Optical Imaging Using VEGF Receptor-Targeted Probe in AOM-Treated Mice

Abstract

Tumor growth is connected with increased vascular growth, where vascular endothelial growth factor (VEGF), and its associated receptor (VEGFR) may be overexpressed, initiating the growth of endothelial cells and increasing tumor vasculature. In a previous study conducted in our lab, a VEGFR-targeted fluorescent dye probe (scVEGF-Cy5.5) was imaged in vivo to aggregate in tumor areas. However, an untargeted probe (inVEGF-Cy5.5) also accumulated in tumors. The purpose of this study is to determine if the mechanism for accumulation differs between targeted and untargeted probes. A combined system of Optical Coherence Tomography (OCT) and Laser Induced Fluorescence (LIF) was used to visualize fluorescent dyes in vivo in tumor and normal colon in four animals. Post imaging, the colon was excised, opened longitudinally, frozen, and multiple sections taken at 8 longitudinal positions. Sequential sections were stained with H&E for diagnosis, immunostained for VEGFR-2, and left unstained for Cy5.5 dye visualization. Analysis showed that scVEGF-Cy5.5 is co-located with regions of VEGFR-2 immunostaining, a match not seen with inVEGF-Cy5.5 probe. InVEGF-Cy5.5 accumulated in adenomas and lymphoid aggregates, normal structures often near tumors in diseased regions. Both probes showed non-specific accumulation on the surface of the colon, perhaps due to the method of application of the dye. Results suggest that both probes will co-localize with tumors, but through different mechanisms.