Confocal and probe microscopy to study gene transfection mediated by cationic liposomes with a cationic cholesterol derivative

Rationale utilization of phospholipid excipients: a distinctive tool for progressing state of the art in research of emerging drug carriers

Phospholipids have a high degree of biocompatibility and are deemed ideal pharmaceutical excipients in the development of lipid-based drug delivery systems, because of their unique features (permeation, solubility enhancer, emulsion stabilizer, micelle forming agent, and the key excipients in solid dispersions) they can be used in a variety of pharmaceutical drug delivery systems, such as liposomes, phytosomes, solid lipid nanoparticles, etc. The primary usage of phospholipids in a colloidal pharmaceutical formulation is to enhance the drug's bioavailability with low aqueous solubility [i.e. Biopharmaceutical Classification System (BCS) Class II drugs], Membrane penetration (i.e. BCS Class III drugs), drug uptake and release enhancement or modification, protection of sensitive active pharmaceutical ingredients (APIs) from gastrointestinal degradation, a decrease of gastrointestinal adverse effects, and even masking of the bitter taste of orally delivered drugs are other uses. Phospholipid-based colloidal drug products can be tailored to address a wide variety of product requirements, including administration methods, cost, product stability, toxicity, and efficacy. Such formulations that are also a cost-effective method for developing medications for topical, oral, pulmonary, or parenteral administration. The originality of this review work is that we comprehensively evaluated the unique properties and special aspects of phospholipids and summarized how the individual phospholipids can be utilized in various types of lipid-based drug delivery systems, as well as listing newly marketed lipid-based products, patents, and continuing clinical trials of phospholipid-based therapeutic products. This review would be helpful for researchers responsible for formulation development and research into novel colloidal phospholipid-based drug delivery systems.

Escaping the endosome: assessing cellular trafficking mechanisms of non-viral vehicles

Non-viral vehicles hold therapeutic promise in advancing the delivery of a variety of cargos in vitro and in vivo, including small molecule drugs, biologics, and especially nucleic acids. However, their efficacy at the cellular level is limited by several delivery barriers, with endolysosomal degradation being most significant. The entrapment of vehicles and their cargo in the acidified endosome prevents access to the cytosol, nucleus, and other subcellular compartments. Understanding the factors that contribute to uptake and intracellular trafficking, especially endosomal entrapment and release, is key to overcoming delivery obstacles within cells. In this review, we summarize and compare experimental techniques for assessing the extent of endosomal escape of a variety of non-viral vehicles and describe proposed escape mechanisms for different classes of lipid-, polymer-, and peptide-based delivery agents. Based on this evaluation, we present forward-looking strategies utilizing information gained from mechanistic studies to inform the rational design of efficient delivery vehicles.

Codelivery of paclitaxel and small interfering RNA by octadecyl quaternized carboxymethyl chitosan-modified cationic liposome for combined cancer therapy

Conventional therapeutic approaches for cancer are limited by cancer cell resistance, which has impeded their clinical applications. The main goal of this work was to investigate the combined antitumor effect of paclitaxel with small interfering RNA modified by cationic liposome formed from modified octadecyl quaternized carboxymethyl chitosan. The cationic liposome was composed of 3β-[N-(N', N'-dimethylaminoethane)-carbamoyl]-cholesterol, dioleoylphosphatidylethanolamine, and octadecyl quaternized carboxymethyl chitosan. The cationic liposome properties were characterized by Fourier transform infrared spectroscopy, dynamic light scattering and zeta potential measurements, transmission electron microscopy, atomic force microscopy, and gel retardation assay. The cationic liposome exhibited good properties, such as a small particle size, a narrow particle size distribution, a good spherical shape, a smooth surface, and a good binding ability with small interfering RNA. Most importantly, when combined with paclitaxel and small interfering RNA, the composite cationic liposome induced a great enhancement in the antitumor activity, which showed a significantly higher in vitro cytotoxicity in Bcap-37 cells than liposomal paclitaxel or small interfering RNA alone. In conclusion, the results indicate that cationic liposome could be further developed as a codelivery system for chemotherapy drugs and therapeutic small interfering RNAs.

Atomic force microscopy probing of receptor-nanoparticle interactions for riboflavin receptor targeted gold-dendrimer nanocomposites

Riboflavin receptors are overexpressed in malignant cells from certain human breast and prostate cancers, and they constitute a group of potential surface markers important for cancer targeted delivery of therapeutic agents and imaging molecules. Here we report on the fabrication and atomic force microscopy (AFM) characterization of a core–shell nanocomposite consisting of a gold nanoparticle (AuNP) coated with riboflavin receptor-targeting poly(amido amine) dendrimer. We designed this nanocomposite for potential applications such as a cancer targeted imaging material based on its surface plasmon resonance properties conferred by AuNP. We employed AFM as a technique for probing the binding interaction between the nanocomposite and riboflavin binding protein (RfBP) in solution. AFM enabled precise measurement of the AuNP height distribution before (13.5 nm) and after chemisorption of riboflavin-conjugated dendrimer (AuNP–dendrimer; 20.5 nm). Binding of RfBP to the AuNP–dendrimer caused a height increase to 26.7 nm, which decreased to 22.8 nm when coincubated with riboflavin as a competitive ligand, supporting interaction of AuNP–dendrimer and its target protein. In summary, physical determination of size distribution by AFM imaging can serve as a quantitative approach to monitor and characterize the nanoscale interaction between a dendrimer-covered AuNP and target protein molecules in vitro.

