Electroporation as a method for high-level nonviral gene transfer to the lung

Spleen Tyrosine Kinase phosphorylates VE-cadherin to cause endothelial barrier disruption in acute lung injury

Increased endothelial cell (EC) permeability is a cardinal feature of acute lung injury/acute respiratory distress syndrome (ALI/ARDS). Tyrosine phosphorylation of VE-cadherin is a key determinant of EC barrier disruption. However, the identity and role of tyrosine kinases in this context are incompletely understood. Here we report that Spleen Tyrosine Kinase (Syk) is a key mediator of EC barrier disruption and lung vascular leak in sepsis. Inhibition of Syk by pharmacological or genetic approaches, each reduced thrombin-induced EC permeability. Mechanistically, Syk associates with and phosphorylates VE-cadherin to cause EC permeability. To study the causal role of endothelial Syk in sepsis-induced ALI, we used a remarkably efficient and cost-effective approach based on gene transfer to generate EC-ablated Syk mice. These mice were protected against sepsis-induced loss of VE-cadherin and inflammatory lung injury. Notably, the administration of Syk inhibitor R788 (fostamatinib); currently in phase II clinical trial for the treatment of COVID-19, mitigated lung injury and mortality in mice with sepsis. These data identify Syk as a novel kinase for VE-cadherin and a druggable target against ALI in sepsis.

Exosomes as an Emerging Plasmid Delivery Vehicle for Gene Therapy

Despite its introduction more than three decades ago, gene therapy has fallen short of its expected potential for the treatment of a broad spectrum of diseases and continues to lack widespread clinical use. The fundamental limitation in clinical translatability of this therapeutic modality has always been an effective delivery system that circumvents degradation of the therapeutic nucleic acids, ensuring they reach the intended disease target. Plasmid DNA (pDNA) for the purpose of introducing exogenous genes presents an additional challenge due to its size and potential immunogenicity. Current pDNA methods include naked pDNA accompanied by electroporation or ultrasound, liposomes, other nanoparticles, and cell-penetrating peptides, to name a few. While the topic of numerous reviews, each of these methods has its own unique set of limitations, side effects, and efficacy concerns. In this review, we highlight emerging uses of exosomes for the delivery of pDNA for gene therapy. We specifically focus on bovine milk and colostrum-derived exosomes as a nano-delivery "platform". Milk/colostrum represents an abundant, scalable, and cost-effective natural source of exosomes that can be loaded with nucleic acids for targeted delivery to a variety of tissue types in the body. These nanoparticles can be functionalized and loaded with pDNA for the exogenous expression of genes to target a wide variety of disease phenotypes, overcoming many of the limitations of current gene therapy delivery techniques.

Gene Therapy for Acute Respiratory Distress Syndrome

Acute respiratory distress syndrome (ARDS) is a devastating clinical syndrome that leads to acute respiratory failure and accounts for over 70,000 deaths per year in the United States alone, even prior to the COVID-19 pandemic. While its molecular details have been teased apart and its pathophysiology largely established over the past 30 years, relatively few pharmacological advances in treatment have been made based on this knowledge. Indeed, mortality remains very close to what it was 30 years ago. As an alternative to traditional pharmacological approaches, gene therapy offers a highly controlled and targeted strategy to treat the disease at the molecular level. Although there is no single gene or combination of genes responsible for ARDS, there are a number of genes that can be targeted for upregulation or downregulation that could alleviate many of the symptoms and address the underlying mechanisms of this syndrome. This review will focus on the pathophysiology of ARDS and how gene therapy has been used for prevention and treatment. Strategies for gene delivery to the lung, such as barriers encountered during gene transfer, specific classes of genes that have been targeted, and the outcomes of these approaches on ARDS pathogenesis and resolution will be discussed.

Gene transfer of MRCKα rescues lipopolysaccharide-induced acute lung injury by restoring alveolar capillary barrier function

Acute Lung Injury/Acute Respiratory Distress Syndrome (ALI/ARDS) is characterized by alveolar edema accumulation with reduced alveolar fluid clearance (AFC), alveolar-capillary barrier disruption, and substantial inflammation, all leading to acute respiratory failure. Enhancing AFC has long been considered one of the primary therapeutic goals in gene therapy treatments for ARDS. We previously showed that electroporation-mediated gene delivery of the Na⁺, K⁺-ATPase β1 subunit not only increased AFC, but also restored alveolar barrier function through upregulation of tight junction proteins, leading to treatment of LPS-induced ALI in mice. We identified MRCKα as an interaction partner of β1 which mediates this upregulation in cultured alveolar epithelial cells. In this study, we investigate whether electroporation-mediated gene transfer of MRCKα to the lungs can attenuate LPS-induced acute lung injury in vivo. Compared to mice that received a non-expressing plasmid, those receiving the MRCKα plasmid showed attenuated LPS-increased pulmonary edema and lung leakage, restored tight junction protein expression, and improved overall outcomes. Interestingly, gene transfer of MRCKα did not alter AFC rates. Studies using both cultured microvascular endothelial cells and mice suggest that β1 and MRCKα upregulate junctional complexes in both alveolar epithelial and capillary endothelial cells, and that one or both barriers may be positively affected by our approach. Our data support a model of treatment for ALI/ARDS in which improvement of alveolar-capillary barrier function alone may be of more benefit than improvement of alveolar fluid clearance.

Pulmonary gene delivery-Realities and possibilities

Delivery of genetic material to tissues in vivo is an important technique used in research settings and is the foundation upon which clinical gene therapy is built. The lung is a prime target for gene delivery due to a host of genetic, acquired, and infectious diseases that manifest themselves there, resulting in many pathologies. However, the in vivo delivery of genetic material to the lung remains a practical problem clinically and is considered the major obstacle needed to be overcome for gene therapy. Currently there are four main strategies for in vivo gene delivery to the lung: viral vectors, liposomes, nanoparticles, and electroporation. Viral delivery uses several different genetically modified viruses that enter the cell and express desired genes that have been inserted to the viral genome. Liposomes use combinations of charged and neutral lipids that can encapsulate genetic cargo and enter cells through endogenous mechanisms, thereby delivering their cargoes. Nanoparticles are defined by their size (typically less than 100 nm) and are made up of many different classes of building blocks, including biological and synthetic polymers, cell penetrant and other peptides, and dendrimers, that also enter cells through endogenous mechanisms. Electroporation uses mild to moderate electrical pulses to create pores in the cell membrane through which delivered genetic material can enter a cell. An emerging fifth category, exosomes and extracellular vesicles, may have advantages of both viral and non-viral approaches. These extracellular vesicles bud from cellular membranes containing receptors and ligands that may aid cell targeting and which can be loaded with genetic material for efficient transfer. Each of these vectors can be used for different gene delivery applications based on mechanisms of action, side-effects, and other factors, and their use in the lung and possible clinical considerations is the primary focus of this review.

