Enhanced cutaneous gene delivery following intradermal injection of naked DNA in a high ionic strength solution

Molecule(s) of Interest: I. Ionic Liquids-Gateway to Newer Nanotechnology Applications: Advanced Nanobiotechnical Uses', Current Status, Emerging Trends, Challenges, and Prospects

Ionic liquids are a potent class of organic compounds exhibiting unique physico-chemical properties and structural compositions that are different from the classical dipolar organic liquids. These molecules have found diverse applications in different chemical, biochemical, biophysical fields, and a number of industrial usages. The ionic liquids-based products and procedural applications are being developed for a number of newer industrial purposes, and academic uses in nanotechnology related procedures, processes, and products, especially in nanobiotechnology and nanomedicine. The current article overviews their uses in different fields, including applications, functions, and as parts of products and processes at primary and advanced levels. The application and product examples, and prospects in various fields of nanotechnology, domains of nanosystem syntheses, nano-scale product development, the process of membrane filtering, biofilm formation, and bio-separations are prominently discussed. The applications in carbon nanotubes; quantum dots; and drug, gene, and other payload delivery vehicle developments in the nanobiotechnology field are also covered. The broader scopes of applications of ionic liquids, future developmental possibilities in chemistry and different bio-aspects, promises in the newer genres of nanobiotechnology products, certain bioprocesses controls, and toxicity, together with emerging trends, challenges, and prospects are also elaborated.

Basic concepts, current evidence, and future potential for gene therapy in managing cutaneous wounds

OBJECTIVE

Several studies have investigated the role of gene therapy in the healing process. The aim of this review is to explain the gene delivery systems in wound area.

RESULTS

Ninety-two studies were included and comprehensively overviewed. We described the importance of viral vectors such as adenoviruses, adeno-associated viruses, and retroviruses, and conventional non-viral vectors such as naked DNA injections, liposomes, gene gun, electroporation, and nanoparticles in achieving high-level expression of genes. Application of viral transfection, liposomal vectors, and electroporation were the main gene delivery systems. Genes encoding for growth factors or cytokines have been shown to result in a better wound closure in comparison to application of the synthetic growth factors. In addition, a combination of stem cell and gene therapy has been found an effective approach in regeneration of cutaneous wounds.

CONCLUSIONS

This article gives an overview of the methods and investigations applied on gene therapy in wound healing. However, clinical investigations need to be undertaken to gain a better understanding of gene delivery technologies and their roles in stimulating wound repair.

Development of a bio-electrospray system for cell and non-viral gene delivery

The NVG-BES system facilitated to introduce DNA to cells and delivered cells to a target simultaneously. In this method, a cationic polymer was used as non-viral carrier with electric force by bio-electrospray (BES) system to electrospray living cells onto a target.

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.

Short-fragment DNA-mediated in vivo DNA electroporation delivery

Electroporation is an effective physical delivery method. A variety of factors have been shown to affect the electroporation-mediated gene delivery efficiency. Here we report the usefulness of noncoding short-fragment DNA (sf-DNA) for facilitating electroporation-mediated gene transfer. The plasmid pGL3-control encoding firefly luciferase was injected into tissue together with or without sf-DNA in different length or dose. Immediately after injection, the tissues were electroporated and the level of luciferase activity was assessed 24 h later. The results showed that plasmid DNA formulated with sf-DNA resulted in significant improvement in electroporation-mediated gene transfer efficiency. The effect is dose and length dependent, and also found in low-voltage electroporation. These results indicated that sf-DNA can be used as a helper molecule to improve the electroporation-mediated gene transfection efficiency.

Skin electroporation of a plasmid encoding hCAP-18/LL-37 host defense peptide promotes wound healing

Host defense peptides, in particular LL-37, are emerging as potential therapeutics for promoting wound healing and inhibiting bacterial growth. However, effective delivery of the LL-37 peptide remains limiting. We hypothesized that skin-targeted electroporation of a plasmid encoding hCAP-18/LL-37 would promote the healing of wounds. The plasmid was efficiently delivered to full-thickness skin wounds by electroporation and it induced expression of LL-37 in the epithelium. It significantly accelerated reepithelialization of nondiabetic and diabetic wounds and caused a significant VEGFa and interleukin (IL)-6 induction. IL-6 was involved in LL-37-mediated keratinocyte migration in vitro and IL-6 neutralizing antibodies delivered to mice were able to suppress the wound healing activity of the hCAP-18/LL-37 plasmid. In a hindlimb ischemia model, electroporation of the hCAP-18/LL-37 plasmid increased blood perfusion, reduced muscular atrophy, and upregulated the angiogenic chemokines VEGFa and SDF-1a, and their receptors VEGF-R and CXCR-4. These findings demonstrate that a localized gene therapy with LL-37 is a promising approach for the treatment of wounds.

