Cationic lipids destabilize lysosomal membrane in vitro

A Comparison of Cellular Uptake Mechanisms, Delivery Efficacy, and Intracellular Fate between Liposomes and Extracellular Vesicles

A key aspect for successful drug delivery via lipid-based nanoparticles is their internalization in target cells. Two prominent examples of such drug delivery systems are artificial phospholipid-based carriers, such as liposomes, and their biological counterparts, the extracellular vesicles (EVs). Despite a wealth of literature, it remains unclear which mechanisms precisely orchestrate nanoparticle-mediated cargo delivery to recipient cells and the subsequent intracellular fate of therapeutic cargo. In this review, internalization mechanisms involved in the uptake of liposomes and EVs by recipient cells are evaluated, also exploring their intracellular fate after intracellular trafficking. Opportunities are highlighted to tweak these internalization mechanisms and intracellular fates to enhance the therapeutic efficacy of these drug delivery systems. Overall, literature to date shows that both liposomes and EVs are predominantly internalized through classical endocytosis mechanisms, sharing a common fate: accumulation inside lysosomes. Studies tackling the differences between liposomes and EVs, with respect to cellular uptake, intracellular delivery and therapy efficacy, remain scarce, despite its importance for the selection of an appropriate drug delivery system. In addition, further exploration of functionalization strategies of both liposomes and EVs represents an important avenue to pursue in order to control internalization and fate, thereby improving therapeutic efficacy.

LXR inhibitor SR9243-loaded immunoliposomes modulate lipid metabolism and stemness in colorectal cancer cells

Reprogrammed metabolism and active stemness contribute to cancer stem cells' (CSCs) survival and tumorigenesis. LXR signaling regulates the metabolism of different cancers. A selective LXR inhibitor, SR9243 (SR), can target and eradicate non-CSC tumor cells. CD133 is a stem marker in solid tumors-associated CSCs within the active lipogenesis, and anti-CD133 mAb targeting liposomal drug delivery systems expected to increase drug internalization and improve the therapeutic efficacy of poor-in water solubility drugs, e, g., SR. In this study, anti-CD133 mAbs-targeted Immunoliposomes (ILipo) were developed for specific delivery of SR into MACS-enriched CD133 + CSCs and induce their functional effects. Results have shown that ILipo having an average size of 64.79 nm can encapsulate SR in maximum proportion, and cell association studies have shown cationic ILipo and targeting CD133 provide the CSCs binding. Also, FCM analysis of RhoB has demonstrated that the ILipo uptake was higher in CD133 + CSCs than in the non-targeted liposomes. ILipo-SR was significantly more toxic in CD133 + CSCs compared to the free SR and non-targeted ones. More efficient than Lipo-SR, ILipo-SR improved the reduction of clonogenicity, stemness, and lipogenesis in CD133 + CSCs in vitro, boosted ROS generation, and induced apoptosis. Our study revealed the dual targeting of CD133 and LXR appears to be a promising strategy for targeting CD133 + CSCs-presenting dynamic metabolism and self-renewal potentials.

Vesicular trafficking permits evasion of cGAS/STING surveillance during initial human papillomavirus infection

Oncogenic human papillomaviruses (HPVs) replicate in differentiating epithelium, causing 5% of cancers worldwide. Like most other DNA viruses, HPV infection initiates after trafficking viral genome (vDNA) to host cell nuclei. Cells possess innate surveillance pathways to detect microbial components or physiological stresses often associated with microbial infections. One of these pathways, cGAS/STING, induces IRF3-dependent antiviral interferon (IFN) responses upon detection of cytosolic DNA. Virion-associated vDNA can activate cGAS/STING during initial viral entry and uncoating/trafficking, and thus cGAS/STING is an obstacle to many DNA viruses. HPV has a unique vesicular trafficking pathway compared to many other DNA viruses. As the capsid uncoats within acidic endosomal compartments, minor capsid protein L2 protrudes across vesicular membranes to facilitate transport of vDNA to the Golgi. L2/vDNA resides within the Golgi lumen until G2/M, whereupon vesicular L2/vDNA traffics along spindle microtubules, tethering to chromosomes to access daughter cell nuclei. L2/vDNA-containing vesicles likely remain intact until G1, following nuclear envelope reformation. We hypothesize that this unique vesicular trafficking protects HPV from cGAS/STING surveillance. Here, we investigate cGAS/STING responses to HPV infection. DNA transfection resulted in acute cGAS/STING activation and downstream IFN responses. In contrast, HPV infection elicited minimal cGAS/STING and IFN responses. To determine the role of vesicular trafficking in cGAS/STING evasion, we forced premature viral penetration of vesicular membranes with membrane-perturbing cationic lipids. Such treatment renders a non-infectious trafficking-defective mutant HPV infectious, yet susceptible to cGAS/STING detection. Overall, HPV evades cGAS/STING by its unique subcellular trafficking, a property that may contribute to establishment of infection.

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

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

Targeted Interleukin-22 Gene Delivery in the Liver by Polymetformin and Penetratin-Based Hybrid Nanoparticles to Treat Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is now a leading cause of chronic liver disease, and there is currently no available treatment strategy. Interleukin-22 (IL-22) has been recognized as a promising agent for alleviating NAFLD, but the efficacy of IL-22 is far from satisfactory because safe dose of IL-22 elicited limited improvement, whereas higher concentration might induce serious side effects and off-target toxicities. Thus, targeted and sustained expression of IL-22 in the liver is necessary. To meet the challenge, we elaborately developed a novel polymetformin carrier by conjugating biguanide to chitosan, termed chitosan-metformin (CM), which could exert advanced gene delivery efficiency and possess intrinsic therapeutic efficacy from metformin for NAFLD. CM accompanied with penetratin and DSPE-PEG2000 could self-assemble to form stable nanocomplexes with IL-22 gene via electrostatic interaction. This nanoparticle (CDPIA) exerted desirable particle size at ∼100 nm, fine morphology, and efficient cellular internalization. Furthermore, CDPIA also demonstrated a unique superiority in endosomal escape capacity and satisfactory biocompatibility as well as predominant liver accumulation. Most importantly, CDPIA distinctly alleviated hepatic steatosis, restored insulin sensitivity, and improved metabolic syndrome in high-fat-diet-fed mice model. This liver-targeted delivery of IL-22 activated STAT3/Erk1/2 and Nrf2/SOD1 signaling transductions as well as modulated lipid-metabolism-related gene expression. These findings altogether demonstrated that the polymetformin and penetratin-based hybrid nanoparticles could be exploited as a novel safe and efficient strategy for the improvement of NAFLD.

