Antiangiogenic drugs in the management of ocular diseases: Focus on antivascular endothelial growth factor

High-accuracy 3D segmentation of wet age-related macular degeneration via multi-scale and cross-channel feature extraction and channel attention

Wet age-related macular degeneration (AMD) is the leading cause of visual impairment and vision loss in the elderly, and optical coherence tomography (OCT) enables revolving biotissue three-dimensional micro-structure widely used to diagnose and monitor wet AMD lesions. Many wet AMD segmentation methods based on deep learning have achieved good results, but these segmentation results are two-dimensional, and cannot take full advantage of OCT's three-dimensional (3D) imaging characteristics. Here we propose a novel deep-learning network characterizing multi-scale and cross-channel feature extraction and channel attention to obtain high-accuracy 3D segmentation results of wet AMD lesions and show the 3D specific morphology, a task unattainable with traditional two-dimensional segmentation. This probably helps to understand the ophthalmologic disease and provides great convenience for the clinical diagnosis and treatment of wet AMD.

AP-2β Is a Downstream Effector of PITX2 Required to Specify Endothelium and Establish Angiogenic Privilege During Corneal Development

PURPOSE

The homeodomain transcription factor, PITX2, is at the apex of a genetic pathway required for corneal development, but the critical effector genes regulated by the PITX2 remain unknown. The purpose of this study was to discover and validate PITX2-dependent mechanisms required for specifying cell lineages and establishing angiogenic privilege within the developing cornea.

METHODS

Microarrays were used to compare gene expression in corneas isolated from temporal Pitx2 knockout embryos and control littermates. Quantitative RT-PCR and immunohistochemistry was used to further validate Tfap2b expression differences in Pitx2 knockout versus control corneas. In situ hybridization and protein immunohistochemistry were used to assay eyes of a Tfap2b allelic series of embryos to identify differentiated cellular lineages in the cornea, blood vessel endothelium, or lymphatic vessel endothelium.

RESULTS

We show that PITX2 is required for the expression of Tfap2b, encoding the AP-2β transcription factor, in the neural crest during corneal development. Markers of differentiated corneal epithelium and stroma are expressed in the absence of AP-2β. In contrast, markers of differentiated corneal endothelium are not expressed in the absence of AP-2β. Endomucin+ blood vessels are present throughout the developing corneal stroma in the absence of AP-2β, whereas LYVE1+ lymphatic vessels are not found.

CONCLUSIONS

The AP-2β transcription factor is an important effector of PITX2 function during corneal development, required for differentiation of corneal endothelium and establishment of angiogenic privilege. Unlike PITX2, AP-2β is not required for the early expression of available lineage specific markers for the corneal epithelium and stroma during embryogenesis, nor establishment of lymphangiogenic privilege. Therefore, additional PITX2-dependent factors likely regulate these latter processes during embryonic development. These results extend our understanding of the genetic mechanisms regulating cornea development.

Screening of antiangiogenic potential of twenty two marine invertebrate extracts of phylum Mollusca from South East Coast of India

OBJECTIVE

To evaluate the antiangiogenic potential of twenty two marine invertebrate species of Phylum Mollusca from south east coast of India.

METHODS

Live specimens of molluscan species were collected and their methanolic extracts were evaluated for preliminary antiangiogenic activity using the in ovo chick chorio-allantoic membrane assay. The extracts were further evaluated for in vivo antiangiogenic activity using chemical cautery induced corneal neovascularization assay in rats and oxygen induced retinopathy assay in rat pups.

RESULTS

In the chick chorio-allantoic membrane assay, four methanolic extracts of marine molluscan species viz. Meretrix meretrix, Meretrix casta, Telescopium telescopium and Bursa crumena methanolic extracts exhibited noticeable antiangiogenic activity at the tested concentration of 200 µg whereby they significantly inhibited the VEGF induced proliferation of new blood vessels. Among these four extracts, the methanolic extract of Meretrix casta exhibited relatively higher degree of antiangiogenic activity with an inhibitiory percentage (64.63%) of the VEGF induced neovascularization followed by the methanolic extracts of Telescopium telescopium (62.02%), Bursa crumena (60.48%) and Meretrix meretrix (47.01%). These four methanolic extracts were further evaluated for in vivo antiangiogenic activity whereby the methanolic extract of Telescopium telescopium exhibited most noticeable inhibition (42.58%) of the corneal neovascularization in rats in comparison to the sham treated group, and also exhibited most noticeable inhibition (31.31%) of the oxygen induced retinal neovascularization in rat pups in comparison to the hyperoxia group that was observed for considerable retinal neovascularization.

