Suppression and regression of choroidal neovascularization by the multitargeted kinase inhibitor pazopanib

Anti-angiogenic effects of the receptor tyrosine kinase inhibitor, pazopanib, on choroidal neovascularization in rats

Neovascularization in the eye is a major cause of irreversible vision loss. The present study was undertaken to determine mechanisms through which pazopanib, a drug that targets multiple receptor tyrosine kinases such as VEGF receptors, inhibits angiogenesis and experimental choroidal neovascularization (CNV). Pazopanib inhibited VEGF expression by retinal pigment epithelium (RPE) cells and choroidal endothelial cells (CEC), decreased VEGF-induced cellular migration in a dose-dependent manner and suppressed extracellular signal-regulated kinase (ERK)-1/-2 phosphorylation. To assess the impact of pazopanib in vivo, CNV was induced in rats by rupturing the Bruch's membrane by laser coagulation. These experiments demonstrated that twice-daily topical eye drop treatment significantly (P<0.001) decreased leakage from photocoagulated lesions by 89.5%. Furthermore, the thickness of the developed CNV lesions was significantly inhibited by 71.7% (P<0.001) in pazopanib-treated eyes, and immunoreactivity of VEGF was lower than in control eyes. Our data suggest that pazopanib is a promising inhibitor of angiogenesis leading to an effective inhibition of CNV development in vivo. This activity can be largely ascribed to the down-regulation of VEGF release in the retina as well as to impaired VEGF-induced signaling and chemotaxis. Using a convenient topical dosing regimen, pazopanib may prove useful for treating a variety of ocular neovascular diseases such as neovascular age-related macular degeneration.

Ocular drug delivery

Ocular drug delivery has been a major challenge to pharmacologists and drug delivery scientists due to its unique anatomy and physiology. Static barriers (different layers of cornea, sclera, and retina including blood aqueous and blood-retinal barriers), dynamic barriers (choroidal and conjunctival blood flow, lymphatic clearance, and tear dilution), and efflux pumps in conjunction pose a significant challenge for delivery of a drug alone or in a dosage form, especially to the posterior segment. Identification of influx transporters on various ocular tissues and designing a transporter-targeted delivery of a parent drug has gathered momentum in recent years. Parallelly, colloidal dosage forms such as nanoparticles, nanomicelles, liposomes, and microemulsions have been widely explored to overcome various static and dynamic barriers. Novel drug delivery strategies such as bioadhesive gels and fibrin sealant-based approaches were developed to sustain drug levels at the target site. Designing noninvasive sustained drug delivery systems and exploring the feasibility of topical application to deliver drugs to the posterior segment may drastically improve drug delivery in the years to come. Current developments in the field of ophthalmic drug delivery promise a significant improvement in overcoming the challenges posed by various anterior and posterior segment diseases.

Digoxin inhibits retinal ischemia-induced HIF-1alpha expression and ocular neovascularization

Digoxin and other cardiac glycosides inhibit hypoxia-inducible factor-1 (HIF-1) transcriptional activity in cultured cells and suppress tumor xenograft growth. We tested the hypothesis that digoxin reduces HIF-1 levels in ischemic tissue in vivo and suppresses neovascularization. Well-established murine models of ocular neovascularization were used to test our hypothesis. In mice with ischemic retinopathy, intraocular or intraperitoneal injection of digoxin markedly reduced retinal levels of HIF-1alpha protein and mRNAs encoding multiple hypoxia-regulated proangiogenic proteins and their receptors. Daily intraperitoneal injection of 2 mg/kg starting at postnatal day (P) 12 or a single intravitreous injection of 100 ng of digoxin at P12 reduced retinal neovascularization by >70% at P17. Digoxin also reduced the number of CXCR4(+) cells and F4/80(+) macrophages in ischemic retina and significantly reduced choroidal neovascularization at Bruch's membrane rupture sites. Digoxin suppresses retinal and choroidal neovascularization by reducing HIF-1alpha levels, which blocks several proangiogenic pathways. Since digoxin suppresses multiple pathways in addition to VEGF signaling, it may provide advantages over specific VEGF antagonists for treatment of patients with retinal and choroidal diseases complicated by neovascularization and/or excessive vascular permeability. It may also be useful for treatment of neovascular diseases in other tissues.

Selective inhibition of retinal angiogenesis by targeting PI3 kinase

Ocular neovascularisation is a pathological hallmark of some forms of debilitating blindness including diabetic retinopathy, age related macular degeneration and retinopathy of prematurity. Current therapies for delaying unwanted ocular angiogenesis include laser surgery or molecular inhibition of the pro-angiogenic factor VEGF. However, targeting of angiogenic pathways other than, or in combination to VEGF, may lead to more effective and safer inhibitors of intraocular angiogenesis. In a small chemical screen using zebrafish, we identify LY294002 as an effective and selective inhibitor of both developmental and ectopic hyaloid angiogenesis in the eye. LY294002, a PI3 kinase inhibitor, exerts its anti-angiogenic effect in a dose-dependent manner, without perturbing existing vessels. Significantly, LY294002 delivered by intraocular injection, significantly inhibits ocular angiogenesis without systemic side-effects and without diminishing visual function. Thus, targeting of PI3 kinase pathways has the potential to effectively and safely treat neovascularisation in eye disease.