Corneal gene therapy

Local delivery of adeno-associated viral vectors with electrospun gelatin nanofiber mats

Adeno-associated viral (AAV) vectors play a significant role in gene therapy, yet the typical delivery methods, like systemic and local AAV injections, often lead to unintended off-target distribution and tissue damage due to injection. In this study, we propose a localized delivery approach for AAV vectors utilizing electrospun gelatin nanofiber mats, which are cross-linked with glutaraldehyde. The AAV vectors, which encoded a green fluorescent protein (GFP), were loaded onto the mats by immersing them in a solution containing the vectors. The amount of AAV vector loaded onto the mats increased as the vector concentration in the solution increased. The loaded AAV vector was steadily released into the cell culture medium over 3 days. The mats incubated for 3 days also showed the ability to transduce into the cells cultured on them. We evaluated the effectiveness of this delivery system by attaching the mats to mouse livers. GFP expression was visible on the surface of the liver beneath the attached mats, but not in areas in direct contact with the mats. These findings suggest that the attachment of AAV vector-loaded electrospun gelatin nanofiber mats to a target site present a promising solution for localized gene delivery while reducing off-target distribution.

Corneal gene therapy: Structural and mechanistic understanding

Cornea, a dome-shaped and transparent front part of the eye, affords 2/3rd refraction and barrier functions. Globally, corneal diseases are the leading cause of vision impairment. Loss of corneal function including opacification involve the complex crosstalk and perturbation between a variety of cytokines, chemokines and growth factors generated by corneal keratocytes, epithelial cells, lacrimal tissues, nerves, and immune cells. Conventional small-molecule drugs can treat mild-to-moderate traumatic corneal pathology but requires frequent application and often fails to treat severe pathologies. The corneal transplant surgery is a standard of care to restore vision in patients. However, declining availability and rising demand of donor corneas are major concerns to maintain ophthalmic care. Thus, the development of efficient and safe nonsurgical methods to cure corneal disorders and restore vision in vivo is highly desired. Gene-based therapy has huge potential to cure corneal blindness. To achieve a nonimmunogenic, safe and sustained therapeutic response, the selection of a relevant genes, gene editing methods and suitable delivery vectors are vital. This article describes corneal structural and functional features, mechanistic understanding of gene therapy vectors, gene editing methods, gene delivery tools, and status of gene therapy for treating corneal disorders, diseases, and genetic dystrophies.

Corneal Regeneration Using Gene Therapy Approaches

One of the most remarkable advancements in medical treatments of corneal diseases in recent decades has been corneal transplantation. However, corneal transplants, including lamellar strategies, have their own set of challenges, such as graft rejection, delayed graft failure, shortage of donor corneas, repeated treatments, and post-surgical complications. Corneal defects and diseases are one of the leading causes of blindness globally; therefore, there is a need for gene-based interventions that may mitigate some of these challenges and help reduce the burden of blindness. Corneas being immune-advantaged, uniquely avascular, and transparent is ideal for gene therapy approaches. Well-established corneal surgical techniques as well as their ease of accessibility for examination and manipulation makes corneas suitable for in vivo and ex vivo gene therapy. In this review, we focus on the most recent advances in the area of corneal regeneration using gene therapy and on the strategies involved in the development of such therapies. We also discuss the challenges and potential of gene therapy for the treatment of corneal diseases. Additionally, we discuss the translational aspects of gene therapy, including different types of vectors, particularly focusing on recombinant AAV that may help advance targeted therapeutics for corneal defects and diseases.

New Frontier in the Management of Corneal Dystrophies: Basics, Development, and Challenges in Corneal Gene Therapy and Gene Editing

ABSTRACT

Corneal dystrophies represent a group of heterogeneous hereditary disorders causing progressive corneal opacification and blindness. Current corneal transplant management for corneal dystrophies faces the challenges of repeated treatments, complex surgical procedures, shortage of appropriate donor cornea, and, more importantly, graft rejection. Genetic medicine could be an alternative treatment regime to overcome such challenges. Cornea carries promising scope for a gene-based therapy involving gene supplementation, gene silencing, and gene editing in both ex vivo and in vivo platforms. In the cornea, ex vivo gene therapeutic strategies were attempted for corneal graft survival, and in vivo gene augmentation therapies aimed to prevent herpes stromal keratitis, neovascularization, corneal clouding, and wound healing. However, none of these studies followed a clinical trial-based successful outcome. CRISPR/Cas system offers a broad scope of gene editing and engineering to correct underlying genetic causes in corneal dystrophies. Corneal tissue--specific gene correction in vitro with minimal off-target effects and optimal gene correction efficiency followed by their successful surgical implantation, or in vivo CRISPR administration targeting pathogenic genes finds a way to explore therapeutic intervention for corneal dystrophies. However, there are many limitations associated with such CRISPR-based corneal treatment management. This review will look into the development of corneal gene therapy and CRISPR-based study in corneal dystrophies, associated challenges, potential approaches, and future directions.

Six-Month In Vivo Safety Profiling of Topical Ocular AVV5-Decorin Gene Transfer

Purpose

A significant remission of corneal fibrosis and neovascularization in rabbit eye in vivo was observed from a tissue-selective localized adeno-associated virus (AAV)5–Decorin (Dcn) gene therapy. This study sought to investigate 6-month toxicity profiling of this gene therapy for the eye in vivo using a rabbit model.