Genetic Delivery and Gene Therapy in Pulmonary Hypertension

Pulmonary hypertension (PH) is a progressive complex fatal disease of multiple etiologies. Hyperproliferation and resistance to apoptosis of vascular cells of intimal, medial, and adventitial layers of pulmonary vessels trigger excessive pulmonary vascular remodeling and vasoconstriction in the course of pulmonary arterial hypertension (PAH), a subgroup of PH. Multiple gene mutation/s or dysregulated gene expression contribute to the pathogenesis of PAH by endorsing the proliferation and promoting the resistance to apoptosis of pulmonary vascular cells. Given the vital role of these cells in PAH progression, the development of safe and efficient-gene therapeutic approaches that lead to restoration or down-regulation of gene expression, generally involved in the etiology of the disease is the need of the hour. Currently, none of the FDA-approved drugs provides a cure against PH, hence innovative tools may offer a novel treatment paradigm for this progressive and lethal disorder by silencing pathological genes, expressing therapeutic proteins, or through gene-editing applications. Here, we review the effectiveness and limitations of the presently available gene therapy approaches for PH. We provide a brief survey of commonly existing and currently applicable gene transfer methods for pulmonary vascular cells in vitro and describe some more recent developments for gene delivery existing in the field of PH in vivo.

Caveolin-1 gene therapy inhibits inflammasome activation to protect from bleomycin-induced pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a devastating and fatal disease and characterized by increased deposition of extracellular matrix proteins and scar formation in the lung, resulting from alveolar epithelial damage and accumulation of inflammatory cells. Evidence suggests that Caveolin-1 (Cav-1), a major component of caveolae which regulates cell signaling and endocytosis, is a potential target to treat fibrotic diseases, although the mechanisms and responsible cell types are unclear. We show that Cav-1 expression was downregulated both in alveolar epithelial type I cells in bleomycin-injured mouse lungs and in lung sections from IPF patients. Increased expression of IL-1β and caspase-1 has been observed in IPF patients, indicating inflammasome activation associated with IPF. Gene transfer of a plasmid expressing Cav-1 using transthoracic electroporation reduced infiltration of neutrophils and monocytes/macrophages and protected from subsequent bleomycin-induced pulmonary fibrosis. Overexpression of Cav-1 suppressed bleomycin- or silica-induced activation of caspase-1 and maturation of pro-IL-1β to secrete cleaved IL-1β both in mouse lungs and in primary type I cells. These results demonstrate that gene transfer of Cav-1 downregulates inflammasome activity and protects from subsequent bleomycin-mediated pulmonary fibrosis. This indicates a pivotal regulation of Cav-1 in inflammasome activity and suggests a novel therapeutic strategy for patients with IPF.

Controlling ionic conductivity through transprotein electropores in human aquaporin 4: a non-equilibrium molecular-dynamics study

Electroporation is a matter of intensive ongoing research interest, and a much-neglected topic in trans-membrane proteins, particularly in view of such promising potential applications in medicine and biotechnology. In particular, selected such novel and exciting applications are predicated on controlling ionic conductivity through electro-pores. Here, we scrutinise the mechanisms of ions' electric conductivity, by means of structural rearrangements, through quasi-stable electro-pores through human-AQP4 as a well-representative prototype of trans-membrane ionic conduction, achieving exquisite control over ionic permeability manipulated by the application of intense static electric fields.

Delivery of nucleic acids to ex vivo porcine airways using electrospray

AIM OF THE STUDY

Nucleic acid-based therapies have the potential to provide clinically meaningful benefit across a wide spectrum of lung disease. However, in vivo delivery remains a challenge. Here we examined the feasibility of using electrospray to deliver nucleic acids to both porcine tracheal tissue sections and whole lung ex vivo.

MATERIALS AND METHODS

The effect of electrospray solution, emitter gauge, flow rate and voltage on plasmid DNA integrity was examined by analyzing supercoiled:open circle structure ratio by gel electrophoresis. Optimal parameters were used to deliver luciferase DNA and mRNA and siRNA-FITC to tracheal tissue sections. Luciferase mRNA was delivered to whole porcine lungs ex vivo using a catheter and bronchoscope system. Luciferase activity and fluorescence were analyzed by luminometry and microscopy respectively.

RESULTS

The incidence of DNA plasmid nicking was greatest in a low salt solution without ethanol compared with 1% and 20% ethanol with salt. From a range of emitters tested, a 32 gauge emitter produced the best supercoiled:open circle structure ratio, likely because less voltage was required to produce a stable electrospray with this emitter. Lower flow rates also showed a trend towards reduced DNA nicking. GFP DNA electrosprayed at 5 kV and 6 kV resulted in lower levels of GFP expression in A549 lung cells following lipofection compared with 3 kV and 4 kV. Optimised parameters of 20% ethanol solution, 32 gauge emitter, low flow rates and voltages of 3-5 kV, nucleic acid molecules were successful for delivery of luciferase DNA and mRNA as well as siRNA-FITC to porcine tracheal tissue sections and for delivery of luciferase mRNA to whole porcine lungs via bronchoscope.

CONCLUSIONS

We report ex vivo delivery of nucleic acids to porcine lung tissue via electrospray and bronchoscopic electrospray delivery of nucleic acid to an ex vivo porcine lung model.

Electroporation-mediated delivery of FER gene enhances innate immune response and improves survival in a murine model of pneumonia

Previously, we reported that electroporation-mediated (EP) delivery of the FER gene improved survival in a combined trauma-pneumonia model. The mechanism of this protective effect is unknown. In this paper, we performed a pneumonia model in C57/BL6 mice with 500 CFU of Klebsiella pneumoniae. After inoculation, a plasmid encoding human FER was delivered by EP into the lung (PNA/pFER-EP). Survival of FER-treated vs. controls (PNA; PNA/EP-pcDNA) was recorded. In parallel cohorts, bronchial alveolar lavage (BAL) and lung were harvested at 24 and 72 h with markers of infection measured. FER-EP-treated animals reduced bacterial counts and had better 5-day survival compared to controls (80 vs. 20 vs. 25%; p < 0.05). Pre-treatment resulted in 100% survival. With FER, inflammatory monocytes were quickly recruited into BAL. These cells had increased surface expression for Toll-receptor 2 and 4, and increased phagocytic and myeloperoxidase activity at 24 h. Samples from FER electroporated animals had increased phosphorylation of STAT transcription factors, varied gene expression of IL1β, TNFα, Nrf2, Nlrp3, Cxcl2, HSP90 and increased cytokine production of TNF-α, CCL-2, KC, IFN-γ, and IL-1RA. In a follow-up experiment, using Methicillin-resistant Staphylococcus aureus (MRSA) similar bacterial reduction effects were obtained with FER gene delivery. We conclude that FER overexpression improves survival through STAT activation enhancing innate immunity and accelerating bacterial clearance in the lung. This constitutes a novel mechanism of inflammatory regulation with therapeutic potential in the setting of hospital-acquired pneumonia.