Hyaluronic acid-modified cationic niosomes for ocular gene delivery: improving transfection efficiency in retinal pigment epithelium

OBJECTIVES

Recent years, gene therapy to treat retinal diseases has been paid much attention. The key to successful therapy is utilizing smart delivery system to achieve efficient gene delivery and transfection. In this study, hyaluronic acid (HA) modified cationic niosomes (HA-C-niosomes) have been designed in order to achieve retinal pigment epithelium (RPE) cells targeted gene delivery and efficient gene transfection.

METHODS

Cationic niosomes composed of tween 80/squalene/1, 2-dioleoyl-3-trimethylammonium-propane (DOTAP) were prepared by the ethanol injection method. After that, HA-DOPE was further added into cationic niosomes to form HA-C-niosomes. Cellular uptake and transfection have been investigated in ARPE-19 cells. In vivo pEGFP transfection efficiency was evaluated in rats.

KEY FINDINGS

Twenty percentage HA-C-niosomes were about 180 nm, with -30 mV, and showing spherical shape in TEM. 2 times higher transfection efficiency was found in the group of HA-C-niosomes with 20% HA modification. No toxicity was found in niosome preparations. In vivo evaluation in Sprague Dawley (SD) rats revealed that HA-C-niosomes could specifically target to the retina layer. In the group of pEGFP-loaded HA-C-niosomes, 6-6.5 times higher gene transfection has been achieved, compared with naked pEGFP.

CONCLUSIONS

Hyaluronic acid-C-niosomes might provide a promising gene delivery system for successful retinal gene therapy.

Cystic Fibrosis, Cystic Fibrosis Transmembrane Conductance Regulator and Drugs: Insights from Cellular Trafficking

The eukaryotic cell is organized into membrane-delineated compartments that are characterized by specific cadres of proteins sustaining biochemically distinct cellular processes. The appropriate subcellular localization of proteins is key to proper organelle function and provides a physiological context for cellular processes. Disruption of normal trafficking pathways for proteins is seen in several genetic diseases, where a protein's absence for a specific subcellular compartment leads to organelle disruption, and in the context of an individual, a disruption of normal physiology. Importantly, several drug therapies can also alter protein trafficking, causing unwanted side effects. Thus, a deeper understanding of trafficking pathways needs to be appreciated as novel therapeutic modalities are proposed. Despite the promising efficacy of novel therapeutic agents, the intracellular bioavailability of these compounds has proved to be a potential barrier, leading to failures in treatments for various diseases and disorders. While endocytosis of drug moieties provides an efficient means of getting material into cells, the subsequent release and endosomal escape of materials into the cytosol where they need to act has been a barrier. An understanding of cellular protein/lipid trafficking pathways has opened up strategies for increasing drug bioavailability. Approaches to enhance endosomal exit have greatly increased the cytosolic bioavailability of drugs and will provide a means of investigating previous drugs that may have been shelved due to their low cytosolic concentration.

Translocation of the papillomavirus L2/vDNA complex across the limiting membrane requires the onset of mitosis

The human papillomavirus type 16 (HPV16) L2 protein acts as a chaperone to ensure that the viral genome (vDNA) traffics from endosomes to the trans-Golgi network (TGN) and eventually the nucleus, where HPV replication occurs. En route to the nucleus, the L2/vDNA complex must translocate across limiting intracellular membranes. The details of this critical process remain poorly characterized. We have developed a system based on subcellular compartmentalization of the enzyme BirA and its cognate substrate to detect membrane translocation of L2-BirA from incoming virions. We find that L2 translocation requires transport to the TGN and is strictly dependent on entry into mitosis, coinciding with mitotic entry in synchronized cells. Cell cycle arrest causes retention of L2/vDNA at the TGN; only release and progression past G2/M enables translocation across the limiting membrane and subsequent infection. Microscopy of EdU-labeled vDNA reveals a rapid and dramatic shift in vDNA localization during early mitosis. At late G2/early prophase vDNA egresses from the TGN to a pericentriolar location, accumulating there through prometaphase where it begins to associate with condensed chromosomes. By metaphase and throughout anaphase the vDNA is seen bound to the mitotic chromosomes, ensuring distribution into both daughter nuclei. Mutations in a newly defined chromatin binding region of L2 potently blocked translocation, suggesting that translocation is dependent on chromatin binding during prometaphase. This represents the first time a virus has been shown to functionally couple the penetration of limiting membranes to cellular mitosis, explaining in part the tropism of HPV for mitotic basal keratinocytes.

Cationic liposomes promote antigen cross-presentation in dendritic cells by alkalizing the lysosomal pH and limiting the degradation of antigens

Cationic liposomes (CLs) have been widely examined as vaccine delivery nanoparticles since they can form complexes with biomacromolecules, promote delivery of antigens and adjuvant molecules to antigen-presenting cells (APCs), and mediate cellular uptake of vaccine components. CLs are also known to trigger antigen cross-presentation - the process by which APCs internalize extracellular protein antigens, degrade them into minimal CD8⁺ T-cell epitopes, and present them in the context of major histocompatibility complex-I (MHC-I). However, the precise mechanisms behind CL-mediated induction of cross-presentation and cross-priming of CD8⁺ T-cells remain to be elucidated. In this study, we have developed two distinct CL systems and examined their impact on the lysosomal pH in dendritic cells (DCs), antigen degradation, and presentation of peptide:MHC-I complexes to antigen-specific CD8⁺ T-cells. To achieve this, we have used 3β-[N-(N',N'-dimethylaminoethane)-carbamoyl] cholesterol (DC-Chol) and 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) as the prototypical components of CLs with tertiary amine groups and compared the effect of CLs and anionic liposomes on lysosomal pH, antigen degradation, and cross-presentation by DCs. Our results showed that CLs, but not anionic liposomes, elevated the lysosomal pH in DCs and reduced antigen degradation, thereby promoting cross-presentation and cross-priming of CD8⁺ T-cell responses. These studies shed new light on CL-mediated cross-presentation and suggest that intracellular fate of vaccine components and subsequent immunological responses can be controlled by rational design of nanomaterials.