Methods

A small epithelial scrape followed by corneal drying was performed unilaterally in 12 rabbit eyes and either AAV5–Dcn (n = 6) or naked vector (n = 6) was delivered topically using a cloning cylinder technique. Contralateral eyes served as naïve control (n = 6). Safety and tolerability measurements in live rabbits were performed periodically until month 6 using multimodel clinical ophthalmic imaging tools—a slit lamp, stereomicroscope, and HRT3-RCM in vivo confocal microscope. Thereafter, corneas were excised and subjected to hematoxylin and eosin staining, Mason trichome staining, propidium iodide nuclear staining, and quantitative real-time polymerase chain reaction analyses.

Results

Clinical eye examinations based on the modified Hackett–McDonald ocular scoring system, and in vivo confocal imaging of the cornea showed no signs of ocular toxicity in rabbit eyes given AAV5–Dcn gene transfer vs control eyes (P > 0.05) through 6 months after treatment. The histologic and molecular analyses showed no significant differences in AAV5–Dcn vs AAV naked or naïve control groups (P > 0.05) and were in accordance with the masked clinical ophthalmic observations showing no abnormalities.

Conclusions

Topical tissue-targeted localized AAV5–Dcn gene therapy seems to be safe and nontoxic to the rabbit eye in vivo.

Translational Relevance

AAV5–Dcn gene therapy has the potential to treat corneal fibrosis and neovascularization in vivo safely without significant ocular toxicity.

Application of Nanomaterials in the Treatment and Diagnosis of Ophthalmology Diseases

Eye diseases often lead to impaired vision and seriously affect the daily life of patients. Local administration of ophthalmic drugs is one of the most important approaches for the treatment of ophthalmic diseases. However, due to the special biochemical environment of the ocular tissue and the existence of many barriers, the bioavailability of conventional ophthalmic preparations in the eye is very low. Nanomaterials can be utilized as carriers of drugs, which can improve the absorption, distribution, metabolism and bioavailability of drugs in eyes. Nanomaterials have also the advantages of small size, simple preparation, good degradability, strong targeting, and little stimulation to biological tissues, providing an innovative and practical method for the drug delivery of ophthalmic diseases. In addition, nanomaterials can be used as an auxiliary means for early diagnosis of ophthalmic diseases by improving the specificity and accuracy of detection methods. Nanomaterials help clinicians and researchers delve deeper into the physiology and pathology of the eye at the nanoscale. We summarize the application of nanomaterials in the diagnosis and treatment of ophthalmic diseases in this review.

Macular Corneal Dystrophy: An Updated Review

Macular Corneal Dystrophy is an autosomal recessive form of corneal dystrophy due to a mutation in CHST6 gene, which results in abnormal proteoglycan synthesis. There is accumulation of abnormal glycosaminoglycans in the corneal stroma and endothelium. The deposition results in progressive loss of corneal transparency and visual acuity. The histopathology shows characteristic alcian blue positive deposits. Management in the cases with visual loss requires keratoplasty either full thickness or lamellar. The decision about the ideal type of keratoplasty depends on age and pre-operative clinical features. Although prognosis after keratoplasty is good, recurrences can occur. Future research should be targeted towards gene therapy in this condition.

The prominence of the dosage form design to treat ocular diseases

The eye is susceptible to various diseases commonly difficult to treat. To overcome the barriers imposed by this organ for required drugs penetration, technological strategies have been implemented to ocular formulations. Among them are the use of temperature or electric stimuli and the development of nanoparticles. The objective of this review is to present the main barriers to ocular drug delivery and to discuss strategies used in the development of ocular dosage forms, primarily for topical delivery, to increase the local bioavailability of drugs, target their delivery and increase patient compliance. Results obtained in the last years related to the topical administration of liposomes, dendrimers, iontophoresis, among other nanoparticulate systems focused on ophthalmic delivery, will be addressed. Finally, some clinical trials and marketed formulations that use nanotechnology to topically treat eye diseases will be presented.

Gene-based Therapeutic Tools in the Treatment of Cornea Disease

BACKGROUND

As one of the main blinding ocular diseases, corneal blindness resulted from neovascularization that disrupts the angiogenic privilege of corneal avascularity. Following neovascularization, inflammatory cells are infiltrating into cornea to strengthen corneal injury. How to maintain corneal angiogenic privilege to treat corneal disease has been investigated for decades.

METHODOLOGY

Local administration of viral and non-viral-mediated anti-angiogenic factors reduces angiogenic protein expression in situ with limited or free of off-target effects upon gene delivery. Recently, Mesenchymal Stem Cells (MSCs) have been studied to treat corneal diseases. Once MSCs are manipulated to express certain genes of interest, they could achieve superior therapeutic efficacy after transplantation.

DISCUSSION

In the text, we first introduce the pathological development of corneal disease in the aspects of neovascularization and inflammation. We summarize how MSCs become an ideal candidate in cell therapy for treating injured cornea, focusing on cell biology, property and features. We provide an updated review of gene-based therapies in animals and preclinical studies in the aspects of controlling target gene expression, safety and efficacy. Gene transfer vectors are potent to induce candidate protein expression. Delivered by vectors, MSCs are equipped with certain characters by expressing a protein of interest, which facilitates better for MSC-mediated therapeutic intervention for the treatment of corneal disease.

