Therapeutic success and efficacy of nonviral liposomal cDNA gene transfer to the skin in vivo is dose dependent

Gene Therapy for Regenerative Medicine

The development of biological methods over the past decade has stimulated great interest in the possibility to regenerate human tissues. Advances in stem cell research, gene therapy, and tissue engineering have accelerated the technology in tissue and organ regeneration. However, despite significant progress in this area, there are still several technical issues that must be addressed, especially in the clinical use of gene therapy. The aims of gene therapy include utilising cells to produce a suitable protein, silencing over-producing proteins, and genetically modifying and repairing cell functions that may affect disease conditions. While most current gene therapy clinical trials are based on cell- and viral-mediated approaches, non-viral gene transfection agents are emerging as potentially safe and effective in the treatment of a wide variety of genetic and acquired diseases. Gene therapy based on viral vectors may induce pathogenicity and immunogenicity. Therefore, significant efforts are being invested in non-viral vectors to enhance their efficiency to a level comparable to the viral vector. Non-viral technologies consist of plasmid-based expression systems containing a gene encoding, a therapeutic protein, and synthetic gene delivery systems. One possible approach to enhance non-viral vector ability or to be an alternative to viral vectors would be to use tissue engineering technology for regenerative medicine therapy. This review provides a critical view of gene therapy with a major focus on the development of regenerative medicine technologies to control the in vivo location and function of administered genes.

Therapeutic delivery of nucleic acids for skin wound healing

Though wound care has advanced, treating chronic wounds remains a challenge and there are many clinical issues that must be addressed. Gene therapy is a recent approach to treating chronic wounds that remains in its developmental stage. The limited reports available describe the therapeutic applications of various forms of nucleic acid delivery for treating chronic wounds, including DNA, mRNA, siRNA, miRNA and so on. Though these bioactive molecules represent great therapeutic potential, sustaining their bioactivity in the wound bed is a challenge. To overcome this hurdle, delivery systems are also being widely investigated. In this review, nucleic acid-based therapy and its delivery for treating chronic wounds is discussed in detail.

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.

The micrograft concept for wound healing: strategies and applications

The standard of care for wound coverage is to use an autologous skin graft. However, large or chronic wounds become an exceptionally challenging problem especially when donor sites are limited. It is important that the clinician be aware of various treatment modalities for wound care and incorporate those methods appropriately in the proper clinical context. This report reviews an alternative to traditional meshed skin grafting for wound coverage: micrografting. The physiological concept of micrografting, along with historical context, and the evolution of the technique are discussed, as well as studies needed for micrograft characterization and future applications of the technique.

Insulin-like growth factor-1 gene therapy and cell transplantation in diabetic wounds

BACKGROUND

Impaired wound healing is a frequent phenomenon in diabetes mellitus. However, little is known of the fundamental cause of this pathology. The present study examined the effect of human insulin-like growth factor (hIGF)-1 overexpression in combination with autologous cell transplantation to diabetic wounds in a preclinical large-animal model.

METHODS

Diabetes was induced in Yorkshire pigs with streptozotocin. Keratinocytes were cultured and transfected with hIGF-1 or LacZ transgene. Plasmids were lipoplexed with either Lipofectin or Lipofectamin 2000. Transgene expression was assessed by enzyme-linked immunosorbent assay or X-gal staining. For in vivo studies, full-thickness wounds were created and dressed with a sealed chamber. Transfected cells were transplanted into the wounds. Wound contraction was monitored and biopsies were obtained for measurement of re-epithelialization. Wound fluid was collected and analysed for IGF-1 concentrations.

RESULTS

Quantification showed up to 740 ng/ml IGF-1 in vitro and significantly higher concentrations over 14 days compared to controls for the Lipofectamin 2000 group. Lipofectin-mediated gene transfer showed peak expression on day 2 with 68.5 ng/ml. In vivo, transfected cells showed peak expression of 457 ng/ml at day 1, followed by subsequent decline to 5 ng/ml on day 12 with Lipofectamin 2000. For Lipofectin, no significant IGF-1 expression could be detected. Gene therapy caused significantly faster wound closure (83%) than both controls (native-cell therapy = 57%; control wounds = 32%).

