their macromolecular cargo into the cytosol of cells. In this review, we describe several examples of prototypical synthetic reagents that are capable of endosomal escape and examine their mechanisms of action, their efficiencies, and their effects on cells. Although these delivery systems are chemically distinct, some commonalities in how they interact with cellular membranes can be inferred. This, in turn, sheds some light on the process of endosomal escape, and may help guide the development and optimization of next-generation delivery tools.

Morphological Analysis of Trafficking and Processing of Anionic and Cationic Liposomes in Cultured Cells

Liposomes, artificial phospholipid vesicles, have been developed as a non-viral drug delivery system to allow contained agents to be efficiently delivered to target sites via systemic circulation. Liposomes have been used as a gene transfer tool with cultured cells; however, their precise trafficking and processing remain uncertain. Furthermore, liposomes with different surface charges are known to exhibit distinct properties. The purpose of the current study was to elucidate the intracellular trafficking and processing of liposomes with anionic and cationic surface charges from a morphological view point. We found that cationic liposomes (CLs) were more effectively taken by the cells than anionic liposomes (ALs). Confocal laser scanning microscopy and transmission electron microscopy demonstrated distinct intracellular localization and processing patterns of ALs and CLs. ALs and their contents were localized in lysosomes but not in cytosol, indicating that ALs are subjected to the endosome-lysosome system. In contrast, contents of CLs were distributed mainly in the cytosol. CLs appear to disturb the cell membrane and then collapse to release their contents into the cytosol. It is feasible that the contents of CLs enter the cytosol directly rather than via the endosome-lysosome system.

Inclusion of oligonucleotide antimicrobials in biocompatible cationic liposomes: A structural study

HYPOTHESIS

Transcription factor decoys (TFD) are short oligonucleotides designed to block essential genetic pathways in bacteria and defeat resistant infections. TFD protection in biological fluids and their delivery to the site of infection require formulation in appropriate delivery systems. In this work, we build on a classical phosphatidylcholine/phosphatidylethanolamine (POPC/DOPE) scaffold to design TFD-loaded cationic liposomes by combining the DNA-complexing abilities of a bolaamphiphile, (1,1'-(dodecane-1,12-diyl)-bis-(9-amino-1,2,3,4-tetrahydroacridinium) chloride (12-bis-THA), with the biocompatible cationic lipid ethyl-phosphatidylcholine (DPePC). The goal is to perform a structural study to determine the impact of the bolaamphiphile and TFD incorporation on the liposome structure, the capacity for TFD encapsulation, and the colloidal stability in saline media and cell culture environments.

EXPERIMENTS

The systems are characterized by means of dynamic light scattering, small-angle X-ray scattering, and ζ-potential measurements, to provide a clear picture of the liposome structure. Circular dichroism (CD) spectroscopy is used to assess the compaction of the oligonucleotide in a psi form, while steady-state fluorescence and fluorescence correlation spectroscopies give insight into the entrapment rate and distribution of the TFD in the liposomes.

FINDINGS

We found that the combination of the two cationic species, 12-bis-THA and DPePC, allows encapsulation of 90% of the TFD. Results of CD experiments revealed that the TFD is condensed, therefore likely protected from the lytic action of serum nucleases. Finally, the systems showed colloidal stability in aqueous dispersion with ionic strength comparable to biologically relevant media.

Novel layer-by-layer self-assembled peptide nanocarriers for siRNA delivery

Novel stable diphenylalaninamide peptide based nanocarriers were designed by layer-by-layer polyelectrolyte deposition to load siRNA for gene silencing.

Fluorometric Analysis of Individual Cationic Lipid-DNA Complexes

Lipoplex preparations are heterogeneous mixtures of lipoplex particles of different structure. Because these structures determine the efficiency of genetic material delivery, it is important to characterize the distribution of particles of different types in lipoplex preparations with good statistics. We describe the application of flow fluorometry which allow producing such distributions (in terms of lipoplex particle size and composition) within minutes using basic flow cytometer (Pozharski and MacDonald, Anal Biochem 341:230-240, 2005).

