Nonclinical work in retinal and optic nerve disease

Glaucoma, retinitis pigmentosa and related conditions involve progressive loss of retinal or optic nerve function. For a nonclinical programme this area differs from most others in one respect that governs the whole package: the target tissue is reached by local administration into the eye rather than systemically, and that changes what has to be measured and what a standard toxicology design can tell you.

Stem-cell-derived retinal neurons

Differentiating retinal ganglion cells from pluripotent stem cells is an established technique rather than a single institution achievement, and the published literature has moved on to a more specific question: whether the subtypes obtained matter for what the culture is used to test.^[S3] That question is the practical one for a screening application, because retinal ganglion cells are not a uniform population and a compound acting on one subtype may not be detected in a preparation dominated by another. Stem cell approaches in ocular disease more broadly are reviewed alongside their current limitations.^[S4]

The animal models

Three model types cover most work in this area, and they answer different questions. Models that raise intraocular pressure in the rat address glaucoma, and a systematic review compares the methods used to produce that elevation.^[S1] Laser-induced choroidal neovascularization in the mouse addresses the neovascular component of macular disease, with published characterization of both the vascular progression and the accompanying retinal dysfunction.^[S2] Optic nerve crush produces a defined injury to the ganglion cell axons and is used where the question is neuroprotection rather than vascular or pressure-related.^[S5]

What to settle before placing the work

• {'items': ['The route, stated as it will be in patients. An intravitreal product tested by systemic administration has not been tested.', 'Whether the species eye can accommodate that route at the intended volume, which often decides the species before any other consideration does.', 'How local tolerance will be assessed, by whom, and against what scoring system.', 'How systemic exposure from a local dose will be measured, since the systemic safety assessment rests on it rather than on the administered amount.', 'For a cell-based product, which cell types the preparation actually contains, given that retinal ganglion cell preparations are heterogeneous.^[S3]', 'Which studies are exploratory pharmacology, normally outside the good laboratory practice regulation, and which support the submission.^[S7][S8]']}

Summary

The models in this area are well established and each answers a narrow question: pressure, neovascularization or axonal injury.^[S1][S2][S5] The decision that most often goes wrong is not the model but the route. A programme whose product will be injected into the eye has to be designed around that from the start, because the species choice, the tolerance assessment and the exposure calculation all follow from it.