Inhibition of corneal neovascularization with plasmid pigment epithelium-derived factor (p-PEDF) delivered by synthetic amphiphile INTeraction-18 (SAINT-18) vector in an experimental model of rat corneal angiogenesis

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.

Ocular-Surface Regeneration Therapies for Eye Disorders: The State of the Art

The ocular surface is a complex structure that includes cornea, conjunctiva, limbus, and tear film, and is critical for maintaining visual function. When the ocular-surface integrity is altered by a disease, conventional therapies usually rely on topical drops or tissue replacement with more invasive procedures, such as corneal transplants. However, in the last years, regeneration therapies have emerged as a promising approach to repair the damaged ocular surface by stimulating cell proliferation and restoring the eye homeostasis and function. This article reviews the different strategies employed in ocular-surface regeneration, including cell-based therapies, growth-factor-based therapies, and tissue-engineering approaches. Dry eye and neurotrophic keratopathy diseases can be treated with nerve-growth factors to stimulate the limbal stem-cell proliferation and the corneal nerve regeneration, whereas conjunctival autograft or amniotic membrane are used in subjects with corneal limbus dysfunction, such as limbal stem-cell deficiency or pterygium. Further, new therapies are available for patients with corneal endothelium diseases to promote the expansion and migration of cells without the need of corneal keratoplasty. Finally, gene therapy is a promising new frontier of regeneration medicine that can modify the gene expression and, potentially, restore the corneal transparency by reducing fibrosis and neovascularization, as well as by stimulating stem-cell proliferation and tissue regeneration.

Gene therapy in the anterior eye segment

This review provides comprehensive information about the advances in gene therapy in the anterior segment of the eye including cornea, conjunctiva, lacrimal gland, and trabecular meshwork. We discuss gene delivery systems including viral and non-viral vectors as well as gene editing techniques, mainly CRISPR-Cas9, and epigenetic treatments including antisense and siRNA therapeutics. We also provide a detailed analysis of various anterior segment diseases where gene therapy has been tested with corresponding outcomes. Disease conditions include corneal and conjunctival fibrosis and scarring, corneal epithelial wound healing, corneal graft survival, corneal neovascularization, genetic corneal dystrophies, herpetic keratitis, glaucoma, dry eye disease, and other ocular surface diseases. Although most of the analyzed results on the use and validity of gene therapy at the ocular surface have been obtained in vitro or using animal models, we also discuss the available human studies. Gene therapy approaches are currently considered very promising as emerging future treatments of various diseases, and this field is rapidly expanding.

Ocular delivery of CRISPR/Cas genome editing components for treatment of eye diseases

A variety of inherited or multifactorial ocular diseases call for novel treatment paradigms. The newly developed genome editing technology, CRISPR, has shown great promise in treating these diseases, but delivery of the CRISPR/Cas components to target ocular tissues and cells requires appropriate use of vectors and routes of administration to ensure safety, efficacy and specificity. Although adeno-associated viral (AAV) vectors are thus far the most commonly used tool for ocular gene delivery, sustained expression of CRISPR/Cas components may cause immune reactions and an increased risk of off-target editing. In this review, we summarize the ocular administration routes and discuss the advantages and disadvantages of viral and non-viral vectors for delivery of CRISPR/Cas components to the eye. We review the existing studies of CRISPR/Cas genome editing for ocular diseases and discuss the major challenges of the technology in ocular applications. We also discuss the most recently developed CRISPR tools such as base editing and prime editing which may be used for future ocular applications.

Comparison of Topical Pigment Epithelium-Derived Factor (PEDF) with Topical Bevacizumab for Accelerating the Regression of Corneal Neovascularization in an Experimental Model of Rabbit Corneal Angiogenesis

Purpose: To evaluate the anti-angiogenic effect of topical administration of Pigment epithelium-derived factor (PEDF) on the reduction of corneal neovascularization (NV) in comparison to topical Bevacizumab.Methods: 18 eyes of 18 New Zealand rabbits were enrolled. Corneal NV was induced by a 7-0 silk suture. After suture removal, rabbits were randomly divided into three groups. In every group, one eye randomly treated with topical bevacizumab or topical PEDF or saline for 14 days. The area and length of neovascularization were measured by Image J. Histological studies were done in three groups.Results: After 14 days, the mean decrease of corneal NV length was 1.84 ± 0.17 mm (P < .001) in PEDF group and 1.6 ± 0.07 mm (P < .001) in bevacizumab group which was significantly more than the saline group (P = .001 and P < .001, respectively). There was no significant difference between PEDF and bevacizumab group in the reduction of corneal NV length (P = .85). The mean decrease of corneal NV area was 4.94 ± 0.55 mm² (P < .001) in PEDF group and 4.23 ± 0.29 mm² in the bevacizumab group (P < .001). PEDF and bevacizumab significantly decreased corneal NV area in comparison to the saline group (p = .017, p = .001, respectively). The mean decrease of corneal NV area did not show a significant difference between PEDF and bevacizumab groups (P = .72).Conclusion: Topical PEDF might be an effective and safe treatment option as bevacizumab in a short-term use, indicating that it is as good as the standard. However, long-term effect is required to be investigated.

