Structural characteristics of supramolecular assemblies formed by guanidinium-cholesterol reagents for gene transfection

Elucidating Structural Configuration of Lipid Assemblies for mRNA Delivery Systems

The development of mRNA delivery systems utilizing lipid-based assemblies holds immense potential for precise control of gene expression and targeted therapeutic interventions. Despite advancements in lipid-based gene delivery systems, a critical knowledge gap remains in understanding how the biophysical characteristics of lipid assemblies and mRNA complexes influence these systems. Herein, we investigate the biophysical properties of cationic liposomes and their role in shaping mRNA lipoplexes by comparing various fabrication methods. Notably, an innovative fabrication technique called the liposome under cryo-assembly (LUCA) cycle, involving a precisely controlled freeze-thaw-vortex process, produces distinctive onion-like concentric multilamellar structures in cationic DOTAP/DOPE liposomes, in contrast to a conventional extrusion method that yields unilamellar liposomes. The inclusion of short-chain DHPC lipids further modulates the structure of cationic liposomes, transforming them from multilamellar to unilamellar structures during the LUCA cycle. Furthermore, the biophysical and biological evaluations of mRNA lipoplexes unveil that the optimal N/P charge ratio in the lipoplex can vary depending on the structure of initial cationic liposomes. Cryo-EM structural analysis demonstrates that multilamellar cationic liposomes induce two distinct interlamellar spacings in cationic lipoplexes, emphasizing the significant impact of the liposome structures on the final structure of mRNA lipoplexes. Taken together, our results provide an intriguing insight into the relationship between lipid assembly structures and the biophysical characteristics of the resulting lipoplexes. These relationships may open the door for advancing lipid-based mRNA delivery systems through more streamlined manufacturing processes.

Lipids and Lipid Derivatives for RNA Delivery

RNA-based therapeutics have shown great promise in treating a broad spectrum of diseases through various mechanisms including knockdown of pathological genes, expression of therapeutic proteins, and programmed gene editing. Due to the inherent instability and negative-charges of RNA molecules, RNA-based therapeutics can make the most use of delivery systems to overcome biological barriers and to release the RNA payload into the cytosol. Among different types of delivery systems, lipid-based RNA delivery systems, particularly lipid nanoparticles (LNPs), have been extensively studied due to their unique properties, such as simple chemical synthesis of lipid components, scalable manufacturing processes of LNPs, and wide packaging capability. LNPs represent the most widely used delivery systems for RNA-based therapeutics, as evidenced by the clinical approvals of three LNP-RNA formulations, patisiran, BNT162b2, and mRNA-1273. This review covers recent advances of lipids, lipid derivatives, and lipid-derived macromolecules used in RNA delivery over the past several decades. We focus mainly on their chemical structures, synthetic routes, characterization, formulation methods, and structure-activity relationships. We also briefly describe the current status of representative preclinical studies and clinical trials and highlight future opportunities and challenges.

X-ray induced photodynamic therapy (PDT) with a mitochondria-targeted liposome delivery system

In this study, we constructed multifunctional liposomes with preferentially mitochondria-targeted feature and gold nanoparticles-assisted synergistic photodynamic therapy. We systemically investigated the in vitro X-ray triggered PDT effect of these liposomes on HCT 116 cells including the levels of singlet oxygen, mitochondrial membrane potential, cell apoptosis/necrosis and the expression of apoptosis-related proteins. The results corroborated that synchronous action of PDT and X-ray radiation enhance the generation of cytotoxic reactive oxygen species produced from the engineered liposomes, causing mitochondrial dysfunction and increasing the levels of apoptosis.

Tetrafunctional Block Copolymers Promote Lung Gene Transfer in Newborn Piglets

Tetrafunctional block copolymers are molecules capable of complexing DNA. Although ineffective in vitro, studies in mice have shown that the tetrafunctional block copolymer 704 is a more efficient lung gene transfer agent than the cationic liposome GL67A, previously used in a phase II clinical trial in cystic fibrosis patients. In the present study, we compared the gene transfer capacity of the 704-DNA formulation and a cationic liposome-DNA formulation equivalent to GL67A in a larger-animal model, the newborn piglet. Our results indicate an efficacy of the 704-DNA formulation well above one order of magnitude higher than that of the cationic liposome-DNA formulation, with no elevated levels of interleukin-6 (IL-6), taken as a marker of inflammation. Transgene expression was heterogeneous within lung lobes, with expression levels that were below the detection threshold in some samples, while high in other samples. This heterogeneity is likely to be due to the bolus injection procedure as well as to the small volume of injection. The present study highlights the potential of tetrafunctional block copolymers as non-viral vectors for lung gene therapy.