CONCLUSIONS

The significant antiangiogenic activity evinced by the extract of Telescopium telescopium merits further investigation for ocular neovascular diseases.

FoxC1-dependent regulation of vascular endothelial growth factor signaling in corneal avascularity

Angiogenesis is a crucial process whereby new blood vessels are formed from pre-existing vessels, and it occurs under both normal and pathophysiological conditions. The process is precisely regulated through the balance between proangiogenic and anti-angiogenic mechanisms, and many of these mechanisms have been well-characterized through extensive research. However, little is known about how angiogenesis is regulated at the transcriptional level. We have recently shown that deletion of the Forkhead box (Fox) transcription factor Foxc1 in cells of neural crest (NC) lineage leads to aberrant vessel growth in the normally avascular corneas of mice, and that the effect is cell type-specific because the corneas of mice lacking Foxc1 expression in vascular endothelial cells remained avascular. The NC-specific Foxc1 deletion was also associated with elevated levels of both proangiogenic factors, such as the matrix metalloproteases (MMPs) MMP-3, MMP-9, and MMP-19 and the angiogenic inhibitor soluble vascular endothelial growth factor receptor 1 (sVEGFR-1). Thus, FoxC1 appears to control angiogenesis by regulating two distinct and opposing mechanisms; if so, vascular development could be determined, at least in part, by a competitive balance between proangiogenic and anti-angiogenic FoxC1-regulated pathways. In this review, we describe the mechanisms by which FoxC1 regulates vessel growth and discuss how these observations could contribute to a more complete understanding of the role of FoxC1 in pathological angiogenesis.

Ocular medicines in children: the regulatory situation related to clinical research

Background

Many ocular medications are prescribed for paediatric patients, but the evidence for their rational use is very scant. This study was planned to compare the availability and the licensing status of ocular medications marketed in Italy, the United Kingdom (UK), and the United States of America (USA) related to the amount of published and un-published RCTs testing these drugs in the paediatric population.

Methods

A quantitative analysis was performed to evaluate the number of ocular medications with a paediatric license in Italy, the UK, and the USA. A literature search was also performed in MEDLINE, EMBASE, and The Cochrane Central Register of Controlled Trials for randomized controlled trials (RCTs) on ophthalmic pharmacological therapy in children aged < 18 years, published up to December 2010. A search in the international clinical trial registries, the list of paediatric investigation plans (PIPs) approved by European Medicines Agency (EMA), and the table of medicines with new paediatric information approved by Food and Drug Administration (FDA) was also performed.

Results

In all, of 197 drugs identified, 68 (35%) single drugs are licensed for paediatric use at least in one considered country, while 23 (12%) were marketed in all three countries. More specifically, in Italy 43 single drugs (48% of those marketed) had a paediatric license, while 39 (64%) did in the UK and 22 (54%) did in the USA. Only 13 drugs were marketed with a paediatric license in all countries.

The percentage of drugs licensed for paediatric use and for which at least one RCT had been performed ranged between 51% in Italy and 55% in the USA. No published RCTs were found for 11 (48%) drugs licensed for paediatric use in all three countries. In all, 74 (35%) of the retrieved RCTs involved mydriatic/cycloplegic medications.

A total of 62 RCTs (56% completed) on 46 drugs were found in the international clinical trial registries. Cyclosporin and bevacizumab were being studied in many ongoing trials. Twenty-six drugs had new paediatric information approved by FDA based on new paediatric clinical trials, while only 4 PIPs were approved by EMA.

Conclusions

There is a pressing need for further research and clinical development in the pediatric ophthalmic area, where effective up-to-date treatments, and additional research and education on use in children, remain priorities.

Forkhead box transcription factor FoxC1 preserves corneal transparency by regulating vascular growth

Normal vision requires the precise control of vascular growth to maintain corneal transparency. Here we provide evidence for a unique mechanism by which the Forkhead box transcription factor FoxC1 regulates corneal vascular development. Murine Foxc1 is essential for development of the ocular anterior segment, and in humans, mutations have been identified in Axenfeld-Rieger syndrome, a disorder characterized by anterior segment dysgenesis. We show that FOXC1 mutations also lead to corneal angiogenesis, and that mice homozygous for either a global (Foxc1(-/-)) or neural crest (NC)-specific (NC-Foxc1(-/-)) null mutation display excessive growth of corneal blood and lymphatic vessels. This is associated with disorganization of the extracellular matrix and increased expression of multiple matrix metalloproteinases. Heterozygous mutants (Foxc1(+/-) and NC-Foxc1(+/-)) exhibit milder phenotypes, such as disrupted limbal vasculature. Moreover, environmental exposure to corneal injury significantly increases growth of both blood and lymphatic vessels in both Foxc1(+/-) and NC-Foxc1(+/-) mice compared with controls. Notably, this amplification of the angiogenic response is abolished by inhibition of VEGF receptor 2. Collectively, these findings identify a role for FoxC1 in inhibiting corneal angiogenesis, thereby maintaining corneal transparency by regulating VEGF signaling.