Cationic DOPC-Detergent Conjugates for Safe and Efficient in Vitro and in Vivo Nucleic Acid Delivery

The ability of a nonviral nucleic acid carrier to deliver its cargo to cells with low associated toxicity is a critical issue for clinical applications of gene therapy. We describe biodegradable cationic DOPC-C12 E4 conjugates in which transfection efficiency is based on a Trojan horse strategy. In situ production of the detergent compound C12 E4 through conjugate hydrolysis within the acidic endosome compartment was expected to promote endosome membrane destabilization and subsequent release of the lipoplexes into cytosol. The transfection efficiency of the conjugates has been assessed in vitro, and associated cytotoxicity was determined. Cellular uptake and intracellular distribution of the lipoplexes have been investigated. The results show that direct conjugation of DOPC with C12 E4 produces a versatile carrier that can deliver both DNA and siRNA to cells in vitro with high efficiency and low cytotoxicity. SAR studies suggest that this compound might represent a reasonable compromise between the membrane activity of the released detergent and susceptibility of the conjugate to degradation enzymes in vitro. Although biodegradability of the conjugates had low impact on carrier efficiency in vitro, it proved critical in vivo. Significant improvement of transgene expression was obtained in the mouse lung tuning biodegradability of the carrier. Importantly, this also allowed reduction of the inflammatory response that invariably characterizes cationic-lipid-mediated gene transfer in animals.

Characterization and comparison of two novel nanosystems associated with siRNA for cellular therapy

To direct stem cell fate, a delicate control of gene expression through small interference RNA (siRNA) is emerging as a new and safe promising strategy. In this way, the expression of proteins hindering neuronal commitment may be transiently inhibited thus driving differentiation. Mesenchymal stem cells (MSC), which secrete tissue repair factors, possess immunomodulatory properties and may differentiate towards the neuronal lineage, are a promising cell source for cell therapy studies in the central nervous system. To better drive their neuronal commitment the repressor Element-1 silencing transcription (REST) factor, may be inhibited by siRNA technology. The design of novel nanoparticles (NP) capable of safely delivering nucleic acids is crucial in order to successfully develop this strategy. In this study we developed and characterized two different siRNA NP. On one hand, sorbitan monooleate (Span(®)80) based NP incorporating the cationic components poly-l-arginine or cationized pullulan, thus allowing the association of siRNA were designed. These NP presented a small size (205 nm) and a negative surface charge (-38 mV). On the other hand, lipid nanocapsules (LNC) associating polymers with lipids and allowing encapsulation of siRNA complexed with lipoplexes were also developed. Their size was of 82 nm with a positive surface charge of +7 mV. Both NP could be frozen with appropriate cryoprotectors. Cytotoxicity and transfection efficiency at different siRNA doses were monitored by evaluating REST expression. An inhibition of around 60% of REST expression was observed with both NP when associating 250 ng/mL of siRNA-REST, as recommended for commercial reagents. Span NP were less toxic for human MSCs than LNCs, but although both NP showed a similar inhibition of REST over time and the induction of neuronal commitment, LNC-siREST induced a higher expression of neuronal markers. Therefore, two different tailored siRNA NP offering great potential for human stem cell differentiation have been developed, encouraging the pursuit of further in vitro and in vivo in studies.

(-)-Oleocanthal rapidly and selectively induces cancer cell death via lysosomal membrane permeabilization

(-)-Oleocanthal (OC), a phenolic compound present in extra-virgin olive oil (EVOO), has been implicated in the health benefits associated with diets rich in EVOO. We investigated the effect of OC on human cancer cell lines in culture and found that OC induced cell death in all cancer cells examined as rapidly as 30 minutes after treatment in the absence of serum. OC treatment of non-transformed cells suppressed their proliferation but did not cause cell death. OC induced both primary necrotic and apoptotic cell death via induction of lysosomal membrane permeabilization (LMP). We provide evidence that OC promotes LMP by inhibiting acid sphingomyelinase (ASM) activity, which destabilizes the interaction between proteins required for lysosomal membrane stability. The data presented here indicate that cancer cells, which tend to have fragile lysosomal membranes compared to non-cancerous cells, are susceptible to cell death induced by lysosomotropic agents. Therefore, targeting lysosomal membrane stability represents a novel approach for the induction of cancer-specific cell death.

Endocytosis and intracellular trafficking as gateways for nanomedicine delivery: opportunities and challenges

More than 40 nanomedicines are already in routine clinical use with a growing number following in preclinical and clinical development. The therapeutic objectives are often enhanced disease-specific targeting (with simultaneously reduced access to sites of toxicity) and, especially in the case of macromolecular biotech drugs, improving access to intracellular pharmacological target receptors. Successful navigation of the endocytic pathways is usually a prerequisite to achieve these goals. Thus a comprehensive understanding of endocytosis and intracellular trafficking pathways in both the target and bystander normal cell type(s) is essential to enable optimal nanomedicine design. It is becoming evident that endocytic pathways can become disregulated in disease and this, together with the potential changes induced during exposure to the nanocarrier itself, has the potential to significantly impact nanomedicine performance in terms of safety and efficacy. Here we overview the endomembrane trafficking pathways, discuss the methods used to determine and quantitate the intracellular fate of nanomedicines, and review the current status of lysosomotropic and endosomotropic delivery. Based on the lessons learned during more than 3 decades of clinical development, the need to use endocytosis-relevant clinical biomarkers to better select those patients most likely to benefit from nanomedicine therapy is also discussed.

Cytotoxicity studies of Dynasan 114 solid lipid nanoparticles (SLN) on RAW 264.7 macrophages—impact of phagocytosis on viability and cytokine production

Solid lipid nanoparticles (SLN) based on Dynasan 114 (D114) were tested using RAW 264.7 cells. The influence of different surfactants on the cytotoxicity of this type of SLN was examined, expressed as 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) viability and the production of cytokines such as interleukin 6 (IL-6), IL-12 and tumour necrosis factor-α (TNF-α). Results were compared with previously obtained data when peritoneal mouse macrophages were used. SLN produced with stabilizers/surfactants such as poloxamer 188, sodium cholate, Lipoid S75, Tween 80, Poloxamine 908 and sodium dodecylsulfate were shown to be nontoxic towards RAW 264.7 cells. Cytokine production was reduced and stimulation, expressed in elevated cytokine levels, could not be found. Using cetylpyridinium chloride (CPC) as stabilizing surfactant, SLN became cytotoxic in a concentration-dependent manner. Not only were the viabilities reduced but also cytokine production. Cytotoxic effects of CPC stabilized SLN could be antagonized using cytochalasin B to block phagocytosis. D114-SLN produced with pharmaceutically accepted surfactants for intravenous injection (poloxamer 188, Lipoid S75, sodium cholate, Tween 80) were very well tolerated by the cells. Even sodium dodecylsulfate-stabilized D114-SLN did not exert toxic effects. Comparison of the RAW 264.7 data with previously obtained data from toxicity studies of D114-SLN towards peritoneal mouse macrophages showed similar results. This offers the possibility of using the RAW 264.7 cell line for cytotoxicity studies of colloidal drug carrier systems, rather than using laboratory animals as source of macrophages for these kinds of studies.