Dual Functional LipoMET Mediates Envelope-type Nanoparticles to Combinational Oncogene Silencing and Tumor Growth Inhibition

The success of small interfering RNA (siRNA)-mediated gene silencing for cancer therapy is still limited because of its instability and poor intracellular internalization. Traditional cationic carriers cannot adequately meet the need for clinical application of siRNA. We herein report a dual-functional liposome containing a cholesterol derivative of metformin, i.e., LipoMET, which takes advantage of the fusogenic activity as well as intrinsic tumor apoptosis inducing ability of biguanide moiety to achieve a combinational anti-oncogenic effect. In this study, the vascular endothelial growth factor (VEGF)-specific siRNAs were first electrostatically condensed into a ternary nanocomplex composed of polycation and hyaluronate, which was subsequently enveloped by LipoMET through membrane fusion. In comparison with common cationic control group, the resulting envelope-type nanoparticles (PH@LipoMET nanoparticles [NPs]) showed the ability of rapid cellular internalization and effective endosomal escape of siRNA during intracellular trafficking studies. Systemic administration of the targeted LipoMETs was capable of inducing apoptosis and tumor growth inhibition in the NCI-H460 xenograft model. When carrying VEGF-specific siRNAs, PH@LipoMET NPs remarkably downregulated the expression of VEGF and led to even more tumor suppression in vivo. Thus, LipoMET originated envelope-type nanoparticles may serve as a potential dual-functional siRNA delivery system to improve therapeutic effect of oncogene silencing.

Important role of phosphoramido linkage in imidazole-based dioleyl helper lipids for liposome stability and primary cell transfection

BACKGROUND

To optimize synthetic gene delivery systems, there is a need to develop more efficient lipid formulations. Most cationic lipid formulations contain 'helper' neutral lipids because of their ability to increase DNA delivery, in particular by improving endosomal escape of DNA molecules via the pH-buffering effect of protonatable groups and/or fusion with the lipid bilayer of endosomes.

METHODS

We evaluated the influence of the linker structure between the two oleyl chains in the helper lipid on transfection efficiency in cell lines, as well as in primary cells (hepatocytes/cardiomyocytes). We reported the synthesis of two new pH-buffering imidazole helper lipids characterized by a polar headgroup containing one (compound 6) or two (compound 5) imidazole groups and two oleyl chains linked by an amide group. We studied their association with the aminoglycoside lipidic derivative dioleylsuccinylparomomycin (DOSP), which contains two oleyl chains linked to the aminoglycoside polar headgroup via an amide function. We compared the morphology and transfection properties of such binary liposomes of DOSP/5 and DOSP/6 with those of liposomes combining DOSP with another imidazole-based dioleyl helper lipid (MM27) in which a phosphoramido group acts as a linker between the two oleyl chains and imidazole function.

RESULTS

The phosphoramido linker in the helper lipid induces a major difference in terms of morphology and resistance to decomplexation at physical pH for DOSP/helper lipid complexes.

CONCLUSIONS

This hybrid dioleyl linker composition of DOSP/MM27 led to higher transfection efficiency in cell lines and in primary cells compared to complexes with homogeneous dioleyl linker.

A Simplified Direct Lipid Mixing Lipoplex Preparation: Comparison of Liposomal-, Dimethylsulfoxide-, and Ethanol-Based Methods

Established transfection methodology often uses commercial reagents, which must be formed into liposomes in a sequence of about half a dozen steps. The simplified method reported here is a direct lipid mixing approach that requires fewer steps, less manipulation, and is less time-consuming. Results are comparable to those obtained with more commonly used methods, as judged by a variety of analytical techniques and by comparisons of transfection results. The method reported here may be applied to non-liposome-forming compounds, thereby greatly expanding the range of structures that can be tested for transfection ability.

Fluorescent mimics of cholesterol that rapidly bind surfaces of living mammalian cells

Mammalian cells acquire cholesterol, a critical membrane constituent, through multiple mechanisms. We synthesized mimics of cholesterol, fluorescent N-alkyl-3β-cholesterylamine-glutamic acids, that are rapidly incorporated into cellular plasma membranes compared with analogous cholesteryl amides, ethers, esters, carbamates, and a sitosterol analogue. This process was inhibited by ezetimibe, indicating a receptor-mediated uptake pathway.

Dynamitin affects cell-surface expression of voltage-gated sodium channel Nav1.5

The major cardiac voltage-gated sodium channel Nav1.5 associates with proteins that regulate its biosynthesis, localization, activity and degradation. Identification of partner proteins is crucial for a better understanding of the channel regulation. Using a yeast two-hybrid screen, we identified dynamitin as a Nav1.5-interacting protein. Dynamitin is part of the microtubule-binding multiprotein complex dynactin. When overexpressed it is a potent inhibitor of dynein/kinesin-mediated transport along the microtubules by disrupting the dynactin complex and dissociating cargoes from microtubules. The use of deletion constructs showed that the C-terminal domain of dynamitin is essential for binding to the first intracellular interdomain of Nav1.5. Co-immunoprecipitation assays confirmed the association between Nav1.5 and dynamitin in mouse heart extracts. Immunostaining experiments showed that dynamitin and Nav1.5 co-localize at intercalated discs of mouse cardiomyocytes. The whole-cell patch-clamp technique was applied to test the functional link between Nav1.5 and dynamitin. Dynamitin overexpression in HEK-293 (human embryonic kidney 293) cells expressing Nav1.5 resulted in a decrease in sodium current density in the membrane with no modification of the channel-gating properties. Biotinylation experiments produced similar information with a reduction in Nav1.5 at the cell surface when dynactin-dependent transport was inhibited. The present study strongly suggests that dynamitin is involved in the regulation of Nav1.5 cell-surface density.

