A Dual VEGFR/JAK2 Kinase Inhibitor Suitable for Topical Delivery Inhibits Choroid Neovascularization in Mice

Abstract

Purpose:: Both erythropoietin (EPO) and vascular endothelial growth factor (VEGF) have been linked to the pathogenesis of diabetic retinopathy (DR), and VEGF has been clinically implicated in the pathogenesis of age-related macular degeneration (AMD). A novel compound (TG101095) was designed to inhibit both VEGF receptors (VEGFR) and JAK2 (a key signaling kinase downstream of EPO), and its effects on suppressing choroid neovascularization (CNV) was evaluated in a murine laser-induced CNV model.

Methods:: TG101095 was assessed at the biochemical level for its ability to directly inhibit protein kinases such VEGFR and JAK2. To assess pharmacokinetic distribution, C57BL/6 mice were dosed bilaterally with 1% TG101095 eyedrops (10 µl/eye), and compound distribution to the retina and choroid/sclera was followed 2 and 7 hours post dosing using mass spectrometry (n= 3/group). To assess potential therapeutic efficacy, C57BL/6 mice (8-10 week old females) were subjected to laser photocoagulation of the choroid, and then randomly assigned to either 1% TG101095 or vehicle treatment groups (n= 12/group). Topical treatment applications commenced immediately following laser surgery (10 µl/eye, twice daily for a total of 14 days), after which animals were perfused with fluorescein isothiocyanate-dextran (FITC-dextran, 2x10⁶ daltons) so as to quantify CNV area in choroidal wholemounts (using image analysis software).

Results:: Both VEGFR2 and JAK2 kinases were inhibited by TG101095, with IC₅₀ of 38 nM and 17 nM, respectively. A single dose of the 1% TG101095 eyedrops applied to mice achieved concentrations of 33 µM and 1.8 µM in the choroid/sclera and retina, respectively, by 2 hrs, well exceeding their IC₅₀. Twice daily application of 1% TG101095 eyedrops reduced neovascularization at lesion sites by 41% compared with the vehicle-dosed group (P=0.026) in the laser-induced CNV model. Gross and slit lamp exams indicated that 1% TG101095 was well tolerated.

Conclusions:: Topical application of TG101095 allows for rapid distribution of the compound to both the choroid/sclera and retina at concentrations approximately 1.5-log greater than those required to inhibit VEGFR and JAK2 kinases. Dosing twice daily for 14 days was well tolerated in laser-injured mice, and lesion neovascularization was effectively reduced. TG101095 therefore shows strong potential as a novel topical treatment for proliferative diseases such as DR and AMD.

Keywords: age-related macular degeneration • choroid: neovascularization • drug toxicity/drug effects