Basis of pulmonary toxicity associated with cationic lipid-mediated gene transfer to the mammalian lung

Correction of enzymatic and lysosomal storage defects in Fabry mice by adenovirus-mediated gene transfer

Fabry disease is a recessive, X-linked disorder caused by a deficiency of the lysosomal hydrolase alpha-galactosidase A. Deficiency of this enzyme results in progressive deposition of the glycosphingolipid globotriaosylceramide (GL-3) in the vascular lysosomes, with resultant distension of the organelle. The demonstration of a secretory pathway for lysosomal enzymes and their subsequent recapture by distant cells through the mannose 6-phosphate receptor pathway has provided a rationale for somatic gene therapy of lysosomal storage disorders. Toward this end, recombinant adenoviral vectors encoding human alpha-galactosidase A (Ad2/CEHalpha-Gal, Ad2/CMVHIalpha-Gal) were constructed and injected intravenously into Fabry knockout mice. Administration of Ad2/CEHalpha-Gal to the Fabry mice resulted in an elevation of alpha-galactosidase A activity in all tissues, including the liver, lung, kidney, heart, spleen, and muscle, to levels above those observed in normal animals. However, enzymatic expression declined rapidly such that by 12 weeks, only 10% of the activity observed on day 3 remained. Alpha-galactosidase A detected in the plasma of injected animals was in a form that was internalized by Fabry fibroblasts grown in culture. Such internalization occurred via the mannose 6-phosphate receptors. Importantly, concomitant with the increase in enzyme activity was a significant reduction in GL-3 content in all tissues to near normal levels for up to 6 months posttreatment. However, as expression of alpha-galactosidase A declined, low levels of GL-3 reaccumulated in some of the tissues at 6 months. For protracted treatment, we showed that readministration of recombinant adenovirus vectors could be facilitated by transient immunosuppression using a monoclonal antibody against CD40 ligand (MR1). Together, these data demonstrate that the defects in alpha-galactosidase A activity and lysosomal storage of GL-3 in Fabry mice can be corrected by adenovirus-mediated gene transfer. This suggests that gene replacement therapy represents a viable approach for the treatment of Fabry disease and potentially other lysosomal storage disorders.

Characterization of endotoxin and cationic liposome interaction

The objective of this study was to characterize the interaction of endotoxin with cationic liposomes used in nonviral gene delivery. Endotoxin-cationic liposome interaction was characterized using fluorescent anisotropy, and the Limulus amebocyte lysate (LAL) assay. Cellular toxicity of endotoxin-cationic liposome complex was examined using a dimethylthiazol diphenyltetrazolium bromide (MTT) assay. The effect of endotoxin on the lipid-DNA complex and subsequent transfection into COS-1 cells was also examined. A competitive interaction occurred between fluoroscein isothiocyanate (FITC)-labeled endotoxin and plasmid DNA for binding dioleoyl glycero trimethylammonium propane:dioleoyl glycero phosphoethanolamine (DOTAP:DOPE) liposomes using fluorescent anisotropy techniques. The LAL assay demonstrated no change in endotoxin activity upon interaction with liposomes. No loss of COS cell viability was detected via the MTT assay during a 5-hr exposure to endotoxin. Transient transfection studies indicate that increasing levels of endotoxin lowered activity more than 90% at 50,000 endotoxin units (EU)/ml. Endotoxin and cationic liposomes interact mainly by an electrostatic attraction. Endotoxin contamination can potentially impact transfection efficiency via competition with plasmid DNA for cationic liposome binding by increasing transfection variability at 50 EU/ml, a concentration of endotoxin contamination that can occur with small-scale plasmid preparations used for in vitro cell transfections, but would not be expected with typical GLP or GMP preparations used in clinical studies.

Effect of immune response on gene transfer to the lung via systemic administration of cationic lipidic vectors

Cationic lipid-mediated intravenous gene delivery shows promise in treating pulmonary diseases including lung tumor metastases, pulmonary hypertension, and acute respiratory distress syndrome. Nevertheless, clinical applications of cationic lipidic vectors via intravenous administration are limited by their transient gene expression. In addition, repeated dosing is not effective at frequent intervals. In an effort to elucidate the mechanism of gene inactivation, we report in this study that cationic lipid-protamine-DNA (LPD) complexes, but not each component alone, can induce a high level of cytokine production, including interferon-gamma and tumor necrosis factor-alpha. Furthermore, we demonstrate that LPD administration triggers apoptosis in the lung, a phenomenon that may be mediated in part by the two cytokines. Treatment of mice with antibodies against the two cytokines prolongs the duration of gene expression and also improves lung transfection on a second administration of LPD. Although the mechanism underlying LPD-induced cytokine production is unclear, methylation of the DNA significantly decreased the level of both interferon-gamma and tumor necrosis factor-alpha, suggesting that unmethylated CpG sequences in plasmid DNA play an important role. These data suggest that decreasing the CpG-mediated immune response while not affecting gene expression may be a useful therapeutic strategy to improve cationic lipid-mediated intravenous gene delivery to the lung.