Applications of synchrotron-based spectroscopic techniques in studying nucleic acids and nucleic acid-functionalized nanomaterials

In this review, we summarize recent progress in the application of synchrotron-based spectroscopic techniques for nucleic acid research that takes advantage of high-flux and high-brilliance electromagnetic radiation from synchrotron sources. The first section of the review focuses on the characterization of the structure and folding processes of nucleic acids using different types of synchrotron-based spectroscopies, such as X-ray absorption spectroscopy, X-ray emission spectroscopy, X-ray photoelectron spectroscopy, synchrotron radiation circular dichroism, X-ray footprinting and small-angle X-ray scattering. In the second section, the characterization of nucleic acid-based nanostructures, nucleic acid-functionalized nanomaterials and nucleic acid-lipid interactions using these spectroscopic techniques is summarized. Insights gained from these studies are described and future directions of this field are also discussed.

Aspects of nonviral gene therapy: correlation of molecular parameters with lipoplex structure and transfection efficacy in pyridinium-based cationic lipids

This study seeks correlations between the molecular structures of cationic and neutral lipids, the lipid phase behavior of the mixed-lipid lipoplexes they form with plasmid DNA, and the transfection efficacy of the lipoplexes. Synthetic cationic pyridinium lipids were co-formulated (1:1) with the cationic lipid 1,2-dimyristoyl-sn-glycero-3-ethylphosphocholine (EPC), and these lipids were co-formulated (3:2) with the neutral lipids 1,2-dioleoyl-sn-glycero-3-phosphatidylethanolamine (DOPE) or cholesterol. All lipoplex formulations exhibited plasmid DNA binding and a level of protection from DNase I degradation. Composition-dependent transfection (beta-galactosidase and GFP) and cytotoxicity was observed in Chinese hamster ovarian-K1 cells. The most active formulations containing the pyridinium lipids were less cytotoxic but of comparable activity to a Lipofectamine 2000™ control. Molecular structure parameters and partition coefficients were calculated for all lipids using fragment additive methods. The derived shape parameter values correctly correlated with observed hexagonal lipid phase behavior of lipoplexes as derived from small-angle X-ray scattering experiments. A transfection index applicable to hexagonal phase lipoplexes derived from calculated parameters of the lipid mixture (partition coefficient, shape parameter, lipoplex packing) produced a direct correlation with transfection efficiency.

Efficient topical delivery of plasmid DNA to lung in vivo mediated by putative triggered, PEGylated pDNA nanoparticles

Non-viral vectors are considered safer than viral vectors and show clinical potential, but remain less efficient in terms of DNA delivery. Here we report how cationic liposomes, prepared from new cationic lipid, N',N',-dioctadecyl-N-4,8-diaza-10-aminodecanoylglycine amide (DODAG) and neutral lipid dioleoyl-L-α-phos-phatidylethanolamine (DOPE), can be formulated with plasmid DNA (pDNA) in the presence of stabilizer cholesteryl-oxycarbonylpolyethlylene glycol(4600) (PEG(4600)-Chol) giving PEGylated pDNA nanoparticles (pDNA-ABC nanoparticles) that are proposed to be half-life triggered nanoparticles. In particular, the PEGylated pDNA nanoparticle formulation DODAG/DOPE/PEG(4600)-Chol (43:43:14, m/m/m)-pDNA (total lipid/pDNA ratio 4:1 w/w) (pTRANSplus nanoparticles) is shown to mediate efficient transfection of murine lung tissue in vivo. Levels of transfection compare well with the results of polyethylenimine (PEI) mediated pDNA transfection in vivo and even of adenovirus mediated transduction. Cryo-EM imaging indicates that pTRANSplus formulations are somewhat heterogeneous but do consist primarily of bilammellar lipoplex nanoparticles with a few multilammellar nanoparticle aggregates. Lung histology confirms that pTRANSplus mediated transfection in vivo targets substantially the epithelial cells of bronchii and bronchioli airway passages. The pTRANSplus nanoparticle system is a useful new starting point for nucleic acid therapeutic strategies to counter lung disorders such as viral infection and possibly cystic fibrosis.

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.

Amphiphilic block copolymers enhance the cellular uptake of DNA molecules through a facilitated plasma membrane transport

Amphiphilic block copolymers have been developed recently for their efficient, in vivo transfection activities in various tissues. Surprisingly, we observed that amphiphilic block copolymers such as Lutrol® do not allow the transfection of cultured cells in vitro, suggesting that the cell environment is strongly involved in their mechanism of action. In an in vitro model mimicking the in vivo situation we showed that pre-treatment of cells with Lutrol®, prior to their incubation with DNA molecules in the presence of cationic lipid, resulted in higher levels of reporter gene expression. We also showed that this improvement in transfection efficiency associated with the presence of Lutrol® was observed irrespective of the plasmid promoter. Considering the various steps that could be improved by Lutrol®, we concluded that the nucleic acids molecule internalization step is the most important barrier affected by Lutrol®. Microscopic examination of transfected cells pre-treated with Lutrol® confirmed that more plasmid DNA copies were internalized. Absence of cationic lipid did not impair Lutrol®-mediated DNA internalization, but critically impaired endosomal escape. Our results strongly suggest that in vivo, Lutrol® improves transfection by a physicochemical mechanism, leading to cellular uptake enhancement through a direct delivery into the cytoplasm, and not via endosomal pathways.

