Retinitis Pigmentosa (RP) causes the progressive degeneration of rod and cone photoreceptor cells in the retina, which over time diminishes night and peripheral vision and eventually leads to blindness.

Although the symptoms of RP may occur at any age, they most commonly appear in young adults. RP is the most common inherited cause of blindness in people between the ages of 20 and 60 and affects 1.5 million people worldwide and more than 100,000 people in the United States¹. High doses of Vitamin A have been shown to provide some benefit for RP patients but, at this time, there is no known cure or effective treatment for RP. To learn more about RP, please visit the Foundation Fighting Blindness website.

¹National Eye Institute

Clinical Studies in Retinitis Pigmentosa

Phase 2 Retinitis Pigmentosa Studies
In May 2009, Neurotech announced the results of two Phase 2 trials of NT-501 for the treatment of visual loss associated with RP—one trial with patients with earlier stage disease (60 patients) and the second trial consisting of patients with later stage disease (60 patients). NT-501 utilizes Neurotech's proprietary Encapsulated Cell Technology (ECT) platform and consists of encapsulated human cells genetically modified to secrete ciliary neurotrophic factor (CNTF). CNTF is a growth factor capable of rescuing dying photoreceptors in the retina and protecting them from degeneration. NT-501 is designed to continually deliver a low, safe and therapeutic dose of CNTF into the back of the eye.

Both Phase 2 RP trials are randomized, multi-centered, double-masked, sham-controlled dose ranging studies designed to evaluate the safety and efficacy of NT-501. Patients enrolled in the study received either a high or low dose NT-501 implant in one eye and a sham-treatment in the other eye. Best corrected visual acuity (BCVA) was the primary efficacy endpoint for the late stage RP study and visual field sensitivity was the primary efficacy endpoint for the early stage RP study. In both studies, there was a statistically significant (p<0.001 for the high dose group in each study), dose-dependent increase in retinal thickness involving photoreceptor layers as measured by optical coherence tomography (OCT). This statistically significant effect is similar to that observed in the Phase 2 NT-501 GA study. However, at 12 months no trend in visual benefit was observed in either study for these functions nor was any chance in visual function observed for either active or control study arms, likely due to the slow progression of the disease. RP patients in general have a gradual progression of vision loss, often over many years or decades.

Of note, in a separate study of a select number of patients from the earlier stage NT-501 RP trial, it was observed with objective measurement that there was a highly statistically significant preservation of photoreceptors in those subjects treated with NT-501/CNTF compared with those in the sham control group.

In total, 133 subjects were enrolled in these two studies and all have reached the 18-month time point post-implantation. No serious adverse events have been reported that are associated with either the surgical procedure or implant. In general, the surgical procedure has been well-tolerated. There have been no reported incidences of retinal detachment, no increase in intraocular pressure, no infection and no serious inflammation.

Neurotech has received Orphan Drug designation and Fast Track designation for NT-501 for the treatment of visual loss in RP from the U.S. Food and Drug Administration.

Phase 1 Retinitis Pigmentosa Study
A Phase 1 clinical study of NT-501 for the treatment of retinal degeneration associated with RP was completed in 2005 and results were published in the March 7, 2006 issue of the Proceedings of the National Academy of Sciences (PNAS). The primary objective of the study was to investigate the safety of NT-501 implants designed to secrete two dosage levels of CNTF over a six month period of implantation in 10 late stage RP patients. Results confirmed that CNTF can be safely delivered into the vitreous cavity of the eyes of patients with RP and that the ECT device was well tolerated by all patients. Visual acuity showed improved but variable trends from baseline in the treatment group while in the control arm, visual acuity was essentially unchanged. These results also encouraged Neurotech to study NT-501 in patients with an advanced stage of dry AMD affecting their central vision, known as geographic atrophy, because this type of cone photoreceptor degeneration is similar to that seen in the late stage RP patients enrolled in the Phase 1 study. Click here to view the full text PNAS article containing the Phase 1 data.