Electrotransfer of Different Control Plasmids Elicits Different Antitumor Effectiveness in B16.F10 Melanoma

Several studies have shown that different control plasmids may cause antitumor action in different murine tumor models after gene electrotransfer (GET). Due to the differences in GET protocols, plasmid vectors, and experimental models, the observed antitumor effects were incomparable. Therefore, the current study was conducted comparing antitumor effectiveness of three different control plasmids using the same GET parameters. We followed cytotoxicity in vitro and the antitumor effect in vivo after GET of control plasmids pControl, pENTR/U6 scr and pVAX1 in B16.F10 murine melanoma cells and tumors. Types of cell death and upregulation of selected cytosolic DNA sensors and cytokines were determined. GET of all three plasmids caused significant growth delay in melanoma tumors; nevertheless, the effect of pVAX1 was significantly greater than pControl. While DNA sensors in vivo were not upregulated significantly, cytokines IFN β and TNF α were upregulated after GET of pVAX1. In vitro, the mRNAs of some cytosolic DNA sensors were overexpressed after GET; however, with no significant difference among the three plasmids. In summary, although differences in antitumor effects were observed among control plasmids in vivo, no differences in cellular responses to plasmid GET were detected in tumor cells in vitro. Thus, the tumor microenvironment as well as some plasmid properties are most probably responsible for the antitumor effectiveness.

Genetically modified mesenchymal stromal cells in cancer therapy

The cell therapy industry has grown rapidly over the past 3 decades, and multiple clinical trials have been performed to date covering a wide range of diseases. The most frequently used cell is mesenchymal stromal cells (MSCs), which have been used largely for their anti-inflammatory actions and in situations of tissue repair and although they have demonstrated a good safety profile, their therapeutic efficacy has been limited. In addition to these characteristics MSCs are being used for their homing and engraftment properties and have been genetically modified to enable targeted delivery of a variety of therapeutic agents in both malignant and nonmalignant conditions. This review discusses the science and technology behind genetically modified MSC therapy in malignant disease and how potential problems have been overcome to enable their use in two novel clinical trials in metastatic gastrointestinal and lung cancer.

Featured Article: Electroporation-mediated gene delivery of surfactant protein B (SP-B) restores expression and improves survival in mouse model of SP-B deficiency

Surfactant Protein B Deficiency is a rare but lethal monogenetic, congenital lung disease of the neonate that is unresponsive to any treatment except lung transplantation. Based on the potential that gene therapy offers to treat such intractable diseases, our objective was to test whether an electroporation-based gene delivery approach could restore surfactant protein B expression and improve survival in a compound knockout mouse model of surfactant protein B deficiency. Surfactant protein B expression can be shut off in these mice upon withdrawl of doxycycline, resulting in decreased levels of surfactant protein B within four days and death due to lung dysfunction within four to seven days. Control or one of several different human surfactant protein B-expressing plasmids was delivered to the lung by aspiration and electroporation at the time of doxycycline removal or four days later. Plasmids expressing human surfactant protein B from either the UbC or CMV promoter expressed surfactant protein B in these transgenic mice at times when endogenous surfactant protein B expression was silenced. Mean survival was increased 2- to 5-fold following treatment with the UbC or CMV promoter-driven plasmids, respectively. Histology of all surfactant protein B treated groups exhibited fewer neutrophils and less alveolar wall thickening compared to the control groups, and electron microscopy revealed that gene transfer of surfactant protein B resulted in lamellar bodies that were similar in the presence of electron-dense, concentric material to those in surfactant protein B-expressing mice. Taken together, our results show that electroporation-mediated gene delivery of surfactant protein B-expressing plasmids improves survival, lung function, and lung histology in a mouse model of surfactant protein B deficiency and suggest that this may be a useful approach for the treatment of this otherwise deadly disease. Impact statement Surfactant protein B (SP-B) deficiency is a rare but lethal genetic disease of neonates that results in severe respiratory distress with no available treatments other than lung transplantation. The present study describes a novel treatment for this disease by transferring the SP-B gene to the lungs using electric fields in a mouse model. The procedure is safe and results in enough expression of exogenous SP-B to improve lung histology, lamellar body structure, and survival. If extended to humans, this approach could be used to bridge the time between diagnosis and lung transplantation and could greatly increase the likelihood of affected neonates surviving to transplantation and beyond.

Involvement of a Rac1-Dependent Macropinocytosis Pathway in Plasmid DNA Delivery by Electrotransfection

Electrotransfection is a widely used method for delivering genes into cells with electric pulses. Although different hypotheses have been proposed, the mechanism of electrotransfection remains controversial. Previous studies have indicated that uptake and intracellular trafficking of plasmid DNA (pDNA) are mediated by endocytic pathways, but it is still unclear which pathways are directly involved in the delivery. To this end, the present study investigated the dependence of electrotransfection on macropinocytosis. Data from the study demonstrated that electric pulses induced cell membrane ruffling and actin cytoskeleton remodeling. Using fluorescently labeled pDNA and a macropinocytosis marker (i.e., dextran), the study showed that electrotransfected pDNA co-localized with dextran in intracellular vesicles. Furthermore, electrotransfection efficiency could be decreased significantly by reducing temperature or treatment of cells with a pharmacological inhibitor of Rac1 and could be altered by changing Rac1 activity. Taken together, the findings suggested that electrotransfection of pDNA involved Rac1-dependent macropinocytosis.