Cancer-specific transgene expression mediated by systemic injection of nanoparticles

The lack of safe and efficient systemic gene delivery vectors has largely reduced the potential of gene therapy in the clinic. Previously, we have reported that polypropylenimine dendrimer PPIG3/DNA nanoparticles are capable of tumor transfection upon systemic administration in tumor-bearing mice. To be safely applicable in the clinic, it is crucial to investigate the colloidal stability of nanoparticles and to monitor the exact biodistribution of gene transfer in the whole body of the live subject. Our biophysical characterization shows that dendrimers, when complexed with DNA, are capable of forming spontaneously in solution a supramolecular assembly that possesses all the features required to diffuse in experimental tumors through the enhanced permeability and retention effect. We show that these nanoparticles are of sizes ranging from 33 to 286 nm depending on the DNA concentration, with a colloidal stable and well-organized fingerprint-like structure in which DNA molecules are condensed with an even periodicity of 2.8 nm. Whole-body nuclear imaging using small-animal nano-single-photon emission computed tomography/computer tomography scanner and the human Na/I symporter (NIS) as reporter gene shows unique and highly specific tumor targeting with no detection of gene transfer in any of the other tissues of tumor-bearing mice. Tumor-selective transgene expression was confirmed by quantitative reverse transcription-PCR at autopsy of scanned animals, whereas genomic PCR showed that the tumor sites are the predominant sites of nanoparticle accumulation. Considering that NIS imaging of transgene expression has been recently validated in humans, our data highlight the potential of these nanoparticles as a new formulation for cancer gene therapy.

Practical synthesis of 3beta-amino-5-cholestene and related 3beta-halides involving i-steroid and retro-i-steroid rearrangements

Derivatives of 3beta-amino-5-cholestene (3beta-cholesterylamine) are of substantial interest as cellular probes and have potential medicinal applications. However, existing syntheses of 3beta-amino-5-cholestene are of limited preparative utility. We report here a practical method for the stereoselective preparation of 3beta-amino-5-cholestene, 3beta-chloro-5-cholestene, 3beta-bromo-5-cholestene, and 3beta-iodo-5-cholestene from inexpensive cholesterol. A sequential i-steroid/retro-i-steroid rearrangement promoted by boron trifluoride etherate and trimethylsilyl azide converted cholest-5-en-3beta-ol methanesulfonate to 3beta-azido-cholest-5-ene with retention of configuration in 93% yield.

Galactosylated multimodular lipoplexes for specific gene transfer into primary hepatocytes

BACKGROUND

Numerous synthetic cationic vectors have been synthesized and are successfully used for in vitro gene transfer but an excess of positive charges can lead to cytotoxicity and does not enable specific transfection.

METHODS

We decided to develop alternative molecular systems consisting of neutral, colloidally stable bioassemblies equipped with ligands for specific cell targeting. Consequently, we directed our efforts toward the development of a multimodular non-viral gene delivery system consisting of a condensed core of DNA with cationic liposomes of bis(guanidinium)-tren-cholesterol and an external corona of poly(ethylene oxide) stretches harbored by the steric stabilizers used to stabilize lipoplexes colloidally. A ligand capable of cell targeting by receptor-mediated endocytosis was covalently linked at the poly(ethylene oxide) extremity of steric stabilizers. Steric stabilizers were functionalized by a one-step enzymatic galactosylation to develop new supramolecular assemblies of lipoplexes able to target asialoglycoprotein receptors located on primary hepatocytes.

RESULTS

Cryo-TEM and fluorescence experiments showed that DNA was condensed within lamellar complexes whose size ranged between 100 to 300 nm in diameter. Bis(guanidinium)-tren-cholesterol-DNA lipoplexes, colloidally stabilized by galactosylated steric stabilizers at a galactosylated steric stabilizer/DNA ratio of 300, led to specific transfection of primary hepatocytes whereas ungalactosylated steric stabilizer did not transfect.

CONCLUSIONS

Our findings confirm the receptor-mediated endocytosis pathway of galactosylated multimodular lipoplexes. Thus, we conclude that the fabrication of a multimodular assembly harboring a ligand without non-specific interaction with cell membranes is possible and a highly promising system to transfect other primary or cultured cells specifically through a receptor-dependent mechanism.

