Research Perspectives and the Promise of Clinical Trials for Treatment of RP and Allied Diseases: ohenetihool L Gerald J. Chader, Ph.D., M.D.hc Doheny Eye Institute Los Angeles, CA USA os Angeles, CA University atlo October 22, 2009

Specifically, I would like to summarize work in 6 different areas that can lead to treatments for the RD diseases. But, before talking about specific treatments, we must first understand the 2 different disease situations that will determine which type of therapy might or might not be applied.

The first disease situation is… When most or all of the photoreceptor cells do not function or are dead. Here we use treatments that replace the dead cells or at least replace their function. These could be: 1)Cell transplantation – use of normal cells or the use of stem cells 2) Electronic Prosthetic Devices (Artificial Vision) 3) Optogenetics

The second disease situation is… When at least some photoreceptor cells yet are alive. Here, we would use treatments that prolong photoreceptor life and make them function better such as: 4) Neuroprotection 5) Antioxidants 6) Gene Therapy But -- let’s start off with methods of cell replacement – Transplantation.

1) Photoreceptor Transplantation If photoreceptor cells are dead, why not just transplant normal photoreceptor cells into the RD retina from a normal donor retina? Unfortunately, this has shown only limited success in many previous animal studies and even in one human clinical trial. So, is there anything new? Yes, there are many recent breakthrough studies using cell transplantation.

For example, Ali et al. used transplantation of very young rod photoreceptor cells called “rod precursors” into the diseased retinas to improve vision in a mouse model of vision loss. After transplantation, visual signals travel to the brain with resulting restoration of some vision. Ali et al. have shown repair of degenerate retinas by photoreceptor transplantation in 6 different mouse RD models. “Good integration” of the transplanted cells was observed even in late stage disease. Finally, there is also the use of stem cells for transplantation.

Stem Cell Transplantation Stem cells are multipotential cells that have the ability to develop into all different adult cell types – such as photoreceptor cells. So, stem cells transplanted into the retina might replenish the supply of photoreceptor cells that died due to degeneration.

There are several examples of rescue in RP animal models: Reh et al. developed retinal progenitor cells from human embryonic stem cells (hESC). When injected into the eye of mice with a form of LCA, the hESCs migrated into the retina, settled in the photoreceptor layer and expressed rod and cone photoreceptor cell biochemical markers. Importantly, light responses are restored in the animals. Some investigators are planning a clinical trial for this stem cell therapy.

2) Use of stem cells gives good results in the RCS rat model, one of the oldest animal models for RP. 3) Advanced Cell Technology (ACT) is conducting a clinical trial using embryonic stem cells to supply fresh RPE cells in Stargardt Disease and dry AMD. This will be a good model for future studies on RP.

Future Treatment? Direct Photoreceptor cell transplantation: Not yet but coming! ESC→Photoreceptor Cells: good research is continuing. Many opportunities are now available for sight restoration through transplantation.

2) Artificial Vision Uses an electronic prosthetic device to replace the function of dead photoreceptors. This is one of the big success stories in restoration of vision with successful clinical trials and commercial products now available

Second Sight Medical Products has successfully completed its clinical trial. There has been restoration of at least some functional vision in RP patients. Safety is very good. Results have persisted long term – 10 years. ARGUS II is commercially available in Europe and in the USA.

Other academic groups and companies are doing excellent clinical work on other types of retinal devices that should lead to commercial products in the next few years. Groups in Germany, Japan, Korea, Australia, Ireland, USA. Dr. Eberhart Zrenner (Retina Implant AG) in Tuebingen is an outstanding leader in this field along with researchers at Intelligent Implants GmbH. Retina Implant has the European CE Mark for use of their device

Future Treatments? Several groups are doing human testing including at least three companies. SSMP has a device that is available for general implantation in advanced RP as does Retina Implant AG. Technologies are being improved to allow for face recognition and reading ability.

This is NOT Vision of Terminator or Geordi from Star Trek…..Yet

3) Optogenetics (Photoswitches) Many animal and plant cells have proteins that react to light and produce an electrical signal. Molecular engineering can be used to insert channelrhodopsin molecules into retinal cells, e.g., ganglion cells in animals to make them light sensitive. These light signals can be passed on to the brain which can distinguish a “lights on” or “lights off” situation. Chlamydomonas is a tiny one celled algae that contains a light- sensitive protein called channel rhodopsin

For example, Roska and coworkers have shown that light- activated channels targeted to a particular type of inner retinal cell can restore visual function in the rd1 mouse model of retinal degeneration. Roska also showed that another photoswitch called “halorhodopsin” can be used in cone cells to substitute for the defective native proteins used in the visual process and restore light sensitivity to a mouse RP model.

