Selection of a KDR Kinase Inhibitor for Local Delivery to the Eye

Abstract

Purpose: : Vascular endothelial growth factor (VEGF) and its receptors have been extensively studied as mediators of the ocular angiogenic component of wet age-related macular degeneration (AMD). The purpose of our studies was to select a VEGFR2 (KDR) kinase inhibitor suitable for local delivery to the eye.

Methods: : Candidate KDR inhibitors were evaluated based on physicochemical properties, potency, in vivo efficacy, pharmacokinetics (PK), and ocular safety. Potency was assessed using a KDR enzyme assay and a cell-based ELISA assay. In vivo efficacy, PK, and safety experiments were performed in Dutch Belted rabbits; compound administration was by intravitreal injection. For determination of in vivo efficacy, compounds were injected 60 minutes prior to intravitreal administration of VEGF. Retinas were dissected 20 minutes later, and inhibition of KDR autophosphorylation was measured by ELISA. To assess vitreal half-life (t_1/2), vitreous was collected over a time course for analysis of drug levels by LCMS. Non-GLP safety data was gathered from clinical ophthalmic exams, electroretinography, and histopathology.

Results: : Based on in vitro potency (79nM in enzyme assay, 18nM in cell culture), candidate compound KDR4 was advanced to in vivo screening. Preliminary efficacy experiments suggested an in vivo IC₅₀ of 30nM, while PK determination yielded a t_1/2 of 4.9 hours. Rabbit eyes injected with KDR4 exhibited no treatment-related adverse effects by clinical exam. Histopathologic alterations were limited to occasional mononuclear inflammatory cells in the posterior vitreous at the two higher doses.

Conclusions: : The screening cascade described above (and associated selection criteria) resulted in the selection of KDR4 for further formulation development. The properties of the compound suggest that KDR4 is suitable for intravitreal delivery to the eye via sustained-release formulation.

Keywords: receptors: pharmacology/physiology • vascular endothelial growth factor • age-related macular degeneration