Brewster angle microscopy and PMIRRAS study of DNA interactions with BGTC, a cationic lipid used for gene transfer

The lipid bis(guanidinium)-tris(2-aminoethyl)amine-cholesterol (BGTC) is a cationic cholesterol derivative bearing guanidinium polar headgroups which displays high transfection efficiency in vitro and in vivo when used alone or formulated as liposomes with the neutral colipid 1,2-di-[ cis-9-octadecenoyl]- sn-glycero-3-phosphoethanolamine (DOPE). Since transfection may be related to the structural and physicochemical properties of the self-assembled supramolecular lipid-DNA complexes, we used the Langmuir monolayer technique coupled with Brewster angle microscopy (BAM) and polarization modulation infrared reflection absorption spectroscopy (PMIRRAS) to investigate DNA-BGTC and DNA-BGTC/DOPE interactions at the air/water interface. We herein show that BGTC forms stable monolayers at the air/water interface. When DNA is injected into the subphase, it adsorbs to BGTC at 20 mN/m. Whatever the (+/-) charge ratio of the complexes used, defined as the ratio of positive charges of BGTC in the monolayer versus negative charges of DNA injected in the subphase, the DNA interacts with the cationic lipid and forms either an incomplete (no constituent in excess) or a complete (DNA in excess) monolayer of oriented double strands parallel to the lipid monolayer plan. We also show that, under a homogeneous BGTC/DOPE (3/2) monolayer at 20 mN/m, DNA adsorbs homogeneously to form an organized but incomplete layer whatever the charge ratio used (DNA in default or in excess). Compression beyond the collapse of these mixed DNA-BGTC/DOPE systems leads to the formation of dense DNA monolayers under an asymmetric lipid bilayer with a bottom layer of BGTC in contact with DNA and a top layer mainly constituted of DOPE. These results allow a better understanding of the mechanisms underlying the formation of the supramolecular BGTC-DNA complexes efficient for gene transfection.

Cationic liposomes as non-viral carriers of gene medicines: resolved issues, open questions, and future promises

The clinical success of gene therapy is critically dependent on the development of efficient and safe gene delivery reagents, popularly known as "transfection vectors." The transfection vectors commonly used in gene therapy are mainly of two types: viral and non-viral. The efficiencies of viral transfection vectors are, in general, superior to their non-viral counterparts. However, the myriads of potentially adverse immunogenic aftermaths associated with the use of viral vectors are increasingly making the non-viral gene delivery reagents as the vectors of choice. Among the existing arsenal of non-viral gene delivery reagents, the distinct advantages associated with the use of cationic transfection lipids include their: (a) robust manufacture; (b) ease in handling and preparation techniques; (c) ability to inject large lipid:DNA complexes; and (d) low immunogenic response. The present review highlights the major achievements in the area of designing efficacious cationic transfection lipids, some of the more recent advances in the field of cationic liposomes-mediated gene transfer and targeted gene delivery, some unresolved issues and challenges in liposomal gene delivery, and future promises of cationic liposomes as gene-carriers in non-viral gene therapy.

Self-assembled lamellar complexes of siRNA with lipidic aminoglycoside derivatives promote efficient siRNA delivery and interference

RNA interference requires efficient delivery of small double-stranded RNA molecules into the target cells and their subsequent incorporation into RNA-induced silencing complexes. Although current cationic lipids commonly used for DNA transfection have also been used for siRNA transfection, a clear need still exists for better siRNA delivery to improve the gene silencing efficiency. We synthesized a series of cationic lipids characterized by head groups bearing various aminoglycosides for specific interaction with RNA. siRNA complexation with such lipidic aminoglycoside derivatives exhibited three lipid/siRNA ratio-dependent domains of colloidal stability. Fluorescence and dynamic light-scattering experiments showed that cationic lipid/siRNA complexes were formed at lower charge ratios, exhibited a reduced zone of colloidal instability, and had smaller mean diameters compared with our previously described guanidinium-based cationic lipids. Cryo-transmission electron microscopy and x-ray-scattering experiments showed that, although the final in toto morphology of the lipid/siRNA complexes depended on the aminoglycoside type, there was a general supramolecular arrangement consisting of ordered lamellar domains with an even spacing of 67 A. The most active cationic lipid/siRNA complexes for gene silencing were obtained with 4,5-disubstituted 2-deoxystreptamine aminoglycoside derivatives and were characterized by the siRNA being entrapped in small particles exhibiting lamellar microdomains corresponding to siRNA molecules sandwiched between the lipid bilayers. These results clearly show that lipidic aminoglycoside derivatives constitute a versatile class of siRNA nanocarriers allowing efficient gene silencing.

Dramatic influence of the orientation of linker between hydrophilic and hydrophobic lipid moiety in liposomal gene delivery