Efficient Cellular Knockdown Mediated by siRNA Nanovectors of Gemini Cationic Lipids Having Delocalizable Headgroups and Oligo-Oxyethylene Spacers

The use of small interfering RNAs (siRNAs) to silence specific genes is one of the most promising approaches in gene therapy, but it requires efficient nanovectors for successful cellular delivery. Recently, we reported liposomal gene carriers derived from a gemini cationic lipid (GCL) of the 1,2-bis(hexadecyl dimethyl imidazolium) oligo-oxyethylene series ((C16Im)2(C2H4O)nC2H4 with n = 1, 2, or 3) and 1,2-dioleyol phosphatidylethanolamine as highly efficient cytofectins for pDNA. On the basis of the satisfactory outcomes of the previous study, the present work focuses on the utility of coliposomes of these gemini lipids with the biocompatible neutral lipid mono oleoyl glycerol (MOG) as highly potent vectors for siRNA cellular transport in the presence of serum. The (C16Im)2(C2H4O)nC2H4/MOG-siRNA lipoplexes were characterized through (i) a physicochemical study (zeta potential, cryo-transmission electron microscopy, small-angle X-ray scattering, and fluorescence anisotropy) to establish the relationship between size, structure, fluidity, and the interaction between siRNA and the GCL/MOG gene vectors and (ii) a biological analysis (flow cytometry, fluorescence microscopy, and cell viability) to report the anti-GFP siRNA transfections in HEK 293T, HeLa, and H1299 cancer cell lines. The in vitro biological analysis confirms the cellular uptake and indicates that a short spacer, a very low molar fraction of GCL in the mixed lipid, and a moderate effective charge ratio of the lipoplex yielded maximum silencing efficacy. At these experimental conditions, the siRNA used in this work is compacted by the GCL/MOG nanovectors by forming two cubic structures (Ia3d and Pm3n) that are correlated with excellent silencing activity. These liposomal nanocarriers possess high silencing activity with a negligible cytotoxicity, which strongly supports their practical use for in vivo knockdown studies.

Biocompatible cationic lipids for the formulation of liposomal DNA vectors

Ethylphosphocholine lipids are highly biocompatible cationic amphiphiles that can be used for the formulation of liposomal DNA vectors, with negligible toxic effects on cells and organisms. Here we report the characterization of EDPPC (1,2-dipalmitoyl-sn-glycero-O-ethyl-3-phosphocholine chloride) liposomes, containing two different zwitterionic helper lipids, POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) and DOPE (1,2-dioleoyl-sn-glycero-3-phosphoethanolamine). Depending on the nature of the helper lipid, a phase separation in the bilayer is found at room temperature, where domains enriched in the cationic component coexist in a relatively large temperature range with regions where the zwitterionic lipids are predominant. We studied DNA complexation, the internal structure of lipoplexes and their docking and fusogenic ability with model target bilayers. The structural and functional modifications caused by DNA binding were studied using Dynamic Light Scattering (DLS), zeta potential, and small and wide angle X-ray scattering (SAXS-WAXS) measurements, while the interaction with membranes was assessed by using Giant Unilamellar Vesicles (GUVs) as model target bilayers. The results presented establish a connection between the physicochemical properties of lipid bilayers, and in particular of lipid demixing, with the phase state of the complexes and their ability to interact with model membranes.

Structural dynamics and physicochemical properties of pDNA/DODAB:MO lipoplexes: effect of pH and anionic lipids in inverted non-lamellar phases versus lamellar phases

