Detailed analysis of structures and formulations of cationic lipids for efficient gene transfer to the lung

Folate-equipped nanolipoplexes mediated efficient gene transfer into human epithelial cells

Since recombinant viral vectors have been associated with serious side effects, such as immunogenicity and oncogenicity, synthetic delivery systems represent a realistic alternative for achieving efficacy in gene therapy. A major challenge for non-viral nanocarriers is the optimization of transgene expression in the targeted cells. This goal can be achieved by fine-tuning the chemical carriers and the adding specific motifs to promote cellular penetration. Our study focuses on the development of novel folate-based complexes that contain varying quantities of folate motifs. After controlling for their physical properties, neutral folate-modified lipid formulations were compared in vitro to lipoplexes leading to comparable expression levels. In addition, no cytotoxicity was detected, unlike what was observed in the cationic controls. Mechanistically, the delivery of the transgene appeared to be, in part, due to endocytosis mediated by folate receptor targeting. This mechanism was further validated by the observation that adding free folate into the medium decreased luciferase expression by 50%. In vivo transfection with the folate-modified MM18 lipid, containing the highest amount of FA-PEG(570)-diether co-lipid (w:w; 90:10), at a neutral charge ratio, gave luciferase transgene expression. These studies indicate that modification of lipids with folate residues could enhance non-toxic, cell-specific gene delivery.

Peptoids and polyamines going sweet: Modular synthesis of glycosylated peptoids and polyamines using click chemistry

Sugar moieties are present in a wide range of bioactive molecules. Thus, having versatile and fast methods for the decoration of biomimetic molecules with sugars is of fundamental importance. The glycosylation of peptoids and polyamines as examples of such biomimetic molecules is reported here. The method uses Cu-catalyzed azide alkyne cycloaddition to promote the reaction of azidosugars with either polyamines or peptoids. In addition, functionalized nucleic acids were attached to polyamines via the same route. Based on a modular solid-phase synthesis of peralkynylated peptoids with up to six alkyne groups, the latter were modified with azidosugar building blocks by using copper-catalyzed azide alkyne cycloadditions. In addition, the up-scaling of some particular azide-modified sugars is described.

Assessment of the nuclear pore dilating agent trans-cyclohexane-1,2-diol in differentiated airway epithelium

BACKGROUND

The nuclear membrane of differentiated airway epithelial cells is a significant barrier for nonviral vectors. Trans-cyclohexane-1,2-diol (TCHD) is an amphipathic alcohol that has been shown to collapse nuclear pore cores and allow the uptake of macromolecules that would otherwise be too large for nuclear entry. Previous studies have shown that TCHD can increase lipid-mediated transfection in vitro.

METHODS

We aimed to reproduce these in vitro studies using the cationic lipid GL67A, which we are currently assessing in cystic fibrosis trials and, more importantly, we assessed the effects of TCHD on transfection efficiency in differentiated airway epithelium ex vivo and in mouse lung in vivo using three different drug delivery protocols (nebulisation and bolus administration of TCHD to the mouse lung, as well as perfusion of TCHD to the nasal epithelium, which prolongs contact time between the airway epithelium and drug).

RESULTS

TCHD (0.5-2%) dose-dependently increased Lipofectamine 2000 and GL67A-mediated transfection of 293T cells by up to 2 logs. Encouragingly, exposure to 8% TCHD (but not 0.5% or 2.0%) increased gene expression in fully differentiated human air liquid interface cultures by approximately 20-fold, although this was accompanied by significant cell damage. However, none of the TCHD treated mice in any of the three protocols had higher gene expression compared to no TCHD controls.

CONCLUSIONS

Although TCHD significantly increases gene transfer in cell lines and differentiated airway epithelium ex vivo, this effect is lost in vivo and further highlights that promising in vitro findings often cannot be translated into in vivo applications.

We still have a long way to go to effectively deliver genes!