Cationic poly(amidoamine) dendrimer induces lysosomal apoptotic pathway at therapeutically relevant concentrations

Poly(amidoamine) (PAMAM) dendrimers carrying different amounts of surface amino groups were synthesized and tested for their effects on cellular cytotoxicity, lysosomal pH, and mitochondria-dependent apoptosis. In KB cells, the PAMAM dendrimers were taken up into the lysosomal compartment, and they increased the lysosomal pH and cytotoxicity as a function of the number of surface amino groups on the dendrimer. PAMAM dendrimers that were surface-neutralized by acetylation of >80% of the surface amino groups failed to show any cytotoxicity. The positively charged, amine-terminated PAMAM dendrimer induced cellular apoptosis, as demonstrated by mitochondrial membrane potential changes and caspase activity measurements. These results suggest that PAMAM dendrimers are endocytosed into the KB cells through a lysosomal pathway, leading to lysosomal alkalinization and induction of mitochondria-mediated apoptosis.

Intracellular fate of bioresponsive poly(amidoamine)s in vitro and in vivo

Linear poly(amidoamine)s (PAAs) have been designed to exhibit minimal non-specific toxicity, display pH-dependent membrane lysis and deliver genes and toxins in vitro. The aim of this study was to measure PAA cellular uptake using ISA1-OG (and as a reference ISA23-OG) in B16F10 cells in vitro and, by subcellular fractionation, quantitate intracellular trafficking of (125)I-labelled ISA1-tyr in liver cells after intravenous (i.v.) administration to rats. The effect of time after administration (0.5-3h) and ISA1 dose (0.04-100mg/kg) on trafficking, and vesicle permeabilisation (N-acetyl-b-D-glucosaminidase (NAG) release from an isolated vesicular fraction) were also studied. ISA1-OG displayed approximately 60-fold greater B16F10 cell uptake than ISA23-OG. Passage of ISA1 along the liver cell endocytic pathway caused a transient decrease in vesicle buoyant density (also visible by TEM). Increasing ISA1 dose from 10mg/kg to 100mg/kg increased both radioactivity and NAG levels in the cytosolic fraction (5-10 fold) at 1h. Moreover, internalised ISA1 provoked NAG release from an isolated vesicular fraction in a dose-dependent manner. These results provide direct evidence, for the first time, of PAA permeabilisation of endocytic vesicular membranes in vivo, and they have important implications for potential efficacy/toxicity of such polymeric vectors.

Serum-free transfection of CHO cells with chemically defined transfection systems and investigation of their potential for transient and stable transfection

The generation of transgenic cell lines is acquired by facilitating the uptake and integration of DNA. Unfortunately, most of the systems generating stable expression systems are cost and time-consuming and transient expression is optimized to generate milligram amounts of the recombinant protein. Therefore we improved and compared two transfection systems, one based on cationic liposomes consisting of DOTAP/DOPE and the second one on polyethylenimine (PEI). Both systems have been used as chemically defined transfection systems in combination with serum-free cultivated host cell line. At first we had determined the toxicity and ideal ratio of DNA to PEI followed by determination of the optimal transfection conditions in order to achieve maximum transfection efficiency. We then directly compared DOTAP/DOPE and PEI in transient transfection experiments using enhanced green fluorescence protein (EGFP) and a human monoclonal antibody, mAb 2F5, as a model protein. The results which were achieved in case of EGFP were more than 15% transfectants at a viability of 85%. Despite the fact that expression of the mAb was found negligible we used both techniques to generate stable mAb 2F5 expressing cell lines that underwent several cycles of screening and amplification with methotrexate, and resulted in cell lines with similar volumetric production titers. These experiments serve to demonstrate the potential of stable cell lines even in case where the transient systems did not show satisfying results.

DNA Internalized via Caveolae Requires Microtubule-dependent, Rab7-independent Transport to the Late Endocytic Pathway for Delivery to the Nucleus

Using cationic liposomes to mediate gene delivery by transfection has the advantages of improved safety and simplicity of use over viral gene therapy. Understanding the mechanism by which cationic liposome:DNA complexes are internalized and delivered to the nucleus should help identify which transport steps might be manipulated in order to improve transfection efficiencies. We therefore examined the endocytosis and trafficking of two cationic liposomes, DMRIE-C and Lipofectamine LTX, in CHO cells. We found that DMRIE-C-transfected DNA is internalized via caveolae, while LTX-transfected DNA is internalized by clathrin-mediated endocytosis, with both pathways converging at the late endosome or lysosome. Inhibition of microtubule-dependent transport with nocodazole revealed that DMRIE-C:DNA complexes cannot enter the cytosol directly from caveosomes. Lysosomal degradation of transfected DNA has been proposed to be a major reason for poor transfection efficiency. However, in our system dominant negatives of both Rab7 and its effector RILP inhibited late endosome to lysosome transport of DNA complexes and LDL, but did not affect DNA delivery to the nucleus. This suggests that DNA is able to escape from late endosomes without traversing lysosomes and that caveosome to late endosome transport does not require Rab7 function. Lysosomal inhibition with chloroquine likewise had no effect on transfection product titers. These data suggest that DMRIE-C and LTX transfection complexes are endocytosed by separate pathways that converge at the late endosome or lysosome, but that blocking lysosomal traffic does not improve transfection product yields, identifying late endosome/lysosome to nuclear delivery as a step for future study.

Serum-free transfection of CHO-cells with tailor-made unilamellar vesicles

At present, a number of transfection techniques are available to introduce foreign DNA into cells, but still minimal intrusion or interference with normal cell physiology, low toxicity, reproducibility, cost efficiency and successful creation of stable transfectants are highly desirable properties for improved transfection techniques.For all previous transfection experiments done in our labs, using serum-free cultivated host cell lines, an efficiency value of approximately 0.1% for selection of stable cell lines has not been exceeded, consequently we developed and improved a transfection system based on defined liposomes, so-called large unilamellar vesicles, consisting of different lipid compositions to facilitate clone selection and increase the probability for creation of recombinant high-production clones. DNA and DOTAP/DOPE or CHEMS/DOPE interact by electrostatic means forming so-called lipoplexes (Even-Chen and Barenholz 2000) and the lipofection efficiency of those lipoplexes has been determined via confocal microscopy.In addition, the expression of the EGFP was determined by FACS to investigate transient as well as stable transfection and the transfection efficiency of a selection of different commercially available transfection reagents and kits has been compared to our tailor-made liposomes.

