A multidisciplinary research team of scientists, clinicians and biostatisticians led by John Guy, MD, professor of ophthalmology and director of the ocular gene therapy laboratory at the Bascom Palmer Eye Institute of the University of Miami Miller School of Medicine, has pioneered a gene therapy approach for Leber’s hereditary optic neuropathy, an inherited genetic disorder that causes rapid, permanent and bilateral loss of vision in people of all ages, but primarily males ages 20 to 40.
The field of human mitochondrial genetics was born a quarter century ago and the list of neurodegenerative disorders associated with mutated mitochondrial DNA keeps growing. While many different experimental approaches have been proposed, development of a clinically effective therapy has been elusive until now. LHON is caused by genetic defects inside mitochondria, the energy factories inside cells. Through this trial, patients who have visual loss from LHON will receive an injection of a mitochondrial gene into the vitreous. While there have been approximately 1,800 reported clinical trials using gene therapy, all but one have targeted the nucleus, the home for most of the cell’s DNA. This new trial is among the first to target a disease caused by a defective gene located inside the mitochondria.
“A wide range of other conditions, including aging, cancer and Parkinson’s disease, are also caused by mutations in the mitochondria,” said Dr. Guy. “This novel approach shows the vast potential for genetic-therapy applications, while helping to address a significant cause of blindness.” About half of all patients with LHON have mutations in the mitochondrial gene ND4, and most other patients carry mutations in one of two related mitochondrial genes. The ND4 protein is part of Complex I, an essential protein that works as part of an assembly line for producing energy inside mitochondria.
The approach in the clinical trial for therapeutic intervention is to in,troduce a normal copy of the defective gene into retinal ganglion cells, the cell type exclusively affected in LHON. Replacing a defective gene has been the basis for more than 1,500 gene therapy clinical trials worldwide, but only one involving a mitochondrial disease. One of the major drawbacks for treating mitochondrial diseases by gene therapy has been a lack of availability of practical methods.
Dr. Guy developed an approach to deliver the normal ND4 gene into retinal cells using a virus. But since viruses are designed by nature to infiltrate and take over a cell’s nucleus, the next challenge was how to target the gene into mitochondria. Dr. Guy’s solution was to create an ND4 gene that is delivered to the nucleus, but modified so that the ND4 protein carries a mitochondrial address label. In experimental models, they have found that this approach is safe and effective to replace the ND4 gene and that doing so prevents deterioration of the retinal cells that form the optic nerve. This research demonstrates that when efficiently introduced into mitochondria, normal DNA can correct a biochemical defect in cellular energy production and restore visual function.
“Other research studies have shown that LHON patients who have lost their vision still have some sensitivity to light,” said Dr. Guy. “This indicates that if you can restore the functioning of those cells through gene therapy, those patients could see again.” In conjunction with his research, Dr. Guy explored why only about 50 percent of male patients with the genetic mutation develop LHON. Known for exploring gene therapy as a potential treatment for diseases of the optic nerve, Dr. Guy holds several patents related to mitochondrial gene therapy. He and his team recently advanced their research significantly by demonstrating that the vector (the adeno-associated virus, AAV, with the ND4 gene) was made human-grade and proven safe in experimental models that are closest to the human eye. With the Food and Drug Administration having recently approved the investigational new drug (AAV-ND4 gene), a Phase I trial of the approach will begin in April 2014 and conclude five years later.
Louise Wideroff, PhD, a program director in the NEI Division of Extramural Research, stated, “The continuing progress in this research—especially its movement from the lab into human trials—is cause for excitement and optimism, not only for families with LHON but for families affected by other mitochondrial disorders.”
Immune System Targets Diseased Blood Vessels
A new report published online in The FASEB Journal may lead the way toward new treatments or a cure for proliferative retinopathies. Specifically, scientists have discovered that the body’s innate immune system does more than help ward off external pathogens. It also helps remove sight-robbing abnormal blood vessels, while leaving healthy cells and tissue intact. This discovery is significant as the retina is part of the central nervous system and its cells cannot be replaced once lost. Identifying ways to leverage the innate immune system to “clean out” abnormal blood vessels in the retina may lead to treatments that could prevent or delay blindness, or restore sight.