Gene therapy is emerging as a revolutionary alternative to conventional therapeutic approaches. However, its clinical application is still hampered by the lack of safe and effective gene delivery techniques. Among the plethora of diverse approaches used to ferry nucleic acids into target cells, non-viral vectors represent promising and safer alternatives to viruses and physical techniques. Both cationic lipids and polymers spontaneously wrap and shrink the genetic material in complexes named lipoplexes and polyplexes, respectively, thereby protecting it and shielding its negative charges. The development of non-viral vectors commenced more than two decades ago. Since then, some major classes of interesting molecules have been identified and modified to optimize their properties. However, the way towards the final goal of gene delivery, i.e. protein expression or gene silencing, is filled with obstacles and current non-viral carriers still have concerns about their overall efficiency. We strongly believe that the future of non-viral gene delivery relies on the development of multifunctional vectors specifically tailored with diverse functionalities that act more like viruses. Although these vectors are still a long way from clinical practice they are the ideal platform to effectively shuttle the genetic material to target cells in a safe and controlled way. In this review, after briefly introducing the basis of gene delivery and therapeutic applications we discuss the main polymeric and lipidic vectors utilized for gene delivery, focusing on the strategies adopted to overcome the major weaknesses inherent to their still limited activity, on the way towards ideal multifunctional vectors.

Phoenix rising: gene therapy makes a comeback

Despite the first application of gene therapy in 1990, gene therapy has until recently failed to meet the huge expectations set forth by researchers, clinicians, and patients, thus dampening enthusiasm for an imminent cure for many life-threatening genetic diseases. Nonetheless, in recent years we have witnessed a strong comeback for gene therapy, with clinical successes in young and adult subjects suffering from inherited forms of blindness or from X-linked severe combined immunodeficiency disease. In this review, various gene therapy vectors progressing into clinical development and pivotal advances in gene therapy trials will be discussed.

Polymers for siRNA delivery: inspired by viruses to be targeted, dynamic, and precise

Synthetic small interfering RNA (siRNA) presents an exciting novel medical opportunity. Although researchers agree that siRNA could have a great therapeutic impact, the required extracellular and intracellular delivery of these molecules into the disease-associated target cells presents the primary roadblock for the broader translation of these molecules into medicines. Thus, the design of adequate delivery technologies has utmost importance. Viruses are natural masterpieces of nucleic acid delivery and present chemists and drug delivery experts with a template for the design of artificial carriers for synthetic nucleic acids such as siRNA. They have been developed into gene vectors and have provided convincing successes in gene therapy. Optimized by biological evolution, viruses are programmed to be dynamic and bioresponsive as they enter living cells, and they carry out their functions in a precisely defined sequence. However, because they are synthesized within living cells and with naturally available nucleotides and amino acids, the chemistry of viruses is limited. With the use of diverse synthetic molecules and macromolecules, chemists can provide delivery solutions beyond the scope of the natural evolution of viruses. This Account describes the design and synthesis of "synthetic siRNA viruses." These structures contain elements that mimic the delivery functions of viral particles and surface domains that shield against undesired biological interactions and enable specific host cell receptor binding through the presentation of multiple targeting ligands. For example, cationic polymers can reversibly package one or more siRNA molecules into nanoparticle cores to protect them against a degradative bioenvironment. After internalization by receptor-mediated endocytosis into the acidifying endosomes of cells, synthetic siRNA can escape from these vesicles through the activation of membrane-disruption domains as viruses do and reach the cytoplasm, the location of RNA interference. This multistep task presents an attractive challenge for chemists. Similar to the design of prodrugs, the functional domains of these systems have to be activated in a dynamic mode, triggered by conformational changes or bond cleavages in the relevant microenvironment such as the acidic endosome or disulfide-reducing cytoplasm. These chemical analogues of viral domains are often synthetically simpler and more easily accessible molecules than viral proteins. Their precise assembly into multifunctional macromolecular and supramolecular structures is facilitated by improved analytical techniques, precise orthogonal conjugation chemistries, and sequence-defined polymer syntheses. The chemical evolution of microdomains using chemical libraries and macromolecular and supramolecular evolution could provide key strategies for optimizing siRNA carriers to selected medical indications.