Liposomes and liposome-like vesicles for drug and DNA delivery to mitochondria

Mitochondrial research is presently one of the fastest growing disciplines in biomedicine. Since the early 1990s, it has become increasingly evident that mitochondrial dysfunction contributes to a large variety of human disorders, ranging from neurodegenerative and neuromuscular diseases, obesity, and diabetes to ischemia-reperfusion injury and cancer. Most remarkably, mitochondria, the "power house" of the cell, have also become accepted as the "motor of cell death" reflecting their recognized key role during apoptosis. Based on these recent exciting developments in mitochondrial research, increasing pharmacological efforts have been made leading to the emergence of "Mitochondrial Medicine" as a whole new field of biomedical research. The identification of molecular mitochondrial drug targets in combination with the development of methods for selectively delivering biologically active molecules to the site of mitochondria will eventually launch a multitude of new therapies for the treatment of mitochondria-related diseases, which are based either on the selective protection, repair, or eradication of cells. Yet, while tremendous efforts are being undertaken to identify new mitochondrial drugs and drug targets, the development of mitochondria-specific drug carrier systems is lagging behind. To ensure a high efficiency of current and future mitochondrial therapeutics, colloidal vectors, i.e., delivery systems, need to be developed able to selectively transport biologically active molecules to and into mitochondria within living human cells. Here we review ongoing efforts in our laboratory directed toward the development of different phospholipid- and non-phospholipid-based mitochondriotropic drug carrier systems.

Lipoplexes prepared from cationic liposomes and mammalian DNA induce CpG-independent, direct cytotoxic effects in cell cultures and in mice

BACKGROUND

Recent studies demonstrated the cytotoxic activity of bacterial DNA (pDNA) complexed with cationic lipids. This cytotoxicity is related to the ability of pDNA to induce potently the immune system, which is associated with release of inflammatory cytokines. Both activities seem to be related to the nonmethylated CpG sequences present in the pDNA. Here we study the cytotoxic activity of nonbacterial DNA complexed with cationic lipids against various tumor cell lines.

METHODS

Various nucleic acids complexed with cationic liposomes were prepared and their cytotoxic activity was studied in cell cultures and in tumor-bearing mice. Cell uptake of lipoplexes was evaluated, and mechanism of DNA cytotoxic activity was studied.

RESULTS

We found that nonbacterial (vertebrate) genomic DNA when complexed with cationic lipids is highly cytotoxic against C-26 and M-109 tumor cells. Cationic lipids alone were not toxic to these cells. The cytotoxic activity does not result from nonspecific acidification of the intracellular milieu, as substitution of DNA by poly-L-glutamate did not result in cytotoxicity, although the level of uptake of anionic charges per cell was similar to that of the nucleic acids, suggesting that this cytotoxic effect is specific to nucleic acids. By studying the nucleic acid fate using confocal microscopy, we found that cytotoxicity correlated with the release of DNA into the cytoplasm following uptake of lipoplexes. Injection of calf thymus DNA-based lipoplexes to mice with peritoneal C-26 metastases resulted in doubling of median survival time and long-term survival in 20% of the tumor-bearing mice. Judging by low levels of IFN-gamma, TNF-alpha and IL-6 in the treated mice, this effect cannot be ascribed to Th-1 inflammation, but rather to a direct cytotoxic effect on the tumor cells.

CONCLUSIONS

The above data provide a new insight into the mechanisms of lipoplex-mediated antitumor effects in vitro and in vivo and new perspectives in cancer therapy.

Quantitative Comparison of Intracellular Trafficking and Nuclear Transcription between Adenoviral and Lipoplex Systems

To develop nonviral gene vectors that are sufficient for clinical application, it is necessary to understand why and to what extent nonviral vectors are inferior to viral vectors, which in general show a more efficient transfection activity. This study describes a systematic and quantitative comparison of the cellular uptake and subsequent intracellular distribution (e.g., endosome/lysosome, cytosol, and nucleus) of exogenous DNA transfected by viral and nonviral vectors in living cells, using a combination of TaqMan PCR and a recently developed confocal image-assisted three-dimensionally integrated quantification method. As a model, adenovirus (Ad) and Lipofectamine Plus (LFN) were used for comparison since they are highly potent and widely used viral and nonviral vectors, respectively. The findings indicate that the efficiency of cellular uptake for LFN is significantly higher than that for Ad. Once taken up by a cell, Ad exhibited comparable endosomal escape and slightly higher nuclear transfer efficiency compared with LFN. In contrast, LFN requires 3 orders of magnitude more intranuclear gene copies to exhibit a transgene expression comparable to that of the Ad, suggesting that the difference in transfection efficiency principally arises from differences in nuclear transcription efficiency and not from a difference in intracellular trafficking between Ad and LFN.

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.

Cationic submicron emulsions for pulmonary DNA immunization

Pulmonary immunization against inhaled pathogens such as Mycobacterium tuberculosis would induce local and systemic immune responses and protect from entry and dissemination of the pathogen. The aim of this study was to evaluate cationic submicron emulsion as a potential carrier for DNA vaccines to the lung. DNA loaded emulsions were 128-152 nm in size and retained positive zeta potential above +40 mV during 3 months of storage. Loading efficiency was above 99%, DNA was protected from DNase I degradation up to 60 min and was stable in presence of 75% fetal calf serum (FCS). The plasmid DNA was detected in the endo-lysosomal compartment of the human bronchial cell line, Calu-3, 6 h after application. No cytotoxic effect on these cells was observed. Human dendritic cells were matured in presence of DNA loaded emulsion, although to a lesser extent than DNA solution indicating slower release and lower exposure to unmethylated CpG sequences. These results indicate that cationic submicron emulsions are potential DNA vaccine carriers to the lung since they are able to transfect pulmonary epithelial cells, which possibly induce cross priming of antigen presenting cells and directly activate dendritic cells, resulting in stimulation of antigen specific T-cells.

