The possibility of gene therapy for the treatment of choroidal neovascularization

Clinical significance of TIMP-3 and RASSF1A expression in colorectal cancer

AIM: To investigate the correlation between TIMP-3 and RASSF1A expression and clinicopathologic features of colorectal cancer.

METHODS: The expression of TIMP-3 and RASSF1A was detected by immunohistochemistry in colorectal cancer, tumor-adjacent colorectal tissue and normal colorectal tissue specimens. The correlation between TIMP-3 and RASSF1A expression and clinicopathologic features, such as patient's age, gender, infiltration degree, and lymph node metastasis, was analyzed. The correlation between TIMP-3 and RASSF1A expression was also determined by spearman′s rank correlation analysis.

RESULTS: The positive rates of TIMP-3 expression in normal colorectal mucosa, tumor adjacent tissue and colorectal cancer were 90.0%, 70.0% and 16.7%, respectively, and those of RASSF1A were 83.3%, 63.3% and 23.3%. In colorectal cancer, the expression of TIMP-3 and RASSF1A was related to lymph node metastasis, depth of invasion, and degree of tumor differentiation (all P < 0.05). Spearman rank correlation analysis showed that there is a positive correlation between TIMP-3 and RASSF1A expression in colorectal adenocarcinoma (r = 0.256, P < 0.05).

CONCLUSION: The expression of TIMP-3 is significantly correlated with that of RASSF1A in colorectal cancer. The down-regulation of TIMP-3 and RASSF1A may be involved in the genesis of colorectal cancer and may be used as an index for evaluation of tumor malignancy.

A new model of experimental subretinal neovascularization in the rabbit

Existing animal models of choroidal neovascularization (CNV) present several problems: they are hard to reproduce, they are inefficient, and the CNV created is not sustainable. The purpose of this study is to develop a highly efficient, reliable, sustainable rabbit model of CNV to facilitate the study of anti-angiogenic and anti-proliferative therapies for ocular diseases. Twenty-two pigmented rabbits were used in this study. Eleven rabbits received subretinal injections of either 10 microl of Matrigel with 500 ng of vascular endothelial growth factor (VEGF) or 20 microl of Matrigel with 750 ng of VEGF; eight rabbits received subretinal injections of either 10 or 20 microl of Matrigel only; three rabbits used as controls received subretinal injections of 20 microl phosphate-buffered saline (PBS) alone. Fundus photography, fluorescein angiography, optical coherence tomography, and histologic examinations were performed 1, 2, 4, and 9 weeks after injection. All experimental eyes showed angiographic leakage within this localized area 1 week after injection. The amount of leakage usually increased at weeks 2 and 4 and, in most cases, persisted at week 9. Control eyes demonstrated no leakage at any time point. Optical coherence tomography of treated eyes showed subretinal fluid and the presence of a lesion, possibly vascular or fibrotic, at the site of the leakage. Histologic analysis confirmed the presence of new subretinal blood vessels in the areas of Matrigel deposit. In conclusion, this novel method provides a highly reproducible, reliable, and sustainable rabbit model of experimental choroidal neovascularization. Such a model may prove useful for screening new anti-angiogenic therapies in a larger animal eye.

Long-term safety of GDNF gene delivery in the retina

PURPOSE

To examine retinal function after the long-term, gene therapy-delivered expression of exogenous glial cell line-derived neurotrophic factor (GDNF).

METHODS

Forty Sprague-Dawley rats each received an intravitreal injection of recombinant adeno-associated virus expressing GDNF (rAAV-GDNF) in their right eye. The left eye was untreated. One year after viral transduction in ocular tissues, retinal morphology and function were compared between rAAV-GDNF-injected and normal naïve eyes. Synthesis and accumulation of GDNF within the retina were immunohistologically confirmed using enzyme-linked immunosorbent assay. Morphological analyses included light microscope examination of retinal sections and the counting of retinal ganglion cells. Inflammation by infiltration of leukocytes in retina was assessed immunohistochemically. Retinal function was assessed using electroretinography.

RESULTS

GDNF expression was confirmed. There was no obvious abnormality in retinal section or increased infiltration by leukocytes after retinal transduction of rAAV-GDNF for 1 year. Counts of retinal ganglion cells were not decreased in rAAV-GDNF-injected eyes. There were no statistical differences in amplitude as well as latency of the electroretinogram-determined a- and b-waves between transduced and untreated eyes.