Dioctadecyldimethylammonium bromide (DODAB):Monoolein (MO) lipoplexes have mainly been studied within the range of high molar ratios of DODAB, with noticeable transfection efficiencies in the Human Embryonic Kidney (HEK, a.k.a. 293T) cell line. In this work, we intend to study the effect of high MO content on the structure and physicochemical properties of pDNA/DODAB:MO lipoplexes to achieve some correlation with their transfection efficiency. Static/Dynamic Light Scattering and Cryo-TEM imaging were used to characterize the size/morphology of DNA/DODAB:MO lipoplexes at different DODAB:MO contents (2:1, 1:1, 1:2) and charge ratios (CRs) (+/-). Nile Red fluorescence emission was performed to detect changes in microviscosity, hydration and polarity of DNA/DODAB:MO systems. Lipoplexes stability at physiological pH values and in the presence of anionic lipids was evaluated by Förster Resonance Energy Transfer (FRET). Physicochemical/structural data were complemented with transfection studies in HEK cells using the β-galactosidase reporter gene activity assay. This work reports the coexistence of multilamellar and non-lamellar inverted phases in MO-richer lipoplexes (DODAB:MO 1:2 and 1:4), leading to transfection efficiencies comparable to those of multilamellar (DODAB-richer) lipoplexes, but at higher charge ratios [CR (+/-)=6.0] and without dose-effect response. These results may be related to the structural changes of lipoplexes promoted by high MO content.

Peptide nanovesicles formed by the self-assembly of branched amphiphilic peptides

Peptide-based packaging systems show great potential as safer drug delivery systems. They overcome problems associated with lipid-based or viral delivery systems, vis-a-vis stability, specificity, inflammation, antigenicity, and tune-ability. Here, we describe a set of 15 & 23-residue branched, amphiphilic peptides that mimic phosphoglycerides in molecular architecture. These peptides undergo supramolecular self-assembly and form solvent-filled, bilayer delimited spheres with 50–200 nm diameters as confirmed by TEM, STEM and DLS. Whereas weak hydrophobic forces drive and sustain lipid bilayer assemblies, these all-peptide structures are stabilized potentially by both hydrophobic interactions and hydrogen bonds and remain intact at low micromolar concentrations and higher temperatures. A linear peptide lacking the branch point showed no self-assembly properties. We have observed that these peptide vesicles can trap fluorescent dye molecules within their interior and are taken up by N/N 1003A rabbit lens epithelial cells grown in culture. These assemblies are thus potential drug delivery systems that can overcome some of the key limitations of the current packaging systems.

Intracellular trafficking of cationic liposome-DNA complexes in living cells

Three-dimensional single-particle tracking (SPT) was used to calculate the mean square displacement (MSD) and the diffusion coefficients of multicomponent cationic liposome-DNA complexes (lipoplexes) in CHO-K1 living cells. In untreated (NT) control cells, we found that the intracellular lipoplex motion was either directed or Brownian with active transportation being definitely more frequent (more than 70%) than Brownian diffusion. The MSD analysis was supported by the calculation of the three-dimensional asphericity, A₃, which was close to unity, denoting the preponderant occurrence of movement along a direction. To elucidate the role of the cytoskeleton structure in the lipoplex trafficking, cells were treated with cytoskeleton (actin microfilaments and microtubules) polymerization inhibitors (latrunculin B and nocodazole, respectively). When cells were treated with inhibitors, the lipoplex movement tended towards a random walk at the expense of directed motion. The disassembly of microtubules had a stronger effect on the reduction of directional movement than that of actin microfilaments. Relevance of the results for enhanced gene delivery is discussed.

Highly efficient cationic ethylphosphatidylcholine siRNA carrier for GFP suppression in modified breast cancer cells

AIM

Cationic ethylphosphatidylcholines (ePCs) were evaluated for the delivery of siRNA in modified breast cancer cells.

MATERIALS AND METHODS

Dimyristoleoyl-ePC (C14), dioleoyl-ePC (C18), and dilauroyl-ePC (C12) nanoparticles were complexed with siRNA for green fluorescent protein (GFP) suppression in modified MCF-7 breast cancer cells. The kinetics of GFP suppression were followed over the course of 72 hours.

RESULTS

C14, which has been previously found to be particularly effective in gene transfection into primary human umbilical artery endothelial cells, was also remarkably effective as siRNA carrier, with an efficacy exceeding that of Lipofectamine RNAiMAX. The C14 toxicity remained comparable to that of RNAiMAX. The efficacy of the other tested cationic ePC formulations was less than that of C14 and RNAiMAX.

CONCLUSION

The cationic lipid C14 is a highly efficient siRNA carrier that could be used for the development of new formulations for siRNA delivery into cancer cells. A valuable advantage of the C14 formulations is the fact that they are simple, and do not require adjuvants or complex preparation procedures.