Electroporation-mediated delivery of the FER gene in the resolution of trauma-related fatal pneumonia

Injured patients with lung contusion (LC) are at risk of developing bacterial pneumonia (PNA) followed by sepsis and death. A recent genome-wide association study (GWAS) showed FER gene expression positively correlating with survival rates among individuals with above conditions. We sought to determine whether electroporation (EP)-mediated delivery of FER gene could indeed improve survival, in a lethal model of combined LC and PNA. C57BL/6 mice sustained unilateral LC, which preceded a 500 Klebsiella colony forming unit (CFU) inoculation by 6 h. In-between these insults, human FER plasmid (pFER) was introduced into the lungs followed by eight EP pulses applied externally (10 ms at 200 V cm^-1). Control groups included EP of empty vector (pcDNA3) or Na⁺/K⁺-ATPase genes (pPump) and no treatment (LC+PNA). We recorded survival, histology, lung mechanics, bronchial alveolar lavage (BAL) fluid, FER and inflammatory gene expression and bacteriology. The data show that 7-day survival was significantly improved by pFER compared with control groups. pFER increased BAL monocytes and activated antibacterial response genes (nitric oxide synthase (NOS), Fizz). pFER treatment showed decreased lung and blood Klebsiella counts reaching, in some cases, complete sterilization. In conclusion, FER gene delivery promoted survival in LC+PNA mice via recruitment of activated immune cells, improving efficiency of bacterial clearance within contused lung.

Applications of the CRISPR/Cas9 system in murine cancer modeling

Advanced biological technologies allowing for genetic manipulation of the genome are increasingly being used to unravel the molecular pathogenesis of human diseases. The clustered regulatory interspaced short palindromic repeat/CRISPR-associated protein (CRISPR/Cas) technology started a revolution of this field owing to its flexibility and relative ease of use. Recently, application of the CRISPR/Cas9 system has been extended to in vivo approaches, leveraging its potential for human disease modeling. Particularly in oncological research, where genetic defects in somatic cells are tightly linked to etiology and pathological phenotypes, the CRISPR/Cas technology is being used to recapitulate various types of genetic aberrations. Here we review murine cancer models that have been developed via combining the CRISPR/Cas9 technology with in vivo somatic gene transfer approaches. Exploiting these methodological advances will further accelerate detailed investigations of tumor etiology and treatment.

β1-Na(+),K(+)-ATPase gene therapy upregulates tight junctions to rescue lipopolysaccharide-induced acute lung injury

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are associated with diverse disorders and characterized by disruption of the alveolar-capillary barrier, leakage of edema fluid into the lung, and substantial inflammation leading to acute respiratory failure. Gene therapy is a potentially powerful approach to treat ALI/ARDS through repair of alveolar epithelial function. Herein, we show that delivery of a plasmid expressing β1-subunit of the Na(+),K(+)-ATPase (β1-Na(+),K(+)-ATPase) alone or in combination with epithelial sodium channel (ENaC) α1-subunit using electroporation not only protected from subsequent lipopolysaccharide (LPS)-mediated lung injury, but also treated injured lungs. However, transfer of α1-subunit of ENaC (α1-ENaC) alone only provided protection benefit rather than treatment benefit although alveolar fluid clearance had been remarkably enhanced. Gene transfer of β1-Na(+),K(+)-ATPase, but not α1-ENaC, not only enhanced expression of tight junction protein zona occludins-1 (ZO-1) and occludin both in cultured cells and in mouse lungs, but also reduced pre-existing increase of lung permeability in vivo. These results demonstrate that gene transfer of β1-Na(+),K(+)-ATPase upregulates tight junction formation and therefore treats lungs with existing injury, whereas delivery of α1-ENaC only maintains pre-existing tight junction but not for generation. This indicates that the restoration of epithelial/endothelial barrier function may provide better treatment of ALI/ARDS.

Multiplexed pancreatic genome engineering and cancer induction by transfection-based CRISPR/Cas9 delivery in mice

Mouse transgenesis has provided fundamental insights into pancreatic cancer, but is limited by the long duration of allele/model generation. Here we show transfection-based multiplexed delivery of CRISPR/Cas9 to the pancreas of adult mice, allowing simultaneous editing of multiple gene sets in individual cells. We use the method to induce pancreatic cancer and exploit CRISPR/Cas9 mutational signatures for phylogenetic tracking of metastatic disease. Our results demonstrate that CRISPR/Cas9-multiplexing enables key applications, such as combinatorial gene-network analysis, in vivo synthetic lethality screening and chromosome engineering. Negative-selection screening in the pancreas using multiplexed-CRISPR/Cas9 confirms the vulnerability of pancreatic cells to Brca2-inactivation in a Kras-mutant context. We also demonstrate modelling of chromosomal deletions and targeted somatic engineering of inter-chromosomal translocations, offering multifaceted opportunities to study complex structural variation, a hallmark of pancreatic cancer. The low-frequency mosaic pattern of transfection-based CRISPR/Cas9 delivery faithfully recapitulates the stochastic nature of human tumorigenesis, supporting wide applicability for biological/preclinical research.

CRISPR/Cas9 technology has been used for genome engineering in vivo. Here, the authors use a transfection technique to deliver multiple guide RNAs to the pancreas of adult mice, allowing genetic screening and chromosome engineering in pancreatic cancer.

Gene Electrotransfer: A Mechanistic Perspective

Gene electrotransfer is a powerful method of DNA delivery offering several medical applications, among the most promising of which are DNA vaccination and gene therapy for cancer treatment. Electroporation entails the application of electric fields to cells which then experience a local and transient change of membrane permeability. Although gene electrotransfer has been extensively studied in in vitro and in vivo environments, the mechanisms by which DNA enters and navigates through cells are not fully understood. Here we present a comprehensive review of the body of knowledge concerning gene electrotransfer that has been accumulated over the last three decades. For that purpose, after briefly reviewing the medical applications that gene electrotransfer can provide, we outline membrane electropermeabilization, a key process for the delivery of DNA and smaller molecules. Since gene electrotransfer is a multipart process, we proceed our review in describing step by step our current understanding, with particular emphasis on DNA internalization and intracellular trafficking. Finally, we turn our attention to in vivo testing and methodology for gene electrotransfer.

Electroporation-mediated gene delivery of Na+,K+ -ATPase, and ENaC subunits to the lung attenuates acute respiratory distress syndrome in a two-hit porcine model

INTRODUCTION

Acute respiratory distress syndrome (ARDS) is a common cause of organ failure with an associated mortality rate of 40%. The initiating event is disruption of alveolar-capillary interface causing leakage of edema into alveoli.

HYPOTHESIS

Electroporation-mediated gene delivery of epithelial sodium channel (ENaC) and Na+,K+ -ATPase into alveolar cells would improve alveolar clearance of edema and attenuate ARDS.

METHODS

Pigs were anesthetized and instrumented, and the superior mesenteric artery was clamped to cause gut ischemia/reperfusion injury and peritoneal sepsis by fecal clot implantation. Animals were ventilated according to ARDSnet protocol. Four hours after injury, animals were randomized into groups: (i) treatment: Na+,K+ -ATPase/ENaC plasmid (n = 5) and (ii) control: empty plasmid (n = 5). Plasmids were delivered to the lung using bronchoscope. Electroporation was delivered using eight-square-wave electric pulses across the chest. Following electroporation, pigs were monitored 48 h.