“Our findings begin to identify a new role of the innate immune system by which endogenous mediators selectively target the pathologic retinal vasculature for removal,” said Kip M. Connor, PhD, a researcher involved in the work from the Department of Ophthalmology at the Harvard Medical School and Massachusetts Eye and Ear Infirmary Angiogenesis Laboratory in Boston. “It is our hope that future studies will allow us to develop specific therapeutics that harness this knowledge, resulting in a greater visual outcome and quality of life for patients suffering from diabetic retinopathy or retinopathy of prematurity.”
To make this discovery, Dr. Connor and colleagues compared two groups of mice, a genetically modified group which lacked activity in the innate immune complement system, and a normal group with a fully functional innate immune system. Researchers placed both groups in an environment that induced irregular blood vessel growth in the eye, mimicking what happens in many human ocular diseases. The mice that were lacking a functional innate immune system developed significantly more irregular blood vessels than the normal mice, indicating that the complement system is a major regulator of abnormal blood vessel growth within the eye. Importantly, in the normal mice, scientists were able to visualize the immune system targeting and killing only the irregular blood vessels while leaving healthy cells unharmed.
“Knowing how the complement system works to keep our retinas clean is an important first step toward new treatments that could mimic this activity,” said Gerald Weissmann, MD, editor in chief of The FASEB Journal. “It’s a new understanding of how proliferative retinopathies rob us of sight, and promises to let us see the path ahead clearly.”
Drops Warrant Caution in ROP Examinations
Eyedrops administered to infants as part of routine outpatient retinopathy of prematurity screening can have life-threatening consequences. A case report published in the current issue of the Journal of the American Association for Pediatric Ophthalmology and Strabismus describes cardiopulmonary arrest in a 27-week-old infant following administration of three sets of cyclopentolate 0.2%/phenylephrine 1% (Cyclomydril) eyedrops.
“Cardiopulmonary arrest can occur from just instillation of eyedrops in a premature infant seen for ROP in an outpatient setting, and pediatric ophthalmologists should be prepared to handle such an emergency in their office,” says Sylvia Kodsi, MD, professor of ophthalmology at Hofstra North Shore-LIJ School of Medicine. “This can be particularly perilous in outpatient offices where patient monitoring and emergency back-up is not as readily available as in the hospital setting.”
ROP primarily affects premature infants who weigh 2.75 pounds or less who are born before 31 weeks of gestation. Each year, about 28,000 infants in the United States fall into this category and about half are affected to some degree by ROP. About 400 to 600 of these children with ROP become legally blind. ROP occurs when babies are born before blood vessels in the eye have had a chance to reach the edges of the retina. Abnormal blood vessels form, resulting in inadequate blood supply, retinal scarring and retinal detachment.
Professional organizations such as the American Association for Pediatric Ophthalmology and Strabismus, American Academy of Pediatrics and American Academy of Ophthalmology recommend that at-risk infants be regularly screened for changes associated with ROP.
In the case that was reported, a 27-week-old, low-birth-weight infant presented for a follow-up ROP screening examination at 41 weeks’ corrected gestational age. The patient had previously undergone several such examinations, beginning at 30 weeks corrected gestational age and every two weeks thereafter. For all those examinations, the infant received three sets (one drop per eye) of Cyclomydril, a combination of cyclopentolate (an anticholinergic that blocks pupillary constriction and eye muscle contraction), and phenylephrine (an alpha-adrenergic agent that causes mydriasis).
Fifteen minutes after the last set of drops was administered, but prior to the eye examination, the baby suffered a cardiopulmonary arrest and was revived within a few minutes. After transport to the hospital, she experienced another episode of apnea and bradycardia and was found to have new-onset pulmonary hypertension.