Nanotechnological Approaches for Genetic Immunization

Genetic immunization is one of the important findings that provide multifaceted immunological response against infectious diseases. With the advent of r-DNA technology, it is possible to construct vector with immunologically active genes against specific pathogens. Nevertheless, site-specific delivery of constructed genetic material is an important contributory factor for eliciting specific cellular and humoral immune response. Nanotechnology has demonstrated immense potential for the site-specific delivery of biomolecules. Several polymeric and lipidic nanocarriers have been utilized for the delivery of genetic materials. These systems seem to have better compatibility, low toxicity, economical and capable to delivering biomolecules to intracellular site for the better expression of desired antigens. Further, surface engineering of nanocarriers and targeting approaches have an ability to offer better presentation of antigenic material to immunological cells. This chapter gives an overview of existing and emerging nanotechnological approaches for the delivery of genetic materials.

siRNA delivery into tumor cells by lipid-based nanoparticles composed of hydroxyethylated cholesteryl triamine

Previously, we reported that cationic nanoparticles (NP) composed of cholesteryl diamine (OH-Chol, (3S)-N-(2-(2-hydroxyethylamino)ethyl)cholesteryl-3-carboxamide) and Tween 80 could deliver plasmid DNA (pDNA) and small interfering RNA (siRNA) with high transfection efficiency into various tumor cells. In this study, to facilitate the endosomal escape of siRNA transfected by lipid-based nanoparticles, we synthesized new cationic cholesteryl triamine (OH-N-Chol, (3S)-N-(2-(2-(2-hydroxyethylamino)ethylamino)ethyl)cholesteryl-3-carboxamide) with an ethylenimine extension and prepared cationic nanoparticles (NP-N) composed of cholesteryl triamine and Tween 80. Although NP-N/siRNA complex (NP-N nanoplex) after mixing NP-N with siRNA was >350 nm in size, the vortex-mixing during the nanoplex formation decreased it to about 200 nm, which was an injectable size. NP-N nanoplex was mainly internalized by macropinocytosis-mediated endocytosis, as was NP nanoplex, and showed higher gene knockdown efficiency than NP nanoplex in human cervical carcinoma SiHa cells. From these results, cationic nanoparticles composed of OH-N-Chol and Tween 80 may have potential as a gene vector for siRNA transfection to tumor cells.

Characterization of an established endothelial cell line from primary cultures of fetal sheep hypothalamus

Immortalized cell lines from fetal brain are an experimental model for studying the in vitro molecular pathways regulating neural cell differentiation and the development of neural networks. The procedures are described to obtain an established cell line from the 90-day old fetal sheep hypothalamus. Viral oncogene LT-SV40 transformation was used to isolate a stable cell line (ENOS-01) that was characterized immunocytochemically. Immortalized cells can be classified as an endothelial cell line of hypothalamic microvasculature. Furthermore, mRNA expression and immunocytochemical of estrogen receptors α and β were also evaluated. Since it is known that cerebral vessels are directly targeted by sex steroids, our established cell line represents an alternative system to study estradiol/receptor interactions during brain development. Our in vitro model can provide a tool to investigate the complex relationships among the cell types forming the blood-brain barrier, which is known to be involved in the pathogenesis of sheep transmissible neurological diseases.

Grafting of cell-penetrating peptide to receptor-targeted liposomes improves their transfection efficiency and transport across blood-brain barrier model

We report bifunctional liposomal delivery system, combining transferrin (Tf)-mediated receptor targeting and poly-L-arginine (PR)-facilitated cell penetration, which overcomes the drawback of saturation of delivery. PR was conjugated to the distal end of distearoyl phosphoethanolamine-polyethylene glycol (PEG) 2000 and was incorporated with other phospholipids in chloroform/methanol (2:1) to form PR liposomes using thin-film hydration technique. Tf-PEG phospholipid micelles were incorporated into PR liposomes using postinsertion technique to form Tf-PR liposomes. The bifunctional liposomes demonstrated significantly (p < 0.05) higher cellular uptake by brain endothelial cells (bEnd.3) and about eightfold higher transfection in primary culture of glial cells as compared with the Tf liposomes. Cell viabilities of Tf-conjugated and bifunctional liposomes were not markedly different; however, transport across in vitro blood-brain barrier model improved considerably after dual modification. The study underlines the potential of bifunctional liposomes as high-efficiency and low-toxicity gene delivery system for the treatment of central nervous system disorders.

Technologies for enhanced efficacy of DNA vaccines

Despite many years of research, human DNA vaccines have yet to fulfill their early promise. Over the past 15 years, multiple generations of DNA vaccines have been developed and tested in preclinical models for prophylactic and therapeutic applications in the areas of infectious disease and cancer, but have failed in the clinic. Thus, while DNA vaccines have achieved successful licensure for veterinary applications, their poor immunogenicity in humans when compared with traditional protein-based vaccines has hindered their progress. Many strategies have been attempted to improve DNA vaccine potency including use of more efficient promoters and codon optimization, addition of traditional or genetic adjuvants, electroporation, intradermal delivery and various prime-boost strategies. This review summarizes these advances in DNA vaccine technologies and attempts to answer the question of when DNA vaccines might eventually be licensed for human use.

Novel cationic lipid that delivers siRNA and enhances therapeutic effect in lung cancer cells

We have developed lipid-polycation-DNA (LPD) nanoparticles containing DOTAP and targeted with polyethylene glycol (PEG) tethered with anisamide (AA) to specifically deliver siRNA to H460 human lung carcinoma cells which express the sigma receptor. A novel non-glycerol based cationic lipid which contains both a guanidinium and a lysine residue as the cationic headgroup, i.e. DSGLA, downregulated pERK more efficiently in H460 cells than DOTAP. As demonstrated by using fluorescently labeled siRNA, LPD-PEG-AA prepared with DSGLA efficiently delivered siRNA to the cytoplasm of the H460 cells. Although the siRNA delivered by LPD-PEG-AA containing either DOTAP or DSGLA could effectively silence EGFR expression, a synergistic cell killing effect in promoting cellular apoptosis was only observed with DSGLA. The fluorescently labeled siRNA was efficiently delivered into the cytoplasm of H460 xenograft tumor by the LPD-PEG-AA containing either DOTAP or DSGLA 4 h after intravenous injection. Three daily injections (0.6 mg/kg) of siRNA formulated in the LPD-PEG-AA containing either DOTAP or DSGLA could effectively silence the epidermal growth factor receptor (EGFR) in the tumor, but the formulation containing DSGLA could induce more cellular apoptosis. A significant improvement in tumor growth inhibition was observed after dosing with LPD-PEG-AA containing DSGLA. Thus, DSGLA served as both a formulation component as well as a therapeutic agent which synergistically enhanced the activity of siRNA.

