Johns Hopkins biomedical engineers have teamed up with clinicians to create a new drug-delivery strategy for neovascular age-related macular degeneration. In addition to testing a new drug that effectively stops neovascularization in mice, the team gave the drug a biodegradable coating to keep it in the eye longer. If proven effective in humans, the engineers say, it could mean only two or three injections per year instead of the monthly injections that are the current standard of care.
The new drug, in its time-release coating, was tested in mice with abnormalities similar to those experienced by people with wet AMD. A description of the study results, currently available online, will be published in the October issue of the journal Biomaterials.
“If you lose central vision, you can’t drive a car and you can’t see your grandchildren,” says Jordan Green, PhD, assistant professor of biomedical engineering and ophthalmology at the Johns Hopkins University. “You’re willing to do what it takes to keep your sight. We hope that our system will work in people, and make invasive treatments much less frequent, and therefore easier to comply with, and safer.”
Approximately 200,000 Americans suffer from central vision loss caused by wet AMD and are treated with frequent (as often as once a month) injections into the eye of a drug that blocks one of the major stimulators of abnormal blood vessel growth. “The frequent visits for injections are a burden and each injection carries a small risk of infection, so one of our goals is to find new approaches that allow for fewer visits and injections.” says Peter Campochiaro, MD, the George S. & Dolores Doré Eccles Professor of Ophthalmology & Neuroscience at Johns Hopkins.
Dr. Green’s laboratory, which specializes in designing new drug-delivery systems, worked with Dr. Campochiaro and Aleksander Popel, PhD, professor of biomedical engineering, whose laboratory discovered the new drug—a short piece of protein that blocks the growth of unwanted blood vessels. (The drugs currently on the market for treating wet AMD are longer protein pieces or full-length proteins that could become inactive if given a biodegradable coating.)
When the team tested the drug on cells grown in the lab, they found that it killed blood vessel cells and prevented growth of new blood vessels. The same effect was found when the drug was injected into the eyes of mice with abnormal blood vessels like those seen in wet AMD, but, as with the current standard treatment, the drug was only effective for about four weeks since the watery contents inside the eye gradually flushed it out.
The team’s solution, says Dr. Green, was to slow the release and depletion of the drug by covering it in non-toxic, biodegradable coatings. They first created nanoparticles filled with the drug. When the spheres were placed in a watery environment, the water gradually broke down the coating and released the drug a little at a time. To maximize this effect, the team created larger spheres, called microparticles, filled with about a hundred nanoparticles per microparticle, and held together by another type of biodegradable glue. Testing their microparticles in mice, the team found that the drug persisted in their eyes for at least 14 weeks, more than three times as long as the current treatment. Dr. Green says that the treatments may last longer in humans than in mice, but clinical trials will not begin before further testing in other animals.
A team at the University College London has reported the discovery of a protein that encourages blood vessel growth, and especially the kind that characterize diseases as diverse as cancer, age-related macular degeneration and rheumatoid arthritis. The report appeared in the journal Nature.
The team at the UCL Institute of Ophthalmology discovered the new protein, called LRG1, by screening for mouse genes that are over-expressed in abnormal retinal blood vessels in diseased eyes.
In these diseased retinas, the LRG1 protein is expressed by blood vessel endothelial cells, which line blood
vessel walls. LRG1 is also present in the eyes of patients with proliferative diabetic retinopathy.
The study shows that, in mouse models, LRG1 promotes angiogenesis. Conversely, inhibition of LRG1 in mouse models reduces the harmful blood vessel growth associated with retinal disease.
The authors of the study suggest that blocking LRG1’s activity is a promising target for future therapy.
Professor John Greenwood, senior author of the research from the UCL Institute of Ophthalmology said: “We have discovered that a secreted protein, LRG1, promotes new blood vessel growth and its inhibition prevents pathological blood vessel growth in ocular disease.
“Our findings suggest that LRG1 has less of a role in normal blood vessel growth and so may be particularly applicable to ‘bad’ blood vessel growth. This makes LRG1 an especially attractive target for therapeutic intervention in conditions where vessel growth contributes to disease.”
Angiogenesis plays a role in many diseases where new vessel growth can be harmful: in the retina, uncontrolled and irregular blood vessel growth in diseases such as AMD and diabetic retinopathy; and in the growth of cancerous solid tumors. Angiogenesis is also an important feature of rheumatoid arthritis, where it contributes to the inflammation of the joint.
The mechanism by which LRG1 promotes angiogenesis is by modifying the signaling of a multifunctional secreted growth factor called transforming growth factor beta. TGF-beta regulates both the maintenance of normal blood vessels, and the unwanted growth of harmful blood vessels, but precisely how it promotes two opposing outcomes is a biological paradox.
This study indicates that in the retinal diseases investigated, LRG1 production is “turned on” in blood vessels. This causes a switch in TGF-beta signaling away from a normal vessel maintenance pathway towards a pathway that promotes the growth of new, harmful blood vessels.
Professor Stephen Moss, senior author from the UCL Institute of Ophthalmology said: “Genetic studies have revealed that the gene that codes for LRG1 is conserved in vertebrates, and this study confirms that mouse and human blood vessels express LRG1.
“We predict, therefore, that abnormal blood vessel growth is also a conserved process and that the role of LRG1 is equally applicable to human pathological angiogenesis.”
He added: “Work is already under way to develop a therapeutic antibody that targets LRG1.”
Researchers at the Massachusetts Eye and Ear Infirmary, Harvard Medical School, report the unexpected finding that in mice genetically engineered to have an inherited form of macular degeneration, turning off the animals’ complement system, a part of the immune system, prevented the disease. Their work was published in mid-August in Human Molecular Genetics.
This is the first report to demonstrate a role for the complement system in an inherited macular degeneration. Previous genetic studies have shown that variants in the genes that encode several complement system components are important risk factors for AMD. Based on this, drugs that inhibit specific complement system activities are being tested clinically as treatments for AMD. However, it is not entirely clear how alterations in complement system components lead to AMD.
The results reported suggest that complement activation by abnormalities in the extracellular matrix or the scaffold secreted by retinal cells plays an important role in the formation of basal deposits, one of the earliest stages of macular degeneration. Basal deposits are precursors of drusen; their presence is the first clinical indication of a risk of developing macular degeneration.
The findings are important because they suggest that inherited macular degenerations share common features with AMD, such as a complement-mediated response to abnormal extracellular matrix. The results also suggest that alterations in the activity of the complement system are involved in the earliest stages of disease pathogenesis. This finding has important implications for the use of drugs that modulate the complement system for treating macular degenerations.
For these studies, the investigators used a mouse model of inherited macular dystrophy. As a first step in their studies, the researchers used proteomic techniques to identify the proteins present in the basal deposits of the mice. Like they do in people, these deposits form between the retinal pigment epithelial cells and Bruch’s membrane, composed of extracellular matrix. These studies showed that the basal deposits are composed of normal extracellular matrix components that are present in abnormal amounts. This is logical because the EFEMP1 protein is secreted by retinal cells and is thought to be required for maturation of elastin fibers, which are part of Bruch’s membrane.
The proteomic analyses also suggest that the altered extracellular matrix stimulates a local immune response, including activation of the complement system. The complement system is part of our innate immune system, and helps fend off infections, but under certain circumstances can also lead to cell and tissue damage.