CONCLUSIONS

The present study demonstrates that optimized nonviral gene transfer increased IGF-1 expression in diabetic wounds by up to 900-fold. This high IGF-1 concentration in combination with cell therapy improved diabetic wound healing significantly.

Transient non-viral cutaneous gene delivery in burn wounds

BACKGROUND

Gene transfer to burn wounds could present an alternative to conventional and often insufficient topical and systemic application of therapeutic agents to aid in wound healing. The goals of this study were to assess and optimize the potential of transient non-viral gene delivery to burn wounds.

METHODS

HaCaT cells were transfected with luciferase or beta-galactosidase transgene using either pure plasmid DNA (pDNA) or complexed with Lipofectamine 2000, FuGENE6, or DOTAP-Chol. Expression was determined by bioluminescence and fluorescence. Forty male Sprague-Dawley rats received naked pDNA, lipoplexes, or carrier control intradermally into either unburned skin, superficial, partial, or full-thickness scald burn. Animals were sacrificed after 24 h, 48 h, or 7 days, and transgene expression was assessed.

RESULTS

Gene transfer to HaCaT cells showed the overall highest expression for DOTAP/Chol (77.85 ng luciferase/mg protein), followed by Lipofectamine 2000 (33.14 ng luciferase/mg protein). pDNA-derived gene transfer to superficial burn wounds showed the highest expression among burn groups (0.77 ng luciferase/mg protein). However, lipoplex-derived gene transfer to superficial burns and unburned skin failed to show higher expression.

CONCLUSIONS

Lipofectamine 2000 and DOTAP/Chol lipoplex showed significantly enhanced gene transfer, whereas no transfection was detectable for naked DNA in vitro. In contrast to the in vitro study, naked DNA was the only agent with which gene delivery was successful in experimental burn wounds. These findings highlight the limited predictability of in vitro analysis for gene delivery as a therapeutic approach.

Gene therapy and wound healing

Wound repair involves the sequential interaction of various cell types, extracellular matrix molecules, and soluble mediators. During the past 10 years, much new information on signals controlling wound cell behavior has emerged. This knowledge has led to a number of novel therapeutic strategies. In particular, the local delivery of pluripotent growth factor molecules to the injured tissue has been intensively investigated over the past decade. Limited success of clinical trails indicates that a crucial aspect of the growth factor wound healing strategy is the effective delivery of these polypeptides to the wound site. A molecular approach in which genetically modified cells synthesize and deliver the desired growth factor in regulated fashion has been used to overcome the limitations associated with the (topical) application of recombinant growth factor proteins. We have summarized the molecular and cellular basis of repair mechanisms and their failure, and we give an overview of techniques and studies applied to gene transfer in tissue repair.

Gene-modified tissue-engineered skin: the next generation of skin substitutes

Tissue engineering combines the principles of cell biology, engineering and materials science to develop three-dimensional tissues to replace or restore tissue function. Tissue engineered skin is one of most advanced tissue constructs, yet it lacks several important functions including those provided by hair follicles, sebaceous glands, sweat glands and dendritic cells. Although the complexity of skin may be difficult to recapitulate entirely, new or improved functions can be provided by genetic modification of the cells that make up the tissues. Gene therapy can also be used in wound healing to promote tissue regeneration or prevent healing abnormalities such as formation of scars and keloids. Finally, gene-enhanced skin substitutes have great potential as cell-based devices to deliver therapeutics locally or systemically. Although significant progress has been made in the development of gene transfer technologies, several challenges have to be met before clinical application of genetically modified skin tissue. Engineering challenges include methods for improved efficiency and targeted gene delivery; efficient gene transfer to the stem cells that constantly regenerate the dynamic epidermal tissue; and development of novel biomaterials for controlled gene delivery. In addition, advances in regulatable vectors to achieve spatially and temporally controlled gene expression by physiological or exogenous signals may facilitate pharmacological administration of therapeutics through genetically engineered skin. Gene modified skin substitutes are also employed as biological models to understand tissue development or disease progression in a realistic three-dimensional context. In summary, gene therapy has the potential to generate the next generation of skin substitutes with enhanced capacity for treatment of burns, chronic wounds and even systemic diseases.