Lentivirus vector driven by polybiquitin C promoter without woodchuck posttranscriptional regulatory element and central polypurine tract generates low level and short-lived reporter gene expression

Lentivirus (LV) encoding woodchuck posttranscriptional regulatory element (WPRE) and central polypurine tract (cPPT) driven by CMV promoter have been proven to act synergistically to increase both transduction efficiency and gene expression. However, the inclusion of WPRE and cPPT in a lentiviral construct may pose safety risks when administered to human. A simple lentiviral construct driven by an alternative promoter with proven extended duration of gene expression without the two regulatory elements would be free from the risks. In a non-viral gene delivery context, gene expression driven by human polybiquitin C (UbC) promoter resulted in higher and more persistent expression in mouse as compared to cytomegalovirus (CMV) promoter. In this study, we measured the efficiency and persistency of green fluorescent protein (GFP) reporter gene expression in cells transduced with LV driven by UbC (LV/UbC/GFP) devoid of the WPRE and cPPT in comparison to the established LV construct encoding WPRE and cPPT, driven by CMV promoter (LV/CMV/GFP). However, we found that LV/UbC/GFP was inferior to LV/CMV/GFP in many aspects: (i) the titer of virus produced; (ii) the levels of reporter gene expression when MOI value was standardized; and (iii) the transduction efficiency in different cell types. The duration of reporter gene expression in selected cell lines was also determined. While the GFP expression in cells transduced with LV/CMV/GFP persisted throughout the experimental period of 14 days, expression in cells transduced with LV/UbC/GFP declined by day 2 post-transduction. In summary, the LV driven by the UbC promoter without the WPRE and cPPT does not exhibit enhanced or durable transgene expression.

Gene and cell therapy for cystic fibrosis: from bench to bedside

Clinical trials in cystic fibrosis (CF) patients established proof-of-principle for transfer of the wild-type cystic fibrosis transmembrane conductance regulator (CFTR) gene to airway epithelial cells. However, the limited efficacy of gene transfer vectors as well as extra- and intracellular barriers have prevented the development of a gene therapy-based treatment for CF. Here, we review the use of new viral and nonviral gene therapy vectors, as well as human artificial chromosomes, to overcome barriers to successful CFTR expression. Pre-clinical studies will surely benefit from novel animal models, such as CF pigs and ferrets. Prenatal gene therapy is a potential alternative to gene transfer to fully developed lungs. However, unresolved issues, including the possibility of adverse effects on pre- and postnatal development, the risk of initiating oncogenic or degenerative processes and germ line transmission require further investigation. Finally, we discuss the therapeutic potential of stem cells for CF lung disease.

Selective modification of HK peptides enhances siRNA silencing of tumor targets in vivo

Our research has focused on systemic delivery of small interference RNA (siRNA) by branched peptides composed of histidine and lysine. After studying several histidine-lysine (HK) peptides, one four-branched peptide, H3K(+H)4b, with a predominant repeating pattern of -HHHK-, was found to be an effective carrier of siRNA. Although the unmodified H3K(+H)4b carrier of siRNA targeting an oncogene was previously shown to have promise in a tumor-bearing mouse model, we sought to develop a more effective HK carrier of siRNA in this study. Our primary goal was to determine whether different ligand (cyclic RGD)-pegylation patterns on the H3K(+H)4b peptide affect siRNA delivery in vitro and in vivo. We compared the unmodified H3K(+H)4b with two modified H3K(+H)4b peptides for their ability to deliver siRNA in a tumor-bearing mouse model; one modified HK peptide, (RGD-PEG)(4)-H3K(+H)4b, had four cyclic RGD-polyethylene glycol (cRGD-PEG) conjugates per molecule, whereas the other peptide, (RGD-PEG)-H3K(+H)4b, had one cRGD-PEG per molecule. Although the modified HK peptides by themselves did not form stable nanoplexes with siRNA, combination of a highly charged unmodified HK peptide, H2K4b, with either of the modified HK peptides did form stable siRNA nanoparticles. For in vitro experiments with MDA-MB-435 cells that expressed luciferase (Luc), the H3K(+H)4b siRNA nanoplexes targeting Luc decreased its activity by 90% compared with negligible downregulation by the modified H3K(+H)4b nanoplexes (P<0.01). In contrast, the two modified H3K(+H)4b siRNA nanoplexes administered intravenously were more effective than the H3K(+H)4b nanoplexes in silencing Luc in a tumor xenograft model. The Luc activity in tumor lysates of mice administered H3K(+H)4b, (RGD-PEG)-H3K(+H)4b and (RGD-PEG)(4)-H3K(+H)4b nanoplexes decreased by 18, 35 and 75%, respectively. Thus, the siRNA nanoplex incorporating the highly modified peptide, (RGD-PEG)(4)-H3K(+H)4b, was the most effective at silencing its target in vivo (P<0.01). These studies demonstrate that selectively modified HK polymers are promising candidates for targeting oncogenes with siRNA.

