Human nerve growth factor delivery to the retina: Quantitative methodology and mathematical modeling in preclinical settings.

Nerve growth factor (NGF) plays a critical neuroprotective role in retinal health, supporting neuronal survival and regeneration. Recombinant human NGF (rhNGF) holds promise for treating retinal degenerative diseases such as glaucoma, retinitis pigmentosa, and optic neuropathies. However, efficient retinal delivery of rhNGF remains a major challenge due to anatomical barriers and rapid clearance from conventional routes. Here, we integrate in vivo experimentation with mathematical modeling to identify and validate optimized delivery strategies for rhNGF. By using stable isotope-labeled rhNGF, we quantified ocular biodistribution in rats and rabbits following topical eye drops, intravitreal (IVT) injections, and sustained-release formulations. Eye drop administration resulted in negligible retinal exposure (<0.04% of instilled dose), while IVT injection achieved ∼34% vitreous retention with sustained delivery to the retina and optic nerve over 60 days. A mechanistic compartmental model was developed and validated against the in vivo data to simulate route-specific drug transport and estimate delivery losses via a penalty factor ( $f_B$ ). The model identified key parameters governing retinal exposure and guided the design of dose-release profiles to sustain therapeutic concentrations. Controlled-release platforms, such as bioadhesive tablets and gels, exhibited in vitro release rates (0.002-0.015 h⁻¹) aligned with model-predicted requirements for prolonged exposure. Together, these results highlight the importance of route-specific delivery design and demonstrate that combining isotope tracing with mechanistic modeling can quantitatively guide development of long-acting retinal therapeutics. This platform provides a translational framework for optimizing macromolecular drug delivery to the posterior eye.