Short noncoding DNA fragment improve efficiencies of in vivo electroporation-mediated gene transfer

BACKGROUND

A major obstacle to the application of gene therapy methods in experimental and clinical practice is the lack of safe and efficient gene delivery systems. Electroporation has been shown to an effective physical delivery method. A variety of factors have been shown to affect the electroporation-mediated gene delivery efficiency. In the present study, we assessed the usefulness of noncoding short-fragment DNA (sf-DNA) for facilitating electroporation-mediated gene transfer.

METHODS

The plasmid pGL3-control encoding firefly luciferase was injected into tissues together with or without sf-DNA. Immediately after injection, the tissues were electroporated and the level of luciferase activity was assessed 24 h later. Different types of DNA fragments with different molecular weights, structures and doses were compared. The transfection efficiencies of sf-DNA-mediated electroporation in different tissues or with different electric field strengths were examined.

RESULTS

Plasmid DNA formulated with 300-bp sf-DNA resulted in a significant improvement in electroporation-mediated gene transfer efficiency. The effect is dose-dependent and is also affected by DNA fragment length and structure. It was useful for intramuscular electroporation application, as well as intratumoral application with various pulse voltage parameters.

CONCLUSIONS

The data obtained in the present study indicate that sf-DNA can be used as a helper molecule to improve electroporation-mediated gene transfection efficiency.

Electrically mediated delivery of plasmid DNA to the skin, using a multielectrode array

The easy accessibility of skin makes it an excellent target for gene transfer protocols. To take full advantage of skin as a target for gene transfer, it is important to establish an efficient and reproducible delivery system. Electroporation is a strong candidate to meet this delivery criterion. Electroporation of the skin is a simple, direct, in vivo method to deliver genes for therapy. Previously, delivery to the skin was performed by means of applicators with relatively large distances between electrodes, resulting in significant muscle stimulation and pain. These applicators also had limitations in controlling the directionality of the applied field. To resolve this issue, a system consisting of an array of electrodes that decreased the distance between them and that were independently addressable for directional control of the field was developed. This new multielectrode array (MEA) was compared with an established electrode. In a rat model, comparable reporter expression was seen after delivery with each electrode. Delivery was also evaluated in a guinea pig model to determine the potential of this approach in an animal model with skin thickness and structure similar to human skin. The results clearly showed that effective delivery was related to both the electrode and the parameters chosen. With the MEA, the muscle twitching associated with application of electric fields was notably reduced compared with conventional electrode systems. This is important, as it will facilitate the translation of electroporation-mediated gene delivery to skin for clinical use with DNA vaccines or for therapies for cancer or protein deficiencies.

Effect of Mg ions on efficiency of gene electrotransfer and on cell electropermeabilization

Gene electrotransfer is a promising nonviral method that enables DNA to be transferred into living cells with electric pulses. However, there are many parameters that determine gene electrotransfer efficiency. One of the steps involved in gene electrotransfer is interaction of DNA with the cell membrane. Divalent cations in the electroporative media can influence the anchoring of DNA to the cell membrane and by that gene electrotransfer efficiency. Here we report the effect of different concentrations of Mg2+ on electropermeabilization for small molecule (propidium iodide), gene electrotransfer and viability of the cells. We also used TOTO-1 dye to visualize DNA-cell membrane interaction for different [Mg]. For this purpose, we used different electroporative media with increasing [Mg]. Our study shows that higher [Mg] lead to higher electropermeabilization for propidium iodide and higher viability, while causing lower gene electrotransfer efficiency. Because we observed higher TOTO-1 labeled DNA at cell surface when using higher [Mg], we suggest that Mg2+ ions can bind DNA at cell surface at such strength that cannot pass into the cell during application of electric pulses, which can lead to lower gene transfection. There may also be other mechanisms involved, since there are many steps of gene electrotransfer on which Mg2+ ions can have an effect on. Our results also imply that membrane permeability changes are not sufficient for an efficient gene electrotransfer.