Adenovirus vector-mediated assay system for hepatitis C virus replication

The efficient delivery of the hepatitis C virus (HCV) RNA subgenomic replicon into cells is useful for basic and pharmaceutical studies. The adenovirus (Ad) vector is a convenient and efficient tool for the transduction of foreign genes into cells in vitro and in vivo. However, an Ad vector expressing the HCV replicon has never been developed. In the present study, we developed Ad vector containing an RNA polymerase (pol) I-dependent expression cassette and a tetracycline-controllable RNA pol I-dependent expression system. We prepared a hybrid promoter from the tetracycline-responsive element and the RNA pol I promoter. Ad vector particles coding the hybrid promoter-driven HCV replicon could be amplified, and interferon, an inhibitor of HCV replication, reduced HCV replication in cells transduced with the Ad vector coding HCV replicon. This is the first report of the development of an Ad vector-mediated HCV replicon system.

Secreted Gaussia luciferase as a sensitive reporter gene for in vivo and ex vivo studies of airway gene transfer

The cationic lipid GL67A is one of the more efficient non-viral gene transfer agents (GTAs) for the lungs, and is currently being evaluated in an extensive clinical trial programme for cystic fibrosis gene therapy. Despite conferring significant expression of vector-specific mRNA following transfection of differentiated human airway cells cultured on air liquid interfaces (ALI) cultures and nebulisation into sheep lung in vivo we were unable to detect robust levels of the standard reporter gene Firefly luciferase (FLuc). Recently a novel secreted luciferase isolated from Gaussia princeps (GLuc) has been described. Here, we show that (1) GLuc is a more sensitive reporter gene and offers significant advantages over the traditionally used FLuc in pre-clinical models for lung gene transfer that are difficult to transfect, (2) GL67A-mediated gene transfection leads to significant production of recombinant protein in these models, (3) promoter activity in ALI cultures mimics published in vivo data and these cultures may, therefore, be suitable to characterise promoter activity in a human ex vivo airway model and (4) detection of GLuc in large animal broncho-alveolar lavage fluid and serum facilitates assessment of duration of gene expression after gene transfer to the lungs. In summary, we have shown here that GLuc is a sensitive reporter gene and is particularly useful for monitoring gene transfer in difficult to transfect models of the airway and lung. This has allowed us to validate that GL67A, which is currently in clinical use, can generate significant amounts of recombinant protein in fully differentiated human air liquid interface cultures and the ovine lung in vivo.

Pulmonary Delivery of Plasmid DNA for Disease Prevention and Therapy

For gene delivery to the lung, the challenges are high, but successful treatment of cystic fibrosis or achieving immunity against the global infectious diseases provide an allure that cannot be ignored. This chapter summarizes and reviews nonviral DNA delivery for both gene therapy and DNA vaccination in the lung. Aerosolization of DNA is evaluated, and the stability during this process is discussed. Carriers for DNA are then discussed including lipoplexes and polyplexes, with a particular focus on systems that achieve good transfection and minimize potential toxicity. Then principles of DNA vaccination are introduced, and the advantages of pulmonary vaccination are discussed. Finally, the transport of plasmid DNA vaccines into the lungs is reviewed.