Gene therapy in the treatment of lower extremity wounds

This article presents a brief overview of the etiology of chronic wounds of the lower extremities and their current medical and surgical treatment. Gene therapy as a potential tool for treating therapeutically challenging wounds is described in terms of the vectors employed in gene transfer, as well as the strategies used to promote wound healing. Results from animal model studies, as well as clinical trials, are presented.

Interaction of exogenous liposomal insulin-like growth factor-I cDNA gene transfer with growth factors on collagen expression in acute wounds

Growth factors have been shown to modulate the complex cascade of wound healing, however, interaction between different growth factors during dermal and epidermal regeneration is still not entirely defined. We have recently shown that exogenous liposomal gene transfer of cDNA results in physiologic expression and response in an acute wound. In the present study we determined the interaction between insulin-like growth factor-I (IGF-I), a mesenchymal growth factor, administered as liposomal cDNA, with other dermal and epidermal growth factors on collagen synthesis in an acute wound. Sprague-Dawley rats were given a scald burn to inflict an acute wound and divided into two groups to receive weekly subcutaneous injections of liposomes plus a beta-galactosidase containing plasmid (Lac Z [0.2 microg, vehicle]), or liposomes plus the IGF-I cDNA containing plasmid (2.2 microg) and Lac Z (0.2 microg). Immunological assays, histological and immunohistochemical techniques were used to determine growth factor concentration and different types of collagen (I, III, and IV) after IGF-I cDNA gene transfer. IGF-I cDNA transfer accelerated reepithelization and was associated with increased levels of IGF-I, fibroblast growth factor, keratinocyte growth factor, vascular endothelial cell growth factor, and platelet-derived growth factor protein expression. IGF-I cDNA had no effect on transforming growth factor-beta. IGF-I cDNA significantly increased type IV collagen while it had no effect on types I and III collagen. Exogenously administered IGF-I cDNA increased protein concentrations of keratinocyte growth factor, fibroblast growth factor, platelet-derived growth factor, and type IV collagen. We conclude that liposomal IGF-I gene transfer can accelerate wound healing without causing an increase in types I and III collagen expression.

Gene transfer in tissue repair: status, challenges and future directions

Wound repair involves a complex interaction of various cell types, extracellular matrix molecules and soluble mediators. Details on signals controlling wound cell activities are beginning to emerge. In recent years this knowledge has been applied to a number of therapeutic strategies in soft tissue repair. Key challenges include re-adjusting the adult repair process in order to augment diseased healing processes, and providing the basis for a regenerative rather than a reparative wound environment. In particular, the local delivery of pluripotent growth factor molecules to the injured tissue has been intensively investigated over the past decade. Limited success of clinical trials indicates that an important aspect of the growth factor wound-healing paradigm is the effective delivery of these polypeptides to the wound site. A molecular genetic approach in which genetically modified cells synthesise and deliver the desired growth factor in a time-regulated manner is a powerful means to overcome the limitations associated with the (topical) application of recombinant growth factor proteins. This article summarises repair mechanisms and their failure, and gives an overview of techniques and studies applied to gene transfer in tissue repair. It also provides perspectives on potential targets for gene transfer technology.

