Implant may aid visual function

Royal Oak, MI-A new therapy is being evaluated for the treatment of dry age-related macular degeneration (AMD), an indication that has been neglected by drug developers until recently. An implant (NT-501, Neurotech) has resulted in increased retinal thickness and more stable visual function in subjects with dry AMD involving geographic atrophy (GA), said George A. Williams, MD.

"CNTF is a growth factor capable of photoreceptor rescue and protection in the retinal degenerative process," Dr. Williams said. "This has been demonstrated in a wide variety of animal models across multiple species. CNTF has resulted in a dose-dependent retinal thickening and outer nuclear layer protection in dogs and rabbits."

CNTF is delivered via an encapsulated cell technology (ECT) implant that is based on the concept of immunoisolation.

"NT-501 ECT implants contain human pigment epithelial cells that are genetically engineered to express the CNTF molecule," Dr. Williams said. "An immunoisolatory membrane encapsulates the cells and prevents immunoactivation while allowing the exchange of oxygen and nutrients as the therapeutic factor is released."

This approach has several advantages in overcoming obstacles when treating chronic retinal diseases. The technology enables the long-term, controlled, continuous delivery of a biologic treatment to the retina (up to 18 months or more), thereby bypassing the blood-retinal barrier. The implant is placed in the vitreous body during a simple, 20-minute outpatient procedure.

Geographic atrophy studies

In a phase II study of the implant for the treatment of GA, the investigators sought to identify the safety profile of the implant and any effect of CNTF in terms of structure or function, to determine a dose and primary endpoint for subsequent studies.

The primary endpoint was best-corrected visual acuity (BCVA) at 12 months following implantation in a randomized, multicentered, double-masked, sham-controlled study that enrolled 51 patients. Twenty-seven patients were randomly assigned to receive a high-dose implant, 12 to a low-dose implant, and 12 to a sham treatment. The inclusion criteria included the presence of GA in the study eye with category 3 or 4 AMD and loss of vision in that eye associated with the GA, Dr. Williams said. All patients had BCVA at baseline of 20/50 or less and 20/200 or greater.