Glaucoma is one of the leading causes of blindness in the world. This chronic and progressive optic neuropathy is characterized by loss of axons of the retinal ganglion cells (RGC) that constitute the optic nerve. Reduction of elevated intraocular pressure, the only modifiable causative factor, slow the onset and progression of the disease, yet no treatment is available to restore optic nerve damage (8, 9). Nerve growth factor (NGF) is an endogenous neurotrophin that exerts trophic and differentiating activity on neurons of the central and peripheral nervous systems with protective and/or regenerative effects observed in degenerative diseases or following injury. NGF applied topically to the eye has been shown to significantly prevent RGC degeneration in experimental rat models of glaucoma. In 3 patients with advanced glaucoma, treatment with topical NGF (eye drop) improved visual acuity, contrast sensitivity, and electrophysiological functions without undesired side effects. NGF binds to both tyrosine kinase receptor TrkA and receptor P75NTR (TNF receptor superfamily). Importantly, the binding of NGF to TrkA alone promotes RGC?s survival and proliferation. In contrast, binding of NGF to p75NTR leads to apoptosis. rNGF (recombinant NGF) is currently produced in non- human cell systems. Due to the importance of pro-sequence for efficient folding or refolding, the in vitro (trypsin) or in vivo (furin) post-proteolytic modifications of pro-NGF, and the requirement of forming disulfide bonded monomer and non-covalent homodimer, expression yields from current manufacturing process are low and the NGF protein was in low quality. We have developed a cost-effective and scalable expression system to produce therapeutic human proteins from a proprietary HEK293 cell line. In the preliminary studies, we have established a cell pool of NGF which exhibited >10-fold higher yield than current expression systems with the ex vivo activity comparable to that of the murine wildtype NGF (wtNGF). In this study, we will first optimize the NGF to selectively activate TrkA receptor without compromising the expression yield or protein stability. We will then select top stable HEK293 cell clones for TrkA selective NGF mutant, which will be suitable for future large-scale cGMP manufacturing. Since there are substantial similarities between the rodent and human eyes, we will validate the efficacy and safety in an established rat model of glaucoma.
Specific aims i nclude: 1: To optimize rNGF as a TrkA-specific agonist and select top stable HEK293 cell clones suitable for future large-scale cGMP manufacturing. 2: To determine whether topical treatment with TrkA selective NGF mutant more effectively preserves retinal integrity and function compared to the wtNGF in a rat glaucoma model of episcleral vein by hypertonic saline injections.