Electroporation as an efficient physical enhancer for skin drug delivery

Transdermal drug delivery offers an attractive alternative to the conventional drug delivery methods of oral administration and injection. However, the stratum corneum acts as a barrier that limits the penetration of substances through the skin. Application of high-voltage pulses to the skin increases its permeability (electroporation) and enables the delivery of various substances into and through the skin. The application of electroporation to the skin has been shown to increase transdermal drug delivery. Moreover, electroporation, used alone or in combination with other enhancement methods, expands the range of drugs (small to macromolecules, lipophilic or hydrophilic, charged or neutral molecules) that can be delivered transdermally. The efficacy of transport depends on the electrical parameters and the physicochemical properties of drugs. The in vivo application of high-voltage pulses is well tolerated, but muscle contractions are usually induced. The electrode and patch design is an important issue to reduce the discomfort of the electrical treatment in humans. This review presents the main findings in the field of electroporation-namely, transdermal drug delivery. Particular attention is paid to proposed enhancement mechanisms and trends in the field of topical and transdermal delivery.

Comparison of electrically mediated and liposome-complexed plasmid DNA delivery to the skin

BACKGROUND

Electroporation is an established technique for enhancing plasmid delivery to many tissues in vivo, including the skin. We have previously demonstrated efficient delivery of plasmid DNA to the skin utilizing a custom-built four-plate electrode. The experiments described here further evaluate cutaneous plasmid delivery using in vivo electroporation. Plasmid expression levels are compared to those after liposome mediated delivery.

METHODS

Enhanced electrically-mediated delivery, and less extensively, liposome complexed delivery, of a plasmid encoding the reporter luciferase was tested in rodent skin. Expression kinetics and tissue damage were explored as well as testing in a second rodent model.

RESULTS

Experiments confirm that electroporation alone is more effective in enhancing reporter gene expression than plasmid injection alone, plasmid conjugation with liposomes followed by injection, or than the combination of liposomes and electroporation. However, with two time courses of multiple electrically-mediated plasmid deliveries, neither the levels nor duration of transgene expression are significantly increased. Tissue damage may increase following a second treatment, no further damage is observed after a third treatment. When electroporation conditions utilized in a mouse model are tested in thicker rat skin, only higher field strengths or longer pulses were as effective in plasmid delivery.

CONCLUSION

Electroporation enhances reporter plasmid delivery to the skin to a greater extent than the liposome conjugation method tested. Multiple deliveries do not necessarily result in higher or longer term expression. In addition, some impact on tissue integrity with respect to surface damage is observed. Pulsing conditions should be optimized for the model and for the expression profile desired.

Age-dependent impairment of HIF-1alpha expression in diabetic mice: Correction with electroporation-facilitated gene therapy increases wound healing, angiogenesis, and circulating angiogenic cells

Wound healing is impaired in elderly patients with diabetes mellitus. We hypothesized that age-dependent impairment of cutaneous wound healing in db/db diabetic mice: (a) would correlate with reduced expression of the transcription factor hypoxia-inducible factor 1alpha (HIF-1alpha) as well as its downstream target genes; and (b) could be overcome by HIF-1alpha replacement therapy. Wound closure, angiogenesis, and mRNA expression in excisional skin wounds were analyzed and circulating angiogenic cells (CACs) were quantified in db/db mice that were untreated or received electroporation-facilitated HIF-1alpha gene therapy. HIF-1alpha mRNA levels in wound tissue were significantly reduced in older (4-6 months) as compared to younger (1.5-2 months) db/db mice. Expression of mRNAs encoding the angiogenic cytokines vascular endothelial growth factor (VEGF), angiopoietin 1 (ANGPT1), ANGPT2, platelet-derived growth factor B (PDGF-B), and placental growth factor (PLGF) was also impaired in wounds of older db/db mice. Intradermal injection of plasmid gWIZ-CA5, which encodes a constitutively active form of HIF-1alpha, followed by electroporation, induced increased levels of HIF-1alpha mRNA at the injection site on day 3 and increased levels of VEGF, PLGF, PDGF-B, and ANGPT2 mRNA on day 7. CACs in peripheral blood increased 10-fold in mice treated with gWIZ-CA5. Wound closure was significantly accelerated in db/db mice treated with gWIZ-CA5 as compared to mice treated with empty vector. Thus, HIF-1alpha gene therapy corrects the age-dependent impairment of HIF-1alpha expression, angiogenic cytokine expression, and CACs that contribute to the age-dependent impairment of wound healing in db/db mice.