DNA vaccines: ready for prime time?

Since the discovery, over a decade and a half ago, that genetically engineered DNA can be delivered in vaccine form and elicit an immune response, there has been much progress in understanding the basic biology of this platform. A large amount of data has been generated in preclinical model systems, and more sustained cellular responses and more consistent antibody responses are being observed in the clinic. Four DNA vaccine products have recently been approved, all in the area of veterinary medicine. These results suggest a productive future for this technology as more optimized constructs, better trial designs and improved platforms are being brought into the clinic.

Hydroxyethylated cationic cholesterol derivatives in liposome vectors promote gene expression in the lung

Three cationic cholesterol derivatives (CCDs), which differ in their types of amine and bear a hydroxyethyl group at the amine group, were synthesized and formulated into liposomes and nanoparticles as gene delivery vectors. In vitro transfection into A549 cells proved that liposomes formulated with CCDs and dioleoylphosphatidylethanolamine (DOPE) of 1/2 molar ratio were more effective than the corresponding nanoparticles with CCDs and Tween 80 at charge ratios (+/-) of 1/2, 3/1 and 5/1. Among the liposomal formulations, non-hydroxyethylated CCDs were more effective than hydroxyethylated ones in vitro. However, gene transfection in the lung through intratracheal injection showed opposite results to those in vitro, with liposomes containing hydroxyethylated CCDs being more potent than those containing non-hydroxyethylated CCDs. Transfection by liposomes with N,N-methyl hydroxyethyl aminopropane carbamoyl cholesterol iodide (MHAPC) showed the highest luciferase activity, resulting in 2- and 60-fold higher gene expression than jet-PEI and naked DNA, respectively. The distribution of MHAPC lipoplex after intratracheal injection was heterogeneous, and luciferase was expressed in epithelial cells lining the bronchi and bronchioles. All the lipoplexes led to higher TNF-alpha levels in the lung compared to the nanoplex and jet-PEI, but our findings suggested that modification of the cationic cholesterol with a hydroxyethyl group at the tertiary amine terminal, MHAPC, promoted gene expression in the lung without increasing the toxicity compared with other CCDs. This work firstly proved that liposomes containing hydroxyethylated CCDs could promote gene expression in the lung through intratracheal injection.

NBD-conjugated biosurfactant (MEL-A) shows a new pathway for transfection

Gene transfection is a fundamental technology for molecular and cell biology, and also clinical gene therapy. A variety of non-viral vectors have been investigated for gene transfection, but their gene delivery had remained an inefficient process. Recently, we found that a biosurfactant, mannosylerythritol lipid (MEL)-A, dramatically increased the efficiency in transfection of plasmid DNA mediated by cationic liposomes. However, its mechanism has not been understood yet. Here we examined the mechanism of the transfection mediated by cationic liposomes with NBD-conjugated MEL-A. We found that MEL-A first gradually distributed on the intracellular membranes through the plasma membranes of target cells, while the cationic liposomes with MEL-A fused to the plasma membranes in 20-35 min. Thereafter, the oligonucleotide released from the vesicles was immediately transferred to the nucleus. The present results showed a new role of non-viral vectors in transfection.

Synergy in lipofection by cationic lipid mixtures: superior activity at the gel-liquid crystalline phase transition

Some mixtures of two cationic lipids including phospholipid compounds (O-ethylphosphatidylcholines) as well as common, commercially available cationic lipids, such as dimethylammonium bromides and trimethylammonium propanes, deliver therapeutic DNA considerably more efficiently than do the separate molecules. In an effort to rationalize this widespread "mixture synergism", we examined the phase behavior of the cationic lipid mixtures and constructed their binary phase diagrams. Among a group of more than 50 formulations, the compositions with maximum delivery activity resided unambiguously in the solid-liquid crystalline two-phase region at physiological temperature. Thus, the transfection efficacy of formulations exhibiting solid-liquid crystalline phase coexistence is more than 5 times higher than that of formulations in the gel (solid) phase and over twice that of liquid crystalline formulations; phase coexistence occurring at physiological temperature thus appears to contribute significantly to mixture synergism. This relationship between delivery activity and physical property can be rationalized on the basis of the known consequences of lipid-phase transitions, namely, the accumulation of defects and increased disorder at solid-liquid crystalline phase boundaries. Packing defects at the borders of coexisting solid and liquid crystalline domains, as well as large local density fluctuations, could be responsible for the enhanced fusogenicity of mixtures. This study leads to the important conclusion that manipulating the composition of the lipid carriers so that their phase transition takes place at physiological temperature can enhance their delivery efficacy.

Highly efficient cationic hydroxyethylated cholesterol-based nanoparticle-mediated gene transfer in vivo and in vitro in prostate carcinoma PC-3 cells

Optimal gene therapy for tumors must deliver DNA to tumor cells with high efficiency and minimal toxicity. It has been reported that in non-viral gene delivery, the hydroxyethyl group at the amino terminal in cationic lipid was important for high transfection efficiency. Therefore, in this study, we developed new cationic nanoparticles (NP-OH) composed of cholesteryl-3beta-carboxyamidoethylene-N-hydroxyethylamine and Tween 80, and optimized in vitro and in vivo transfections for potential use as a non-viral DNA vector into human prostate tumor PC-3 cells and xenografts. In vitro transfection resulted in efficient DNA transfer when positive-charged nanoplex was prepared in the presence of sodium chloride (NaCl). In in vivo transfection, negative-charged nanoplex formed in water strongly induced the gene expression compared with positive-charged nanoplex when directly transfected into xenografts. These transfection efficiencies in vitro and in vivo were comparable to each commercial product. Furthermore, NP-OH nanoplexes displayed no induction of tumor necrosis factor (TNF)-alpha when administered by intravenous injection. The results of the experiments provided optimal conditions to form NP-OH nanoplex for gene delivery in vitro and in vivo. NP-OH is a potential non-viral DNA vector for the local treatment of tumor and in vitro.

