Designing topical VEGF-A inhibitors with high retinal bioavailability using ex vivo permeability modelling

Abstract

Purpose : Intra-ocular injection of biologics targeting VEGF is currently the standard of care for retinal vascular diseases. Delivery of potent small molecules to the retina as eye drops would be a treatment paradigm shift but remains an unmet need due to insufficient retinal delivery. We aimed to design compounds with the physicochemical properties required for eye drop delivery in large eyes using ex vivo permeability modelling.

Methods : Full thickness fresh porcine eye tissue was clamped into a scaffold with drug formulations nearest the sclera. Tissues were dissected at 24 h and compound levels analysed by mass spectrometry. 186 inhibitors were screened and a further 80 compounds were rationally designed based on chemical properties. For PK in a large eye, pigmented rabbits were administered a single eye drop for successive timepoints or dosed bid for 6 days. Eyes were dissected into regional segments and compound levels analysed by mass spectrometry (Mann-Whitney and Spearman tests for correlation). Non-human primate (NHP) ocular and systemic PK was determined after 21 days b.i.d. dosing up to 0.15% of compound 1.

Results : We identified potent and selective SRPK1 inhibitors that reduced angiogenic VEGF-A levels, with high trans-scleral permeability ex vivo that is orders of magnitude higher than previously developed compounds (4.71 x 10^-6cm/s compared to 0.2 x 10^-6cm/s for regorafenib). Multiple regression analysis generated predicted permeability values that could be refined based on structural class, which correlated with ex vivo permeability and in vivo retinal PK in rabbits (Pearson p=<0.0001). SRPK1 inhibitors were detected at higher concentrations (44.0nM, SEM 3.695 compound 1) than pazopanib (0.2nM, SEM 0.2) and at low concentrations in plasma (2.4nM, SEM 0.6 compound 1), n=3. Lead compounds had prolonged exposure compatible with twice daily eye drop administration in rabbit and NHP.

Conclusions : Ex vivo permeability screening enabled design of novel compounds with improved permeability which correlated with in vivo retinal delivery. Due to increased potency and ocular permeability, our novel SRPK1 inhibitors show potential to reach therapeutic levels in the retina following eye drop administration and improve treatment for patients with retinal vascular diseases.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.