Influence of charge ratio of liposome/DNA complexes on their size after extrusion and transfection efficiency

BACKGROUND

Physicochemical characteristics of liposome/DNA complexes influence transfection efficiency and affect each other in a very intricate way. The result of this is discrepancies in conclusions drawn about the individual influence of each one.

METHODS

Aiming to elucidate the influence of liposome/DNA charge ratio and size on transfection efficiency and on each other, we used liposome/DNA complexes with charge ratio (+/-) in the range of 1-50 and extruded through membranes of 400, 200, and 100 nm. Plasmid DNA encoding green fluorescent protein was used to measure transfection efficiency by flow cytometry. Sizes of liposome/DNA complexes were measured by dynamic light scattering.

RESULTS

Liposome size was reduced after extrusion but this was mainly driven by the charge ratio and not by the size of the membrane pores. Reduction of complex size at each charge ratio positively correlated with transfection efficiency. When the size of the complexes was approximately constant, increasing the charge ratio was found to promote transfection efficiency. Cationic lipid N-(1-(2,3-dioleoyloxy)propyl)N,N,N trimethylammonium chloride was used for modulation of positive charge and a cytotoxicity test showed that increasing its amount increases cytotoxicity.

CONCLUSION

It can be concluded that charge ratio dictates the size of the complex whereas overall size reduction and higher charge ratios promote transfection efficiency in vitro.

Probing the in vitro mechanism of action of cationic lipid/DNA lipoplexes at a nanometric scale

Cationic lipids are used for delivering nucleic acids (lipoplexes) into cells for both therapeutic and biological applications. A better understanding of the identified key-steps, including endocytosis, endosomal escape and nuclear delivery is required for further developments to improve their efficacy. Here, we developed a labelling protocol using aminated nanoparticles as markers for plasmid DNA to examine the intracellular route of lipoplexes in cell lines using transmission electron microscopy. Morphological changes of lipoplexes, membrane reorganizations and endosomal membrane ruptures were observed allowing the understanding of the lipoplex mechanism until the endosomal escape mediated by cationic lipids. The study carried out on two cationic lipids, bis(guanidinium)-tris(2-aminoethyl)amine-cholesterol (BGTC) and dioleyl succinyl paramomycin (DOSP), showed two pathways of endosomal escape that could explain their different transfection efficiencies. For BGTC, a partial or complete dissociation of DNA from cationic lipids occurred before endosomal escape while for DOSP, lipoplexes remained visible within ruptured vesicles suggesting a more direct pathway for DNA release and endosome escape. In addition, the formation of new multilamellar lipid assemblies was noted, which could result from the interaction between cationic lipids and cellular compounds. These results provide new insights into DNA transfer pathways and possible implications of cationic lipids in lipid metabolism.

Synthesis and transfection properties of a series of lipidic neamine derivatives

With the view to develop novel bioinspired nonviral vectors for gene delivery, we synthesized a series of cationic lipids with a neamine headgroup, which incorporates rings I and II of the natural antibiotic aminoglycoside neomycin B. Indeed, we reasoned that neamine might constitute a straightforward and versatile building block for synthesizing a variety of lipophilic aminoglycosides and modulating their characteristics such as size, topology, lipophilicity, number of charges, and charge density. Neamine derivatives bearing long dialkyl chains, one or two neamine headgroups, and four to ten protonatable amine functions were prepared through the selective alkylation of the 4'- or 5-hydroxyl function in ring I and ring II of neamine, respectively. The transfection activity of the twelve derivatives synthesized was investigated in vitro in gene transfection experiments using several mammalian cell lines. The results allowed us to unveil interesting structure-activity relationships and to identify a formulation incorporating a small neamine derivative as a highly efficient gene delivery system.

Fluorometric Analysis of Individual Cationic Lipid-DNA Complexes

Lipoplex preparations are heterogeneous mixtures of lipoplex particles of different structures. As these structures determine the efficiency of the delivery of genetic material, it is important to characterize the distribution of particles of different types in lipoplex preparations with good statistics. We describe the application of flow fluorometry which allows producing such distributions (in terms of lipoplex particle size and composition) within minutes using basic flow cytometer (Anal Biochem 341:230-240, 2005).