Contribution of plasmid DNA to inflammation in the lung after administration of cationic lipid:pDNA complexes

Cationic lipid-mediated gene transfer to the mouse lung induces a dose-dependent inflammatory response that is characterized by an influx of leukocytes and elevated levels of the cytokines interleukin 6 (IL-6), tumor necrosis factor alpha (TNF-alpha), and interferon gamma (IFN-gamma). We have examined the contribution of plasmid DNA (pDNA) to this observed toxicity, specifically the role of unmethylated CpG dinucleotides, which have been previously shown to be immunostimulatory. We report here that complexes of cationic lipid GL-67 and unmethylated pDNA (pCF1-CAT) instilled into the lungs of BALB/c mice induced highly elevated levels of the cytokines TNF-alpha, IFN-gamma, IL-6, and IL-12 in the bronchoalveolar lavage fluids (BALF). In contrast, BALF of animals administered either GL-67 alone or GL-67 complexed with SssI-methylated pDNA contained low levels of these cytokines. Similar results were observed using a plasmid (pCF1-null) that does not express a transgene, demonstrating that expression of chloramphenicol acetyltransferase (CAT) was not responsible for the observed inflammation. The response observed was dose dependent, with animals receiving increasingly higher amounts of unmethylated pDNA exhibiting progressively higher levels of the cytokines. Concomitant with this increase in cytokine levels were also elevated numbers of neutrophils in the BALF, suggesting a possible cause- and-effect relationship between neutrophil influx and generation of cytokines. Consistent with this proposal is the observation that reduction of neutrophils in the lung by administration of antibodies against Mac-1alpha and LFA-1 also diminished cytokine levels. This reduction in cytokine levels in the BALF was accompanied by an increase in transgene expression. In an attempt to abate the inflammatory response, sequences in the pDNA encoding the motif RRCGYY, shown to be most immunostimulatory, were selectively mutagenized. However, instillation of a plasmid in which 14 of the 17 CpG sites were altered into BALF/c mice did not reduce the levels of cytokines in the BALF compared with the unmodified vector. This suggests that other unmethylated motifs, in addition to RRCGYY, may also contribute to the inflammatory response. Together, these findings indicate that unmethylated CpG residues in pDNA are a major contributor to the induction of specific proinflammatory cytokines associated with instillation of cationic lipid:pDNA complexes into the lung. Strategies to abate this response are warranted to improve the efficacy of this nonviral gene delivery vector system for the treatment of chronic diseases.

Encapsulation of plasmid DNA in biodegradable poly(D, L-lactic-co-glycolic acid) microspheres as a novel approach for immunogene delivery

A plasmid DNA encoding bacterial beta-galactosidase gene was encapsulated in poly(d,l-lactic-co-glycolic acid) (PLGA) microspheres. Plasmid DNA extracted from PLGA microspheres retained both structural and functional integrity as evidenced by its restriction endonuclease digestion pattern and its ability to transfect COS-1 cells in vitro. PLGA microspheres protected plasmid DNA from digestion by deoxyribonuclease I (DNase I) in vitro. The encapsulation efficiency of plasmid DNA and its release rate depended on the molecular mass of PLGA. Lastly, J-774A macrophages phagocytosed PLGA microspheres loaded with plasmid DNA. Co-encapsulated monophosphoryl lipid A increased the rate of phagocytosis. These results suggest that biodegradable PLGA microspheres can deliver intact and functional plasmid DNA at controlled rates. Thus, PLGA microspheres may be used to jointly deliver genes and other biologically active molecules, e.g., immunomodulators, to antigen presenting cells.