A number of prior studies have demonstrated that the DNA-binding and gene transfection efficacies of cationic amphiphiles crucially depend on their various structural parameters including hydrophobic chain lengths, headgroup functionalities, and the nature of the linker-functionality used in tethering the polar headgroup and hydrophobic tails. However, to date addressing the issue of linker orientation remains unexplored in liposomal gene delivery. Toward probing the influence of linker orientation in cationic lipid mediated gene delivery, we have designed and synthesized two structurally isomeric remarkably similar cationic amphiphiles 1 and 2 bearing the same hydrophobic tails and the same polar headgroups connected by the same ester linker group. The only structural difference between the cationic amphiphiles 1 and 2 is the orientation of their linker ester functionality. While lipid 1 showed high gene transfer efficacies in multiple cultured animal cells, lipid 2 was essentially transfection incompetent. Findings in both transmission electron microscopic and dynamic laser light scattering studies revealed no significant size difference between the lipoplexes of lipids 1 and 2. Findings in confocal microscopic and fluorescence resonance energy transfer (FRET) experiments, taken together, support the notion that the remarkably higher gene transfer efficacies of lipid 1 compared to those of lipid 2 presumably originate from higher biomembrane fusogenicity of lipid 1 liposomes. Differential scanning calorimetry (DSC) and fluorescence anisotropy studies revealed a significantly higher gel-to-liquid crystalline temperature for the lipid 2 liposomes than that for lipid 1 liposomes. Findings in the dye entrapment experiment were also consistent with the higher rigidity of lipid 2/cholesterol (1:1 mole ratio) liposomes. Thus, the higher biomembrane fusibility of lipid 1 liposomes than that of lipid 2 liposomes presumably originates from the more rigid nature of lipid 2 cationic liposomes. Taken together, the present findings demonstrate for the first time that even as minor a structural variation as linker orientation reversal in cationic amphiphiles can profoundly influence DNA-binding characteristics, membrane rigidity, membrane fusibility, cellular uptake, and consequently gene delivery efficacies of cationic liposomes.

PEO−PPO Block Copolymer Vectors Do Not Interact Directly with DNA but with Lipid Membranes

Small angle neutron (SANS) and light scattering was used to study the interaction between fragments of double stranded deoxyribonucleic acid (DNA) and a synthetic triblock [poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)] amphiphilic polymer, known as L64, a potential vector for gene therapy. The mechanism of action of this vector is yet unknown. The contrast variation method was used to separate the partial structure factors of the different components in mixtures of triblock and DNA. It has been found that the copolymer and DNA molecules exhibit repulsive interactions. Further, the interaction between the copolymer and a model lipid membrane was investigated in order to explain the action of the vector. Electrical measurements on black lipid membranes indicated that the main effect of L64 as a vector is to permeabilize the cell's membrane.

Amphiphilic polyether branched molecules to increase the circulation time of cationic particles

The preparation, physicochemical and biological properties of amphiphilic polyether branched molecules is described. These 'bunch shaped' molecules when inserted into cationic liposomes/DNA complexes have shown efficient surface charge shielding. As a consequence they efficiently inhibited the non specific interactions with blood components and significantly enhanced circulation time of the particles in the blood track. Formulations containing these molecules compared positively with those containing PEG lipids, providing a 5-fold increase in circulation time.

Physicochemical properties affecting lipofection potency of a new series of 1,2-dialkoylamidopropane-based cationic lipids

The in vitro transfection activity of a novel series of N,N'-diacyl-1,2-diaminopropyl-3-carbamoyl-(aminoethane) derivatives was evaluated against a mouse melanoma cell line at different +/- charge ratios, in the presence and absence of helper lipids. Only the unsaturated derivative N,N'-dioleoyl-1,2-diaminopropyl-3-carbamoyl-(aminoethane), (1,2lmp[5]) mediated significant increase in the reporter gene level which was significantly boosted in the presence of DOPE peaking at +/- charge ratio of 2. The electrostatic interactions between the cationic liposomes and plasmid DNA were investigated by gel electrophoresis, fluorescence spectroscopy, dynamic light scattering and electrophoretic mobility techniques. In agreement with the transfection results, 1,2lmp[5]/DOPE formulation was most efficient in associating with and retarding DNA migration. The improved association between the dioleoyl derivative and DNA was further confirmed by ethidium bromide displacement assay and particle size distribution analysis of the lipoplexes. Differential scanning calorimetry studies showed that 1,2lmp[5] was the only lipid that exhibited a main phase transition below 37 degrees C. Likewise, 1,2lmp[5] was the only lipid found to form all liquid expanded monolayers at 23 degrees C. In conclusion, the current findings suggest that high in vitro transfection activity is mediated by cationic lipids characterized by increased acyl chain fluidity and high interfacial elasticity.

Monomolecular DNA nanoparticles for intravenous delivery of genes

Delivery is the major obstacle to success of nucleic-acid-based therapies. We have neutralized DNA with a cationic detergent (C12CCP) obtained by amide bond formation between dodecanoic acid, cysteinyl-cysteine, and diaminopropane. Subsequent detergent polymerization by formation of intermolecular disulfide bonds within the condensed plasmid DNA leads to 32-nm-large neutral particles. (C12CCP)n/DNA complexes are more stable than those formed with other gene delivery agents toward exchange with extracellular polyanions such as glycosaminoglycans. Yet exposure to phosphatidylserine, an ubiquitous intracellular anionic lipid, still releases DNA from the complexes for transcription of the carried gene. Pharmacokinetics and biodistribution in mice showed that 25% of the complexes were still circulating after 30 min (2% for other cationic lipid vectors) in a form essentially not bound to blood cells. Altogether, straightforward control over size and surface charge, stability toward aggregation or exchange, and favorable pharmacokinetics make these complexes attractive vehicles for reaching tumor metastases after injection in the blood circulation.

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.