RESULTS

The Pao2/Fio2 ratio and lung compliance were higher in the treatment group. Lung wet/dry ratio was lower in the treatment group. Relative expression of the Na+,K+ -ATPase transgene was higher throughout lungs receiving treatment plasmids. Quantitative histopathology revealed a reduction in intra-alveolar fibrin in the treatment group. Bronchoalveolar lavage showed increased surfactant protein B in the treatment group. Survival was improved in the treatment group.

CONCLUSIONS

Electroporation-mediated transfer of Na+,K+ -ATPase/ENaC plasmids improved lung function, reduced fibrin deposits, decreased lung edema, and improved survival in a translational porcine model of ARDS. Gene therapy can attenuate ARDS pathophysiology in a high-fidelity animal model, suggesting a potential new therapy for patients.

Oxidative Stress and Plasma Membrane Repair in Single Myoblasts After Femtosecond Laser Photoporation

Cell membranes are susceptible to biophysical damages. These biophysical damages often present themselves in challenging oxidative environments, such as in chronic inflammation. Here we report the damage evolution after single myoblasts were individually subjected to femtosecond (fs) laser photoporation on their plasma membranes under normal and oxidative conditions. A well-characterized tunable fs laser was coupled with a laser scanning confocal microscope. The post-damage wound evolution was documented by real-time imaging. The fs laser could generate a highly focused hole at a targeted site of the myoblast plasma membrane. The initial hole size depended on the laser dosage in terms of power and exposure duration. With the same laser power and irradiation duration, photoporation invoked bigger holes in the oxidative groups than in the control. Myoblasts showed difficulty in repairing holes with initial size beyond certain threshold. Within the threshold, holes could apparently be resealed within 100 s under the normal condition; while in oxidative condition, the resealing process could take 100-300 s. The hole-resealing capacity of myoblasts was compromised under oxidative stress particularly when the oxidative exposure was chronic. It is interesting to note that brief exposure to oxidative stress apparently could promote resealing in myoblasts after photoporation.

Improved Specificity of Gene Electrotransfer to Skin Using pDNA Under the Control of Collagen Tissue-Specific Promoter

In order to ensure safe, efficient and controlled gene delivery to skin, the improvement of delivery methods together with proper design of DNA is required. Non-viral delivery methods, such as gene electrotransfer, and the design of tissue-specific promoters are promising tools to ensure the safety of gene delivery to the skin. In the scope of our study, we evaluated a novel skin-specific plasmid DNA with collagen (COL) promoter, delivered to skin cells and skin tissue by gene electrotransfer. In vitro, we determined the specificity of the COL promoter in fibroblast cells. The specific expression under the control of COL promoter was obtained for the reporter gene DsRed as well as for therapeutic gene encoding cytokine IL-12. In vivo, the plasmid with COL promoter encoding the reporter gene DsRed was efficiently transfected to mouse skin. It resulted in the notable and controlled manner, however, in lower and shorter expression, compared to that obtained with ubiquitous promoter. The concentration of the IL-12 in the skin after the in vivo transfection of plasmid with COL promoter was in the same range as after the treatment in control conditions (injection of distilled water followed by the application of electric pulses). Furthermore, this gene delivery was local, restricted to the skin, without any evident systemic shedding of IL-12. Such specific targeting of skin cells, observed with tissue-specific COL promoter, would improve the effectiveness and safety of cutaneous gene therapies and DNA vaccines.

Physical methods for gene transfer

The key impediment to the successful application of gene therapy in clinics is not the paucity of therapeutic genes. It is rather the lack of nontoxic and efficient strategies to transfer therapeutic genes into target cells. Over the past few decades, considerable progress has been made in gene transfer technologies, and thus far, three different delivery systems have been developed with merits and demerits characterizing each system. Viral and chemical methods of gene transfer utilize specialized carrier to overcome membrane barrier and facilitate gene transfer into cells. Physical methods, on the other hand, utilize various forms of mechanical forces to enforce gene entry into cells. Starting in 1980s, physical methods have been introduced as alternatives to viral and chemical methods to overcome various extra- and intracellular barriers that limit the amount of DNA reaching the intended cells. Accumulating evidence suggests that it is quite feasible to directly translocate genes into cytoplasm or even nuclei of target cells by means of mechanical force, bypassing endocytosis, a common pathway for viral and nonviral vectors. Indeed, several methods have been developed, and the majority of them share the same underlying mechanism of gene transfer, i.e., physically created transient pores in cell membrane through which genes get into cells. Here, we provide an overview of the current status and future research directions in the field of physical methods of gene transfer.

Electroporation-mediated gene delivery

Electroporation has been used extensively to transfer DNA to bacteria, yeast, and mammalian cells in culture for the past 30 years. Over this time, numerous advances have been made, from using fields to facilitate cell fusion, delivery of chemotherapeutic drugs to cells and tissues, and most importantly, gene and drug delivery in living tissues from rodents to man. Electroporation uses electrical fields to transiently destabilize the membrane allowing the entry of normally impermeable macromolecules into the cytoplasm. Surprisingly, at the appropriate field strengths, the application of these fields to tissues results in little, if any, damage or trauma. Indeed, electroporation has even been used successfully in human trials for gene delivery for the treatment of tumors and for vaccine development. Electroporation can lead to between 100 and 1000-fold increases in gene delivery and expression and can also increase both the distribution of cells taking up and expressing the DNA as well as the absolute amount of gene product per cell (likely due to increased delivery of plasmids into each cell). Effective electroporation depends on electric field parameters, electrode design, the tissues and cells being targeted, and the plasmids that are being transferred themselves. Most importantly, there is no single combination of these variables that leads to greatest efficacy in every situation; optimization is required in every new setting. Electroporation-mediated in vivo gene delivery has proven highly effective in vaccine production, transgene expression, enzyme replacement, and control of a variety of cancers. Almost any tissue can be targeted with electroporation, including muscle, skin, heart, liver, lung, and vasculature. This chapter will provide an overview of the theory of electroporation for the delivery of DNA both in individual cells and in tissues and its application for in vivo gene delivery in a number of animal models.

Physical energy for drug delivery; poration, concentration and activation

Techniques for controlling the rate and duration of drug delivery, while targeting specific locations of the body for treatment, to deliver the cargo (drugs or DNA) to particular parts of the body by what are becoming called "smart drug carriers" have gained increased attention during recent years. Using such smart carriers, researchers have also been investigating a number of physical energy forces including: magnetic fields, ultrasound, electric fields, temperature gradients, photoactivation or photorelease mechanisms, and mechanical forces to enhance drug delivery within the targeted cells or tissues and also to activate the drugs using a similar or a different type of external trigger. This review aims to cover a number of such physical energy modalities. Various advanced techniques such as magnetoporation, electroporation, iontophoresis, sonoporation/mechnoporation, phonophoresis, optoporation and thermoporation will be covered in the review. Special emphasis will be placed on photodynamic therapy owing to the experience of the authors' laboratory in this area, but other types of drug cargo and DNA vectors will also be covered. Photothermal therapy and theranostics will also be discussed.