“Eyedrops used for mydriasis and cycloplegia can be systemically absorbed and cause serious side effects, including oxygen desaturation, apnea, bradycardia, transient hypertension, delayed gastric emptying and transient paralytic ileus. These effects can be more serious in infants because of their lower body mass and immature cardiovascular and nervous systems,” says Dr. Kodsi. “Pediatric ophthalmologists should be equipped to handle this type of emergency, either personally or with ancillary services that are immediately available.”
Early Warning For DR Vision Loss
Indiana University researchers have detected new early warning signs of the potential loss of sight associated with diabetes. This discovery could have far-reaching implications for the diagnosis and treatment of diabetic retinopathy, potentially impacting the care of more than 25 million Americans.
“We had not expected to see such striking changes to the retinas at such early stages,” said Ann Elsner, PhD, professor and associate dean in the IU School of Optometry and lead author of the study. “We set out to study the early signs in volunteer research subjects whose eyes were not thought to have very advanced disease. There was damage spread widely across the retina, including changes to blood vessels that were not thought to occur until the more advanced disease states.”
These important early-warning signs were invisible to existing diagnostic techniques, requiring new technology based on adaptive optics. Stephen Burns, PhD, professor and associate dean at the IU School of Optometry, designed and built an instrument that used small mirrors with tiny moveable segments to reflect light into the eye to overcome the optical imperfections of each person’s eye.
“It is shocking to see that there can be large areas of retina with insufficient blood circulation,” he said. “The consequence for individual patients is that some have far more advanced damage to their retinas than others with the same duration of diabetes.”
Because these changes had not been observable in prior studies, it is not known whether improved control of blood sugar or a change in medications might stop or even reverse the damage. Further research can help determine who has the most severe damage and whether the changes can be reversed.
The changes to the subjects in the study included corkscrew-shaped capillaries. The capillaries were not just a little thicker, and therefore distorted, but instead the blood vessel walls had to grow in length to make these loops. This is visible only at microscopic levels, making it difficult to determine who has the more advanced disease among patients, because these eyes look similar when viewed with the typical instruments found in the clinic. Yet, some of these patients already have sight-threatening complications.
Diabetes also is known to result in a variety of types of damage to capillaries. The more commonly known changes, such as microaneurysms along the capillaries, were also present in the study, but seen in much greater detail. In addition to the corkscrew appearance and microaneurysms, along with the hemorrhages in the later stages of the disease, there is also a thickening of the walls of blood vessels. This is thought to be associated with poor blood flow or failure to properly regulate blood flow.
In the study, patients with diabetes had significantly thicker blood vessel walls than found in controls of similar ages, even for relatively small-diameter blood vessels. The capillaries varied in width in the diabetic patients, with some capillaries closed so that they no longer transported blood within the retina. On average, though, the capillaries that still had flowing blood were broader for the patients with diabetes. These diabetic patients had been thought to have fairly mild symptoms. In fact, the transport of oxygen and glucose to the retina is already compromised.
Previous diagnostic techniques have been unable to uncover several of these changes in living patients. Simply magnifying the image of the retina is not sufficient. The view through the imperfect optics of the human eye has to be corrected.
The study was published in Biomedical Optics Express.
Alimera Moves Forward With Iluvien Review
Alimera Sciences announced that its recent resubmission of the New Drug Application for Iluvien has been acknowledged as received by the Food and Drug Administration as a complete class 2 response to the FDA’s October 2013 letter and that a Prescription Drug User Fee Act (PDUFA) goal date of September 26, 2014 has been established.
In the resubmission, Alimera responded to questions raised in the FDA’s October 2013 letter and provided data from Iluvien patients and from physician experience with the applicator in the United Kingdom and Germany, where Iluvien is currently commercially available.
“We are pleased to have achieved our goal of resubmitting our NDA in the first quarter and to have a PDUFA goal date set for a decision from the FDA,” said Dan Myers, Alimera’s president and chief executive officer. “We look forward to the FDA’s response to our NDA and hope that we will be able to make Iluvien available to patients in the United States who are suffering from chronic DME.” REVIEW