CONCLUSIONS

Long-term expression of GDNF within the eyes can be achieved by intravitreal injection of rAAV vectors in the absence of morphological or functional deficits in the retina.

[RPE transplantation: the challenges and the future]

Transplantation of RPE cells represents a potential therapeutic intervention for various retinal degenerations including complex, multifactorial age-related macular degeneration (AMD). Prerequisite for a successful RPE transplantation is the isolation of suitable cells, which must establish themselves in the host eye to develop functionality similar to that of healthy RPE cells in vivo. Autologous cells can be harvested from the peripheral retina. Ex vivo gene manipulation offers the possibility that even a dysfunctional donor RPE cell can be restored to perform a required specific function in the retina which may in turn help prevent or slow down the degenerative process in the host eye. The problem of cultured RPE cells is that they lose many of their normal phenotypic characteristics, which also leads to a reduction of their functional capacity. Currently highly "stressed" RPE cells are transplanted, whether fresh or cultured, which may not establish their normal in vivo functions. The generation of a genetically engineered cell line with all the functions of a healthy RPE cell and the use of retinal stem cells represent alternative and promising approaches for the future.

Stem cells in the eye

In the adult organism, all tissue renewal and regeneration depends ultimately on somatic stem cells, and the eye is no exception. The importance of limbal stem cells in the maintenance of the corneal epithelium has long been recognised, and such cells are now used clinically for repair of a severely damaged cornea. The slow cycling nature of lens epithelial cells and their ability to terminally differentiate into fiber cells are suggestive of a stem cell lineage. Furthermore, recent studies have identified progenitor cells in the retina and ocular vasculature which may have important implications in health and disease. Although the recent literature has become flooded with articles discussing aspects of stem cells in a variety of tissues our understanding of stem cell biology, especially in the eye, remains limited. For instance, there is no definitive marker for ocular stem cells despite a number of claims in the literature, the patterns of stem cell growth and amplification are poorly understood and the microenvironments important for stem cell regulation and differentiation pathways are only now being elucidated. A greater understanding of ocular stem cell biology is essential if the clinical potential for stem cells is to be realised. For instance; How do we treat stem cell deficiencies? How do we use stem cells to regenerate damaged retinal tissue? How do we prevent stem cell lineages contributing to retinal vascular disease? This review will briefly consider the principal stem cells in the mature eye but will focus in depth on limbal stem cells and corneal epithelium. It will further discuss their role in pathology and their potential for therapeutic intervention.

Gene therapy for genetic and acquired retinal diseases

We present an overview of the current status of basic science and translational research being applied to gene therapy for eye disease, focusing on diseases of the retina. We discuss the viral and nonviral methods being used to transfer genes to the retina and retinal pigment epithelium, and the advantages and disadvantages of each approach. We review the various genetic and somatic treatment strategies that are being used for genetically determined and acquired diseases of the retina, including gene replacement, gene silencing by ribozymes and antisense oligonucleotides, suicide gene therapy, antiapoptosis, and growth factor therapies. The rationales for the specific therapeutic approaches to each disease are discussed. Schematics of gene transfer methods and therapeutic approaches are presented together with a glossary of gene transfer terminology.

Neovascular age-related macular degeneration: present and future treatment options

PURPOSE

To review treatment strategies in neovascular age-related macular degeneration (ARMD).

METHODS

Medline and Embase search.

RESULTS

Age-related macular degeneration (ARMD) is the commonest cause of blindness in the developed world in individuals over 50 years of age. ARMD may lead to loss of vision by atrophy of the retinal pigment epithelium or by the development of choroidal neovascular membranes (CNVM) under the macula, which leak serous fluid and blood and ultimately cause a blinding disciform scar. Treatment options currently being investigated fall into three main approaches: elimination of the CNVM from the subfoveal area (by laser or surgery), modification of the CNVM (by laser, radiotherapy or chemotherapeutic agents) or lastly prevention of the formation of CNVM (by laser prophylaxis, diet or gene targeting). Whilst almost no therapy restores normal visual acuity, any significant visual improvement over the natural history may be regarded as beneficial.

CONCLUSIONS

Both the current and immediate future potential therapies for choroidal neovascularisation in ARMD require considerable advances to be made before they will make any impact on blindness caused by ARMD. Of the current treatments none are curative and the treatment benefits are small. There is an urgent need for new therapies.