Quantitative Three-Dimensional Analysis of the Intracellular Trafficking of Plasmid DNA Transfected by a Nonviral Gene Delivery System Using Confocal Laser Scanning Microscopy

Since endosomal escape and the nuclear delivery of plasmid DNA (pDNA) constitute major barriers for transgene expression, a quantitative evaluation of intracellular trafficking of pDNA would be highly desirable in terms of optimizing a nonviral gene delivery system. In the present study, a novel strategy is proposed for the quantification of rhodamine-labeled pDNA in endosomes/lysosomes, cytosol, and nucleus. Endosomes/lysosomes and nucleus were stained with LysoSensor DND-189 and Hoechst 33258, respectively, to distinguish them from the cytosol. The pixel areas of the clusters derived from the rhodamine were used as an index for the amount of pDNA. This approach was applied to the analysis of the intracellular trafficking of pDNA transfected by LipofectAMINE PLUS, stearylated octaarginine (STR-R8), and octaarginine (R8). In the case of R8, most of the pDNA was trapped by endosomes/lysosomes. STR-R8 exhibited endosomal escape followed by nuclear translocation in a time-dependent manner. LipofectAMINE PLUS was the most effective in rapidly delivering pDNA to the nucleus as well as the cytosol. These differences in the intracellular trafficking of pDNA correlated well with the transgene expression. Therefore, this method enables the quantitative analysis of the intracellular pharmacokinetics of pDNA and promises to provide useful information for optimizing nonviral gene delivery systems.

Insulin receptor activation and down-regulation by cationic lipid transfection reagents

Background

Transfection agents comprised of cationic lipid preparations are widely used to transfect cell lines in culture with specific recombinant complementary DNA molecules. We have found that cells in culture are often resistant to stimulation with insulin subsequent to treatment with transfection agents such as LipofectAMINE 2000™ and FuGENE-6™. This is seen with a variety of different readouts, including insulin receptor signalling, glucose uptake into muscle cells, phosphorylation of protein kinase B and reporter gene activity in a variety of different cell types

Results

We now show that this is due in part to the fact that cationic lipid agents activate the insulin receptor fully during typical transfection experiments, which is then down-regulated. In attempts to circumvent this problem, we investigated the effects of increasing concentrations of LipofectAMINE 2000™ on insulin receptor phosphorylation in Chinese hamster ovary cells expressing the human insulin receptor. In addition, the efficiency of transfection that is supported by the same concentrations of transfection reagent was studied by using a green fluorescent protein construct. Our data indicate that considerably lower concentrations of LipofectAMINE 2000™ can be used than are recommended by the manufacturers. This is without sacrificing transfection efficiency markedly and avoids the problem of reducing insulin receptor expression in the cells.

Conclusion

Widely-used cationic lipid transfection reagents cause a state of insulin unresponsiveness in cells in culture due to fully activating and subsequently reducing the expression of the receptor in cells. This phenomenon can be avoided by reducing the concentration of reagent used in the transfection process.

DQAsome-mediated delivery of plasmid DNA toward mitochondria in living cells

DQAsomes are mitochondriotropic cationic 'bola-lipid'-based vesicles, which have been developed by us for the transport of drugs and DNA to mitochondria in living cells. This has made direct mitochondrial gene therapy feasible for the very first time. Our strategy for the delivery of DNA into the matrix of mitochondria is based upon the DQAsomal transport of a DNA-signal peptide conjugate to mitochondria, the selective liberation of this conjugate from DQAsomes at the mitochondrial membrane followed by DNA uptake via the mitochondrial protein import machinery. Using membrane-mimicking liposomes and isolated rat liver mitochondria we have shown earlier that DQAsome-DNA complexes (DQAplexes) selectively release pDNA when in contact with mitochondria-like membranes. Employing a newly developed protocol for selectively staining free pDNA in the cytosol of living cells and based on confocal fluorescence microscopic imaging we demonstrate here that DQAplexes appear to be able to escape from endosomes without loosing their pDNA load and transport the pDNA to the site of mitochondria at which at least a portion of the pDNA is released from its DQAsomal carrier. Free pDNA could not be detected anywhere else inside the cytosol of transfected cells demonstrating the target-selectivity of DQAsome-mediated DNA delivery to mitochondria.

Vectors based on reducible polycations facilitate intracellular release of nucleic acids

BACKGROUND

Inefficient intracellular delivery of nucleic acids limits the therapeutic usefulness of synthetic vectors such as poly(L-lysine) (PLL)/DNA polyplexes. This article reports on the characterisation of a new type of synthetic vector based on a linear reducible polycation (RPC) that can be cleaved by the intracellular environment to facilitate release of nucleic acids.

METHODS

RPCs of molecular weight (mwt) 45 and 187 kDa were prepared by oxidative polycondensation of the peptide Cys-Lys(10)-Cys and used to condense nucleic acids. The stability of RPC-based polyplexes to reduction was determined using electrophoresis, dynamic light scattering and fluorescence techniques. Transfection activity was studied in several cancer cell lines (HeLa, LNCaP, PC-3 and B16-F10) using luciferase and green fluorescent protein (GFP) genes as reporter genes in the presence of chloroquine or the cationic lipid (N-(1-(2,3-dioleoyloxy)propyl)-N, N, N-trimethylammonium chloride) (DOTAP). A CMV-driven plasmid expressing the nitroreductase (ntr) gene was used to evaluate the therapeutic efficacy of RPC-based delivery vectors.

RESULTS

A 187-fold higher level of gene expression indicated that intracellular delivery of DNA was more efficient using RPC/DOTAP compared with vectors based on non-reducible PLL. Analysis by flow cytometry also showed enhanced delivery of the GFP gene by RPC/DOTAP in HeLa (51.5 +/- 7.9%), LNCaP (55.2 +/- 6.7%) and PC-3 (66.1 +/- 3.7%) cells. Transfection with the ntr gene and treatment with the prodrug CB1954 resulted in significant cell killing, achieving IC(50) values similar to those previously attained with adenoviral vectors. Delivery of mRNA (20-75% of cells) was also more efficient using RPC/DOTAP than PLL/DOTAP (<5% of cells).

CONCLUSIONS

These results demonstrate that lipid-mediated activation of RPC-based polyplexes is a useful strategy to enhance intracellular delivery of nucleic acids and potentiate therapeutic activity.