Influence of cell polarity on retrovirus-mediated gene transfer to differentiated human airway epithelia

Gene transfer with recombinant murine leukemia viruses (MuLV) provides the potential to permanently correct inherited lung diseases, such as cystic fibrosis (CF). Several problems prevent the application of MuLV-based recombinant retroviruses to lung gene therapy: (i) the lack of cell proliferation in mature pulmonary epithelia, (ii) inefficient gene transfer with a vector applied to the apical surface, and (iii) low titers of many retroviral preparations. We found that keratinocyte growth factor (KGF) stimulated proliferation of differentiated human tracheal and bronchial epithelia. Approximately 50% of epithelia divided in response to KGF as assessed by bromodeoxyuridine histochemistry. In airway epithelia stimulated to divide with KGF, high-titer ampho- and xenotropic enveloped vectors preferentially infected cells from the basal side. However, treatment with hypotonic shock or EGTA transiently increased transepithelial permeability, enhancing gene transfer with the vector applied to the mucosal surfaces of KGF-stimulated epithelia. Up to 35% of cells expressed the transgene after gene transfer. By using this approach, cells throughout the epithelial sheet, including basal cells, were targeted. Moreover, the Cl- transport defect in differentiated CF airway epithelia was corrected. These findings suggest that barriers to apical infection with MuLV can be overcome.

Key issues in non-viral gene delivery

The future of non-viral gene therapy depends on a detailed understanding of the barriers to delivery of polynucleotides. These include physicomechanical barriers, which limit the design of delivery devices, physicochemical barriers that influence self-assembly of colloidal particulate formulations, and biological barriers that compromise delivery of the DNA to its target site. It is important that realistic delivery strategies are adopted for early clinical trials in non-viral gene therapy. In the longer term, it should be possible to improve the efficiency of gene delivery by learning from the attributes which viruses have evolved; attributes that enable translocation of viral components across biological membranes. Assembly of stable, organized virus-like particles will require a higher level of control than current practice. Here, we summarize present knowledge of the biodistribution and cellular interactions of gene delivery systems and consider how improvements in gene delivery will be accomplished in the future.

Direct gene transfer to the respiratory tract of mice with pure plasmid and lipid-formulated DNA

Direct gene transfer into the respiratory system could be carried out for either therapeutic or immunization purposes. Here we demonstrate that cells in the lung can take up and express plasmid DNA encoding a luciferase reporter gene whether it is administered in naked form or formulated with cationic liposomes. Depending on the lipid used, the transfection efficiency with liposome-formulated DNA may be higher, the same as, or less than that with pure plasmid DNA. Tetramethyltetraalkylspermine analogs with alkyl groups of 16 or 18 carbons and DMRIE/cholesterol formulations proved particularly effective. Similar results for reporter gene expression in the lung were obtained whether the DNA (naked or lipid formulated) was administered by indirect, noninvasive intranasal delivery (inhaled or instilled) or by invasive, direct intratracheal delivery (injected or via a cannula). Reporter gene expression peaks around 4 days, then falls off dramatically by 9 days. The dose-response is linear, at least up to 100 microg plasmid DNA, suggesting better transfection efficiencies might be realized if there was not a volume limitation. For a given dose of DNA, the best results are obtained when the DNA is mixed with the minimum amount of lipid that can complex it completely. These results are discussed in the context of direct gene transfer for either gene therapy or delivery of a mucosal DNA vaccine.

Target specific optimization of cationic lipid-based systems for pulmonary gene therapy

PURPOSE

Cationic lipids are capable of transferring foreign genes to the pulmonary epithelium in vivo. It is becoming increasingly clear that factors other than lipid molecular structure also influence efficiency of delivery using cationic lipid systems. This study is aimed at evaluating the effect of formulation variables such as cationic lipid structure, cationic lipid/DNA ratio, particle size, co-lipid content and plasmid topology on transgene expression in the lung.

METHODS

The effect of varying the surface and colloidal properties of cationic lipid-based gene delivery systems was assessed by intratracheal instillation into rats. An expression plasmid encoding chloramphenicol acetyl transferase (CAT) was used to measure transgene expression.

RESULTS

Cationic lipid structure, cationic lipid/DNA ratio, particle size, co-lipid content and topology of the plasmid, were found to significantly affect transgene expression. Complexation with lipids was found to have a protective effect on DNA integrity in bronchoalveolar lavage fluid (BALF). DNA complexed with lipid showed enhanced persistence in rat lungs as measured by quantitative polymerase chain reaction.

CONCLUSIONS

Fluorescence microscopy analysis indicated that the instilled formulation reaches the lower airways and alveolar region. Data also suggests cationic lipid-mediated gene expression is primarily localized in the lung parenchyma and not infiltrating cells isolated from the BALF.