CONCLUSION

As the core of this review, we discuss how MSCs could be engineered to be vector system to achieve enhanced therapeutic efficiency after injection.

Controlled Release of rAAV Vectors from APMA-Functionalized Contact Lenses for Corneal Gene Therapy

As an alternative to eye drops and ocular injections for gene therapy, the aim of this work was to design for the first time hydrogel contact lenses that can act as platforms for the controlled delivery of viral vectors (recombinant adeno-associated virus, rAAV) to the eye in an effective way with improved patient compliance. Hydrogels of hydroxyethyl methacrylate (HEMA) with aminopropyl methacrylamide (APMA) (H₁: 40, and H₂: 80 mM) or without (H_c: 0 mM) were synthesized, sterilized by steam heat (121 °C, 20 min), and then tested for gene therapy using rAAV vectors to deliver the genes to the cornea. The hydrogels showed adequate light transparency, oxygen permeability, and swelling for use as contact lenses. Loading of viral vectors (rAAV-lacZ, rAAV-RFP, or rAAV-hIGF-I) was carried out at 4 °C to maintain viral vector titer. Release in culture medium was monitored by fluorescence with Cy3-rAAV-lacZ and AAV Titration ELISA. Transduction efficacy was tested through reporter genes lacZ and RFP in human bone marrow derived mesenchymal stem cells (hMSCs). lacZ was detected with X-Gal staining and quantified with Beta-Glo^®, and RFP was monitored by fluorescence. The ability of rAAV-hIGF-I-loaded hydrogels to trigger cell proliferation in hMSCs was evaluated by immunohistochemistry. Finally, the ability of rAAV-lacZ-loaded hydrogels to transduce bovine cornea was confirmed through detection with X-Gal staining of β-galactosidase expressed within the tissue.

New Frontiers of Corneal Gene Therapy

Corneal diseases are among the most prevalent causes of blindness worldwide. The transparency and clarity of the cornea are guaranteed by a delicate physiological, anatomic, and functional balance. For this reason, all the disorders, including those of genetic origin, that compromise this state of harmony can lead to opacity and eventually vision loss. Many corneal disorders have a genetic etiology, and some are associated with rather rare and complex syndromes. Conventional treatments, such as corneal transplantation, are often ineffective, and to date, many of these disorders are still incurable. Gene therapy carries the promise of being a potential cure for many of these diseases, with solutions and strategies that did not seem possible until a few years ago. With its potential to treat genetic disease by means of deletion, replacement, or editing of a defective gene, the challenge can also be extended to corneal disorders in order to achieve long-term, if not definitive, relief. The aim of this paper is to review the state of the art of the different gene therapy approaches as potential treatments for corneal diseases and the future perspectives for the development of personalized gene-based medicine.

Targeting corneal inflammation by gene therapy: Emerging strategies for keratitis

Inflammation is the underlying process of several diseases within the eye, specifically in the cornea. Current treatment options for corneal inflammation or keratitis, and related neovascularization, are restricted by limited efficacy, adverse effects, and short duration of action. Gene therapy has shown great potential for the treatment of diseases affecting the ocular surface, and major efforts are being targeted to inflammatory mediators and neovascularization, in order to develop potential treatments for corneal inflammation. Gene therapy to treat ocular disorders is still starting, and current therapies are primarily experimental, with most human clinical trials still in research state, although some of them have already shown encouraging results. In this review, we focus on the progress and challenges of gene therapy to treat corneal inflammation. After introducing the inflammation process, we present the main nucleic acid delivery systems, including viral and non-viral vectors, and the most studied strategies to address the therapy: control of neovascularization and regulation of pro- and anti-inflammatory cytokines.

Gene Therapy and Gene Editing for the Corneal Dystrophies

Despite ever-increasing understanding of the genetic underpinnings of many corneal dystrophies, gene therapy designed to ameliorate disease has not yet been reported in any human patient. In this review, we explore the likely reasons for this apparent failure of translation. We identify the requirements for success: the genetic defect involved must have been identified and mapped, vision in the affected patient must be significantly impaired or likely to be impaired, no better or equivalently effective treatment must be available, the treatment must be capable of modulating corneal pathology, and delivery of the construct to the appropriate cell must be practicable. We consider which of the corneal dystrophies might be amenable to treatment by genetic manipulations, summarize existing therapeutic options for treatment, and explore gene editing using clustered regularly interspaced short palindromic repeat/Cas and other similar transformative technologies as the way of the future. We then summarize recent laboratory-based advances in gene delivery and the development of in vitro and in vivo models of the corneal dystrophies. Finally, we review recent experimental work that has increased our knowledge of the pathobiology of these conditions.