Histone H1-mediated transfection: role of calcium in the cellular uptake and intracellular fate of H1-DNA complexes

Previously, we have shown that the transgene expression in the endothelial cell line ECV 304 strongly depends on the presence of low concentrations of Ca2+. However, it remained unclear, which transfection steps are controlled by Ca2+ ions. In the present study, we constructed transfection complexes of digoxigenin-labelled DNA and FITC-labelled histone H1. We monitored the pathway of these complexes with the use of anti-digoxigenin and anti-cathepsin B antibodies and immunofluorescence microscopy. Double labelling of DNA and cathepsin B permitted the localization of transfection complexes into endosomes/lysosomes which suggests an uptake of transfection complexes via endocytosis. It was also found that the uptake of transfection complexes by the cells was independent of the presence or absence of Ca2+ ions in the transfection medium. On the other hand, the presence of Ca2+ in the transfection medium dramatically changed the composition of the transfection complexes inside the endosome/lysosome compartment, which resulted in a strong reduction of H1 binding to DNA. Presence of Ca2+ in the postincubation medium for 24 h resulted in release of the transfection complexes with reduced H1 content from the endosomes/lysosomes into the cytosol. In the absence of Ca2+ the transfection complexes practically disappeared. These results allow us to come to the following conclusions: Ca2+ ions control the reorganization of the transfection complexes in endosomes/lysosomes and their release into the cytosol, which is an important prerequisite for transgene expression, whereas uptake of transfection complexes by the cells is not dependent on Ca2+.

On the mechanism whereby cationic lipids promote intracellular delivery of polynucleic acids

The mechanism whereby cationic lipids destabilize cell membranes to facilitate the intracellular delivery of macromolecules such as plasmid DNA or antisense oligonucleotides is not well understood. Here, we show that cationic lipids can destabilize lipid bilayers by promoting the formation of nonbilayer lipid structures. In particular, we show that mixtures of cationic lipids and anionic phospholipids preferentially adopt the inverted hexagonal (H(II)) phase. Further, the presence of 'helper' lipids such as dioleoylphosphatidylethanolamine or cholesterol, lipids that enhance cationic lipid-mediated transfection of cells also facilitate the formation of the H(II)phase. It is suggested that the ability of cationic lipids to promote nonbilayer structures in combination with anionic phospholipids leads to disruption of the endosomal membrane following uptake of nucleic acid-cationic lipid complexes into cells, thus facilitating cytoplasmic release of the plasmid or oligonucleotide.

Structure and function of lipid-DNA complexes for gene delivery

Owing to the rapid development of in vivo applications for nonviral gene delivery vectors, it is necessary to have a better understanding of how the structure-activity relationships of these lipid-DNA complexes are affected by their environment. Indeed, research in gene therapy first focused on in vitro cell culture studies to determine the mechanisms involved in the delivery of DNA into the cell. New biophysical techniques such as electron microscopy and X-ray diffraction have been developed to discern the structure of the lipid-DNA complex. However, further studies have revealed discrepancies between optimal lipid-DNA formulations for in vitro transfection and for in vivo administration of these vectors. Furthermore, some immune stimulatory effects have been associated with in vivo lipid-DNA administration. This review summarizes the current state of knowledge on in vitro and in vivo lipid-DNA complex transfections. New prospects of vectors for in vivo gene transfer are also discussed.

Kinetic analysis of the initial steps involved in lipoplex--cell interactions: effect of various factors that influence transfection activity

We investigated the mode of interaction of lipoplexes (DOTAP:DOPE/DNA) with HeLa cells, focusing on the analysis of the initial steps involved in the process of gene delivery. We evaluated the effect of different factors, namely the stoichiometry of cationic lipids and DNA, the presence of serum in the cell culture medium, and the incorporation of the ligand transferrin into the lipoplexes, on the extent of binding, association and fusion (lipid mixing) of the lipoplexes with the cells. Parallel experiments were performed upon cell treatment with inhibitors of endocytosis. Our results indicate that a decrease of the net charge of the complexes (upon addition of DNA) generally leads to a decrease in the extent of binding, cell association and fusion, except for the neutral complexes. Association of transferrin to the lipoplexes resulted in a significant enhancement of the interaction processes referred to above, which correlates well with the promotion of transfection observed under the same conditions. Besides triggering internalization of the complexes, transferrin was also shown to mediate fusion with the endosomal membrane. The extent of fusion of this type of complexes was reduced upon their incubation with cells in the presence of serum, suggesting that serum components limit the transferrin fusogenic properties. Results were analyzed by using a theoretical model which allowed to estimate the kinetic parameters involved in lipoplex--cell interactions. The deduced fusion and endocytosis rate constants are discussed and compared with those obtained for other biological systems. From the kinetic studies we found a twofold enhancement of the fusion rate constant (f) for the ternary lipoplexes. We also concluded that HeLa cells yield a relatively low rate of endocytosis. Overall, our results estimate the relative contribution of fusion of lipoplexes with the plasma membrane, endocytosis and fusion with the endosomal membrane to their interactions with cells, this information being of crucial importance for the development of gene therapy strategies.

The thermotropic phase behavior of cationic lipids: calorimetric, infrared spectroscopic and X-ray diffraction studies of lipid bilayer membranes composed of 1,2-di-O-myristoyl-3-N,N,N-trimethylaminopropane (DM-TAP)

The thermotropic phase behavior of lipid bilayer model membranes composed of the cationic lipid 1,2-di-O-myristoyl-3-N,N,N-trimethylaminopropane (DM-TAP) was examined by differential scanning calorimetry, infrared spectroscopy and X-ray diffraction. Aqueous dispersions of this lipid exhibit a highly energetic endothermic transition at 38.4 degrees C upon heating and two exothermic transitions between 20 and 30 degrees C upon cooling. These transitions are accompanied by enthalpy changes that are considerably greater than normally observed with typical gel/liquid--crystalline phase transitions and have been assigned to interconversions between lamellar crystalline and lamellar liquid--crystalline forms of this lipid. Both infrared spectroscopy and X-ray diffraction indicate that the lamellar crystalline phase is a highly ordered, substantially dehydrated structure in which the hydrocarbon chains are essentially immobilized in a distorted orthorhombic subcell. Upon heating to temperatures near 38.4 degrees C, this structure converts to a liquid-crystalline phase in which there is excessive swelling of the aqueous interlamellar spaces owing to charge repulsion between, and undulations of, the positively charged lipid surfaces. The polar/apolar interfaces of liquid--crystalline DM-TAP bilayers are not as well hydrated as those formed by other classes of phospho- and glycolipids. Such differences are attributed to the relatively small size of the polar headgroup and its limited capacity for interaction with moieties in the bilayer polar/apolar interface.