Effective treatment of early endobronchial cancer with regional administration of liposome-p53 complexes

BACKGROUND

Lung cancer originates in a diffusely damaged bronchial epithelium as a result of sequential and cumulative genetic alterations. We investigated the feasibility of in vivo gene replacement in endobronchial precancerous and cancerous cells by a regionally administered nonviral delivery system.

METHODS

After evaluating the in vitro transfection efficiency and cytotoxicity of a variety of cationic liposome-p53 formulations, a specific formulation, DP3-p53, was selected for further in vitro and in vivo evaluation. The ability of DP3-p53 to introduce the p53 gene in the normal bronchial epithelium was studied in transgenic mice that lack the p53 gene. The therapeutic effect of DP3-p53 administered intratracheally was studied in two nude mouse models of endobronchial human lung cancer by use of H358 (p53-null) and H322 (p53-mutant) cells.

RESULTS

DP3-p53 was able to effectively introduce and express the p53 gene and induce G1 arrest and apoptosis in H358 cells in vitro and to introduce and transcribe the p53 gene in the bronchial epithelium of transgenic mice that lack the p53 gene in vivo. In therapeutic experiments using groups of four or five mice each, administration of five intratracheal doses of DP3-p53 (2 microg or 8 microg DNA per dose) on days 4, 8, 12, 16, and 20 after intratracheal tumor inoculation significantly inhibited lung tumor formation and prolonged by approximately twofold the survival of mice bearing H358 or H322 endobronchial tumor cells in contrast to the survival among untreated mice and mice treated with the DP3-empty vector (P = .007 [two-sided logrank test] for mice bearing H358 cells and P = .008 [two-sided logrank test] for those bearing H322 cells).

CONCLUSIONS/IMPLICATIONS

Liposome-based p53 delivery through the airways is a potentially effective strategy for the treatment of early endobronchial cancer. These results have important implications for the gene therapy and prevention of human lung cancer.

Efficiency of cationic lipid-mediated transfection of polarized and differentiated airway epithelial cells in vitro and in vivo

Systematic analysis of a large number of different cationic lipids has led to the identification of novel structures (GL-67) and formulations of cationic lipid:plasmid DNA (pDNA) complexes that facilitate high levels of gene expression in lungs of mice. However, despite significant improvement in gene transfer activity, we show here that the efficiency of GL-67-mediated gene transduction of intact airway epithelia is still relatively low. Administration of GL-67:pCF1-CFTR (encoding the cystic fibrosis transmembrane conductance regulator) complexes into the nasal epithelium of cystic fibrosis (CF) transgenic mice resulted only in marginal correction of the ion transport defects. Measurements of nasal potential differences (PD) showed no correction of the sodium (Na+) transport defect, and only partial restitution of the chloride (Cl-) transport defect was achieved in a small proportion of the animals after perfusion of the nasal epithelium with the complexes. Furthermore, in contrast to results obtained following instillation of GL-67:pDNA complexes into the lungs of mice, perfusion of GL-67:pDNA into the nasal epithelium resulted only in a moderate enhancement of gene transduction activity relative to that attained with naked pDNA alone. To determine the basis for this low efficiency of transfection, a series of studies was conducted to identify some of the barriers governing cationic lipid-mediated gene transfer to the airway epithelium. We show here that the transfection activity of GL-67 was affected by the polarization, differentiation, and proliferative state of the cells. Diminished transfection activity was observed with nonmitotic, highly polarized and differentiated airway epithelial cells. This observed reduction in gene expression with nonmitotic cells was determined to be due in part to inefficient nuclear translocation of the pDNA from the cytoplasm. Together these data indicate that much improvement in the ability of cationic lipids to transfect polarized and differentiated airway epithelial cells is a necessary prerequisite for effective cationic lipid-mediated gene therapy of airway diseases such as CF.