Analysis of lipoplex structure and lipid phase changes

Efficient delivery of genetic material to cells is needed for tasks of utmost importance in the laboratory and clinic, such as gene transfection and gene silencing. Synthetic cationic lipids can be used as delivery vehicles for nucleic acids and are now considered the most promising nonviral gene carriers. They form complexes (lipoplexes) with the polyanionic nucleic acids. A critical obstacle for clinical application of the lipid-mediated DNA delivery (lipofection) is its unsatisfactory efficiency for many cell types. Understanding the mechanism of lipid-mediated DNA delivery is essential for their successful application, as well as for a rational design and synthesis of novel cationic lipoid compounds for enhanced gene delivery. A viewpoint now emerging is that the critical factor in lipid-mediated transfection is the structural evolution of lipoplexes within the cell, upon interacting and mixing with cellular lipids. In particular, recent studies showed that the phase evolution of lipoplex lipids upon interaction and mixing with membrane lipids appears to be decisive for transfection success: specifically, lamellar lipoplex formulations, which were readily susceptible to undergoing lamellar-nonlamellar phase transition upon mixing with cellular lipids and were found rather consistently associated with superior transfection potency, presumably as a result of facilitated DNA release. Thus, understanding the lipoplex structure and the phase changes upon interacting with membrane lipids is important for the successful application of the cationic lipids as gene carriers.

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.

Toward the rational design of lipid gene vectors: shape coupling between lipoplex and anionic cellular lipids controls the phase evolution of lipoplexes and the efficiency of DNA release

A viewpoint now emerging is that a critical factor in lipid-mediated transfection (lipofection) is the structural evolution of lipoplexes upon interaction with anionic cellular lipids, resulting in DNA release. At the early stages of interaction, we found a universal behavior of lipoplex/anionic lipid (AL) mixtures: the lipoplex structure is slightly perturbed, while the one-dimensional DNA lattice between cationic membranes is largely diluted by ALs. This finding is in excellent agreement with previous suggestions on the mechanism of DNA unbinding from lipoplexes by ALs. Upon further interaction, the propensity of a given lipoplex structure to be solubilized by anionic cellular lipids strongly depends on the shape coupling between lipoplex and ALs. Furthermore, we investigated the effect of the membrane charge density and a general correlation resulted: the higher the membrane charge density of anionic membranes, the higher their ability to solubilize the structure of lipoplexes and to promote DNA release. Lastly, the formation of nonlamellar phases in lipoplex/AL mixtures is regulated by the propensity of anionic cellular lipids to adopt nonlamellar phases. Remarkably, also phase transition rates and DNA release were found to be strongly affected by the shape coupling between lipoplex and ALs. It thus seems likely that the structural and phase evolution of lipoplexes may only be meaningful in the context of specific anionic cellular membranes. These results highlight the phase properties of the carrier lipid/cellular lipid mixtures as a decisive factor for optimal DNA release and suggest a potential strategy for the rational design of efficient cationic lipid carriers.

Hydrophobic moiety of cationic lipids strongly modulates their transfection activity

Synthetic cationic lipids are widely used components of nonviral gene carriers, and the factors regulating their transfection efficiency are the subject of considerable interest. In view of the important role that electrostatic interactions with the polyanionic nucleic acids play in formation of lipoplexes, a common empirical approach to improving transfection has been the synthesis and testing of amphiphiles with new versions of positively charged polar groups, while much less attention has been given to the role of the hydrophobic lipid moieties. On the basis of data for approximately 20 cationic phosphatidylcholine (PC) derivatives, here we demonstrate that hydrocarbon chain variations of these lipids modulate by over 2 orders of magnitude their transfection efficiency. The observed molecular structure-activity relationship manifests in well-expressed dependences of activity on two important molecular characteristics, chain unsaturation and total number of carbon atoms in the lipid chains, which is representative of the lipid hydrophobic volume and hydrophilic-lipophilic ratio. Transfection increases with decrease of chain length and increase of chain unsaturation. Maximum transfection was found for cationic PCs with monounsaturated 14:1 chains. It is of particular importance that the high-transfection lipids strongly promote cubic phase formation in zwitterionic membrane phosphatidylethanolamine (PE). These remarkable correlations point to an alternative, chain-dependent process in transfection, not related to the electrostatic cationic-anionic lipid interactions.