Electroporation-mediated gene delivery to the lungs

Electroporation is a safe, efficient, and inexpensive method to transfer naked plasmid DNA into various tissues. For electroporation-mediated gene transfer to the mouse lung, a plasmid solution is delivered to the lungs via the trachea. Immediately after plasmid delivery, eight square wave pulses are delivered by two pre-gelled electrodes placed on each side of the chest. An optimal field strength in mice is 200 V/cm, with a pulse duration of 10 ms each and a 1 s interval between pulses. High level gene expression can be achieved within 24 h in all cell types in the lung with very little inflammation and no apparent trauma.

Electroporation-mediated delivery of genes in rodent models of lung contusion

Several of the biological processes involved in the pathogenesis of acute lung injury and acute respiratory distress syndrome after lung contusion are regulated at a genetic and epigenetic level. Thus, strategies to manipulate gene expression in this context are highly desirable not only to elucidate the mechanisms involved but also to look for potential therapies. In the present chapter, we describe mouse and rat models of inducing blunt thoracic injury followed by electroporation-mediated gene delivery to the lung. Electroporation is a highly efficient and easily reproducible technique that allows circumvention of several of lung gene delivery challenges and safety issues present with other forms of lung gene therapy.

Innovation and translation efforts in wireless medical connectivity, telemedicine and eMedicine: a story from the RFID Center of Excellence at the University of Pittsburgh

Translational research has recently been rediscovered as one of the basic tenants of engineering. Although many people have numerous ideas of how to accomplish this successfully, the fundamental method is to provide an innovative and creative environment. The University of Pittsburgh has been accomplishing this goal though a variety of methodologies. The contents of this paper are exemplary of what can be achieved though the interaction of students, staff, faculty and, in one example, high school teachers. While the projects completed within the groups involved in this paper have spanned other areas, the focus of this paper is on the biomedical devices, that is, towards improving and maintaining health in a variety of areas. The spirit of the translational research is discovery, invention, intellectual property protection, and the creation of value through the spinning off of companies while providing better health care and creating jobs. All but one of these projects involve wireless radio frequency (RF) energy for delivery. The remaining device can be wirelessly connected for data collection.

Cell-specific targeting strategies for electroporation-mediated gene delivery in cells and animals

The use of electroporation to facilitate gene transfer is an extremely powerful and useful method for both in vitro and in vivo applications. One of its great strengths is that it induces functional destabilization and permeabilization of cell membranes throughout a tissue leading to widespread gene transfer to multiple cells and cell types within the electric field. While this is a strength, it can also be a limitation in terms of cell-specific gene delivery. The ability to restrict gene delivery and expression to particular cell types is of paramount importance for many types of gene therapy, since ectopic expression of a transgene could lead to deleterious host inflammatory responses or dysregulation of normal cellular functions. At present, there are relatively few ways to obtain cell-specific targeting of nonviral vectors, molecular probes, small molecules, and imaging agents. We have developed a novel means of restricting gene delivery to desired cell types based on the ability to control the transport of plasmids into the nuclei of desired cell types. In this article, we discuss the mechanisms of this approach and several applications in living animals to demonstrate the benefits of the combination of electroporation and selective nuclear import of plasmids for cell-specific gene delivery.

Viral and nonviral delivery systems for gene delivery

Gene therapy is the process of introducing foreign genomic materials into host cells to elicit a therapeutic benefit. Although initially the main focus of gene therapy was on special genetic disorders, now diverse diseases with different patterns of inheritance and acquired diseases are targets of gene therapy. There are 2 major categories of gene therapy, including germline gene therapy and somatic gene therapy. Although germline gene therapy may have great potential, because it is currently ethically forbidden, it cannot be used; however, to date human gene therapy has been limited to somatic cells. Although numerous viral and nonviral gene delivery systems have been developed in the last 3 decades, no delivery system has been designed that can be applied in gene therapy of all kinds of cell types in vitro and in vivo with no limitation and side effects. In this review we explain about the history of gene therapy, all types of gene delivery systems for germline (nuclei, egg cells, embryonic stem cells, pronuclear, microinjection, sperm cells) and somatic cells by viral [retroviral, adenoviral, adeno association, helper-dependent adenoviral systems, hybrid adenoviral systems, herpes simplex, pox virus, lentivirus, Epstein-Barr virus)] and nonviral systems (physical: Naked DNA, DNA bombardant, electroporation, hydrodynamic, ultrasound, magnetofection) and (chemical: Cationic lipids, different cationic polymers, lipid polymers). In addition to the above-mentioned, advantages, disadvantages, and practical use of each system are discussed.

Electroporation-mediated in vivo gene delivery of the Na+/K+-ATPase pump reduced lung injury in a mouse model of lung contusion

BACKGROUND

Lung contusion (LC) is an independent risk factor for acute respiratory distress syndrome. The final common pathway in ARDS involves accumulation of fluid in the alveoli. In this study, we demonstrate the application of a potential gene therapy approach by delivering the Na+/K+-ATPase pump subunits in a murine model of LC. We hypothesized that restoring the activity of the pump will result in removal of excess alveolar fluid and additionally reduce inflammation.

METHODS

Under anesthesia, C57/BL6 mice were struck along the right posterior axillary line 1 cm above the costal margin with a cortical contusion impactor. Immediately afterward, 100 μg of plasmid DNA coding for the α,β of the Na+/K+-ATPase pump were instilled into the lungs (LC-electroporation-pump group). Contusion only (LC-only) and a sham saline instillation group after contusion were used as controls (LC-electroporation-sham). By using a BTX 830 electroporator, eight electrical pulses of 200 V/cm field strength were applied transthoracically. Mice were killed at 24 hours, 48 hours, and 72 hours after delivery. Bronchial alveolar lavage was recollected to measure albumin and cytokines by enzyme-linked immunosorbent assay. Pulmonary compliance was measured, and lungs were subject to histopathologic analysis.

RESULTS

After the electroporation and delivery of genes coding for the α,β subunits of the Na+/K+-ATPase pump, there was a significant mitigation of acute lung injury as evidenced by reduction in bronchial alveolar lavage levels of albumin, improved pressure volume curves, and reduced inflammation seen on histology.