Chemical adjuvants for plasmid DNA vaccines

Plasmid DNA vaccines are a promising modality for immunization against a variety of human pathogens. Immunization via multiple routes with plasmid DNA can elicit potent cellular immune responses, and these immunogens can be administered repeatedly without inducing anti-vector immunity. Nonetheless, the immunogenicity of plasmid DNA vaccines has been limited by problems associated with delivery. A number of adjuvants have been designed to improve plasmid DNA immunogenicity, either by directly stimulating the immune system or by enhancing plasmid DNA expression. Chemical adjuvants for enhancing plasmid DNA expression include liposomes, polymers, and microparticles, all of which have shown promise for enhancing the expression and immunogenicity of plasmid DNA vaccines in animal models. Micro- and nanoparticles have not been shown to enhance immune responses to plasmid DNA vaccines. However, formulation of plasmid DNA with some non-particulate polymeric adjuvants has led to a statistically significant enhancement of immune responses. Further development of these technologies will significantly improve the utility of plasmid DNA vaccination.

Mechanisms of co-modified liver-targeting liposomes as gene delivery carriers based on cellular uptake and antigens inhibition effect

In order to deliver antisense oligonucleotides (asODN) into hepatocytes orientedly in the treatment of hepatitis B virus (HBV) infection, the liver-targeting cationic liposomes was developed as a gene carrier, which was co-modified with the ligand of the asialoglycoprotein receptor (ASGPR), beta-sitosterol-beta-d-glucoside (sito-G) and the nonionic surfactant, Brij 35. Flow cytometry (FCM) analysis and enzyme-linked immunosorbent assay (ELISA) showed that the asODN-encapsulating cationic liposomes exhibited high transfection efficiency and strong antigens inhibition effect in primary rat hepatocytes and HepG2.2.15 cells, respectively. With the help of several inhibitors acting on different steps during the targeting lipofection, the cellular uptake mechanisms of the co-modified liver-targeting cationic liposomes were investigated through antigens inhibition effect assay and confocal laser scanning microscopy (CLSM) analysis. The cellular uptake with high transfection efficiency seemed to involve both endocytosis and membrane fusion. The ligand sito-G was confirmed to be able to enhance ASGPR-mediated endocytosis, the nonionic surfactant Brij 35 seemed to be able to facilitate membrane fusion, and the co-modification resulted in the most efficient transfection but no enhanced cytotoxicity. These results suggested that the co-modified liver-targeting cationic liposomes would be a specific and effective carrier to transfer asODN into hepatocytes infected with HBV orientedly.

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

Lipoplexes containing a mixture of cationic phospholipids dioleoylethylphosphatidylcholine (EDOPC) and dilauroylethylphosphatidylcholine (EDLPC) are known to be far more efficient agents in transfection of cultured primary endothelial cells than are lipoplexes containing either lipid alone. The large magnitude of the synergy permits comparison of the physical and physico-chemical properties of lipoplexes that have very different transfection efficiencies, but minor chemical differences. Here we report that the superior transfection efficiency of the EDLPC/EDOPC lipoplexes correlates with higher surface activity, higher affinity to interact and mix with negatively charged membrane-mimicking liposomes, and with considerably more efficient DNA release relative to the EDOPC lipoplexes. Observations on cultured cells agree with the results obtained with model systems; confocal microscopy of transfected human umbilical artery endothelial cells (HUAEC) demonstrated more extensive DNA release into the cytoplasm and nucleoplasm for the EDLPC/EDOPC lipoplexes than for EDOPC lipoplexes; electron microscopy of cells fixed and embedded directly on the culture dish revealed contact of EDLPC/EDOPC lipoplexes with various cellular membranes, including those of the endoplasmic reticulum, mitochondria and nucleus. The sequence of events outlining efficient lipofection is discussed based on the presented data.

pH dependent high transfection efficiency of mouse neuroblastomas using TransFectin

Mouse neuroblastoma cell lines are often used in lieu of mouse primary neurons in ex vivo experiments, as they provide an easier platform for transfection, compared to the latter. A well-known inherent problem with this strategy is the relatively low transfection efficiency (15-30%) of mouse neuroblastoma cell lines such as neuro-2A and N1E-115. We were able to improve the transfection efficiency of these cell lines by using the cationic lipid reagent, TransFectin (Bio-Rad, Hercules, CA, USA) to optimise the transfection conditions. Our results, based on fluorescence intensity determinations and Western blotting for enhanced green fluorescence protein (EGFP) over-expression in neuro-2A, demonstrated that pH is a crucial factor in determining the transfection efficiency. Under pH-optimised transfection conditions, flow cytometric analysis revealed high EGFP transfection efficiencies of 76.4 +/- 0.5 and 60.9 +/- 0.6% for neuro-2A and N1E-115, respectively. Notably, the optimised TransFectin-based transfection system did not result in any detectable cytotoxicity to the mouse neuroblastomas. The resultant optimised system is economical, easy to use and does not require any specialised equipment.

[Functional fluctuation]

The discovery of the double-helical structure of DNA, the elucidation of the genetic code, and the determination of the three-dimensional structure of several proteins are some of the outstanding achievements of biochemistry and life sciences in the latter half of the last century. Proteins play key roles in almost all the biological processes and the biological function of a protein depends on its conformation which is defined as the three-dimensional arrangement of the atoms of a molecule. The three-dimensional structure, however, is not rigid but fluctuated. Structural fluctuation plays an important role in bio-macromolecules. How about "functional fluctuation" in biological systems? The present review proposes that functional fluctuation is also very important for understanding the mechanism of supramolecules, biological processes in living cells, and the interaction between biological systems. This new theme is pretty well supported by our recent experiments for neuro-immune crosstalk, gene transfection with cationic liposomes, and cell signaling in embryonic stem cells.