Formulations for DNA delivery via electroporation in vivo

The importance of DNA formulation in safe and efficient electrogene transfer is increasingly recognized as electroporation technology enters into clinical development. A phenomenal increase in naked DNA delivery by electroporation offers new opportunities for nonviral gene therapies previously considered difficult because of insufficient delivery. However, significant tissue damage related to harsh electroporation conditions raises serious safety concerns with the use of electroporation in healthy tissues, which limits its current applications to only nonhealthy tissues such as tumors. DNA formulations designed to minimize tissue damage or enhance expression at weaker electric pulses have been examined to address these concerns. These include formulations fortified with the addition of transfection reagent(s), membrane-permeating agents, tissue matrix modifiers, targeted ligands, or agents modifying electrical conductivity or membrane stability to enhance delivery efficiency or reduce tissue damage. These advancements in DNA formulation could prove to be useful in improving the safety of electroporation protocols for human applications.

Optimization of cutaneous electrically mediated plasmid DNA delivery using novel electrode

The easy accessibility of skin makes it an excellent target for gene transfer protocols. To take advantage of skin as a target for gene transfer, it is important to establish an efficient and reproducible delivery system. Electroporation is an established technique for enhancing plasmid delivery to many tissues in vivo. A critical component of this technique is the electrode configuration. Electroporation parameters were optimized for transgene expression with minimal tissue damage with a novel electrode. The highest transgene expression and efficiency of individual cell transformation with minimal damage was produced with eight 150 ms pulses at field strength of 100 V/cm. This electrode design offers the potential for easier and more reproducible electrically mediated cutaneous plasmid delivery than the simple electrodes currently commercially available. This electrode can be a valuable tool in determining the applicability of electrically mediated cutaneous gene transfer.

Emerging vectors and targeting methods for nonviral gene therapy

Until recently, nonviral vectors were outside the mainstream of gene transfer technology. Recent problems in clinical trials using viral vectors renewed interest in these methods. The clinical usefulness of nonviral methods is still hindered by their relatively low gene delivery/transgene expression efficiencies. Vectors must navigate a series of obstacles before the therapeutic gene can be expressed. This review considers these barriers and the properties of components of nonviral vectors that are essential for nucleic acid transfer. Although developments of new physical methods (hydrodynamic delivery, ultrasound, electroporation) have made a significant impact on gene transfer efficiency, various chemical carriers (lipids and polymers) have been shown to achieve high-level gene delivery and functional expression. Success of nonviral gene targeting will depend not only on the efficacy, but also safety of this methodology, and this aspect is also discussed. Understanding problems associated with nonviral targeting can also help in designing better viral vectors. In fact, interplay between viral and nonviral technologies should lead to a continued refinement of both methodologies.

Cutaneous gene expression of plasmid DNA in excised human skin following delivery via microchannels created by radio frequency ablation

The skin is a valuable organ for the development and exploitation of gene medicines. Delivering genes to skin is restricted however by the physico-chemical properties of DNA and the stratum corneum (SC) barrier. In this study, we demonstrate the utility of an innovative technology that creates transient microconduits in human skin, allowing DNA delivery and resultant gene expression within the epidermis and dermis layers. The radio frequency (RF)-generated microchannels were of sufficient morphology and depth to permit the epidermal delivery of 100 nm diameter nanoparticles. Model fluorescent nanoparticles were used to confirm the capacity of the channels for augmenting diffusion of macromolecules through the SC. An ex vivo human organ culture model was used to establish the gene expression efficiency of a beta-galactosidase reporter plasmid DNA applied to ViaDerm treated skin. Skin treated with ViaDerm using 50 microm electrode arrays promoted intense levels of gene expression in the viable epidermis. The intensity and extent of gene expression was superior when ViaDerm was used following a prior surface application of the DNA formulation. In conclusion, the RF-microchannel generator (ViaDerm) creates microchannels amenable for delivery of nanoparticles and gene therapy vectors to the viable region of skin.