Incorporation of adenovirus in calcium phosphate precipitates enhances gene transfer to airway epithelia in vitro and in vivo

Adenovirus (Ad)-mediated gene transfer to airway epithelia is inefficient because the apical membrane lacks the receptor activity to bind adenovirus fiber protein. Calcium phosphate (CaPi) precipitates have been used to deliver plasmid DNA to cultured cell lines. However, such precipitates are not effective in many primary cultures or in vivo. Here we show that incorporating recombinant adenovirus into a CaPi coprecipitate markedly enhances transgene expression in cells that are resistant to adenovirus infection. Enhancement requires that the virus be contained in the precipitate and viral proteins are required to increase expression. Ad: CaPi coprecipitates increase gene transfer by increasing fiber-independent binding of virus to cells. With differentiated cystic fibrosis (CF) airway epithelia in vitro, a 20-min application of Ad:CaPi coprecipitates that encode CF transmembrane conductance regulator produced as much CF transmembrane conductance regulator Cl- current as a 24-h application of adenovirus alone. We found that Ad:CaPi coprecipitates also increased transgene expression in mouse lung in vivo; importantly, expression was particularly prominent in airway epithelia. These results suggest a new mechanism for gene transfer that may be applicable to a number of different gene transfer applications and could be of value in gene transfer to CF airway epithelia in vivo.

Cationic Lipids Enhance Cytokine and Cell Influx Levels in the Lung Following Administration of Plasmid: Cationic Lipid Complexes

Administration of plasmid/lipid complexes to the lung airways may be associated, in addition to expression of transgene, with a range of other responses. We report here the induction of cytokines and cellular influx in the lung airway following intratracheal administration of an N-[1-(2–3-dioleyloxy)propyl]-N,N,N-trimethylammonium chloride/cholesterol/plasmid positively charged complex in mice. We show that 1) the appearance of the Th1-associated cytokines IFN-γ and IL-12 in bronchoalveolar lavage fluid is caused by unmethylated CpG dinucleotide sequences present within the plasmid, and is enhanced by the lipid formulation; 2) cationic lipids by themselves do not induce IL-12 or IL-12p40; 3) TNF-α is rapidly induced by cationic lipids and plasmid/lipid complex, but not by plasmid alone; 4) an acute cellular influx is induced by cationic lipid alone and by a plasmid/lipid complex, but to a much lesser extent by plasmid alone; and 5) plasmid methylation does not influence the degree of inflammatory cell influx. The induction of the innate immune responses by plasmid/lipid complexes may be advantageous to gene therapy of lung diseases. In particular, induction of the Th1 cell-promoting cytokines by plasmid/lipid complexes could, in conjunction with an expressed transgene, be used to modulate immune responses in the lung airways in disease conditions that are deficient in Th1 cell responses or that have a dominant Th2 phenotype. Alternatively, the elimination of immunostimulatory sequences in plasmids may improve the tolerability and/or efficacy of nonviral gene therapy, especially for diseases requiring chronic administration.

Airway delivery of cationic lipid: DNA complexes for cystic fibrosis

Cationic lipids are under active consideration as gene delivery vehicles for cystic fibrosis. Initial studies have shown cationic lipids to be effective agents of gene transfer to epithelial cells in vitro. Instillation of these vectors into animal models has led to widely different degrees of transfection of the airway epithelia. Newer generations of cationic lipids, with dramatically improved transfection efficiencies, appear to result in mostly alveolar gene delivery. Aerosol delivery of cationic lipid-DNA complexes has resulted in variable transfection of the airways in animal models. Initial human clinical trials using intranasal instillation have shown variable low levels of expression, accompanied by little toxicity. Recent developments in the formulation of cationic lipid-DNA complexes have resulted in an ability to aerosolize high concentrations of the complex, and should permit an evaluation of the efficacy of these delivery vehicles when aerosolized into cystic fibrosis patients.

A concentrated and stable aerosol formulation of cationic lipid:DNA complexes giving high-level gene expression in mouse lung

Advances in gene therapy vectors and techniques hold promise for treatment of many inherited and acquired diseases. For lung indications, especially those involving the epithelium, delivery of the gene therapy vehicle ideally will involve the use of an aerosol. Aerosol delivery of transgenes using cationic lipids is currently limited by the ability to generate highly concentrated formulations of lipid:DNA complexes that are stable and retain their activity following aerosolization. We have examined many of the variables inherent in aerosolizing cationic lipid gene delivery vehicles and have devised a new formulation that incorporates small amounts of a polyethylene glycol-containing lipid. This formulation has allowed the preparation of concentrated dispersions of cationic lipid:plasmid DNA (pDNA) complexes (> 20 mM pDNA) at approximately 10-fold higher concentrations than previously reported. Most of the pDNA in these formulations was bound to the lipid component and thereby protected from nebulizer-induced shearing; the pDNA also maintained full biological activity both in vitro and in vivo. This new formulation thus represents a significant improvement over current methods to prepare concentrated, active cationic lipid gene delivery vectors, and provides a new tool with which to test gene transfer to the lung.