The effect of PS content on the ability of natural membranes to fuse with positively charged liposomes and lipoplexes

Supramolecular aggregates containing cationic lipids have been widely used as transfection mediators due to their ability to interact with negatively charged DNA molecules and biological membranes. First steps of the process leading to transfection are partly electrostatic, partly hydrophobic interactions of liposomes/lipoplexes with cell and/or endosomal membrane. Negatively charged compounds of biological membranes, namely glycolipids, glycoproteins and phosphatidylserine (PS), are responsible for such events as adsorption, hemifusion, fusion, poration and destabilization of natural membranes upon contact with cationic liposomes/lipoplexes. The present communication describes the dependence of interaction of cationic liposomes with natural and artificial membranes on the negative charge of the target membrane, charges which in most cases were generated by charging the PS content or its exposure. The model for the target membranes were liposomes of variable content of PS or PG (phosphatidylglycerol) and erythrocyte membranes in which the PS and other anionic compound content/exposure was modified in several ways. Membranes of increased anionic phospholipid content displayed increased fusion with DOTAP (1,2-dioleoyl-3-trimethylammoniumpropane) liposomes, while erythrocyte membranes partly depleted of glycocalix, its sialic acid, in particular, showed a decreased fusion ability. The role of the anionic component is also supported by the fact that erythrocyte membrane inside-out vesicles fused easily with cationic liposomes. The data obtained on erythrocyte ghosts of normal and disrupted asymmetry, in particular, those obtained in the presence of Ca(2+), indicate the role of lipid flip-flop movement catalyzed by scramblase. The ATP-depletion of erythrocytes also induced an increased sensitivity to hemoglobin leakage upon interactions with DOTAP liposomes. Calcein leakage from anionic liposomes incubated with DOTAP liposomes was also dependent on surface charge of the target membranes. In all experiments with the asymmetric membranes the fusion level markedly increased with an increase of temperature, which supports the role of membrane lipid mobility. The decrease in positive charge by binding of plasmid DNA and the increase in ionic strength decreased the ability of DOTAP liposomes/lipoplexes to fuse with erythrocyte ghosts. Lower pH promotes fusion between erythrocyte ghosts and DOTAP liposomes and lipoplexes. The obtained results indicate that electrostatic interactions together with increased mobility of membrane lipids and susceptibility to form structures of negative curvature play a major role in the fusion of DOTAP liposomes with natural and artificial membranes.

Quantifying the Specific Binding between West Nile Virus Envelope Domain III Protein and the Cellular Receptor αVβ3 Integrin

A previous study has illustrated that the alphaVbeta3 integrin served as the functional receptor for West Nile virus (WNV) entry into cells. Domain III (DIII) of WNV envelope protein (E) was postulated to mediate virus binding to the cellular receptor. In this study, the specificity and affinity binding of WNV E DIII protein to alphaVbeta3 integrin was confirmed with co-immunoprecipitation and receptor competition assay. Binding of WNV E DIII protein to alphaVbeta3 integrin induced the phosphorylation of focal adhesion kinase that is required to mediate ligand-receptor internalization into cells. A novel platform was then developed using the atomic force microscopy to measure this specific binding force between WNV E DIII protein and the cellular receptor, alphaVbeta3 integrin. The single protein pair-interacting force measured was in the range of 45 +/- 5 piconewtons. This interacting force was highly specific as minimal force was measured in the WNV E DIII protein interaction with alphaVbeta5 integrin molecules and heparan sulfate. These experiments provided an insight to quantitate virus-receptor interaction. Force measurement using atomic force microscopy can serve to quantitatively analyze the effect of candidate drugs that modulate virus-host receptor affinity.

Formation and intracellular trafficking of lipoplexes and polyplexes

Cationic lipid/DNA lipoplexes and cationic polymer/DNA polyplexes represent an attractive alternative to viral vectors for cell transfection in vitro and in vivo but still suffer from a relatively low efficiency. Optimization of their transfection efficiency may be attempted by using a trial and error approach consisting of synthesizing and testing a large number of derivatives. On the other hand, rational design of highly efficient cationic lipids and polymers requires a deeper understanding of the interactions between the vector and the DNA as well as the cellular pathways and mechanisms involved in DNA entry into the cell and ultimately the nucleus. In the present review, the pathways and mechanisms involved in lipoplex- and polyplex-mediated transfection are comparatively addressed and unresolved questions are highlighted.

DNA release from lipoplexes by anionic lipids: correlation with lipid mesomorphism, interfacial curvature, and membrane fusion

DNA release from lipoplexes is an essential step during lipofection and is probably a result of charge neutralization by cellular anionic lipids. As a model system to test this possibility, fluorescence resonance energy transfer between DNA and lipid covalently labeled with Cy3 and BODIPY, respectively, was used to monitor the release of DNA from lipid surfaces induced by anionic liposomes. The separation of DNA from lipid measured this way was considerably slower and less complete than that estimated with noncovalently labeled DNA, and depends on the lipid composition of both lipoplexes and anionic liposomes. This result was confirmed by centrifugal separation of released DNA and lipid. X-ray diffraction revealed a clear correlation of the DNA release capacity of the anionic lipids with the interfacial curvature of the mesomorphic structures developed when the anionic and cationic liposomes were mixed. DNA release also correlated with the rate of fusion of anionic liposomes with lipoplexes. It is concluded that the tendency to fuse and the phase preference of the mixed lipid membranes are key factors for the rate and extent of DNA release. The approach presented emphasizes the importance of the lipid composition of both lipoplexes and target membranes and suggests optimal transfection may be obtained by tailoring lipoplex composition to the lipid composition of target cells.