CONCLUSION

Electroporation-mediated gene transfer of the subunits of the Na+/K+-ATPase pump enhanced recovery from acute inflammatory lung injury after LC.

Towards the mechanisms for efficient gene transfer into cells and tissues by means of cell electroporation

INTRODUCTION

Intracellular gene electrotransfer by means of electroporation has been on the increase during the past decade. Significant progress has been achieved both in characterizing mechanisms of gene electrotransfer and in optimizing the protocol in many preclinical trials. Recently this has led to initiation of clinical trials of gene electrotransfer to treat metastatic melanomas. Further progress with the method in various clinical trials requires better understanding of mechanisms of gene electrotransfer.

AREAS COVERED

A summary of recent progress in understanding mechanisms of gene electrotransfer, imparting general knowledge of cell electroporation and intracellular molecule electrotransfer.

EXPERT OPINION

Gene electrotransfer into cells and tissues is a complex process involving multiple steps that lead to plasmid DNA passage from the extracellular region to the cell nucleus crossing the barriers of the plasma membrane, cytoplasm and nucleus membrane. Electrical parameters of pulses used for gene electrotransfer affect the initial steps of DNA translocation through the plasma membrane and play a crucial role in determining the transfection efficiency. When considering gene electrotransfer into tissues it becomes clear that other nonelectrical conditions are also of primary importance.

Gene therapy for ALI/ARDS

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are characterized by acute respiratory failure and are associated with diverse disorders. Gene therapy is a potentially powerful approach to treat diseases related to ALI/ARDS, and numerous viral and nonviral methods for gene delivery to the lung have been developed. Discussed are recent advances in the development of more efficient viral and nonviral gene transfer systems, and the current status of gene therapy applied to ALI/ARDS-associated pulmonary diseases is reviewed. With the development of more efficient gene therapy vectors, gene therapy is a promising strategy for clinical application.

Targeted nonviral gene-based inhibition of Gα(i/o)-mediated vagal signaling in the posterior left atrium decreases vagal-induced atrial fibrillation

BACKGROUND

Pharmacologic and ablative therapies for atrial fibrillation (AF) have suboptimal efficacy. Newer gene-based approaches that target specific mechanisms underlying AF are likely to be more efficacious in treating AF. Parasympathetic signaling appears to be an important contributor to AF substrate.

OBJECTIVE

The purpose of this study was to develop a nonviral gene-based strategy to selectively inhibit vagal signaling in the left atrium and thereby suppress vagal-induced AF.

METHODS

In eight dogs, plasmid DNA vectors (minigenes) expressing Gα(i) C-terminal peptide (Gα(i)ctp) was injected in the posterior left atrium either alone or in combination with minigene expressing Gα(o)ctp, followed by electroporation. In five control dogs, minigene expressing scrambled peptide (Gα(R)ctp) was injected. Vagal- and carbachol-induced left atrial effective refractory periods (ERPs), AF inducibility, and Gα(i/o)ctp expression were assessed 3 days following minigene delivery.

RESULTS

Vagal stimulation- and carbachol-induced effective refractory period shortening and AF inducibility were significantly attenuated in atria receiving a Gα(i2)ctp-expressing minigene and were nearly eliminated in atria receiving both Gα(i2)ctp- and Gα(o1)ctp-expressing minigenes.

CONCLUSION

Inhibition of both G(i) and G(o) proteins is necessary to abrogate vagal-induced AF in the left atrium and can be achieved via constitutive expression of Gα(i/o)ctps expressed by nonviral plasmid vectors delivered to the posterior left atrium.

Magnetically guided lentiviral-mediated transduction of airway epithelial cells

BACKGROUND

Lentiviral (LV) vectors are able to only slowly and inefficiently transduce nondividing cells such as those of the airway epithelium. To address this issue, we have exploited the magnetofection technique in in vitro models of airway epithelium.

METHODS

Magnetofectins were formed by noncovalent interaction between LV particles and polycation-coated iron oxide nanoparticles. Efficiency of LV-mediated transduction (as evaluated through green fluorescent protein (GFP) expression by cytofluorimetric analysis) was measured in bronchial epithelial cells in the presence or absence of a magnetic field. Cytotoxicity was evaluated by lactate dehydrogenase (LDH) release; cell monolayer integrity by measurement of transepithelial resistance (TER) and evaluation of correct zonula occludens-1 (ZO-1) localization at tight junctions (TJs) by immunofluorescence and confocal microscopy.

RESULTS

In nonpolarized cells, magnetofectins enhanced LV-mediated transduction at multiplicity of infection (MOI) of 50 up to 3.9-fold upon a 24-h incubation, to levels that approached those achieved at MOI of 200 for LV alone, in the presence or absence of the magnetic field. Magnetofection significantly increased the percentage of transduced cells up to 186-fold already after 15 min of incubation. In polarized cells, magnetofection increased GFP+ cells up to 24-fold compared to LV alone. Magnetofection did not enhance LDH release and slightly altered TER but not ZO-1 localization at the TJs.

CONCLUSIONS

We conclude that magnetofection can facilitate in vitro LV-mediated transduction of airway epithelial cells, in the absence of overt cytotoxicity and maintaining epithelial integrity, by lowering the necessary vector dose and reducing the incubation time required to achieve efficient transduction.

Metabolically stabilized long-circulating PEGylated polyacridine peptide polyplexes mediate hydrodynamically stimulated gene expression in liver

A novel class of PEGylated polyacridine peptides was developed that mediate potent stimulated gene transfer in the liver of mice. Polyacridine peptides, (Acr-X)_n-Cys-PEG, possessing 2–6 repeats of Lys-acridine (Acr) spaced by either Lys, Arg, Leu or Glu, were Cys derivatized with polyethylene glycol (PEG _{5000 Da}) and evaluated as in vivo gene transfer agents. An optimal peptide of (Acr-Lys)₆-Cys-PEG was able to bind to plasmid DNA (pGL3) with high affinity by polyintercalation, stabilize DNA from metabolism by DNAse and extend the pharmacokinetic half-life of DNA in the circulation for up to 2 hrs. A tail vein dose of PEGylated polyacridine peptide pGL3 polyplexes (1 μg in 50 μl), followed by a stimulatory hydrodynamic dose of normal saline at times ranging from 5–60 min post-DNA administration, led to a high level of luciferase expression in the liver, equivalent to levels mediated by direct hydrodynamic dosing of 1 μg of pGL3. The results establish the unique properties of PEGylated polyacridine peptides as a new and promising class of gene delivery peptides that facilitate reversible binding to plasmid DNA, protecting it from DNase in vivo resulting in an extended circulatory half-life, and release of transfection-competent DNA into the liver to mediate a high-level of gene expression upon hydrodynamic boost.