Gene transfer into the lung by nanoparticle dextran-spermine/plasmid DNA complexes

A novel cationic polymer, dextran-spermine (D-SPM), has been found to mediate gene expression in a wide variety of cell lines and in vivo through systemic delivery. Here, we extended the observations by determining the optimal conditions for gene expression of D-SPM/plasmid DNA (D-SPM/pDNA) in cell lines and in the lungs of BALB/c mice via instillation delivery. In vitro studies showed that D-SPM could partially protect pDNA from degradation by nuclease and exhibited optimal gene transfer efficiency at D-SPM to pDNA weight-mixing ratio of 12. In the lungs of mice, the levels of gene expression generated by D-SPM/pDNA are highly dependent on the weight-mixing ratio of D-SPM to pDNA, amount of pDNA in the complex, and the assay time postdelivery. Readministration of the complex at day 1 following the first dosing showed no significant effect on the retention and duration of gene expression. The study also showed that there was a clear trend of increasing size of the complexes as the amount of pDNA was increased, where the sizes of the D-SPM/pDNA complexes were within the nanometer range.

Acid-labile liposome/pDNA complexes

One of the bottlenecks to achieve gene or drug delivery to cells is the spatio-temporal release of the cargo to effect the correct task wherever and whenever it is supposed to. The aim of this chapter is to describe the synthesis and properties of lipids, which can form liposome complexes with DNA and to fall apart in slight acidic condition such as those encountered in the late endosome, thus destabilizing the liposome membrane and releasing their content.

Low-frequency ultrasound increases non-viral gene transfer to the mouse lung

The aim of the study was to assess if low-frequency ultrasound (US), in the range of 30-35 kHz, increases non-viral gene transfer to the mouse lung. US is greatly attenuated in the lung due to large energy losses at the air/tissue interfaces. The advantages of low-frequency US, compared with high-frequency US are: (i) increased cavitation (responsible for the formation of transient pores in the cell membrane) and (ii) reduced energy losses during lung penetration. Cationic lipid GL67/plasmid DNA (pDNA), polyethylenimine (PEI)/pDNA and naked pDNA were delivered via intranasal instillation and the animals were then exposed to US (sonoporation) at 0.07 or 0.1 MPa for 10 min. Under these conditions, US did not enhance GL67 or PEI-mediated transfection. It did, however, increase naked pDNA gene transfer by approximately 4 folds. Importantly, this was achieved in the absence of microbubbles, which are crucial for the commonly used high-frequency (1 MHz) sonoporation but may not be able to withstand nebulization in a clinically relevant setup. Lung hemorrhage was also assessed and shown to increase with US pressure in a dose-dependent manner. We have thus, established that low-frequency US can enhance lung gene transfer with naked pDNA and this enhancement is more effective than the previously reported 1 MHz US.

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

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

Strategies for the preparation of synthetic transfection vectors

In the late 1980s independent work by Felgner and Behr pioneered the use of cationic materials to complex and deliver nucleic acids into eukaryotic cells. Since this time, a vast number of synthetic transfection vectors, which are typically divided into two main "transfectors", have been developed namely: (1) cationic lipids and (2) polycationic polymers. In this chapter the main synthetic approaches used for the synthesis of these compounds will be reviewed with particular attention paid to: cationic lipids and dendrimers. This review is aimed primarily at the younger audience of doctoral students and non-specialist readers.