Surfactant layering on mixed monolayer-protected gold clusters

Positively-charged monolayer protected gold clusters (MMPCs) were mixed with sodium dodecyl sulfate (SDS). At lower SDS concentration, the initially water-soluble particles became organic-soluble while remaining discrete. Upon further addition of SDS, the particles aggregate and become water-soluble. NaCN decomposition, TEM, and DLS characterization reveal the morphology and properties of these encapsulated assemblies.

Characterization of interaction between cationic lipid-oligonucleotide complexes and cellular membrane lipids using confocal imaging and fluorescence correlation spectroscopy

Complexes formed by cationic liposomes and single-strand oligodeoxynucleotides (CL-ODN) are promising delivery systems for antisense therapy. ODN release from the complexes is an essential step for inhibiting activity of antisense drugs. We applied fluorescence correlation spectroscopy and confocal laser scanning microscopy to monitor CL-ODN complex interaction with membrane lipids leading to ODN release. To model cellular membranes we used giant unilamellar vesicles and investigated the transport of Cy-5-labeled ODNs across DiO-labeled membranes. For the first time, we directly observed that ODN molecules are transferred across the lipid bilayers and are kept inside the giant unilamellar vesicles after release from the carriers. ODN dissociation from the carrier was assessed by comparing diffusion constants of CL-ODN complexes and ODNs before complexation and after release. Freely diffusing Cy-5-labeled ODN (16-nt) has diffusion constant D(ODN) = 1.3 +/- 0.1 x 10(-6) cm2/s. Fluorescence correlation spectroscopy curves for CL-ODN complexes were fitted with two components, which both have significantly slower diffusion in the range of D(CL-ODN) = approximately 1.5 x 10(-8) cm2/s. Released ODN has the mean diffusion constant D = 1.1 +/- 0.2 x 10(-6) cm2/s, which signifies that ODN is dissociated from cationic lipids. In contrast to earlier studies, we report that phosphatidylethanolamine can trigger ODN release from the carrier in the full absence of anionic phosphatidylserine in the target membrane and that phosphatidylethanolamine-mediated release is as extensive as in the case of phosphatidylserine. The presented methodology provides an effective tool for probing a delivery potential of newly created lipid formulations of CL-ODN complexes for optimal design of carriers.

Novel Polyamine−Dialkyl Phosphate Conjugates for Gene Carriers. Facile Synthetic Route via an Unprecedented Dialkyl Phosphate

To develop a novel nonviral gene carrier, three types of polyamine-dialkyl phosphates conjugates were synthesized via an unprecedented synthetic intermediate, dimerized dicetyl phosphate (DCP) anhydride, and the transfection efficiency and the complexation properties of the conjugate-DNA were evaluated. Condensation of DCP by 1,3,5-triisopropylbenzenesulfonyl chloride, TPSCl, gives the dimerized anhydride, which is stable enough to isolate by column chromatography in approximately 90% yield. The anhydride is reactive with various amines, i.e., spermidine, spermine, and polyethylenimine (PEI(1800)), providing corresponding polyamine-DCP conjugates via phosphoramidate linkage. The polyamine-DCP conjugates exhibited moderate transfection efficacy evaluated by beta-galactosidase assay. The conjugate-DNA complex was observed by using an atomic force microscope (AFM), revealing that the PEI(1800)-DCP conjugate, which showed the most efficient transfection, enables the formation of the more compact complex with DNA.

Pulmonary drug delivery. Part II: the role of inhalant delivery devices and drug formulations in therapeutic effectiveness of aerosolized medications

Research in the area of pulmonary drug delivery has gathered momentum in the last several years, with increased interest in using the lung as a means of delivering drugs systemically. Advances in device technology have led to the development of more efficient delivery systems capable of delivering larger doses and finer particles into the lung. As more efficient pulmonary delivery devices and sophisticated formulations become available, physicians and health professionals will have a choice of a wide variety of device and formulation combinations that will target specific cells or regions of the lung, avoid the lung's clearance mechanisms and be retained within the lung for longer periods. It is now recognized that it is not enough just to have inhalation therapy available for prescribing; physicians and other healthcare providers need a basic understanding of aerosol science, inhaled formulations, delivery devices, and bioequivalence of products to prescribe these therapies optimally.

Biosurfactant MEL-A dramatically increases gene transfection via membrane fusion

Biosurfactants, which are surface-active compounds produced by microorganisms growing on water-insoluble substrates, have many biological activities. We studied here three different biosurfactants, mannosylerythritol lipid (MEL) or 4-O-[(4',6'-di-O-acetyl-2',3'-di-O-alkanoyl)-beta-D-mannopyranosyl] meso-erythritol (MEL-A), 4-O-[(6'-O-acetyl-2',3'-di-O-alkanoyl)-beta-D-mannopyranosyl] meso-erythritol (MEL-B) and 4-O-[(4'-O-acetyl-2',3'-di-O-alkanoyl)-beta-D-mannopyranosyl] meso-erythritol (MEL-C). MEL-A enhanced the efficiency of gene transfection by cationic liposomes, but MEL-B and MEL-C did not. We also studied the localization of FITC-conjugated antisense DNAs (15-mer oligonucleotides; phosphorothioate) in the target cells by confocal laser scanning microscopy (CLSM). The FITC-conjugated antisense oligonucleotides were temporarily on the plasma membrane of the target cells, thereafter they were transferred into the nucleus of the target cells. In the case of MEL-B and MEL-C, such localization of DNA was not observed both in the plasma membrane and in the nucleus. The results obtained by CLSM images were in good agreement with the transfection efficiency. This suggests that MEL-A induces the membrane fusion between the target cells and the cationic liposomes, accelerating the efficiency of gene transfection dramatically.

Atomic force microscopy and drug discovery

Atomic force microscopy is being used ever more widely in biological imaging, because of its unique ability to provide structural information at the single molecule level and under near-physiological conditions. Detailed topographic images of potential drug targets, such as proteins and DNA, have been produced, and the folding of modular proteins has been studied using single-molecule force spectroscopy. Recently, atomic force microscopy has been used to examine ligand-protein and ligand-DNA interactions, and to begin to determine the architecture of multi-subunit proteins, including a member of the superfamily of ionotropic receptors. Atomic force microscopy is fast becoming a valuable addition to the pharmaceutical industry's toolkit.

