Effects of altering dosing on cationic liposome-mediated gene transfer to the respiratory epithelium

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.

Use of ultrasound to enhance nonviral lung gene transfer in vivo

We have assessed if high-frequency ultrasound (US) can enhance nonviral gene transfer to the mouse lung. Cationic lipid GL67/pDNA, polyethylenimine (PEI)/pDNA and naked plasmid DNA (pDNA) were delivered via intranasal instillation, mixed with Optison microbubbles, and the animals were then exposed to 1 MHz US. Addition of Optison alone significantly reduced the transfection efficiency of all three gene transfer agents. US exposure did not increase GL67/pDNA or PEI/pDNA gene transfer compared to Optison-treated animals. However, it increased naked pDNA transfection efficiency by approximately 15-fold compared to Optison-treated animals, suggesting that despite ultrasound being attenuated by air in the lung, sufficient energy penetrates the tissue to increase gene transfer. US-induced lung haemorrhage, assessed histologically, increased with prolonged US exposure. The left lung was more affected than the right and this was mirrored by a lesser increase in naked pDNA gene transfer, in the left lung. The positive effect of US was dependent on Optison, as in its absence US did not increase naked pDNA transfection efficiency. We have thus established proof of principle that US can increase nonviral gene transfer, in the air-filled murine lung.

Using magnetic forces to enhance non-viral gene transfer to airway epithelium in vivo

We have assessed whether magnetic forces (magnetofection) can enhance non-viral gene transfer to the airways. TransMAG(PEI), a superparamagnetic particle was coupled to Lipofectamine 2000 or cationic lipid 67 (GL67)/plasmid DNA (pDNA) liposome complexes. In vitro transfection with these formulations resulted in approximately 300- and 30-fold increase in reporter gene expression, respectively, after exposure to a magnetic field, but only at suboptimal pDNA concentrations. Because GL67 has been formulated for in vivo use, we next assessed TransMAG(PEI) in the murine nasal epithelium in vivo, and compared this to naked pDNA. At the concentrations required for in vivo experiments, precipitation of magnetic complexes was seen. After extensive optimization, addition of non-precipitated magnetic particles resulted in approximately seven- and 90-fold decrease in gene expression for naked pDNA and GL67/pDNA liposome complexes, respectively, compared to non-magnetic particles. Thus, whereas exposure to a magnetic field improved in vitro transfection efficiency, translation to the in vivo setting remains difficult.

Pre-clinical and clinical endpoint assays for cystic fibrosis gene therapy

The credibility and hence value of pre-clinical and clinical cystic fibrosis gene therapy studies depend on the assays used to evaluate gene transfer. Awareness of assay suitability, sensitivity and variability is therefore crucial to the design of experimental programmes. Here, we review the assays that are in use to assess the efficacy of gene transfer in pre-clinical and clinical CF gene therapy research, highlight their weaknesses and suggest possible new strategies that may help to overcome current limitations.

Increased non-viral gene transfer levels in mice by concentration of cationic lipid DNA complexes formed under optimized conditions

BACKGROUND

A number of non-viral gene transfer reagents including cationic lipid DNA complexes (LDC) have been developed and were improved by changing the ratio of their components. To determine the effect of other parameters during complex formation affecting the efficacy of LDC, the conditions during complexation were varied without changing the ratios of the components.

METHODS

LDC were formed at fixed ratios of an equimolar mixture of DOTAP and cholesterol to DNA to the condensing agent protamine sulfate according to different protocols at varying final concentrations. The influence of these parameters on transfection efficiency and physical properties of the complexes was determined.

RESULTS

Changing the order of addition of compounds during complex formation affected the size distribution, the charge of the LDC, the interaction between the lipids and the accessibility of the DNA. At fixed ratios of the components, higher transfection efficiencies were observed with more condensed LDC. Complexation in higher volumes increased transduction efficiency of the complexes after intravenous inoculation. Due to restrictions on the injectable volume, the LDC were formed in the optimal volume and subsequently concentrated by ultrafiltration. The concentrated complexes maintained transduction efficiency and up to 60-fold higher in vivo transduction levels were obtained.

CONCLUSIONS

In addition to the ratio of the components of cationic lipid DNA complexes, the final concentration and the order of addition of compounds during complex formation are critical for high transduction efficiency. Concentration of LDC formed under optimal conditions can be used to further increase in vivo gene transfer levels.