Design, Syntheses, and Transfection Biology of Novel Non-Cholesterol-Based Guanidinylated Cationic Lipids

The design of efficacious cationic transfection lipids with guanidinium headgroups is an actively pursued area of research in nonviral gene delivery. Herein, we report on the design, syntheses, and gene transfection properties of six novel non-cholesterol-based cationic amphiphiles (1-6) with a single guanidinium headgroup in transfecting CHO, COS-1, MCF-7, A549, and HepG2 cells. The in vitro gene transfer efficiencies of lipids 1-6 were evaluated using both the reporter gene and the whole cell histochemical X-gal staining assays. The efficiencies of lipids 1-3, in particular, were found to be about 2- to 4-fold higher than that of commercially available LipofectAmine in transfecting COS-1, CHO, A-549, and MCF-7 cells. However, the relative transfection efficiencies of lipids 1-3 and LipofectAmine were found to be comparable in HepG2 cells. Cholesterol was found to be a more efficacious co-lipid than dioleoyllphosphatidyl ethanolamine (DOPE). In general, lipids 1-3 containing the additional quaternized centers were observed to be more transfection efficient than lipids 4-6 with less positive headgroups. MTT-assay-based cell viability measurements in representative CHO cells revealed high (>75%) cell viabilities of lipids 1-6 across the lipid/DNA charge ratios 0.1:1 to 3:1. Electrophoretic gel patterns observed in DNase I protection experiments support the notion that enhanced degradation of DNA associated with lipoplexes of lipids 4-6 might play some role in diminishing their in vitro gene transfer efficacies. Size and global surface charge measurement by a dynamic laser light scattering instrument equipped with zeta-sizing capacity revealed the nanosizes and surface potentials of both the transfection efficient and the incompetent lipoplexes to be within the range of 200-600 nm and +3.4 to -34 mV, respectively. To summarize, given the feasibility of a wide range of structural manipulations in the headgroup regions of non-cholesterol-based cationic amphiphiles, our present findings are expected to broaden the potential of cationic amphiphiles with guanidinium headgroups for use in nonviral gene therapy.

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.

Structural investigations of DNA-polycation complexes

The internal structure of DNA-polycation complexes is investigated by synchrotron small-angle X-ray scattering (SAXS). Hexagonal packing of DNA is observed for DNA complexed with poly-L-lysine (PL), poly-L-arginine (PA), spermine (Sp), and linear and branched polyethyleneimine (lPEI and bPEI, respectively). Variations in the internal spacings and degree of long-range ordering are dependent on both polycation type and concentration of added salt. With increasing concentration of monovalent salt, a discontinuous phase transition is observed from compact to loose bundles and finally to an isotropic network phase. This salt-induced melting transition was found to be universal for all polyplexes studied and is in quantitative agreement with a simple free energy model based solely on electrostatic and entropic contributions. Using the osmotic stress method, bulk modulus (K) is measured for PL-DNA and PA-DNA polyplexes at various salt concentrations. With increasing osmotic force, we show that the salt-induced melting transition is shifted and compression in the loose bundle regime is in qualitative agreement with our model.

Negatively charged self-assembling DNA/poloxamine nanospheres for in vivo gene transfer

Over the past decade, numerous nonviral cationic vectors have been synthesized. They share a high density of positive charges and efficiency for gene transfer in vitro. However, their positively charged surface causes instability in body fluids and cytotoxicity, thereby limiting their efficacy in vivo. Therefore, there is a need for developing alternative molecular structures. We have examined tetrabranched amphiphilic block copolymers consisting of four polyethyleneoxide/polypropyleneoxide blocks centered on an ethylenediamine moiety. Cryo-electron microscopy, ethidium bromide fluorescence and light and X-ray scattering experiments performed on vector-DNA complexes showed that the dense core of the nanosphere consisted of condensed DNA interacting with poloxamine molecules through electrostatic, hydrogen bonding and hydrophobic interactions, with DNA molecules also being exposed at the surface. The supramolecular organization of block copolymer/DNA nanospheres induced the formation of negatively charged particles. These particles were stable in a solution that had a physiological ionic composition and were resistant to decomplexation by heparin. The new nanostructured material, the structure of which clearly contrasted with that of lipoplexes and polyplexes, efficiently transferred reporter and therapeutic genes in skeletal and heart muscle in vivo. Negatively charged supramolecular assemblies hold promise as therapeutic gene carriers for skeletal and heart muscle-related diseases and expression of therapeutic proteins for local or systemic uses.

Synthesis, characterization and transfection activity of new saturated and unsaturated cationic lipids

We synthesized new cationic lipids, analogue to N-[1-(2,3-dioleoyloxy)propyl]-N,N,N-trimethylammonium chloride (DOTMA) and 1,2-dimyristyloxypropyl-3-dimethyl-hydroxyethylammonium bromide (DMRIE), in order to compare those containing a dodecyl chain with those having a relatively long chain with two or five double bonds, such as squalenyl and dihydrofarnesyl derivatives, or complex saturated structures, such as squalane derivatives. The fusogenic helper lipid dioleoylphosphatidylethanolamine (DOPE) was added to cationic lipids to form a stable complex. Liposomes composed of 50:50 w/w cationic lipid/DOPE were prepared and incubated with plasmidic DNA at various charge ratios and the diameter and zeta potential of the complexes were measured. The surface charge of the DNA/lipid complexes can be controlled by adjusting the cationic lipid/DNA ratio. Finally, we tested the in vitro transfection efficiency of the cationic lipid/DNA complexes using different cell lines. The transfection efficiency was highest for the dodecyloxy derivative containing a single hydroxyethyl group in the head, followed by the dodecyloxy and the farnesyloxy trimethylammonium derivatives. Instead the C27 squalenyl and C27 squalanyl derivatives resulted inactive.