The use of carboxymethylcellulose gel to increase non-viral gene transfer in mouse airways

We have assessed whether viscoelastic gels known to inhibit mucociliary clearance can increase lipid-mediated gene transfer. Methylcellulose or carboxymethylcellulose (0.25-1.5%) was mixed with complexes of the cationic lipid GL67A and plasmids encoding luciferase and perfused onto the nasal epithelium of mice. Survival after perfusion with 1% CMC or 1% MC was 90 and 100%, respectively. In contrast 1.5% CMC was uniformly lethal likely due to the viscous solution blocking the airways. Perfusion with 0.5% CMC containing lipid/DNA complexes reproducibly increased gene expression by approximately 3-fold (n=16, p<0.05). Given this benefit, likely related to increased duration of contact, we also assessed the effect of prolonging contact time of the liposome/DNA complexes by delivering our standard 80 microg DNA dose over either approximately 22 or 60 min of perfusion. This independently increased gene transfer by 6-fold (n=8, p<0.05) and could be further enhanced by the addition of 0.5% CMC, leading to an overall 25-fold enhancement (n=8, p<0.001) in gene expression. As a result of these interventions CFTR transgene mRNA transgene levels were increased several logs above background. Interestingly, this did not lead to correction of the ion transport defects in the nasal epithelium of cystic fibrosis mice nor for immunohistochemical quantification of CFTR expression. To assess if 0.5% CMC also increased gene transfer in the mouse lung, we used whole body nebulisation chambers. CMC was nebulised for 1h immediately before, or simultaneously with GL67A/pCIKLux. The former did not increase gene transfer, whereas co-administration significantly increased gene transfer by 4-fold (p<0.0001, n=18). This study suggests that contact time of non-viral gene transfer agents is a key factor for gene delivery, and suggests two methods which may be translatable for use in man.

Non-viral vectors in cystic fibrosis gene therapy: recent developments and future prospects

Gene therapy has been proposed for a wide range of human diseases but few have received the level of attention over such a prolonged period as cystic fibrosis (CF) with over 20 clinical studies undertaken. Following a 10-year interval, clinical trials of an aerosolisable non-viral gene transfer agent have recently been initiated by researchers in the United Kingdom. Here we review the rationale and requirements for effective gene therapy for CF lung disease. The previous non-viral gene therapy trials are discussed and the prospects for the current leading non-viral formulations for CF gene therapy are considered. Factors affecting the selection and design of the plasmid DNA molecule, likely to be of central importance to clinical efficacy, are reviewed and we describe the potential merits of the formulation that has been selected for the forthcoming UK trials.

Solid phase synthesis of novel asymmetric hydrophilic head cholesterol-based cationic lipids with potential DNA delivery

Twenty-four asymmetric divalent head group cholesterol-based cationic lipids were designed and synthesized by parallel solid phase chemistry. These asymmetric head groups composed of amino functionality together with trimethylamino, di(2-hydroxyethyl)amino or guanidinyl groups. Spacers between cationic heads and linker were both equal and unequal in length. These lipids were subjected to evaluation for DNA binding affinities by gel retardation assay and were screened for their transfection efficiency on HEK293 cells. Cationic lipids with equal chain length exhibited high transfection efficiency when polar part contained asymmetric polar heads. In contrast, lipids with unequal chain length exhibited high transfection efficiency when polar part contained symmetric heads. According to the optimal formulation, seven lipids exhibited higher transfection efficiency than the commercially available transfection agents, Effectene, DOTAP and DC-Chol, to deliver DNA into PC3 human prostate adenocarcinoma cells. 3beta-[N-(N'-Guanidinyl)-2'-aminoethyl)-N-(2-aminoethyl)carbamoyl] cholesterol (5) bearing amino and guanidinyl polar heads exhibited highest transfection efficiency with minimal toxicity. The morphology of active liposomes was observed by transmission electron microscopy (TEM) and size of liposomes were around 200-700 nm.