Gene therapy for ocular diseases meditated by ultrasound and microbubbles (Review)

The eye is an ideal target organ for gene therapy as it is easily accessible and immune‑privileged. With the increasing insight into the underlying molecular mechanisms of ocular diseases, gene therapy has been proposed as an effective approach. Successful gene therapy depends on efficient gene transfer to targeted cells to prove stable and prolonged gene expression with minimal toxicity. At present, the main hindrance regarding the clinical application of gene therapy is not the lack of an ideal gene, but rather the lack of a safe and efficient method to selectively deliver genes to target cells and tissues. Ultrasound‑targeted microbubble destruction (UTMD), with the advantages of high safety, repetitive applicability and tissue targeting, has become a potential strategy for gene‑ and drug delivery. When gene‑loaded microbubbles are injected, UTMD is able to enhance the transport of the gene to the targeted cells. High‑amplitude oscillations of microbubbles act as cavitation nuclei which can effectively focus ultrasound energy, produce oscillations and disruptions that increase the permeability of the cell membrane and create transient pores in the cell membrane. Thereby, the efficiency of gene therapy can be significantly improved. The UTMD‑mediated gene delivery system has been widely used in pre‑clinical studies to enhance gene expression in a site‑specific manner in a variety of organs. With reasonable application, the effects of sonoporation can be spatially and temporally controlled to improve localized tissue deposition of gene complexes for ocular gene therapy applications. In addition, appropriately powered, focused ultrasound combined with microbubbles can induce a reversible disruption of the blood‑retinal barrier with no significant side effects. The present review discusses the current status of gene therapy of ocular diseases as well as studies on gene therapy of ocular diseases meditated by UTMD.

Nanotechnology approaches for ocular drug delivery

Blindness is a major health concern worldwide that has a powerful impact on afflicted individuals and their families, and is associated with enormous socio-economical consequences. The Middle East is heavily impacted by blindness, and the problem there is augmented by an increasing incidence of diabetes in the population. An appropriate drug/gene delivery system that can sustain and deliver therapeutics to the target tissues and cells is a key need for ocular therapies. The application of nanotechnology in medicine is undergoing rapid progress, and the recent developments in nanomedicine-based therapeutic approaches may bring significant benefits to address the leading causes of blindness associated with cataract, glaucoma, diabetic retinopathy and retinal degeneration. In this brief review, we highlight some promising nanomedicine-based therapeutic approaches for drug and gene delivery to the anterior and posterior segments.

Gene therapy in corneal transplantation

Corneal transplantation is the most commonly performed organ transplantation. Immune privilege of the cornea is widely recognized, partly because of the relatively favorable outcome of corneal grafts. The first-time recipient of corneal allografts in an avascular, low-risk setting can expect a 90% success rate without systemic immunosuppressive agents and histocompatibility matching. However, immunologic rejection remains the major cause of graft failure, particularly in patients with a high risk for rejection. Corticosteroids remain the first-line therapy for the prevention and treatment of immune rejection. However, current pharmacological measures are limited in their side-effect profiles, repeated application, lack of targeted response, and short duration of action. Experimental ocular gene therapy may thus present new horizons in immunomodulation. From efficient viral vectors to sustainable alternative splicing, we discuss the progress of gene therapy in promoting graft survival and postulate further avenues for gene-mediated prevention of allogeneic graft rejection.

Targeting herpetic keratitis by gene therapy

Ocular gene therapy is rapidly becoming a reality. By November 2012, approximately 28 clinical trials were approved to assess novel gene therapy agents. Viral infections such as herpetic keratitis caused by herpes simplex virus 1 (HSV-1) can cause serious complications that may lead to blindness. Recurrence of the disease is likely and cornea transplantation, therefore, might not be the ideal therapeutic solution. This paper will focus on the current situation of ocular gene therapy research against herpetic keratitis, including the use of viral and nonviral vectors, routes of delivery of therapeutic genes, new techniques, and key research strategies. Whereas the correction of inherited diseases was the initial goal of the field of gene therapy, here we discuss transgene expression, gene replacement, silencing, or clipping. Gene therapy of herpetic keratitis previously reported in the literature is screened emphasizing candidate gene therapy targets. Commonly adopted strategies are discussed to assess the relative advantages of the protective therapy using antiviral drugs and the common gene therapy against long-term HSV-1 ocular infections signs, inflammation and neovascularization. Successful gene therapy can provide innovative physiological and pharmaceutical solutions against herpetic keratitis.

Ex vivo organotypic corneal model of acute epithelial herpes simplex virus type I infection

Herpes keratitis is one of the most severe pathologies associated with the herpes simplex virus-type 1 (HSV-1). Herpes keratitis is currently the leading cause of both cornea-derived and infection-associated blindness in the developed world. Typical presentation of herpes keratitis includes infection of the corneal epithelium and sometimes the deeper corneal stroma and endothelium, leading to such permanent corneal pathologies as scarring, thinning, and opacity. Corneal HSV-1 infection is traditionally studied in two types of experimental models. The in vitro model, in which cultured monolayers of corneal epithelial cells are infected in a Petri dish, offers simplicity, high level of replicability, fast experiments, and relatively low costs. On the other hand, the in vivo model, in which animals such as rabbits or mice are inoculated directly in the cornea, offers a highly sophisticated physiological system, but has higher costs, longer experiments, necessary animal care, and a greater degree of variability. In this video article, we provide a detailed demonstration of a new ex vivo model of corneal epithelial HSV-1 infection, which combines the strengths of both the in vitro and the in vivo models. The ex vivo model utilizes intact corneas organotypically maintained in culture and infected with HSV-1. The use of the ex vivo model allows for highly physiologically-based conclusions, yet it is rather inexpensive and requires time commitment comparable to that of the in vitro model.

