Abstract
Abstract: :
Purpose: MacugenR (pegaptanib sodium injection) aims to treat neovascular Age–related Macular Degeneration (AMD) by inhibiting VEGF. Pharmacokinetic parameters at the site of action play a key role in drug efficacy. This study was designed to determine the IC50 of systemically administered Macugen in a corneal neovascularization model, and to correlate its efficacy at the inhibition of and regression of vessel growth with the actual concentration of Macugen in the cornea. Methods: Corneal neovascularization (CoNV) was induced by removing corneal and limbal epithelia. Macugen was given intraperitoneally (i.p.) at doses ranging from 5 mg/kg to 200 mg/kg for 10 days post–injury (D0 to D9). Macugen efficacy at causing vessel inhibition was measured as the percentage of corneal area that had become vascularized by D10. The corresponding Macugen concentration in cornea tissue was measured using a new PCR–based dual hybridization assay. This technique allows reproducible and sensitive quantitative detection of modified oligonucleotides, including 5’–PEGylated therapeutic aptamers. In order to investigate Macugen efficacy in causing vessel regression over time, animals were treated at later times post–injury (D10 to D19, D20 to D29) with the IC90 dose of Macugen. Macugen’s efficacy and concentration in the cornea were measured on D20 and D30. Results: Macugen was most efficacious at causing vessel inhibition in the CoNV model when injected at D0 following injury (prevention model). We determined Macugen IC50 by injecting animals intraperitoneally from D0 to D9 with Macugen concentrations ranging from 5–200mg/kg. A 7 mg/kg dose of Macugen to the injured cornea inhibited vessel growth by 50%. Based on measurements using the dual hybridization assay, the 7 mg/kg dose yields a corneal Macugen concentration of 0.32 nM. Macugen was less effective at the regression of corneal neovascularization, despite the finding that Macugen levels in the cornea after i.p. dosing were similar in prevention (0–10 day) and regression (10–20; 20–30 day) models. Conclusions: Injury–induced corneal NV is a valuable model to assess the efficacy of anti–angiogenic agents. In combination, with a novel PCR–dual hybridization method, one can accurately determine the effective inhibitory concentration of aptamers such as Macugen. Macugen is less effective at causing vessel regression, especially as neo–vessels have more time to stabilize, supporting the concept that the benefits of anti–VEGF therapies may increase if treatment is provided at earlier stages of the neovascular process.
Keywords: age-related macular degeneration • neovascularization • pharmacology