Gene therapy for cystic fibrosis

Cystic Fibrosis (CF) is an autosomal recessive disorder due to mutations in the CF transmembrane conductance regulator (CFTR) gene that lead to defective ion transport in the conducting pulmonary airways and exocrine glands. Through a process that is not fully understood, CFTR defects predispose affected patients to chronic endobronchial infections with organisms such as Pseudomonas aeruginosa and Staphylococcus aureus. Following the discovery of the CFTR gene in 1989, CF became one of the primary targets for gene therapy research. Early enthusiasm surrounded the new field of gene therapy during most of the 1990s and it led academics and clinicians on a big effort to apply gene therapy for cystic fibrosis. Clinical studies have been pursued using recombinant adenovirus, recombinant adeno-associated virus, cationic liposomes, and cationic polymer vectors. Although to this date no dramatic therapeutic benefits have been observed, a lot of information has been gained from the pre-clinical and clinical studies that were performed. This learning curve has led to the optimization of vector technology and an appreciation of immune and mechanical barriers that have to be overcome for successful delivery.

Structural and formulation factors influencing pyridinium lipid-based gene transfer

A series of pyridinium lipids containing a heterocyclic ring and a nitrogen atom were synthesized to determine the structure-activity relationship for gene delivery. Pyrylium chloroaluminate was synthesized by monoacylation of mesityl oxide and converted into pyrylium hexafluorophosphate, which was used as the key intermediate for reaction with different primary amines, to yield hydroxyethylpyridinium hexafluorophosphate and aminoethylpyridinium hexafluorophosphate. Acylation of these pyridinium salts with different types of fatty acid chlorides afforded the final pyridinium lipids, which were mixed with a co-lipid, such as L-alpha-dioleoylphosphatidylethanolamine (DOPE) and cholesterol (Chol) to prepare cationic liposomes by sonication. These liposomes were mixed with plasmid DNA encoding enhanced green fluorescent protein (pCMS-EGFP) or luciferase (pcDNA3-Luc) and transfected into Chinese hamster ovary (CHO) cells. Several factors including hydrophobic anchor chain length, anchor chain type, configuration of double bond, linker type, co-lipid type, cationic lipid/co-lipid molar ratio, charge ratio (N/P), and cell type had significant influence on transfection efficiency and cytotoxicity. Pyridinium lipids with amide linker showed significantly higher transfection efficiency compared to their ester counterparts. Liposomes prepared at a 1:1 molar ratio of pyridinium lipid and co-lipid showed higher transfection efficiency when either DOPE or cholesterol was used as a co-lipid to prepare cationic liposomes for complex formation with plasmid DNA at 3:1(+/-) charge ratio. Pyridinium liposomes based on a hydrophobic anchor chain length of 16 showed higher transfection efficiency and lower cytotoxicity. The pyridinium lipid with a trans-configuration of the double bond in the fatty acid chain showed higher transfection efficiency than its counterpart with cis-configuration at the same fatty acid chain length. In the presence of serum, C16:0 and Lipofectamine significantly decreased their transfection efficiencies, which were completely lost at a serum concentration of 30% and higher, while C16:1 trans-isomer still had high transfection efficiency under these conditions. In conclusion, pyridinium lipids showed high transfection efficiency and have the potential to be used as transfection reagents in vitro and in vivo.

Tumour gene expression from C12 spermine amphiphile gene delivery systems

Gene therapy requires safe and efficient gene delivery systems. Towards this aim both the gene formulation and tumour transfection ability of C12 spermine amphiphiles were tested. Five amphiphiles were synthesised and characterised: 1-[N,N-bis(3-aminopropyl)-1,4-butane diamine] dodecane (12G0--a C12 spermine amphiphile), a poly(ethylene glycol) (PEG, MW = 2 kDa) derivative of 12G0, 1,12-[N,N-bis(3-aminopropyl)-1,4-butane diamine] dodecane (12G1--a C12 spermine bolaamphiphile) and N-methyl quaternary ammonium derivatives of both 12G0 (12QG0) and 12G1 (12QG1). All amphiphiles except 12G0, which precipitates, yield nanoparticles in aqueous media with and without DNA. Thus when 12G0 is substituted with either quaternary ammonium or PEG groups it forms nanoparticles both with and without DNA. The minimum nitrogen, phosphate ratio required to completely condense DNA (NP) was inversely proportional to the particles' zeta potential (zeta), NP = 1626/zeta(0.98). Biological testing showed that both PEG and quaternary ammonium groups diminished the membrane lytic ability of these C12 amphiphiles. On intratumoural injection, while PEG groups hamper gene transfer, the quaternary ammonium amphiphile (12QG0) produces tumour confined gene expression that is 80% of that produced by linear poly(ethylenimine) (LPEI, MW = 22 kDa); while the intratumoural injection of LPEI produced significant gene expression in the liver and lung, making 12QG0 suitable for the administration of cytotoxic tumouricidal genes.