Poly (D, L-lactide-co-glycolide)/DNA microspheres to facilitate prolonged transgene expression in airway epithelium in vitro, ex vivo and in vivo

Repeat administration of gene therapy for cystic fibrosis is likely to be essential for long-term clinical efficacy. This may be minimized by the use of slow-release gene transfer preparations with more prolonged expression and longer dosing intervals for the patient. Poly(D-L-lactide-co-glycolide) (PLG) is a biodegradable and biocompatible polymer that has been used to encapsulate plasmid DNA. PLG-DNA microspheres were generated and characterized with respect to morphology, size (80% of particles <5.2 microm), and encapsulation efficiency (50.7+/-2.3%, n=6). Gel electrophoresis of DNA re-extracted from the microspheres confirmed that despite a decrease in the proportion of supercoiled conformation, it had not been degraded by the preparation process. Gene transfer efficiency was tested using microspheres encapsulating the reporter gene beta-galactosidase in vitro on Cos 7 cells and a CF airway epithelial line (CFTEo approximately ) and ex vivo in a sheep tracheal (s.t.) model. In both cases, transgene expression was significantly (P<0.01) lower at the first time point tested (24 h in vitro, 48 h ex vivo) compared to lipid-#67-mediated gene transfer. However, PLG-mediated expression in vitro was sustained at 48 h, while lipid #67-mediated expression levels had dropped significantly (P<0.05) to 50.3+/-13.7 and 38.2+/-2.7% (Cos 7 and CFTEo approximately cells, respectively) of the 24-h level. This pattern was also seen in the s.t. model where at 72 h, PLG-mediated expression was 125.4+/-7.2% of the 48-h level demonstrating significantly (P<0.05) better retention of transfection efficiency than lipid #67, where levels had fallen to approximately half the 48 h level. By 96 h, expression was still retained in the PLG-transfected group (87.3+/-12.5% of 48 h expression) but was undetectable in the lipid -#67-transfected s.t. Finally, PLG microspheres, encapsulating the reporter gene chloramphenicol transferase (CAT, 80 microg) were instilled intranasally into Balb/C mice. Compared to lipid-#67-mediated delivery, where whole lung CAT expression was highest at 48 h (13.7 x 10(3)+/-0.05 CAT U/microg protein, n=6) and then not detectable at further time points, CAT expression was not detectable in PLG-transfected mice at 48 h, but was detectable at 7, 14 and 21 days after transfection. These data demonstrate that PLG-mediated gene transfer can produce prolonged gene expression in airway epithelia. However, gene transfer efficiency still requires significant improvement.

The nasal epithelium as a factory for systemic protein delivery

We have previously shown that recombinant Sendai virus (SeV) produces efficient in vivo airway epithelial gene transfer. The ability to produce therapeutic levels of circulating proteins following noninvasive gene transfer would have widespread clinical application. Here, we compared nose, lung, and skeletal muscle for the ability to produce circulating levels of the secreted mouse antiinflammatory cytokine interleukin-10 (IL10) following SeV-mediated gene transfer. High levels of serum IL10 were obtained from each site with a potency order of lung > nose > muscle for a given viral titer. Serum levels from each site were within the likely required range for anti-inflammatory effects. The combination of a high-efficiency gene transfer agent (SeV) and sites that can be assessed noninvasively (nose or lung) may circumvent several current challenges to gene therapy.

Increased persistence of lung gene expression using plasmids containing the ubiquitin C or elongation factor 1alpha promoter

For effective gene therapy of chronic disease, persistent transgene expression at therapeutic levels is required. Clinical studies of airway gene transfer in patients with cystic fibrosis (CF) have resulted in short-lived transgene expression. We used intra-nasal dosing of naked plasmid DNA to the murine lung as a model for investigating the duration of airway gene transfer from a series of reporter expression plasmids. Transgene expression was transient when mediated by the viral promoters CMV, RSV and SV40, falling to less than 10% of peak expression after 2 weeks, although the presence of the adenoviral E4ORF3 gene in cis, resulted in extended duration of reporter activity from the CMV promoter. Transient expression from these promoters was not due to loss of the vector as determined by quantitative TaqMan PCR analysis. However, use of the promoters from the human polybiquitin C (UbC) and the elongation factor 1alpha (EF1alpha) genes resulted in persistent gene expression in the mouse lung. The UbC promoter directed high-level reporter activity which was maintained for up to 8 weeks and was still detectable 6 months after a single administration. Such persistent airway transgene expression from a nonviral vector without the concomitant expression of a potential antigen has not been reported previously. Thus, despite the persistence of vector DNA in vivo, attenuation of promoter function may lead to silencing of transgene expression and careful selection of promoter sequences is recommended for in vivo gene transfer.

