The PKC-Diabetic Retinopathy Study (DRS) was designed to evaluate the safety and effect of an oral treatment, RBX, on retinopathy progression or visual loss in patients with moderately severe to very severe nonproliferative diabetic retinopathy. In the study, patients with type 1 or type 2 diabetes received either RBX or a placebo over three to four years. The study measured the effect of three orally administered doses of RBX on progression of diabetic retinopathy, moderate visual loss and sustained moderate visual loss. The study was conducted at Joslin Diabetes Center and assorted national and international medical centers.
The oral treatment RBX inhibits the activity of the enzyme protein kinase C. PKC is essential to the normal production of energy in the body, but one form of the enzyme – PKC-beta – has been linked to diabetic complications of the eye and other parts of the body. Thus RBX was designed to be selective for the single PKC-beta isoform.
“Our results demonstrate that although RBX did not prevent progression to proliferative diabetic retinopathy, it may reduce the risk of moderate vision loss caused by macular edema,” said study chairman Lloyd Paul Aiello, M.D., Ph.D., head of Joslin’s section on eye research, director of Joslin’s Beetham Eye Institute and associate professor of ophthalmology at Harvard Medical School.