Lasting controversy on ranibizumab and bevacizumab

Vascular endothelial growth factor (VEGF), an important angiogenic factor that is able to stimulate the proliferation and migration of endothelial cells, is the best-studied hallmark of angiogenesis. Neovascularization is a major cause of age-related macular degeneration (AMD) which is a leading cause of blindness in the elderly population. Specific molecular inhibitors of VEGF have been proved to be useful in the treatment of AMD. Ranibizumab and Bevacizumab are structurally similar to anti-VEGF drugs in the treatment of AMD. Many studies have indicated that Ranibizumab and Bevacizumab are of roughly equal short-term efficacy and safety, Bevacizumab is an attractive alternative to Ranibizumab due to its lower cost. However, only Ranibizumab has received Food and Drug Administration (FDA) approval for the treatment of macular degeneration. More multicenter clinical trials are required to compare the relative efficacy and safety of these two drugs and some progress has been achieved. This review discusses the clinical effectiveness, safety, cost and other practical implications of Ranibizumab and Bevacizumab.

The chronic care for age-related macular degeneration study (CHARMED): study protocol for a randomized controlled trial

Background

Neovascular age-related macular degeneration is the leading cause of irreversible blindness in people 50 years of age or older in the developed world. As in other chronic diseases, several effective treatments are available, but in clinical daily practice there is an evidence performance gap. The Chronic Care Model represents an evidence-based framework for the care of chronically ill patients and aims at closing that gap. However, no data are available regarding patients with neovascular age-related macular degeneration.

Methods/Design

CHARMED is a multicenter randomized controlled trial. The study challenges the hypothesis that the implementation of core elements of the Chronic Care Model (patient empowerment, delivering evidence based information, clinical information system, reminder system with structured follow up and frequent monitoring) via a specially trained Chronic Care Coach in Swiss centres for neovascular age-related macular degeneration results in better visual acuity (primary outcome) and an increased disease specific quality of life (secondary outcome) in patients with neovascular age-related macular degeneration. According to the power calculation, a total sample size of 352 patients is needed (drop out rate of 25%). 14 specialised medical doctors from leading ophtalmologic centres in Switzerland will include 25 patients. In each centre, a Chronic Care Coach will provide disease specific care according to the Chronic Care Model for intervention group. Patients from the control group will be treated as usual. Baseline measurements will be taken in month III - XII, starting in March 2011. Follow-up data will be collected after 6 months and 1 year.

Discussion

Multiple studies have shown that implementing Chronic Care Model elements improve clinical outcomes as well as process parameters in different chronic diseases as osteoarthritis, depression or e.g. the cardiovascular risk profile of diabetes patients. This study will be the first to assess this approach in neovascular age-related macular degeneration. If our hypothesis will be confirmed, the implementation of this approach in routine care for patients with with neovascular age-related macular degeneration should be considered.

Trial Registration

Current controlled trials ISRCTN32507927.

Bevasiranib for the treatment of wet, age-related macular degeneration

Age- related Macular Degeneration (AMD) is the leading cause of severe visual impairment in people 65 years and older in industrialized nations. Exudative, or “wet”, AMD is a late form of AMD (as distinguished from atrophic, so-called dry, AMD) and is responsible for over 60% of all cases of blindness due to AMD. It is widely accepted that vascular endothelial growth factor (VEGF) is a key component in the pathogenesis of choroidal neo-vascularization (CNV), which is a precursor to wet AMD. The current gold-standard for treating wet AMD is the monoclonal antibody fragment ranibizumab (trade name Lucentis), which targets VEGF. Other agents used to treat wet AMD include pegaptanib (Macugen), bevacizumab (Avastin; off-label use), and several other experimental agents. The advent of small interfering RNA (siRNA) has presented a whole new approach to inhibiting VEGF. This article reviews the status of a novel siRNA-based therapeutic, bevasiranib, for the treatment of wet AMD. Bevasiranib is believed to work by down regulating VEGF production in the retina. Studies in human cell-lines and animal models have shown that VEGF siRNAs are effective in inhibiting VEGF production. Although there is a lack of sufficient published data on human studies supporting the use of bevasiranib for wet AMD, available data indicates that due to its unique mechanism of action, bevasiranib might hold some promise as a primary or adjunct treatment for wet AMD.