gms | German Medical Science

Background: The aim of this study is to develop a fluorescent molecular probe for anti vascular growth factor(VEGF) using a humanized monoclonal VEGF-antibody to be used for in-vivo imaging of free VEGF in the retina.

Methods: Bevacizumab was covalently attached to a near-infrared indocyanine dye yielding a soluble conjugate. In-vivo reflectance (exc. 488 nm and 830 nm) and fluorescence (exc. 488 nm and 790 nm, em 500–700nm and >800 nm) imaging was performed in C57BL/6 mice using confocal scanning laser ophthalmoscopy. Multiple retinal lesions were placed by argon laser photocoagulation at day 1. At day 7, conventional 10% sodium fluorescein and the fluorescent bevacizumab conjugate were intravenously injected and their retinal uptake recorded in-vivo.

Results: In-vitro studies using cellular VEGF assays showed maintained binding properties of the conjugate compared to untreated antibody. In-vivo imaging before dye injection showed ill-defined retinal lesions at day 7. Directly following injection, a strong fluorescence signal in the retinal vasculature, including retinal capillaries and inside the laser lesions was observed with both markers. At day 8, no more fluorescein signal was detectable, while near-infrared fluorescence imaging revealed a persistent, but weaker signal in the retinal vasculatures. Inside the laser lesions, the signal was relatively increased at the level of the outer retina.

Conclusions: The findings indicate that the fluorescent bevacizumab conjugate can be visualized by in-vivo imaging in the retinal vasculature and its spatio-temporal relationship at the site of VEGF-hyperexpression. Following expanded investigations in animal models, molecular imaging of VEGF may be applicable in patients for earlier diagnosis and more refined individualized anti-VEGF therapies.