Delivery of bioactive molecules into the cell: the Trojan horse approach

In recent years, vast amounts of data on the mechanisms of neural de- and regeneration have accumulated. However, only in disproportionally few cases has this led to efficient therapies for human patients. Part of the problem is to deliver cell death-averting genes or gene products across the blood-brain barrier (BBB) and cellular membranes. The discovery of Antennapedia (Antp)-mediated transduction of heterologous proteins into cells in 1992 and other "Trojan horse peptides" raised hopes that often-frustrating attempts to deliver proteins would now be history. The demonstration that proteins fused to the Tat protein transduction domain (PTD) are capable of crossing the BBB may revolutionize molecular research and neurobiological therapy. However, it was only recently that PTD-mediated delivery of proteins with therapeutic potential has been achieved in models of neural degeneration in nerve trauma and ischemia. Several groups have published the first positive results using protein transduction domains for the delivery of therapeutic proteins in relevant animal models of human neurological disorders. Here, we give an extensive review of peptide-mediated protein transduction from its early beginnings to new advances, discuss their application, with particular focus on a critical evaluation of the limitations of the method, as well as alternative approaches. Besides applications in neurobiology, a large number of reports using PTD in other systems are included as well. Because each protein requires an individual purification scheme that yields sufficient quantities of soluble, transducible material, the neurobiologist will benefit from the experiences of other researchers in the growing field of protein transduction.

Exogenous liposomal IGF-I cDNA gene transfer leads to endogenous cellular and physiological responses in an acute wound

The purpose of the present study was to examine whether exogenous liposomal cDNA gene transfer is recognized by the cell and causes endogenous cellular and physiological responses. When administered as a protein, IGF-I is known to cause adverse side effects due to lack of cellular responses. Therefore, we used IGF-I cDNA as a vector to study cellular and physiological effects after liposomal administration to wounded skin. Sprague-Dawley rats were given a scald burn to inflict an acute wound and were divided into two groups to receive weekly subcutaneous injections of liposomes plus the Lac-Z gene (0.2 μg vehicle) or liposomes plus the IGF-I cDNA (2.2 μg) and Lac Z gene (0.22 μg). Transfection was confirmed by histochemical assays for β-galactosidase. Planimetry, immunological assays, and histological and immunohistochemical techniques were used to determine molecular mechanisms after gene transfer, protein expression, and dermal and epidermal regeneration. IGF-I cDNA transfer increased IGF-I protein expression and caused concomitant cellular responses by increasing IGF binding protein (IGFBP)-3 and decreasing IGFBP-1. IGF-I cDNA gene transfer increased keratinocyte growth factor expression and exerted promitogenic antiapoptotic effects on basal keratinocytes, thus improving epidermal regeneration. IGF-I cDNA improved dermal regeneration by an increased collagen deposition and morphology. IGF-I cDNA increased VEGF concentrations and thus neovascularization. Exogenous-administered IGF-I cDNA is recognized by the cell and leads to similar intracellular responses as the endogenous gene. Liposomal IGF-I gene transfer further leads to improved dermal and epidermal regeneration by interacting with other growth factors.

Epidermal homeostasis: the role of the growth hormone and insulin-like growth factor systems

GH and IGF-I and -II were first identified by their endocrine activity. Specifically, IGF-I was found to mediate the linear growth-promoting actions of GH. It is now evident that these two growth factor systems also exert widespread activity throughout the body and that their actions are not always interconnected. The literature highlights the importance of the GH and IGF systems in normal skin homeostasis, including dermal/epidermal cross-talk. GH activity, sometimes mediated via IGF-I, is primarily evident in the dermis, particularly affecting collagen synthesis. In contrast, IGF action is an important feature of the dermal and epidermal compartments, predominantly enhancing cell proliferation, survival, and migration. The locally expressed IGF binding proteins play significant and complex roles, primarily via modulation of IGF actions. Disturbances in GH and IGF signaling pathways are implicated in the pathophysiology of several skin perturbations, particularly those exhibiting epidermal hyperplasia (e.g., psoriasis, carcinomas). Additionally, many studies emphasize the potential use of both growth factors in the treatment of skin wounds; for example, burn patients. This overview concerns the role and mechanisms of action of the GH and IGF systems in skin and maintenance of epidermal integrity in both health and disease.