Future Treatments? Basic work on Photoswitches is yet in early development. However, excellent work such as by Roska and co-workers and several other groups on insertion of photoswitches into remaining retinal cells in RP animal models gives hope for restoration of functional vision in the future.

The second disease situation is… When at least some photoreceptor cells yet are alive. Here, we would use treatments that prolong photoreceptor life and make them function better such as: 4) Neuroprotection 5) Antioxidants 6) Gene Therapy

4) Neuroprotection Many neuron-survival agents are know which can delay photoreceptor death in several RP animal models. Many (30?) natural factors in brain, retina and other tissues have been found that inhibit photoreceptor cell death. These are now called “Neurotrophic Factors” or “Neuron-Survival Agents”. One of them is named CNTF – Ciliary Neurotrophic Factor.

Clinical Trials? Neurotech is in clinical trials with CNTF on RP and dry AMD subjects. Using a technique called Encapsulated Cell Technology, they deliver the neuron-survival protein CNTF, to the retina. The CNTF leaves the capsule and enters the retina where it helps to protect the sick photoreceptor cells. Along with CNTF, Sahel et al. have shown the Rod-derived Cone Viability Factor (RdCVF) to be a potent agent that promotes cone cell viability.

Future Treatments? The current Neurotech clinical trial should soon be completed. It could produce the first effective and generally available treatment for many forms of RP and dry AMD. BUT - there are many agents to test yet! Drugs, Modifiers, Natural Factors such as RdCVF. Alone or in combination.

5) Antioxidants The use of antioxidants must now be taken seriously. They have been proven to delay the progression of dry AMD, another form of retinal degeneration Specifically in Retinitis Pigmentosa, two research groups - Van Veen and Campochiaro have demonstrated that antioxidants slow the course of retinal degeneration in RP animal models..

Antioxidant Trial Dr. van Veen fed animals with retinal degeneration a special combination of antioxidants and slowed the degeneration process. Together, they are called RetinaComplex. Based on this preclinical work, a small clinical trial in Spain has finished on RP and dry AMD patients. The results were reported to be good but we are waiting for scientific publication of the results. Another mixture of antioxidants is being used in South Africa for RP patients. Ingredients: Lutein, zeaxanthin, alpha-lipoic acid, L-glutathione, extract of lycium barbarum (wolfberry)

Future Treatments? First, the clinical trial on RetinaComplex must be completed. In the future, there are many types of antioxidants that can be tested in RP animal models and then in the human. Until then, take your mother’s advice – Eat your Vegetables!

6) Gene Therapy Gene Therapy replaces defective mutated genes in living cells with new, normal copies of the gene. Different types of Gene Therapy are available for recessive, X-linked and dominant forms of RP. Importantly, long-term, positive effects of Gene Therapy in RP animal models have been shown even if treatment is done fairly late in the disease process after significant photoreceptor loss.

Gene Therapy Clinical Trials The exciting news is that Gene Therapy will restore some visual function in the human. About 5 years ago, Robin Ali et al. started the first gene therapy clinical trial supplying a normal copy of the RPE65 gene to specific patients with LCA. Other groups soon started similar trials and the patients seem to be doing well with some restored vision. The focus now is on early treatment, i.e., children. This success can now be used as a model for treatment of many other types of RP diseases.

Future Treatments? Clinical trials are ongoing or planned for: Forms of dominant, recessive and X- linked RP: MERTK – Abboud –S.A. Forms of LCA: LCA 1 (GUCY2D) – UF; LCA 5 – Lebercillin consortium Stargardt’s Disease - StarGen Retinoschisis –AGTC, NEI Forms of Usher Syndrome – Naash Choroideremia – MacLaren –UK So, as long as there are some photoreceptor cells remaining, gene therapy has a chance of improving vision in almost all patients with RP and allied diseases.

So, looking into the future…. I hope you agree that we are finally passing out of the time of scientific darkness and into the era of enlightened clinical trials. For scientists and clinicians, there are now many opportunities to do meaningful and sight- saving research. For patients, this will lead to new therapies that will save and restore vision in all types of RD.