Mechanism of efficient transfection of the nasal airway epithelium by hypotonic shock

The main barrier to gene transfer in the airway epithelium is the low rate of apical endocytosis limiting naked DNA uptake. Deionized water is known to stimulate the exocytosis of numerous intracellular vesicles during hypotonic cell swelling, in order to expand plasma membrane and prevent cell lysis. This is followed by the phase of regulatory volume decrease (RVD), during which the excess plasma membrane is retrieved by intensive endocytosis. Here we show that the more hypotonic the DNA solution, the higher the transfection of the nasal tissue. P2 receptors are known to be involved in RVD and we demonstrate that some P2 agonists and a P2 antagonist impair transfection in a time-dependent manner. Our study strongly suggests that the nasal airway epithelial cells take up plasmid DNA in deionized water during RVD, within approximately half an hour. Our simple gene delivery system may constitute a promising method for respiratory tract gene therapy.

Enhancement of cellular immune response to a prostate cancer DNA vaccine by intradermal electroporation

Recently it has become clear that more potent methods for DNA vaccine delivery need to be developed to enhance the efficacy of DNA vaccines. In vivo electroporation has emerged as a potent method for DNA vaccine delivery. In a mouse model, we evaluated the CD8(+) T lymphocyte response to a prostate cancer DNA vaccine encoding prostate-specific antigen (PSA) after intradermal electroporation. A significantly increased gene expression (100- to 1000-fold) and higher levels of PSA-specific T cells, compared to DNA delivery without electroporation, was demonstrated. Interestingly, investigation of a panel of different electroporation conditions showed that only some conditions that induce high levels of gene expression additionally induced cellular immunity. This suggests that electroporation parameters should be carefully optimized, not only to enhance transfection efficiency, but also to enhance the immune response to the vaccine. This study demonstrates the applicability of intradermal electroporation as a delivery method for genetic cancer vaccines and other DNA vaccines relying on antigen-specific T cell induction.

Highly Efficient Constant-Current Electroporation IncreasesIn VivoPlasmid Expression

Electroporation has been demonstrated as an effective technique for enhancing the delivery of plasmids coding for DNA vaccines and therapeutic proteins into skeletal muscle. Nevertheless, constant-voltage techniques do not take into account the resistance of the tissue and result in tissue damage, inflammation, and loss of plasmid expression. In the present study, we have used a software-driven constant-current electroporator to deliver plasmids to mice and small and large pigs. The voltage, amperage, and resistance of the tissue during pulses were recorded and analyzed. Optimal conditions of electroporation were identified in both species, and found to be highly dependent on the individual tissue resistance. Six- to 10-week-old pigs had higher muscle resistance compared to 1- to 2-year-old pigs, but both values were four to five times lower than the resistance of the mouse muscle. In mice, optimum amperage, pulse length, and lag time between plasmid injection and electroporation were identified to be 0.1 Amps, 20 msec and 0 sec. The electroporation pulse pattern among the electrodes also affected plasmid expression. These results indicate that age- and tissue-specific resistance, pulse pattern, and other variables associated with the electroporation need to be optimized for each separate species to achieve maximum plasmid expression.

Tissue-Specific Characteristics of in Vivo Electric Gene: Transfer by Tissue and Intravenous Injection of Plasmid DNA

PURPOSE

To evaluate the tissue-specific characteristics of electric gene transfer after tissue and intravenous injection of naked plasmid DNA (pDNA).

METHODS

pDNA encoding firefly luciferase was injected directly into the liver, kidney, spleen, skin and muscle, or into the tail vein of mice, and electric pulses were then applied to one of these organs. The distribution of transgene expressing cells was evaluated using pDNA encoding beta-galactosidase.