Multipotent mesenchymal stromal cells: optimization and comparison of five cationic polymer-based gene delivery methods

BACKGROUND

Multipotent mesenchymal stromal cells (MSC) are promising candidates in the field of regenerative medicine and in several studies have been genetically modified to bring a new property to or enhance an existing one in these cells. Furthermore, MSC have been used as gene delivery vehicles. The success of these experiments depends on selecting an appropriate method for gene delivery to the cells.

METHODS

MSC were isolated from rat bone marrow; their authenticity was checked by differentiation experiments as well as staining for cell-surface markers. A systematic approach was used to optimize five cationic polymer-based gene delivery methods (Lipofectamin2000, Effecten, Superfect, Polyfect and FuGENE HD). The transfection yield and cell viability of each method was measured after 48 h in three to six separate experiments with nine to 12 different ratios and amounts of DNA/transfection reagent.

RESULTS

The isolated MSC were successfully differentiated to osteoblasts, adipocytes and chondroblasts. They were positive for rat CD90 and CD73 and negative for CD31, CD45, CD11b and VEGFR2 markers. The average transfection rates with optimum conditions were 5.18+/-2.72 (FuGENE HD), 8.72+/-4.52 (Effecten), 9.59+/-3.12 (Superfect), 16.29+/-7.44 (Polyfect) and 19.60+/-3.12 (Lipofectamine 2000). The toxicity was below 20% for all reagents.

DISCUSSION

Moderate levels of transfection and acceptable cell viability could be achieved using Lipofectamine 2000 and Polyfect in optimized conditions. The results could be improved by gating and sorting live cells using a simple FSC-SSC gating.

Structural stability and increase in size rationalize the efficiency of lipoplexes in serum

We have investigated the effect of serum on nanometric structure, size, surface potential, DNA-binding capacity, and transfection efficiency of DDAB-DOPE/DNA and DC-Chol-DOPE/DNA lipoplexes as a function of membrane charge density and cationic lipid/DNA charge ratio. In the absence of serum, the nanometric structure and DNA binding capacity of lipoplexes determined the transfection efficiency. When serum was added, the transfection efficiency of all lipoplex formulations was found to increase. We identified structural stability and an increase in size in serum as major parameters regulating the efficiency of lipofection. By extrapolation, we propose that serum, regulating the size of resistant lipid-DNA complexes, can control the mechanism of internalization of lipoplexes and, in turn, their efficiency.

Quantification of plasmid DNA copies in the nucleus after lipoplex and polyplex transfection

Nuclear uptake of plasmid DNA is one of the many cellular barriers that limit the efficiency of non-viral gene delivery systems. We have determined the number of plasmids that reach the nucleus of a transfected cell using an internally standardized quantitative PCR (qPCR) assay. We isolated nuclei using two different protocols: a density gradient technique and a detergent-based method. The density gradient procedure yielded nuclei with substantially less adhering plasmids on the outside of the nuclei. Using the density gradient protocol we determined that cells transfected with Lipofectamine lipoplexes or polyethylenimine polyplexes contained between 75 and 50,000 plasmids/nucleus, depending on the applied plasmid dose. Any increase above 3000 plasmids/nucleus resulted in only marginal increases in transgene expression. Furthermore, lipoplex-delivered plasmids were more efficiently expressed, on the basis of protein expression per plasmid number in the nucleus, than polyplex-delivered plasmids. This indicates that polymer may remain bound to some plasmids in the nucleus. Lastly, by sorting transfected cells into high- and low-expressing sub-populations, we observe that a sub-population of cells contain 3x greater plasmids/nucleus but express nearly 100x more transgene than other cells within a single transfection reaction. Taken together these results suggest the importance of considering the processes downstream from nuclear entry for strategies to improve the efficiency of gene transfer reagents.

