Novel SRPK1 inhibitors with improved posterior ocular permeability to achieve therapeutic drug levels following topical eye drop administration in wet age-related macular degeneration (wAMD).

Anti-angiogenic VEGF inhibitors are the standard of care for wAMD but must be administeredby intraocular injection. Clinicaltrials repurposingoncology drugs such as pazopanib for wAMD suggest that topical administration cannot reach posterior segments of the eye at therapeutic levels [1]. We aim to develop SRPK1 inhibitors with improved posterior ocular delivery that can be administered as eye drops and specifically inhibit VEGF-driven angiogenesis underlying wAMD. We previously developed SPHINX (5-methyl-N-[2-(morpholin-4-yl)-5-(tri-fluoromethyl)phenyl] furan-2-carboxamide), which inhibits SRPK1 at µM levels and was effective as eye drops in laser-induced choroidal neovascularisation [2]. Through a rational, iterative medicinal chemistry approach based on the structure of SPHINX/SRPK1 we generated novel compounds with a range of physicochemical properties, which selectively bind to SRPK1 and dose-dependently inhibit SRPK1 kinase activity with IC50s <10 nM. To determine the permeability of the eye to the compounds, porcine eyes collected from the abbatoir, were dissected, and full thickness eye tissue (including neural retina, RPE/Choroid and sclera) were clamped into a scaffold containing artificial vitreous in the lower chamber facing the neural retina and drug formulations in the upper chamber nearest the sclera. Tissue types were dissected after 24 h and compound extracted and analysed by mass spectrometry. Potent SRPK1 inhibitors had improved permeability (1-3 cm/s*10-6) compared to pazopanib in this ex vivo porcine ocular trans-scleral permeability assay. Permeability did not correlate with molecular weight or cLogP but could be affected by additional parameters such as melanin binding and these findings were consistent with rabbit in vivo retinal penetration. Following tri-daily eye drop administration for 6 days in unanaesthetised New Zealand White rabbits, animals were killed by overdose of anaesthetic. Eyes were dissected, tissues taken and compounds extracted and analysed by mass spectrometry. SPHINX-A was detected at 0.008 % of the total applied dose (84 ug) and above its target IC50 value compared to pazopanib at 0.006%, below its target IC50 (Figure 1).

Through increased specificity, potency and posterior ocular permeability, novel SRPK1 inhibitors have potential to reach therapeutic levels in posterior eye segments following eye drop administration in large animal eyes and improve treatment for patients with wAMD. Combined analysis of structure, physicochemical characteristics and biological effect indicate a combination of properties that could predict drug efficacy.

References:

1. Csaky KG et al. (2014) American Academy of Ophthalmology (3): 579-88

2. Gammons MV et al. (2013) IOVS 54: 6052–6062