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.

MK2 inhibitor reduces alkali burn-induced inflammation in rat cornea

MK2 activation by p38 MAPK selectively induces inflammation in various diseases. We determined if a MK2 inhibitor (MK2i), improves cornea wound healing by inhibiting inflammation caused by burning rat corneas with alkali. Our study, for the first time, demonstrated that MK2i inhibited alkali burn-induced MK2 activation as well as rises in inflammation based on: a) blunting rises in inflammatory index, inflammatory cell infiltration, ED1⁺ macrophage and PMN⁺ neutrophil infiltration; b) suppressing IL-6 and IL-1β gene expression along with those of macrophage inflammatory protein-1α (MIP-1α), intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1); c) reducing angiogenic gene expression levels and neovascularization (NV) whereas anti-angiogenic PEDF levels increased. In addition, this study found that MK2i did not affect human corneal epithelial cell (HCEC) proliferation and migration and had no detectable side effects on ocular surface integrity. Taken together, MK2i selectively inhibited alkali burn-induced corneal inflammation by blocking MK2 activation, these effects have clinical relevance in the treatment of inflammation related ocular surface diseases.

PEDF and its roles in physiological and pathological conditions: implication in diabetic and hypoxia-induced angiogenic diseases

Pigment epithelium-derived factor (PEDF) is a broadly expressed multifunctional member of the serine proteinase inhibitor (serpin) family. This widely studied protein plays critical roles in many physiological and pathophysiological processes, including neuroprotection, angiogenesis, fibrogenesis and inflammation. The present review summarizes the temporal and spatial distribution patterns of PEDF in a variety of developing and adult organs, and discusses its functions in maintaining physiological homoeostasis. The major focus of the present review is to discuss the implication of PEDF in diabetic and hypoxia-induced angiogenesis, and the pathways mediating PEDF's effects under these conditions. Furthermore, the regulatory mechanisms of PEDF expression, function and degradation are also reviewed. Finally, the therapeutic potential of PEDF as an anti-angiogenic drug is briefly summarized.

Inhibition of corneal neovascularization with the combination of bevacizumab and plasmid pigment epithelium-derived factor-synthetic amphiphile INTeraction-18 (p-PEDF-SAINT-18) vector in a rat corneal experimental angiogenesis model

Bevacizumab, a 149-kDa protein, is a recombinant humanized monoclonal antibody to VEGF. PEDF, a 50-kDa glycoprotein, has demonstrated anti-vasopermeability properties. In this study, we demonstrated that the combination of bevacizumab and plasmid pigment epithelium-derived factor-synthetic amphiphile INTeraction-18 (p-PEDF-SAINT-18) has a favorable antiangiogenic effect on corneal NV. Four groups (Group A: 0 μg + 0 μg, B: 0.1 μg + 0.1 μg, C: 1 μg + 1 μg, and D: 10 μg + 10 μg) of bevacizumab + p-PEDF-SAINT-18 were prepared and implanted into the rat subconjunctival substantia propria 1.5 mm from the limbus on the temporal side. Then, 1 μg of p-bFGF-SAINT-18 was prepared and implanted into the rat corneal stroma 1.5 mm from the limbus on the same side. The inhibition of NV was observed and quantified from days 1 to 60. Biomicroscopic examination, western blot analysis and immunohistochemistry were used to analyze the 18-kDa bFGF, 50-kDa PEDF and VEGF protein expression. No inhibition activity for normal limbal vessels was noted. Subconjunctival injection with the combination of bevacizumab and p-PEDF-SAINT-18 successfully inhibited corneal NV. The bFGF and PEDF genes were successfully expressed as shown by western blot analysis, and a mild immune response to HLA-DR was shown by immunohistochemistry. We concluded that the combination of bevacizumab and p-PEDF-SAINT-18 may have more potent and prolonged antiangiogenic effects, making it possible to reduce the frequency of subconjunctival bevacizumab administration combined with a relatively safe profile and low toxicity.

Nanoparticle-mediated delivery of shRNA.VEGF-a plasmids regresses corneal neovascularization

PURPOSE

To determine the efficacy of a plasmid containing a small hairpin RNA expression cassette (pSEC.shRNA) against VEGF-A-loaded poly(lactic co-glycolic acid) nanoparticles (PLGA NPs) in the sustained regression of murine corneal neovascularization.