Lipid Phases Eye View to Lipofection. Cationic Phosphatidylcholine Derivatives as Efficient DNA Carriers for Gene Delivery

Efficient delivery of genetic material to cells is needed for tasks of utmost importance in laboratory and clinic, such as gene transfection and gene silencing. Synthetic cationic lipids can be used as delivery vehicles for nucleic acids and are now considered the most promising non-viral gene carriers. They form complexes (lipoplexes) with the polyanionic nucleic acids. A critical obstacle for clinical application of the lipid-mediated DNA delivery (lipofection) is its unsatisfactory efficiency for many cell types. Understanding the mechanism of lipid-mediated DNA delivery is essential for their successful application, as well as for rational design and synthesis of novel cationic lipoid compounds for enhanced gene delivery. According to the current understanding, the critical factor in lipid-mediated transfection is the structural evolution of lipoplexes within the cell, upon interacting and mixing with cellular lipids. In particular, recent studies with cationic phosphatidylcholine derivatives showed that the phase evolution of lipoplex lipids upon interaction and mixing with membrane lipids appears to be decisive for transfection success: specifically, lamellar lipoplex formulations, which were readily susceptible to undergoing lamellar-nonlamellar (precisely lamellar-cubic) phase transition upon mixing with cellular lipids, were found rather consistently associated with superior transfection potency, presumably as a result of facilitated DNA release subsequent to lipoplex fusion with the cellular membranes. Further, hydrophobic moiety of the cationic phospholipids was found able to strongly modulate liposomal gene delivery into primary human umbilical artery endothelial cells; superior activity was found for cationic phosphatidylcholine derivatives with two 14-carbon atom monounsaturated hydrocarbon chains, able to induce formation of cubic phase in membranes. Thus, understanding the lipoplex structure and the phase changes upon interacting with membrane lipids is important for the rational design and successful application of cationic lipids as superior nucleotide delivery agents.

Cationic liposomal lipids: from gene carriers to cell signaling

Cationic lipids are positively charged amphiphilic molecules which, for most of them, form positively charged liposomes, sometimes in combination with a neutral helper lipid. Such liposomes are mainly used as efficient DNA, RNA or protein carriers for gene therapy or immunization trials. Over the past decade, significant progress has been made in the understanding of the cellular pathways and mechanisms involved in lipoplex-mediated gene transfection but the interaction of cationic lipids with cell components and the consequences of such an interaction on cell physiology remains poorly described. The data reported in the present review provide evidence that cationic lipids are not just carriers for molecular delivery into cells but do modify cellular pathways and stimulate immune or anti-inflammatory responses. Considering the wide number of cationic lipids currently available and the variety of cellular components that could be involved, it is likely that only a few cationic lipid-dependent functions have been identified so far.

Transfection efficiency boost by designer multicomponent lipoplexes

Cationic liposome-DNA complexes (lipoplexes) have emerged as leading nonviral gene carriers in worldwide gene therapy clinical trials. Arriving at therapeutic dosages requires the full understanding of the mechanism of transfection. We investigated the correlation between structural evolution of multicomponent lipoplexes when interacting with cellular lipids, the extent of DNA release and the efficiency in transfecting mouse fibroblast (NIH 3T3), ovarian (CHO) and tumoral myofibroblast-like (A17) cell lines. We show, for the first time, that the transfection pattern increases monotonically with the number of lipid components and further demonstrate by means of synchrotron small angle X- ray scattering (SAXS) that structural changes of lipoplexes induced by cellular lipids correlate with the transfection efficiency. Specifically, inefficient lipoplexes either fused too rapidly upon interaction with anionic lipids or, alternatively, are found to be extremely resistant to solubilization. The most efficient lipoplex formulations exhibited an intermediate behaviour. The extent of DNA unbinding (measured by electrophoresis on agarose gel) correlates with structural evolution of the lipoplexes but DNA-release does not scale with the extent of transfection. The general meaning of our results is of broad interest in the field of non-viral gene delivery: rational adjusting of lipoplex composition to generate the proper interaction between lipoplexes and cellular lipids may be the most appropriate strategy in optimizing synthetic lipid transfection agents.