IGF-I gene transfer effects on inflammatory elements present after thermal trauma

Major thermal injury results in severe prolonged responses with three components: a hypermetabolic response, inflammatory responses, and endogenous wound-healing processes. We showed that use of liposome-mediated gene transfer of the insulin-like growth factor I (IGF-I) reduces burn-induced inflammatory responses and enhances wound healing. In the present study, we found transient increased levels of IGF-I protein in rats exposed to thermal trauma via liposomal gene transfer in an effort to define the transcriptional events that occur after IGF-I delivery at the site of injury. The beneficial effects of IGF-I gene transfer act partly via amelioration of burn-induced inflammatory responses that mediate cell death through caspase-3 activity and Bax expression. IGF-I gene transfer induces selective stimulation of activation protein-1 DNA-binding activity and activation of antiapoptotic, but not inflammatory, NF-kappaB transcription factors. Data were consistent with our hypothesis that the beneficial effects of IGF-I gene transfer on burned rats act in part via activation protein-1 and NF-kappaB transcriptional regulation and the concordance between the results obtained with antiapoptotic, as opposed to the proapoptotic, sequences as well as the corresponding changes in measures of cell death via Bax and caspase-3 mechanisms.

Non-viral liposomal keratinocyte growth factor (KGF) cDNA gene transfer improves dermal and epidermal regeneration through stimulation of epithelial and mesenchymal factors

Keratinocyte growth factor (KGF) stimulates epithelial cell differentiation and proliferation, which are of major importance for wound healing. Local protein administration, however, has been shown to be ineffective due to enzymes and proteases in the wound fluid. We hypothesized that delivering KGF as a non-viral liposomal cDNA gene complex is a new approach that would effectively enhance dermal and epidermal regeneration. Twenty-two rats were given an acute wound and divided into two groups to receive weekly subcutaneous injections of liposomes plus the LacZ gene (0.2 microg, vehicle), or liposomes plus the KGF cDNA (2.2 microg) and LacZ cDNA (0.2 microg). Transfection was confirmed by histochemical assays for beta-galactosidase. Planimetry, histological and immunohistochemical techniques were used to determine protein expression, dermal and epidermal regeneration. Transfection and subsequent KGF expression was found in diving cells in the granulation tissue. Epidermal regeneration was improved by 170% in rats receiving the KGF cDNA constructs by exhibiting the most rapid area and linear wound re-epithelialization, P < 0.0001. KGF improved epidermal cell net balance by increasing skin cell proliferation and decreasing skin cell apoptosis, P < 0.0001. Dermal regeneration was further improved in KGF cDNA treated animals by an increased collagen deposition and morphology, P < 0.0001. KGF cDNA increased neo-vascularization and concomitant VEGF concentrations when compared with vehicle, P < 0.01. KGF cDNA did not only stimulate epithelial cells, but also mesenchymal cells through increases in IGF-I concentration, P < 0.005. Liposomes containing the KGF cDNA gene constructs were effective in improving epidermal and dermal regeneration. KGF gene transfer to acute wounds may represent a new therapeutic strategy to enhance wound healing.

Cutaneous gene transfer for skin and systemic diseases

Recent progress in molecular genetics has illuminated the basis for a wide variety of inherited and acquired diseases. Gene therapy offers an attractive therapeutic approach capitalizing upon these new mechanistic insights. The skin is a uniquely attractive tissue site for development of new genetic therapeutic approaches both for its accessibility as well as for the large number of diseases that are amenable in principle to cutaneous gene transfer. Amongst these opportunities are primary monogenic skin diseases, chronic wounds and systemic disorders characterized by low or absent levels of circulating polypeptides. For cutaneous gene therapy to be effective, however, significant progress is required in a number of domains. Recent advances in vector design, administration, immune modulation, and regulation of gene expression have brought the field much nearer to clinical utility.