METHODS

PLGA nanoparticles were loaded with pSEC.shRNA.VEGF-A plasmids using the double emulsion-solvent evaporation method. KNV was induced in BALB/c mice by mechanical-alkali injury. Four weeks after induction of KNV, the mice were randomly divided to receive one of four treatments intrastromally: pSEC.shRNA.VEGF-A PLGA NPs (2 μg plasmid); naked pSEC.shRNA.VEGF-A plasmid only (2 μg plasmid); control blank PLGA NPs (equivalent dry weight of NPs); and vehicle. Two and five days after intervention, corneas were harvested to determine VEGF-A gene and protein expression using reverse transcriptase polymerase chain reaction and ELISA, respectively. Four weeks after intervention, corneas were photographed, mice sacrificed, and the corneal whole mounts were immunostained for CD31 (panendothelial cell marker). Immunofluorescence microscopy was performed and the neovascular area was quantitated.

RESULTS

VEGF-A mRNA (49.6 ± 12.4 vs. 82.9 ± 6.0%, P < 0.01) and protein (4.0 ± 5.2 vs. 20.0 ± 7.5 ρg VEGF-A/mg total protein, P < 0.05) expression were significantly reduced in pSEC.shRNA.VEGF-A PLGA NP-treated corneas as compared with control blank NP. The pSEC.shRNA.VEGF-A PLGA NP-treated corneas showed significant regression in the mean fractional areas of KNV (0.125 ± 0.042; 12.5%, P <0.01) compared with both naked plasmid only (0.283 ± 0.004; 28.3%) and control (blank NPs = 0.555 ± 0.072, 55.5%) at 4 weeks post-treatment.

CONCLUSIONS

The pSEC.shRNA.VEGF-A-loaded PLGA NPs are an effective, nonviral, nontoxic, and sustainable form of gene therapy for the regression of murine KNV.

Inflammatory corneal neovascularization: etiopathogenesis

There is a delicate balance between pro-angiogenic stimuli and anti-angiogenic stimuli in the normal cornea. This balance allows the cornea to normally exist in a relatively avascular state, which is needed for optical clarity and vision. However, in the setting of inflammation, this balance may be shifted in favor of neovascularization. This paper reviews the literature on corneal inflammatory neovascularization beginning with the pro-angiogenic factors, such as Vascular Endothelial Growth Factor and Fibroblast Growth Factor, which help to facilitate the development of new corneal vessels. Subsequently the anti-angiogenic factors and their role in preventing neovascularization in the normal cornea are reviewed. Finally, a review of several etiologies of inflammatory neovascularization is presented with attention to the processes that allow the pro-angiogenic stimuli to overwhelm the anti-angiogenic factors.

Targeted decorin gene therapy delivered with adeno-associated virus effectively retards corneal neovascularization in vivo

Decorin, small leucine-rich proteoglycan, has been shown to modulate angiogenesis in nonocular tissues. This study tested a hypothesis that tissue-selective targeted decorin gene therapy delivered to the rabbit stroma with adeno-associated virus serotype 5 (AAV5) impedes corneal neovascularization (CNV) in vivo without significant side effects. An established rabbit CNV model was used. Targeted decorin gene therapy in the rabbit stroma was delivered with a single topical AAV5 titer (100 µl; 5×10¹² vg/ml) application onto the stroma for two minutes after removing corneal epithelium. The levels of CNV were examined with stereomicroscopy, H&E staining, lectin, collagen type IV, CD31 immunocytochemistry and CD31 immunoblotting. Real-time PCR quantified mRNA expression of pro- and anti-angiogenic genes. Corneal health in live animals was monitored with clinical, slit-lamp and optical coherence tomography biomicroscopic examinations. Selective decorin delivery into stroma showed significant 52% (p<0.05), 66% (p<0.001), and 63% (p<0.01) reduction at early (day 5), mid (day 10), and late (day 14) stages of CNV in decorin-delivered rabbit corneas compared to control (no decorin delivered) corneas in morphometric analysis. The H&E staining, lectin, collagen type IV, CD31 immunostaining (57–65, p<0.5), and CD31 immunoblotting (62–67%, p<0.05) supported morphometric findings. Quantitative PCR studies demonstrated decorin gene therapy down-regulated expression of VEGF, MCP1 and angiopoietin (pro-angiogenic) and up-regulated PEDF (anti-angiogenic) genes. The clinical, biomicroscopy and transmission electron microscopy studies revealed that AAV5–mediated decorin gene therapy is safe for the cornea. Tissue-targeted AAV5-mediated decorin gene therapy decreases CNV with no major side effects, and could potentially be used for treating patients.

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.