Polymeric vectors for ocular gene delivery

Gene therapy holds promise for the treatment of many inherited and acquired diseases of the eye. Successful ocular gene therapy interventions depend on efficient gene transfer to targeted cells with minimal toxicity. A major challenge is to overcome both intracellular and extracellular barriers associated with ocular gene delivery. Numerous viral and nonviral vectors were explored to improve transfection efficiency. Among nonviral delivery systems, polymeric vectors have gained significant attention in recent years owing to their nontoxic and non-immunogenic nature. Polyplexes or nanoparticles can be prepared by interaction of cationic polymers with DNA, which facilitate cellular uptake, endolysosomal escape and nuclear entry through active mechanisms. Chemical modification of these polymers allows for the generation of flexible delivery vectors with desirable properties. In this article several synthetic and natural polymeric systems utilized for ocular gene delivery are discussed.

Systematic assessment of microneedle injection into the mouse cornea

Background

Corneal intrastromal injection is an important mode of gene-vector application to subepithelial layers. In a mouse model, this procedure is substantially complicated by the reduced corneal dimensions. Furthermore, it may be difficult to estimate the corneal area reached by the volume of a single injection. This study aimed to investigate intrastromal injections into the mouse cornea using different microneedles and to quantify the effect of injecting varying volumes. A reproducible injection technique is described.

Methods

Forty eyes of 20 129 Sv/J mice were tested. India ink was intrastromally injected using 30° beveled 33 G needles, tri-surface 25° beveled 35 G needles, or hand-pulled and 25° beveled glass needles. Each eye received a single injection of a volume of 1 or 2 μL. Corneoscleral buttons were fixed and flat mounted for computer-assisted quantification of the affected corneal area. Histological assessment was performed to investigate the intrastromal location of the injected dye.

Results

A mean corneal area of 5.0 ±1.4 mm² (mean ± SD) and 7.7 ±1.4 mm² was covered by intrastromal injections of 1 and 2 μL, respectively. The mean percentage of total corneal area reached ranged from 39% to 53% for 1 μL injections, and from 65% to 81% for 2 μL injections. Injections using the 33 G needles tended to provide the highest distribution area. Perforation rates were 8% for 30° beveled 33 G needles and 44% for tri-surface beveled 35 G needles. No perforation was observed with glass needle; however, intrastromal breakage of needle tips was noted in 25% of these cases.

Conclusions

Intracorneal injection using a 30° beveled 33 G needle was safe and effective. The use of tri-surface beveled 35 G needles substantially increased the number of corneal perforations. Glass needles may break inside the corneal stroma. Injections of 1 μL and 2 μL resulted in an overall mean of 49% and 73% respectively of total corneal area involved.

Corneal transduction by intra-stromal injection of AAV vectors in vivo in the mouse and ex vivo in human explants

The cornea is a transparent, avascular tissue that acts as the major refractive surface of the eye. Corneal transparency, assured by the inner stroma, is vital for this role. Disruption in stromal transparency can occur in some inherited or acquired diseases. As a consequence, light entering the eye is blocked or distorted, leading to decreased visual acuity. Possible treatment for restoring transparency could be via viral-based gene therapy. The stroma is particularly amenable to this strategy due to its immunoprivileged nature and low turnover rate. We assayed the potential of AAV vectors to transduce keratocytes following intra-stromal injection in vivo in the mouse cornea and ex vivo in human explants. In murine and human corneas, we transduced the entire stroma using a single injection, preferentially targeted keratocytes and achieved long-term gene transfer (up to 17 months in vivo in mice). Of the serotypes tested, AAV2/8 was the most promising for gene transfer in both mouse and man. Furthermore, transgene expression could be transiently increased following aggression to the cornea.

Dextran and protamine-based solid lipid nanoparticles as potential vectors for the treatment of X-linked juvenile retinoschisis

The goal of the present study was to analyze the potential application of nonviral vectors based on solid lipid nanoparticles (SLN) for the treatment of ocular diseases by gene therapy, specifically X-linked juvenile retinoschisis (XLRS). Vectors were prepared with SLN, dextran, protamine, and a plasmid (pCMS-EGFP or pCEP4-RS1). Formulations were characterized and the in vitro transfection capacity as well as the cellular uptake and the intracellular trafficking were studied in ARPE-19 cells. Formulations were also tested in vivo in Wistar rat eyes, and the efficacy was studied by monitoring the expression of enhanced green fluorescent protein (EGFP) after intravitreal, subretinal, and topical administration. The presence of dextran and protamine in the SLN improved greatly the expression of retinoschisin and EGFP in ARPE-19 cells. The nuclear localization signals of protamine, its ability to protect the DNA, and a shift in the entry mechanism from caveola-mediated to clathrin-mediated endocytosis promoted by the dextran, justify the increase in transfection. After ocular administration of the dextran-protamine-DNA-SLN complex to rat eyes, we detected the expression of EGFP in various types of cells depending on the administration route. Our vectors were also able to transfect corneal cells after topical application. We have demonstrated the potential usefulness of our nonviral vectors loaded with XLRS1 plasmid and provided evidence for their potential application for the management or treatment of degenerative retinal disorders as well as ocular surface diseases.