N-alkylated chitosan as a potential nonviral vector for gene transfection

Alkylated chitosans (ACSs) were prepared by modifying chitosan (CS) with alkyl bromide. The self-aggregation of ACSs in acetic acid solution was characterized by fluorescence spectroscopy and dynamic light scattering method. The results indicate that introducing alkyl side chains leads to the self-aggregation of ACSs, and CS with a 99% deacetylation degree shows no aggregation due to the electrostatic repulsion. The electrophoresis experiment demonstrates that the complex between CS and DNA was formed at a charge ratio (+/-) of 1/1; ACS/DNA complexes were formed at a lower charge ratio (+/-) of 1/4. A small amount of alkylated chitosans play the same shielding role as chitosan in protecting DNA from DNase hydrolysis. Differential scanning calorimetry (DSC) and atomic force microscopy (AFM) were employed separately to investigate the thermodynamic behavior of dipalmitoyl-sn-glycero-3-phosphocholine (DPPC)/CS and DPPC/ACS mixtures and the variation in topological structure of DPPC membrane induced by CS and ACS. It is shown that CS and ACS can cause the fusion of DPPC multilamellar vesicles as well as membrane destabilization. In contrast, the perturbation effect induced by ACS is more evident due to the hydrophobic interaction. CS and ACS were used to transfer plasmid-encoding CAT into C(2)C(12) cell lines. Upon elongating the alkyl side chain, the transfection efficiency is increased and levels off after the number of carbons in the side chain exceeds 8. It is proposed that the higher transfection efficiency of ACS is attributed to the increasing entry into cells facilitated by hydrophobic interactions and easier unpacking of DNA from ACS carriers due to the weakening of electrostatic attractions between DNA and ACS.

Remarkable induction of apoptosis in cancer cells by a novel cationic liposome complexed with a bcl-2 antisense oligonucleotide

We reported recently a novel cationic cholesterol derivative with a hydroxyethylamino head group, cholesteryl-3beta-carboxyamidoethylene-N-hydroxyethylamine (I) for liposome-mediated gene transfection [FEBS Lett., 408 (1997) 232]. In the present paper we have studied whether this novel cationic liposome is prominent in nature to suppress cell growth of human cancer cells. Bcl-2 antisense phosphorothioate oligonucleotides (AS-ODNs) were complexed with the cationic liposomes with the derivative (I) and they were introduced into human cervix epithelial carcinoma cell lines HeLa, and mouse fibroblast NIH3T3 cells. An AS-ODNs targeting/bcl-2 gene induced probably apoptosis (including necrosis in some cases) in HeLa and NIH3T3 cells, however, nonsense oligonucleotides (NS-ODNs) corresponding to a scrambled-sequence control hardly induced apoptosis. Induction of apoptosis was much greater than that by commercially available DC-Chol liposomes. Fluorescence intensities of FITC-conjugated bcl-2 AS-ODNs were specifically found in the nucleus. The intensity of the AS-ODNs was mostly consistent with the amounts of Bcl-2 proteins observed by Western blot analysis in the target cells. The results showed the possibility that this new cationic cholesterol derivative might be very promising to be used for liposome-mediated gene targeting in vitro and in vivo.

Transfection of embryonal carcinoma cells at high efficiency using liposome-mediated transfection

Embryonal carcinoma (EC) cells are recognized as an excellent model system for studying the early stages of mammalian development. Many studies performed with EC cells involve transient transfection with promoter/reporter gene constructs and/or mammalian expression vectors. One of the limitations of working with EC cells is their inability to be transfected at high efficiency. In most cases, EC cells are transfected using the calcium phosphate method. The objective of this study was to identify protocols and culture conditions that significantly increase the transfection efficiency of EC cells. F9 EC cells were used for this purpose, because they are the EC cell line studied most commonly. We show that the transfection efficiency of F9 EC cells using the calcium phosphate method is less than 5%; whereas, their transfection efficiency can be improved approximately 15-fold using optimized culture conditions and liposome-based transfection reagents. Specifically, we demonstrate that more than 50% of F9 EC cells can be transfected using LipofectAMINE 2000. In addition to higher levels of transfection, there is much less plate-to-plate variation with liposome-based reagents as compared to transfection with calcium phosphate. Interestingly, transfection efficiency using these reagents was found to be inversely related to cell density. This contrasts sharply with the recommendation that transfection with LipofectAMINE 2000 or LipofectAMINE in conjunction with the PLUS reagent be performed at high cell densities. Given the improvements in transfection efficiency reported here, it will now be possible to perform studies with F9 EC cells that require transfection at significantly higher levels than that achieved using the calcium phosphate method. Overall, the highest transfection efficiencies were consistently obtained using LipofectAMINE 2000.

The application of confocal microscopy to the study of liposome adsorption onto bacterial biofilms

Confocal laser scanning microscopy has been used to visualise the adsorption of fluorescently labelled liposomes on immobilised biofilms of the bacterium Staphylococcus aureus. The liposomes were prepared with a wide range of compositions with phosphatidylcholines as the predominant lipids using the extrusion technique. They had weight average diameters of 125 +/- 5 nm and were prepared with encapsulated carboxyfluorescein. Cationic liposomes were prepared by incorporating dimethyldioctadecylammonium bromide (DDAB) or 3, beta [N-(N1,N1 dimethylammonium ethane)-carbamoyl] cholesterol (DC-chol) and anionic liposomes were prepared by incorporation of phosphatidylinositol (PI). Pegylated cationic liposomes were prepared by incorporation of DDAB and 1,2-dipalmitoylphosphatidylethanolamine-N-[polyethylene glycol)-2000]. Confocal laser scanned images showed the preferential adsorption of the fluorescent cationic liposomes at the biofilm-bulk phase interface which on quantitation gave fluorescent peaks at the interface when scanned perpendicular (z-direction) to the biofilm surface (x-y plane). The biofilm fluorescence enhancement (BFE) at the interface was examined as a function of liposomal lipid concentration and liposome composition. Studies of the extent of pegylation of the cationic liposomes incorporating DDAB, on adsorption at the biofilm-bulk phase interface were made. The results demonstrated that pegylation inhibited adsorption to the bacterial biofilms as seen by the decline in the peak of fluorescence as the mole% DPPE-PEG-2000 was increased in a range from 0 to 9 mole%. The results indicate that confocal laser scanning microscopy is a useful technique for the study of liposome adsorption to bacterial biofilms and complements the method based on the use of radiolabelled liposomes.