Efficient, specific and targeted delivery of genes to the lung

Many inherited and acquired pulmonary disorders without satisfactory therapies may be amenable to gene therapy. Despite numerous advances, efficient delivery and expression of the therapeutic transgene at physiological levels for phenotypic correction of disease has proved elusive. This article focuses on various strategies aimed at achieving targeted delivery to the lungs. Both physical methods and biological targeting have been successfully applied in various gene delivery systems. Targeting of different cell types has been achieved by pseudotyping of viral vectors with capsids from different serotypes and modification of nonviral vectors with targeting ligands. Both classes of vectors are discussed with respect to their gene delivery and expression efficiencies, longevity of expression and immunogenicity. Moreover, gene therapy clinical trials for different lung diseases are discussed.

Ultrasound-assisted non-viral gene transfer to the salivary glands

We report a non-viral gene transfer method using ultrasound induced microbubble destruction to allow the uptake of plasmid gene transfer vectors to the cells of the mouse salivary gland. The Luciferase (Luc) reporter gene, driven by a cytomegalovirus (CMV) promoter, was delivered unilaterally to the submandibular salivary gland via retroductal cannulation and Luc expression was monitored with in vivo imaging. The CMV-Luc plasmid was delivered to the salivary gland in a carrier solution containing microbubbles composed of lipid-encased perfluoropropane gas, with two different concentrations of microbubbles used (100 and 15% volume/volume). An Adenoviral (Ad) vector using an identical CMV-Luc expression cassette was used as a positive control at two different dosages. Whereas ultrasound-assisted gene transfer (UAGT) with 100% microbubbles was weak and rapidly extinguished, UAGT with the 15% microbubble solution was robust and stable for 28 days. UAGT seems to be a practicable and promising method for non-viral gene delivery to the salivary glands.

Electroporation- and mechanical ventilation-mediated gene transfer to the lung

Our lab has previously demonstrated that cytoplasmic trafficking and subsequent nuclear entry of non-viral plasmid DNA can be significantly enhanced through the application of cyclic stretch following transfection in vitro^1,2. Here, we demonstrate that cyclic stretching of the murine lung using ventilation immediately following the endotracheal administration and transthoracic electroporation of plasmid DNA increases exogenous gene expression up to 4-fold over Our mice that were not ventilated after plasmid administration and transfection via electroporation in vivo. This increase is time and sequence specific (i.e. the ventilation must occur immediately after the transfection event). The ventilation-enhanced gene transfer is also amplitude-dependent, confirming similar studies completed in vitro, and is mediated, at least in part, through the cytoplasmic tubulin deacetylase, HDAC6. Using immunohistochemistry, we demonstrate that this increase in expression is due to an increase in the number of cells expressing the exogenous protein rather than an increase in the amount of protein produced per cell. These studies demonstrate the potential mechanical stimulation has in vivo in significantly increasing non-viral DNA gene expression, and may ultimately pave the way for more successful clinical trials using this type of therapy in the future.

Sonoporation mediated immunogene therapy of solid tumors

Development of gene-based therapies for the treatment of inherited and acquired diseases, including cancer, has seen renewed interest in the use of nonviral vectors coupled to physical delivery modalities. Low-frequency ultrasound (US), with a well-established record in a clinical setting, has the potential to deliver DNA efficiently, accurately and safely. Optimal in vivo parameters for US-mediated delivery of naked plasmid DNA were established using the firefly luciferase reporter gene construct. Optimized parameters were used to administer a therapeutic gene construct, coding for granulocyte-macrophage colony-stimulating factor (GM-CSF) and B7-1 costimulatory molecule, to growing murine fibrosarcoma tumors. Tumor progression and animal survival was monitored throughout the study and the efficacy of the US-mediated gene therapy determined and compared with an electroporation-based approach. Optimal parameters for US-mediated delivery of plasmid DNA to tumors were deduced to be 1.0 W/cm(2) at 20% duty cycle for 5 min (60 J/cm(2)). In vivo US-mediated gene therapy resulted in a 55% cure rate in tumor-bearing animals. The immunological response invoked was cell mediated, conferring resistance against re-challenge and resistance to tumor challenge after transfer of splenocytes to naïve animals. US treatment was noninjurious to treated tissue, whereas therapeutic efficacy was comparable to an electroporation-based approach. US-mediated delivery of an immune-gene construct to growing tumors was therapeutically effective. Sonoporation has the potential to be a major factor in the development of nonviral gene delivery approaches.

The SP-C promoter facilitates alveolar type II epithelial cell-specific plasmid nuclear import and gene expression

Although nonviral gene therapy has great potential for use in the lung, the relative lack of cell-specific targeting has limited its applications. We have developed a new approach for cell-specific targeting based on selective nuclear import of plasmids in non-dividing cells. Using a microinjection and in situ hybridization approach, we tested several potential DNA sequences for the ability to mediate plasmid nuclear import in alveolar type II epithelial (ATII) cells. Of these, only a sequence within the human surfactant protein C (SP-C) promoter was able to mediate nuclear localization of plasmid DNA specifically in ATII cells but not in other cell types. We have mapped the minimal import sequence to the proximal 318 nucleotides of the promoter, and demonstrate that binding sites for NFI, TTF-1, and GATA-6 and the proteins themselves are required for import activity. Using intratracheal delivery of DNA followed by electroporation, we demonstrate that the SP-C promoter sequence will enhance gene expression specifically in ATII cells in mouse lung. This represents a novel activity for the SP-C promoter and thus ATII cell-specific nuclear import of DNA may prove to be a safe and effective method for targeted and enhanced gene expression in ATII cells.

Electroporation and ultrasound enhanced non-viral gene delivery in vitro and in vivo

Non-viral vectors are less efficient than the use of viral vectors for delivery of genetic material to cells in vitro and especially in vivo. However, viral vectors involve the use of foreign proteins that can stimulate both the innate and acquired immune response. In contrast, plasmid DNA can be delivered without carrier proteins and is non-immunogenic. Plasmid gene delivery can be enhanced by the use of physical methods that aid the passage of the plasmid through the cell membrane. Electroporation and microbubble-enhanced ultrasound are two of the most effective physical delivery methods and these can be applied to a range of different cell types in vitro and a broad range of tissues in vivo. Both techniques also have the advantage that, unlike viral vectors, they can be used to target specific tissues with systemic delivery. Although electroporation is often the more efficient of the two, microbubble-enhanced ultrasound causes less damage and is less invasive. This review provides an introduction to the methodology and summarises the range of cells and tissues that have been genetically modified using these techniques.

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.