Nano-vectors for the Ocular Delivery of Nucleic Acid-based Therapeutics

Nucleic acid-based therapeutics have gained a lot of interest for the treatment of diverse ophthalmic pathologies. The first to enter in clinic has been an oligonucleotide, Vitravene^® for the treatment of cytomegalovirus infection. More recently, research on aptamers for the treatment of age related macular degeneration has led to the development of Macugen^®. Despite intense potential, effective ocular delivery of nucleic acids is a major challenge since therapeutic targets for nucleic acid-based drugs are mainly located in the posterior eye segment, requiring repeated invasive administration. Of late, nanotechnology-based nano-vectors have been developed in order to overcome the drawbacks of viral and other non-viral vectors. The diversity of nano-vectors allows for ease of use, flexibility in application, low-cost of production, higher transfection efficiency and enhanced genomic safety. Using nano-vector strategies, nucleic acids can be delivered either encapsulated or complexed with cationic lipids, polymers or peptides forming sustained release systems, which can be tailored according to the ocular tissue being targeted. The present review focuses on developments and advances in various nano-vectors for the ocular delivery of nucleic acid-based therapeutics, the barriers that such delivery systems face and methods to overcome them.

Ocular gene delivery using lentiviral vectors

Substantial advances in our understanding of lentivirus lifecycles and their various constituent proteins have permitted the bioengineering of lentiviral vectors now considered safe enough for clinical trials for both lethal and non-lethal diseases. They possess distinct properties that make them particularly suitable for gene delivery in ophthalmic diseases, including high expression, consistent targeting of various post-mitotic ocular cells in vivo and a paucity of associated intraocular inflammation, all contributing to their ability to mediate efficient and stable intraocular gene transfer. In this review, the intraocular tropisms and therapeutic applications of both primate and non-primate lentiviral vectors, and how the unique features of the eye influence these, are discussed. The feasibility of therapeutic targeting using these vectors in animal models of both anterior and posterior ophthalmic disorders has been established, and has, in combination with substantial progress in enhancing lentiviral vector bio-safety over the past two decades, paved the way for the first human ophthalmic clinical trials using lentivirus-based gene transfer vectors.

Emerging techniques to treat corneal neovascularisation

Neovascularisation is a major cause of visual loss in a number of ophthalmic diseases. This review aims to outline the basic regulators of vessel growth in corneal neovascularisation. An understanding of the underlying principles of physiological and pathophysiological vascular development helps to appreciate current approaches to prevent or treat corneal neovascularisation. Options for future interventions will be discussed in the light of recent evidence provided by animal models of corneal neovascularisation.

Gene therapy in the cornea: 2005--present

Successful restoration of vision in human patients with gene therapy affirmed its promise to cure ocular diseases and disorders. The efficacy of gene therapy is contingent upon vector and mode of therapeutic DNA introduction into targeted cells/tissues. The cornea is an ideal tissue for gene therapy due to its ease of access and relative immune-privilege. Considerable progress has been made in the field of corneal gene therapy in last 5 years. Several new gene transfer vectors, techniques and approaches have evolved. Although corneal gene therapy is still in its early stages of development, the potential of gene-based interventions to treat corneal abnormalities has begun to surface. Identification of next generation viral and nanoparticle vectors, characterization of delivered gene levels, localization, and duration in the cornea, and significant success in controlling corneal disorders, particularly fibrosis and angiogenesis, in experimental animal disease models, with no major side effects have propelled gene therapy a step closer toward establishing gene-based therapies for corneal blindness. Recently, researchers have assessed the delivery of therapeutic genes for corneal diseases and disorders due to trauma, infections, chemical, mechanical, and surgical injury, and/or abnormal wound healing. This review provides an update on the developments in gene therapy for corneal diseases and discusses the barriers that hinder its utilization for delivering genes in the cornea.

Ocular gene therapy: an evaluation of recombinant adeno-associated virus-mediated gene therapy interventions for the treatment of ocular disease

Both gene replacement therapy and alteration of host gene expression are playing increasingly important roles in the treatment of ocular diseases. Ocular gene therapy may provide alternatives to current treatments for eye diseases that are either greatly invasive and thus run the risk of complications, that offer only short-term relief from disease symptoms, or that are unable to directly treat vision loss. The success of three separate phase I clinical trials investigating a gene therapy intervention for the treatment of the retinal degenerative disorder Leber's congenital amaurosis (LCA) has unveiled the therapeutic potential of gene therapy. Preliminary results have demonstrated ocular gene transfer, using nonpathogenic recombinant adeno-associated viral (rAAV) vectors specifically, to be a safe, effective, and long-term treatment for LCA, a previously untreatable disorder. Nonpathogenic rAAV vectors offer the potential for long-term treatment. Many of the genes implicated in human ocular diseases have been identified, and animal models for such diseases have been developed, which have greatly facilitated the application of experimental rAAV-mediated gene therapy. This review highlights the key features of rAAV-mediated gene therapy that make it the most suitable gene therapy treatment approach for ocular diseases. Furthermore, it summarizes the current progress of rAAV-mediated gene therapy interventions/applications for a wide variety of ophthalmologic disorders.