Chitosan and its derivatives--a promising non-viral vector for gene transfection

The ability of a vector to ferry gene into targeted cells is the premise of improving gene-transfer efficiency. Chitosan, a naturally occurring cationic polysaccharide, has been shown to excel in transcellular transport. This attribute has been fully reflected in chitosan-mediated gene transfection systems. The objective of this review is to summarize the recent encouraging advances in unveiling the mechanism of cell entry and application of chitosan and its derivatives as novel non-viral vectors. It is our belief that researchers will uncover more truth about chitosan-based vector and realize the long-term goal of gene transfection--produce the desired clinical effect.

Cationic cholesterol promotes gene transfection using the nuclear localization signal in protamine

PURPOSE

The purpose of this study was to evaluate protamine-mediated gene transfection by liposomes with a novel cationic cholesterol derivative (I) compared to those with DC-Chol or DOTMA (Lipofectin).

METHOD

Plasmid pGL3 DNA was complexed to the cationic liposomes with the derivative (I), DC-Chol, or DOTMA in SFM101(Nissui) at room temperature for 15 min, and thereafter the complex was incubated with target cells (NIH3T3) for 4 h at 37 degrees C. The cells then were washed and cultured for another 40 h in the growth medium at 37 degrees C before luciferase assay.

RESULTS

The transfection efficiency by the liposomes with the derivative (I) was much higher than that by the liposomes with DC-Chol or DOTMA. In addition, its transfection efficiency was enhanced greatly by the addition of protamine. Atomic force microscopy showed clearly how the size of the DNA-liposome complex was changed by protamine. Furthermore, fluorescence microscopic images showed that Cy5-labeled antisense DNAs were transferred quicker into the nucleus of the target cells by the liposomes with the derivative I in the presence of protamine.

CONCLUSION

Although there exist several possible mechanisms, such as improved protection of DNA intracellularly by derivative (I), one possibility is that the DNA-protamine-liposome complex with the derivative (I) promoted gene transfection more significantly into the nucleus of the target cells using the nuclear localization signal of protamine.

Efficient delivery of streptavidin to mammalian cells: clathrin-mediated endocytosis regulated by a synthetic ligand

The efficient delivery of macromolecules to living cells presents a formidable challenge to the development of effective macromolecular therapeutics and cellular probes. We describe herein a novel synthetic ligand termed "Streptaphage" that enables efficient cellular uptake of the bacterial protein streptavidin by promoting noncovalent interactions with cholesterol and sphingolipid-rich lipid raft subdomains of cellular plasma membranes. The Streptaphage ligand comprises an N-alkyl derivative of 3 beta-cholesterylamine linked to the carboxylate of biotin through an 11-atom tether. Molecular recognition between streptavidin and this membrane-bound ligand promotes clathrin-mediated endocytosis, which renders streptavidin partially intracellular within 10 min and completely internalized within 4 h of protein addition. Analysis of protein uptake in Jurkat lymphocytes by epifluorescence microscopy and flow cytometry revealed intracellular fluorescence enhancements of over 300-fold (10 microM ligand) with >99% efficiency and low toxicity. Other mammalian cell lines including THP-1 macrophages, MCF-7 breast cancer cells, and CHO cells were similarly affected. Structurally related ligands bearing a shorter linker or substituting the protonated steroidal amine with an isosteric amide were ineffective molecular transporters. Confocal fluorescence microscopy revealed that Streptaphage-induced uptake of streptavidin functionally mimics the initial cellular penetration steps of Cholera toxin, which undergoes clathrin-mediated endocytosis upon binding to the lipid raft-associated natural product ganglioside GM1. The synthetic ligand described herein represents a designed cell surface receptor capable of targeting streptavidin conjugates into diverse mammalian cells by hijacking the molecular machinery used to organize cellular membranes. This technology has potential applications in DNA delivery, tumor therapy, and stimulation of immune responses.

Activation of receptor tyrosine kinases promotes gene transfection in rat neuronal PC12 cells by cationic liposomes

Cationic liposomes are commonly used to introduce foreign genes to the target cells. However, the methods are not applicable to several types of cells such as neuronal cells. We introduced the luciferase gene to the neuronal pheochromocytoma-12 (PC12) cells by cationic liposomes with a cationic cholesterol derivative (I) or 3- beta - [N - (N',N' - dimethylaminoethane) - carbamoyl]- cholesterol (DC - Chol). Efficiency of gene transfection into undifferentiated naive PC12 cells was extremely higher by the liposomes with the derivative (I) than that by the liposomes with DC - Chol. In addition, when the luciferase gene was transferred into the naive PC12 cells in the presence of nerve growth factor (NGF), the luciferase activity increased much higher than that in the absence of NGF. The transfection efficiency was also promoted by epidermal growth factor in the naive PC12 cells. This high efficiency was maintained in the differentiated PC12 cells obtained by incubating the cells with NGF for 7 days. We found that the transfection efficiency did not depend mainly on the differentiated states of PC12 cells but depended on the activation of receptor tyrosine kinases. It is supposed that the novel liposomes with the derivative (I) will be useful to study the problems in neuron and neuronal tissues for gene transfection.