RESULTS

Tissue injection of pDNA produced a significant degree of transgene expression in any tissue with the greatest amount in the liver, followed by kidney and spleen. The expression in these organs decreased quickly with time, and muscle showed the greatest expression at 7 days. Electroporation significantly increased the expression, and the expression level was comparable among the organs. Intravenous injection of pDNA followed by electroporation resulted in a significant expression in the liver, spleen, and kidney but not in the skin or muscle.

CONCLUSIONS

Electric gene transfer to the liver, kidney, and spleen can be an effective approach to obtain significant amounts of transgene expression by either tissue or intravenous injection of pDNA, whereas it is only effective after tissue injection as far as skin- or muscle-targeted gene transfer is concerned.

Electroporative transfection with KGF-1 DNA improves wound healing in a diabetic mouse model

We recently demonstrated that electroporation enhances transfection in a mouse wound-healing model. Keratinocyte growth factor (KGF) is an inducer of epithelial cell proliferation and differentiation and has been shown to be under expressed in the wounds of diabetic individuals. We hypothesized that KGF delivered into an excisional wound via naked DNA injection with subsequent electroporation would be a novel and potentially effective method to enhance wound closure in a diabetic mouse model. ELISA assays confirmed production of KGF protein in cultured mouse cells and RT-PCR assays confirmed KGF mRNA in skin samples taken from mice. In all, 32 genetically diabetic mice were given two identical excisional wounds of their dorsum and split into two groups with one group receiving KGF DNA injection and electroporation with the other group receiving no treatment. Over 90% of wounds healed in the presence of KGF and electroporation versus 40% in the untreated group by day 12. Histological analysis of the wounds demonstrated that untreated wounds contained microulcers with thin or incomplete epithelium with unresolved inflammation as compared to treated wounds where intact and mature epithelium was observed. Taken together these findings suggest that a single injection of KGF DNA encoded on a plasmid coupled with electroporation improves and accelerates wound closure in a delayed wound-healing model.

A comprehensive study of optimal conditions for naked plasmid DNA transfer into skeletal muscle by electroporation

Efficient gene transfer is a key factor in gene therapy. Reducing the damage caused by gene transfer to muscle by electroporation is very important for its clinical application. Extensive investigation of optimal conditions for gene transfer by electroporation is required. The parameters used for electroporation, including plasmid concentration; injection volume; the plasmid dose of the injection; the concentration of saline media; the size of plasmid DNA; the age of the mice; the lag time between plasmid injection and electroporation; and the effect of repeated gene transfer by electroporation, were systematically investigated in the present study. The efficiencies of gene transfer by electroporation in normal and rodent models of diabetes were also evaluated. We found that electroporation used for non-viral gene transfer could be repeated in the same place in the muscle, but the expression efficiency was closely related to the muscle damage. Increasing pulse times could enhance the efficiency of gene transfer with a lower strength of electric field. It was better to use a higher plasmid concentration than to use a larger dose of plasmid and repeated injection to achieve a high level of transgene expression. Optimal conditions varied in different animal models, being milder for diabetic mice than for normal mice, and it was also shown that the conditions that worked well on these small rodents were not necessarily suitable for larger animals. Our results provide a comprehensive view of the factors that affect the efficiency of gene transfer into skeletal muscle by electroporation.

Inhibition of B16BL6 tumor progression by coadministration of recombinant angiostatin K1-3 and endostatin genes with cationic liposomes

Transfection of the antiangiogenic angiostatin and endostatin genes was shown to be an alternative to high-dose administration of angiostatin or endostatin proteins for cancer therapy. We have systematically investigated whether coadministration of the mouse angiostatin kringle 1-3 gene (pFLAG-AngioK1/3) and the endostatin gene (pFLAG-Endo) complexed with cationic liposomes exhibits enhanced therapeutic efficacy. In vitro, the coexpressed mixture of angiostatin K1-3 and endostatin more effectively reduced angiogenesis in chorioallantoic membranes than either angiostatin K1-3 or endostatin alone. In vivo, subcutaneous co-administration of pFLAG-AngioK1/3 and pFLAG-Endo lipoplexes more effectively inhibited vascularization in Matrigel plugs implanted in mice than either one alone. Additionally, subcutaneous administration of these genes inhibited the growth and formation of pulmonary metastases of B16BL6 melanoma cells in mice. Compared to treatment with an empty vector, treatment with pFLAG-AngioK1/3 plus pFLAG-Endo inhibited 81% of tumor growth, while treatment with pFLAG-AngioK1/3 or pFLAG-Endo inhibited tumor growth 70 and 69%, respectively. Cotreatment with the two plasmids after primary tumor excision induced a 90% inhibition of pulmonary metastases versus 79% for pFLAG-AngioK1/3 or 80% for pFLAG-Endo individually. These results suggest that combined administration of angiostatin K1-3 and endostatin genes complexed with cationic liposomes may be an innovated antiangiogenic strategy for cancer therapy.