AAV serotype influences gene transfer in corneal stroma in vivo

This study evaluated the cellular tropism and relative transduction efficiency of three AAV serotypes, AAV6, AAV8 and AAV9, for corneal gene delivery using mouse cornea in vivo and donor human cornea ex vivo. The AAV6, AAV8 and AAV9 serotypes having AAV2 plasmid encoding for alkaline phosphatase (AP) gene were generated by transfecting HEK 293 cell line with pHelper, pARAP4 and pRep/Cap plasmids. Viral vectors (10(9) vg/microl) were topically applied onto mouse cornea in vivo and human cornea ex vivo after removing the epithelium. Human corneas were processed for transgene delivery at day 5 after viral vector application. Mouse corneas were harvested at 4, 14 and 30 days after vector application for AP staining. Transduction efficiency was calculated by quantifying pixels of AP-stained area using Image J software and also confirmed by functional AP enzyme activity in the corneal lysates. Cellular toxicity of the three AAV serotypes was tested with TUNEL assay. Inflammatory response was detected by immunostaining for CD11b and F4/80. All three AAV serotypes successfully transduced mouse and human corneas. The order of transduction efficiency was AAV9 > AAV8 > AAV6. The transduction efficiency of AAV9 was 1.1-1.4 fold higher (p > 0.05) as compared to AAV8 and 3.5-5.5 fold higher (p < 0.01) as compared to AAV6. The level of transgene expression for all the three serotypes was greater at 14 days compared to 4 days and this high level of transgene expression was maintained up to the tested time point of 30 days. Corneas exposed to any of the three AAV serotypes did not show significant TUNEL positive cells or any inflammatory response as tested by CD11b or F4/80 staining suggesting that tested AAV serotypes do not induce cell death or inflammation and are safe for corneal gene therapy.

Ocular tolerance to a topical formulation of hyaluronic acid and chitosan-based nanoparticles

PURPOSE

Hyaluronic acid-chitosan nanoparticles (HA-CS NPs) have the potential to serve as a reliable drug delivery system to topically treat ocular surface disorders. We evaluated the in vivo uptake by ocular structures, the acute tolerance, and possible alterations of tear film physiology in rabbits.

METHODS

Fluorescent HA-CS NPs (fl-HA-CS NPs) were prepared by ionotropic gelation using fluoresceinamine-labeled hyaluronic acid and resuspended in buffer. fl-HA-CS NPs (30 microL, 0.5 mg/mL) and fluoresceinamine-HA conjugate (30 microL) were instilled into rabbit eyes every 30 minutes for 6 hours. In vivo uptake and acute tolerance were characterized 24 hours after the first instillation and compared with preinstillation measurements. Clinical signs, including tear production, lacrimal drainage system patency and reflux, and ocular surface pathology, were evaluated.

RESULTS

The rabbits showed no signs of ocular discomfort or irritation after exposure to HA-CS NPs. No macroscopic alteration in ocular surface structures was observed. fl-HA-CS NPs were present inside conjunctival and corneal epithelial cells, although the distribution within the cells was different. The fl-HA-CS NPs had no significant effects on tissue morphology and functionality, tear production, or drainage.

CONCLUSION

Taken together, these data demonstrate that HA-CS NPs are a safe drug carrier for ocular surface application.

Gene therapy for diseases of the cornea - a review

The cornea is particularly suited to gene therapy. The cornea is readily accessible, normally transparent, and is somewhat sequestrated from the general circulation and the systemic immune system. The principle of genetic therapy for the cornea is to use an appropriate vector system to transfer a gene to the cornea itself, or to the ocular environs, or systemically, so that a transgenic protein will be expressed that will modulate congenital or acquired disease. The protein may be structural such as a collagen, or functionally active such as an enzyme, cytokine or growth factor that may modulate a pathological process. Alternatively, gene expression may be silenced by the use of modalities such as antisense oligonucleotides. Interestingly, despite a very considerable amount of work in animal models, clinical translation directed to gene therapy of the human cornea has been minimal. This is in contrast to gene therapy for monogenic inherited diseases of the retina, where promising early results of clinical trials for Leber's congenital amaurosis have already been published and a number of other trials are ongoing.

Normalization of wound healing and diabetic markers in organ cultured human diabetic corneas by adenoviral delivery of c-Met gene

Purpose. Diabetic corneas display altered basement membrane and integrin markers, increased expression of proteinases, decreased hepatocyte growth factor (HGF) receptor, c-met proto-oncogene, and impaired wound healing. Recombinant adenovirus (rAV)-driven c-met overexpression in human organ-cultured corneas was tested for correction of diabetic abnormalities. Methods. Forty-six human corneas obtained postmortem from 23 donors with long-term diabetes (5 with diabetic retinopathy) were organ cultured and transduced with rAV-expressing c-met gene (rAV-cmet) under the cytomegalovirus promoter at approximately 10(8) plaque-forming units per cornea for 48 hours. Each control fellow cornea received control rAV (rAV expressing the beta-galactosidase gene or vector alone). After an additional 4 to 5 days of incubation, 5-mm epithelial wounds were created with n-heptanol, and healing was monitored. The corneas were analyzed afterward by immunohistochemistry and Western blot analysis. Signaling molecule expression and role was examined by immunostaining, phosphokinase antibody arrays, Western blot analysis, and inhibitor analysis. Results. rAV-cmet transduction led to increased epithelial staining for c-met (total, extracellular, and phosphorylated) and normalization of the patterns of select diabetic markers compared with rAV-vector-transduced control fellow corneas. Epithelial wound healing time in c-met-transduced diabetic corneas decreased twofold compared with rAV-vector-transduced corneas and became similar to normal. c-Met action apparently involved increased activation of p38 mitogen-activated protein kinase. c-Met transduction did not change tight junction protein patterns, suggesting unaltered epithelial barrier function. Conclusions. rAV-driven c-met transduction into diabetic corneas appears to restore HGF signaling, normalize diabetic marker patterns, and accelerate wound healing. c-Met gene therapy could be useful for correcting human diabetic corneal abnormalities.