DNA-Induced Aggregation of Zwitterionic Oligolamellar Liposome

Liposome consisting of a single zwitterionic lipid as the potential vector for gene therapy has been reported recently; however, whether polyanionic DNA can bind directly with zwitterionic lipid without the aid of multivalent salt still remains unresolved. In this study, we reveal the aggregation of zwitterionic oligolamellar liposomes composed of 1,2-di(cis-9-octadecenoyl)-sn-glycero-3-phosphocholine induced by DNA without the presence of multivalent salt. Our results demonstrate that only a small fraction (<10%) of DNA can bind electrostatically with a portion of the liposomes. Such a low degree of binding, however, induces significant aggregation of these oligolamellar liposomes, yielding large multilamellar particles in which the number of hydrophilic/hydrophobic layer stacking becomes sufficiently large to yield multiple diffraction peaks in the small-angle X-ray scattering profile. Addition of monovalent salt such as NaCl tends to disrupt the multilamellar structure.

Novel Cationic Lipids Incorporating an Acid-Sensitive Acylhydrazone Linker: Synthesis and Transfection Properties

Cationic lipid-mediated gene transfection involves uptake of the lipid/DNA complexes via endocytosis, a cellular pathway characterized by a significant drop in pH. Thus, in the present study, we aimed to explore the impact on transfection efficiency of the inclusion of an acid-sensitive acylhydrazone function in the cationic lipid structure. We synthesized and evaluated the transfection properties of a series of four cationic steroid derivatives characterized by an acylhydrazone linkage connecting a guanidinium-based headgroup to a saturated cholestanone or an unsaturated cholest-4-enone hydrophobic domain. Acid-catalyzed hydrolysis was confirmed for all lipids, its rate being highest for those with a cholestanone moiety. The compound bis-guanidinium bis(2-aminoethyl)amine hydrazone (BGBH)-cholest-4-enone was found to mediate efficient gene transfection into various mammalian cell lines in vitro and into the mouse airways in vivo. In vitro transfection studies with BGBH-cholest-4-enone formulations also showed that incorporation of a degradable acylhydrazone bond led to low cytotoxicity and impacted the intracellular trafficking of the lipoplexes. Thus, our work allowed us to identify a cationic lipid structure with an acid-cleavable acylhydrazone linker capable of mediating efficient gene transfection in vitro and in vivo and it thereby provides a basis for further development of related acid-sensitive gene delivery systems.

Combined suicide gene therapy for pancreatic peritoneal carcinomatosis using BGTC liposomes

Peritoneal dissemination is a common end-stage complication of pancreatic cancer for which novel therapeutic modalities are actively investigated, as there is no current effective therapy. Thus, we evaluated, in a mouse model of pancreatic peritoneal carcinomatosis, the therapeutic potential of a novel nonviral gene therapy approach consisting of bis-guanidinium-tren-cholesterol (BGTC)-mediated lipofection of a combined suicide gene system. Human BxPC-3 pancreatic cells secreting the carcinoembryonic antigen (CEA) tumor marker were injected into the peritoneal cavity of nude mice. After 8 days, intraperitoneal (i.p.) lipofection was performed using BGTC/DOPE cationic liposomes complexed with plasmids encoding the two prodrug-activating enzymes Herpes Simplex Virus thymidine kinase and Escherichia coli cytosine deaminase, the latter being expressed from a bicistronic cassette also encoding E. coli uracil phosphoribosyltransferase. Administration of the lipoplexes was followed by treatment with the corresponding prodrugs ganciclovir and 5-fluorocytosine. The results presented herein demonstrate that BGTC/DOPE liposomes can efficiently mediate gene transfection into peritoneal tumor nodules. Indeed, HSV-TK mRNA was detected in tumor nodule tissues by semiquantitative reverse transcription-polymerase chain reaction analysis. In addition, green fluorescent protein (GFP) fluorescence and X-gal staining were observed in the peritoneal tumor foci following lipofection of the corresponding EGFP and LacZ reporter genes. These expression analyses also showed that transgene expression lasted for about 2 weeks and was preferential for the tumor nodules, this tumor preference being in good agreement with the absence of obvious treatment-related toxicity. Most importantly, mice receiving the full treatment scheme (BGTC liposomes, suicide genes and prodrugs) had significantly lower serum CEA levels than those of the various control groups, a finding indicating that peritoneal carcinomatosis progression was strongly reduced in these mice. In conclusion, our results demonstrate the therapeutic efficiency of BGTC-mediated i.p. lipofection of a combined suicide gene system in a mouse peritoneal carcinomatosis model and suggest that BGTC-based prodrug-activating gene therapy approaches may constitute a potential treatment modality for patients with peritoneal carcinomatosis and minimal residual disease.