Topical NGF Therapy and oral nicotinamide supplementation for Glaucoma

ABSTRACT Glaucoma is a leading cause of irreversible vision loss, which is characterized by progressive degeneration of retinal ganglion cells (RGC) and their optic nerve axons. While age is a key risk factor, elevated intraocular pressure (IOP) is the only modifiable risk factor, with topical IOP-lowering drugs as the first line treatment. However, RGC degeneration and vision loss continues in half the patients taking these medications. By the time when characteristic visual field defects are detected, 30-50% of the RGCs have already been lost. Thus, there is an urgent need to develop novel therapies, independent of IOP reduction, which protect RGCs from degeneration and boost the function of RGCs challenged in the disease. We have designed and validated a human nerve growth factor (NGF) mutein, HC201. The mutein preserves protein stability and expression with enhanced TrkA receptor activities but abrogated p75NTR binding and signaling. In rat models of glaucoma induced by episcleral vein cauterization, topical treatment with HC201 robustly protected RGCs. In contrast, wildtype NGF was not effective. HC201 efficacy was also observed in diabetic corneal ulcer and dry eye disease models. Meanwhile, we have developed a highly cost-effective and scalable process to produce recombinant NGF in mammalian cells by facilitating furin-mediated post-proteolytic modifications of pro-NGF into mature NGF. The treatment with NGF sustains RGC survival and prevents mitochondrial disfunction, but it is not effective in preventing ATP depletion in mitochondria. Nicotinamide (NAM), a precursor of NAD+ which is an essential cofactor for ATP generation in mitochondria and a physiological inhibitor of the major NAD catabolic enzymes, is low in serum of aging and glaucoma patients. Oral supplementation of NAM as a food additive (rather than a drug) rapidly increases retinal NAD+ and mitochondrial ATP in animal models, which leads to improved retinal or visual function in glaucoma patients with a wide therapeutic index. However, somatic and dendritic degeneration persists. Thus, combining HC201 therapy with NAM supplement will further improve RGC survival and function. The Specific Aim of the Phase 1 study is to determine whether combining topical HC201 with oral NAM supplementation for 6 weeks will more effectively improve RGC function compared to either treatment using the microbead occlusion model of glaucoma in mice. The long-term goal is to develop HC201, alone or in combination with nicotinamide supplement, to best preserve vison and even reverse the vision deficit in glaucoma patients.