Adenovirus-driven overexpression of proteinases in organ-cultured normal human corneas leads to diabetic-like changes

Our previous data suggested the involvement of matrix metalloproteinase-10 (MMP-10) and cathepsin F (CTSF) in the basement membrane and integrin changes occurring in diabetic corneas. These markers were now examined in normal human organ-cultured corneas upon recombinant adenovirus (rAV)-driven transduction of MMP-10 and CTSF genes. Fifteen pairs of normal autopsy human corneas were used. One cornea of each pair was transduced with rAV expressing either CTSF or MMP-10 genes. 1-2 x 10(8) plaque forming units of rAV per cornea were added to cultures for 48 h with or without sildenafil citrate. The fellow cornea of each pair received control rAV with vector alone. After 6-10 days additional incubation without rAV, corneas were analyzed by Western blot or immunohistochemistry, or tested for healing of 5-mm circular epithelial wounds caused by topical application of n-heptanol. Sildenafil significantly increased epithelial transduction efficiency, apparently by stimulation of rAV endocytosis through caveolae. Corneas transduced with CTSF or MMP-10 genes or their combination had increased epithelial immunostaining of respective proteins compared to fellow control corneas. Staining for diabetic markers integrin alpha(3)beta(1), nidogen-1, nidogen-2, and laminin gamma2 chain became weaker and irregular upon proteinase transduction. Expression of phosphorylated Akt was decreased in proteinase-transduced corneas. Joint overexpression of both proteinases led to significantly slower corneal wound healing that became similar to that observed in diabetic corneas. The data suggest that MMP-10 and CTSF may be responsible for abnormal marker patterns and impaired wound healing in diabetic corneas. Inhibition of these proteinases in diabetic corneas may alleviate diabetic keratopathy symptoms.

Oligopeptide-mediated gene transfer into mouse corneal endothelial cells: expression, design optimization, uptake mechanism and nuclear localization

Gene transfer to the corneal endothelium has potential in preventing corneal transplant rejection. In this study, we transfected mouse corneal endothelial cells (MCEC) with a class of novel arginine-rich oligopeptides. The peptides featured a tri-block design and mediated reporter gene expression in MCEC more efficiently than the commercial polyethylenimine standard. The functionality of each block was demonstrated to critically influence the performance of the peptide. Results from confocal imaging and flow cytometry then showed that energy-dependent endocytosis was the dominant form of uptake and multiple pathways were involved. Additionally, uptake was strongly dependent on interactions with cell-surface heparan sulphate. Fluorescence resonance energy transfer studies revealed that the peptide/DNA entered cells as an associated complex and some will have dissociated by 8.5 h. Large-scale accumulation of uncondensed DNA within the nucleus can also be observed by 26 h. Finally, as a proof of biological relevance, we transfected MCEC with plasmids encoding for the functional indoleamine 2,3-dioxygenase (IDO) enzyme. We then demonstrated that the expressed IDO could catalyse the degradation of l-tryptophan, which in turn suppressed the growth of CD4+ T-cells in a proliferation assay.

Electrically assisted delivery of macromolecules into the corneal epithelium

Electrically assisted delivery is noninvasive and has been investigated in a number of ocular drug delivery studies. The objectives of this study were to examine the feasibility of electrically assisted delivery of macromolecules such as small interfering RNA (siRNA) into the corneal epithelium, to optimize the iontophoresis and electroporation methods, and to study the mechanisms of corneal iontophoresis for macromolecules. Anodal and cathodal iontophoresis, electroporation and their combinations were the methods examined with mice in vivo. Cyanine 3 (Cy3)-labeled glyceraldehyde-3-phosphate dehydrogenase (GAPDH) siRNA and fluorescein isothiocyanate (FITC)-labeled dextran of different molecular weights (4-70 kDa) were the macromolecules studied. Microscopy and histology after cryostat sectioning were used to analyze and compare the delivery of the macromolecules to the cornea. Iontophoresis was effective in delivering siRNA and dextran up to 70 kDa into the cornea. The electroporation method studied was less effective than that of iontophoresis. Although both iontophoresis and electroporation alone can deliver the macromolecules into the cornea, these methods alone were not as effective as the combination of iontophoresis and electroporation (iontophoresis followed by electroporation). The significant enhancement of dextran delivery in anodal iontophoresis suggests that electroosmosis can be a significant flux-enhancing mechanism during corneal iontophoresis. These results illustrate the feasibility of electrically assisted delivery of macromolecules such as siRNA into the cornea.