Intradermal injection of transforming growth factor-beta1 gene enhances wound healing in genetically diabetic mice

PURPOSE

To evaluate the biologic effect of direct cutaneous TGF-beta1 gene delivery on impaired wound healing models using genetically diabetic mice.

METHODS

Diabetic mice (C57BKS.Cg-m +/+ Leprdb female mice) with 1 cm x 1 cm excisional wounds were intradermally injected with 60 microg of plasmid DNA encoding TGF-beta1 gene. The wound closure was measured up to 14 days postwounding. At days 7 and 14 postwounding, sections of skin were taken for hematoxylin and eosin and Masson's trichome staining to examine the morphology and collagen deposition. The cell proliferation and TGF-beta1 gene expression were studied using immunohistochemical stainings for 5-bromo-2-deoxyuridine and for TGF-beta1.

RESULTS

A higher cell proliferation rate and a denser and more organized new extracellular matrix were observed in the treated wound site. Complete wound closure was detected as early as 7 days for TGF-beta1-treated group in comparison with 11-14 days for the untreated, control plasmid DNA- and PBS-treated groups.

CONCLUSION

A single intradermal injection of TGF-beta1 plasmid DNA was sufficient to enhance wound healing. This approach represents a new strategy that may be applied to the treatment of excisional wounds in human diabetic patients.

Gene therapy progress and prospects: nonviral vectors

The success of gene therapy is largely dependent on the development of the gene delivery vector. Recently, gene transfection into target cells using naked DNA, which is a simple and safe approach, has been improved by combining several physical techniques, for example, electroporation, gene gun, ultrasound and hydrodynamic pressure. Chemical approaches have been utilized to improve the efficiency and cell specificity of gene transfer. Novel gene carrier molecules, which facilitate DNA escape from the endosome into the cytosol, have been developed. Several functional polymers, which enable controlled release of DNA in response to an environmental change, have also been reported. Plasmids with reduced number of CpG motifs, the use of PCR fragments and the sequential injection method have been established for the reduction of immune response triggered by plasmid DNA. Construction of a long-lasting gene expression system is also an important theme for nonviral gene therapy. To date, tissue-specific expression, self-replicating and integrating plasmid systems have been reported. Improvement of delivery methods together with intelligent design of the DNA itself has brought about large degrees of enhancement in the efficiency, specificity and temporal control of nonviral vectors.

Factors controlling electropermeabilisation of cell membranes

Electric field pulses are a new approach for drug and gene delivery for cancer therapy. They induce a localized structural alteration of cell membranes. The associated physical mechanisms are well explained and can be safely controlled. A position dependent modulation of the membrane potential difference is induced when an electric field is applied to a cell. Electric field pulses with an overcritical intensity evoke a local membrane alteration. A free exchange of hydrophilic low molecular weight molecules takes place across the membrane. A leakage of cytosolic metabolites and a loading of polar drugs into the cytoplasm are obtained. The fraction of the cell surface which is competent for exchange is a function of the field intensity. The level of local exchange is strongly controlled by the pulse duration and the number of successive pulses. The permeabilised state is long lived. Its lifetime is under the control of the cumulated pulse duration. Cell viability can be preserved. Gene transfer is obtained but its mechanism is not a free diffusion. Plasmids are electrophoretically accumulated against the permeabilised cell surface and form aggregates due to the field effect. After the pulses, several steps follow: translocation to the cytoplasm, traffic to the nucleus and expression. Molecular structural and metabolic changes in cells remain mostly poorly understood. Nevertheless, while most studies were established on cells in culture (in vitro), recent experiments show that similar effects are obtained on tissue (in vivo). Transfer remains controlled by the physical parameters of the electrical treatment.