Modifications in the Head Group and in the Spacer of Cholesterol-based Cationic Lipids Promote Transfection in Melanoma B16-F10 Cells and Tumours

A series of four cationic lipids derived from cholesterol was synthesised and their efficiencies to vectorise nucleic acids were compared. The investigation concerns the effects of systematic chemical modifications in the polar head and in the spacer. The cationic lipid molecules used are in the same family of 3beta[N-(N',N',N'-trimethylaminoethane)-carbamoyl] cholesterol iodide (TMAEC-Chol), presenting a spacer of two or three carbons and a quaternary ammonium polar head ramified with methyl or ethyl groups. These lipids formed stable liposomes sizing from 100 to 200 nm when prepared with the colipid dioleoyl phosphatidylethanolamine (DOPE). The goal of this work was to investigate the effect of the chemical structure of these cationic lipids on lipofection. Their ability to form complexes with DNA, their cytotoxicity and their transfection efficiency in vitro and in vivo were studied. Results were compared with those obtained from the well known cholesterol-based cationic lipid DC-Chol. In a melanoma cell line (B16-F10), results showed that either the polar head or the spacer affected the cytotoxicity. Cationic lipids with three ethyl groups in the head are more toxic than those with three methyl groups while cationic lipids with three carbons in the spacer are less toxic than those with two carbons in the spacer. The best transfection level was obtained in vitro and in vivo with cationic lipids having 3C in the spacer. Data indicated that among these lipids, in vivo gene transfer is advantaged by the methylated polar head while in vitro the best level was obtained with the ethylated one. Finally, it was observed that the chemical structure influences the transfection in the presence of serum while the complex charge and the DOPE ratios in liposomes preferentially affect the interaction with erythrocytes. Argumentations are proposed to explain the discrepancies between in vitro and in vivo transfection results concerning the optimal charge ratio and the chemical nature of the cationic lipid head group.

A receptor-targeted nanocomplex vector system optimized for respiratory gene transfer

Synthetic vectors for cystic fibrosis (CF) gene therapy are required that efficiently and safely transfect airway epithelial cells, rather than alveolar epithelial cells or macrophages, and that are nonimmunogenic, thus allowing for repeated delivery. We have compared several vector systems against these criteria including GL67, polyethylenimine (PEI) 22 and 25 kd and two new, synthetic vector formulations, comprising a cationic, receptor-targeting peptide K(16)GACSERSMNFCG (E), and the cationic liposomes (L) DHDTMA/DOPE or DOSEP3/DOPE. The lipid and peptide formulations self assemble into receptor-targeted nanocomplexes (RTNs) LED-1 and LED-2, respectively, on mixing with plasmid (D). LED-1 transfected airway epithelium efficiently, while LED-2 and GL67 preferentially transfected alveolar cells. PEI transfected airway epithelial cells with high efficiency, but was more toxic to the mice than the other formulations. On repeat dosing, LED-1 was equally as effective as the single dose, while GL67 was 30% less effective and PEI 22 kd displayed a 90% reduction of efficiency on repeated delivery. LED-1 thus was the only formulation that fulfilled the criteria for a CF gene therapy vector while GL67 and LED-2 may be appropriate for other respiratory diseases. Opportunities for PEI depend on a solution to its toxicity problems. LED-1 formulations were stable to nebulization, the most appropriate delivery method for CF.