Cutaneous vaccination: the skin as an immunologically active tissue and the challenge of antigen delivery

Vaccination is one of the major achievements of modern medicine. As a result of vaccination, diseases such as polio and measles have been controlled and small pox has been eradicated. However, despite these successes there are still many microbial diseases that cause tremendous suffering because there is no vaccine or the vaccines available are inadequate. In addition, even if vaccines were available for all infectious diseases there is no guarantee that people would use them routinely. One of the major impediments to ensuring vaccine efficacy and compliance is that of delivery. Presently most vaccines are given by intramuscular administration. Unfortunately this is often traumatic, especially in infants. Thus, if it was possible to replace intramuscular immunization by mucosal (oral/intranasal) or transdermal delivery it may be possible to both enhance mucosal immunity as well as improve overall compliance rates. The transdermal route has been used by the pharmaceutical industry for the delivery of various low molecular weight drugs. Some of the approaches used for smaller compounds may also have potential for delivery of either protein or polynucleotide vaccines. However, there is a greater challenge to delivering large molecular weight molecules through the skin due to size, charge and other physicochemical properties. This review will describe the recent advances that have been made in dermal and topical delivery as related to vaccines.

Liver-directed gene therapy: promises, problems and prospects at the turn of the century

Although liver-directed gene therapy arrived later than gene therapy directed at bone marrow cells, intrinsic advantages of the liver as a target organ make it likely that gene therapy for liver diseases will be among the first therapeutically relevant applications of this treatment modality at the onset of the 21st century. Vectorology for gene transfer to the liver is advancing rapidly, and it is safe to predict that gene therapy vehicles that will be in clinical use a decade from now, have not yet been developed. None of the currently available modes of gene transfer to the liver is optimal for all types of applications. Nonetheless, the concerted effort of many investigators has provided a wide choice of non-viral and viral vectors for gene transfer to the liver for use in specific situations. Original strategies for liver-directed gene therapy included substitution of missing gene products, overexpression of intrinsic or extrinsic genes and inhibition of expression of specific genes. To the list is now added the possibility of site-specific correction or generation of mutations within specific genes in somatic cells of living adult animals. Thus, despite some initial faux pas, liver-directed gene therapy is poised to make an important impact on health care in the year 2000 and beyond.

Endosomes, lysosomes: their implication in gene transfer

Plasmid DNA, naked or bound to a non-viral vector, is taken up by endocytosis. As a result, it has to travel through the intracellular endocytic pathway involving endosomes and lysosomes. However, some DNA molecules must escape these organelles to reach the nucleus where transcription takes place. In this paper, we consider different factors that could affect the trafficking of plasmid DNA and influence transfection efficiency.

Biophysical and lipofection studies of DOTAP analogs

In order to investigate the relationship between lipid structure and liposome-mediated gene transfer, we have studied biophysical parameters and transfection properties of monocationic DOTAP analogs, systematically modified in their non-polar hydrocarbon chains. Stability, size and (by means of anisotropy profiles) membrane fluidity of liposomes and lipoplexes were determined, and lipofection efficiency was tested in a luciferase reporter gene assay. DOTAP analogs were used as single components or combined with a helper lipid, either DOPE or cholesterol. Stability of liposomes was a precondition for formation of temporarily stable lipoplexes. Addition of DOPE or cholesterol improved liposome and lipoplex stability. Transfection efficiencies of lipoplexes based on pure DOTAP analogs could be correlated with stability data and membrane fluidity at transfection temperature. Inclusion of DOPE led to rather uniform transfection and anisotropy profiles, corresponding to lipoplex stability. Cholesterol-containing lipoplexes were generally stable, showing high transfection efficiency at low relative fluidity. Our results demonstrate that the efficiency of gene transfer mediated by monocationic lipids is greatly influenced by lipoplex biophysics due to lipid composition. The measurement of fluorescence anisotropy is an appropriate method to characterize membrane fluidity within a defined system of liposomes or lipoplexes and may be helpful to elucidate structure-activity relationships.

Calcium enhances the transfection potency of plasmid DNA-cationic liposome complexes

It is shown that calcium increases the in vitro transfection potency of plasmid DNA-cationic liposome complexes from 3- to 20-fold. The effect is Ca(2+) specific as other cations, such as Mg(2+) and Na(+), do not give rise to enhanced transfection and the effect can be inhibited by the presence of EGTA. It is shown that Ca(2+) increases cellular uptake of the DNA-lipid complexes, indicating that increased transfection potency arises from increased intracellular delivery of both cationic lipid and plasmid DNA in the presence of Ca(2+). In particular, it is shown that the levels of intact intracellular plasmid DNA are significantly enhanced when Ca(2+) is present. The generality of the Ca(2+) effect for enhancing complex-mediated transfection is demonstrated for a number of different cell lines and different cationic lipid formulations. It is concluded that addition of Ca(2+) represents a simple and useful protocol for enhancing in vitro transfection properties of plasmid DNA-cationic lipid complexes.

Lipid-based systems for the intracellular delivery of genetic drugs

Currently available delivery systems for genetic drugs have limited utility for systemic applications. Cationic liposome/plasmid DNA or oligonucleotide complexes are rapidly cleared from circulation, and the highest levels of activity are observed in 'first pass' organs, such as the lungs, spleen and liver. Engineered viruses can generate an immune response, which compromises transfection resulting from subsequent injections and lack target specificity. A carrier, which can accumulate at sites of diseases such as infections, inflammations and tumours, has to be a small, neutral and highly serum-stable particle, which is not readily recognized by the fixed and free macrophages of the reticuloendothelial system (RES). This review summarizes lipid-based technologies for the delivery of nucleic acid-based drugs and introduces a new class of carrier systems, which solve, at least in part, the conflicting demands of circulation longevity and intracellular delivery. Plasmid DNA and oligonucleotides are entrapped into lipid particles that contain small amounts of a positively charged lipid and are stabilized by the presence of a polythylene glycol (PEG) coating. These carriers protect nucleic acid-based drugs from degradation by nucleases, are on average 70 nm in diameter, achieve long circulation lifetimes and are capable of transfecting cells.

Cationic lipids (lipofectamine) and disturbance of cellular cholesterol and sphingomyelin distribution modulates gamma-secretase activity within amyloid precursor protein in vitro

To study beta-amyloid protein generation we expressed different amyloid precursor protein (APP) isoforms in the human neuroblastoma cell line SY5Y (for details see (1)). Treatment with lipofectamine, an cationic lipid for eucaryotic cell transfection, inhibits gamma-secretase activity and stimulates the physiological APP cleavage by alpha-secretase activity. Beside the MDL inhibitor (2), this is the second agent that shows modulation of gamma-secretase activity in vitro. Further, we show that disturbance of cellular cholesterol and sphingomyelin distribution in transfected SY5Y cells results in an overproduction of beta-amyloid protein. This provides experimental evidence that membrane instability influenced the proteolytic activity of gamma-secretase within the APP molecule.