Non-viral vectors in cancer gene therapy: principles and progress

This review focuses on the use of synthetic (non-viral) delivery systems for cancer gene therapy. Therapeutic strategies such as gene replacement/mutation correction, immune modulation and molecular therapy/'suicide' gene therapy type approaches potentially offer unique and novel ways of fighting cancer, some of which have already shown promise in early clinical trials. However, the specific and efficient delivery of the genetic material to remote tumors/metastases remains a challenge, which is being addressed using a variety of viral and non-viral systems. Each of these disparate systems has distinct advantages and disadvantages, which need to be taken into account when a specific therapeutic gene is being used. The review concentrates on particulate gene delivery systems, which are formed through non-covalent complexation of cationic carrier molecules (e.g. lipids or polymers) and the negatively charged plasmid DNA. Such systems tend to be comparatively less efficient than viral systems, but have the inherent advantage of flexibility and safety. The DNA-carrier complex acts as a protective package, and needs to be inert and stable while in circulation. Once the remote site has been reached the complex needs to efficiently transfect the targeted (tumor) cells. In order to improve overall transfection specificity and efficiency it is necessary to optimize intracellular trafficking of the DNA complex as well as the performance after systemic administration. Common principles and specific advantages or disadvantages of the individual synthetic gene delivery systems are discussed, and their interaction with tumor-specific and generic biological barriers are examined in order to identify potential strategies to overcome them.

In vivo gene delivery to the lung using polyethylenimine and fractured polyamidoamine dendrimers

BACKGROUND

Gene transfer into the airways could be of importance for the treatment of chronic lung diseases such as cystic fibrosis. In the past few years several attempts have been made to effectively deliver DNA to the lung using different viral and non-viral vector systems. Viral vectors and cationic lipids have been tested intensively but the properties of cationic polymers such as polyethylenimine (PEI) 25 kDa and fractured polyamidoamine dendrimers to deliver DNA to the airways have not been studied. Surfactant preparations have been shown to influence pulmonary adenoviral and naked plasmid DNA mediated gene transfer in vivo. We investigated the gene delivery efficiency of branched PEI 25 kDa and fractured dendrimers to the murine lung in vivo and also examined the effect of surfactant on PEI 25 kDa mediated gene transfer to the lung.

METHODS

Cationic polymer/DNA complexes were prepared in 25 mM HEPES buffer (pH = 7.4) or double distilled water and administered to the lungs of BALB/c mice via cannula intubation. The trachea, left and right lung, heart, liver and esophagus were examined for luciferase activity. Inflammation was assessed by performing standard histology.

RESULTS

PEI/DNA complexes showed a high level of luciferase gene expression in the lung. Complexes formed in double distilled water exhibited higher gene expression than complexes formed in 25 mM HEPES buffer (pH 7.4). The optimal N/P ratio was found to be N/P = 10 in double distilled water. Luciferase activity was only detected in the lung and decreased rapidly in a time-dependent manner. The addition of a natural surfactant preparation, Alveofact, slightly reduced gene transfer of branched PEI 25 kDa. Luciferase gene expression obtained by using fractured dendrimers was very low.

CONCLUSION

The present study demonstrates that PEI 25 kDa, but not polyamidoamine dendrimers, effectively mediates transient gene transfer to the murine lung after intratracheal intubation. In conclusion, branched PEI 25 kDa was found to be an effective vector for pulmonary gene delivery in vivo, being superior to fractured dendrimers.

Pretreatment with cationic lipid-mediated transfer of the Na+K+-ATPase pump in a mouse model in vivo augments resolution of high permeability pulmonary oedema

Resolution of pulmonary oedema is mediated by active absorption of liquid across the alveolar epithelium. A key component of this process is the sodium-potassium ATPase (Na+K+-ATPase) enzyme located on the basolateral surface of epithelial cells and up-regulated during oedema resolution. We hypothesised that lung liquid clearance could be further up-regulated by lipid-mediated transfer and expression of exogenous Na+K+-ATPase cDNA. We demonstrate proof of this principle in a model of high permeability pulmonary oedema induced by intraperitoneal injection of thiourea (2.5 mg/kg) in C57/BL6 mice. Pretreatment of mice (24 h before thiourea) by nasal sniffing of cationic liposome (lipid #67)-DNA complexes encoding the alpha and beta subunits of Na+K+-ATPase (160 microg per mouse), significantly (P<0.01) decreased the wet:dry weight ratios measured 2 h after thiourea injection compared with control animals, pretreated with an equivalent dose of an irrelevant gene. Whole lung Na+K+-ATPase activity was significantly (P<0.05) increased in mice pretreated with Na+K+-ATPase cDNA compared both with untreated control animals as well as animals pretreated with the irrelevant gene. Nested RT-PCR on whole lung homogenates confirmed gene transfer by detection of vector-specific mRNA in three of four mice studied 24 h after gene transfer. This demonstration of a significant reduction in pulmonary oedema following in vivo gene transfer raises the possibility of gene therapy as a novel, localised approach for pulmonary oedema in clinical settings such as ARDS and lung transplantation.