Detection of vascular endothelial growth factor in colon cancer xenografts using bevacizumab based near infrared fluorophore conjugate

Background: The aim of this study was to develop the near infrared fluorescence (NIRF)-based imaging agent for the visualization of vascular endothelial growth factor (VEGF) in colon cancer. AlexaFluor 750 conjugating with bevacizumab, and injected intravenously into nude mice bearing VEGF over-expressing HT29 human colorectal cancer. Optical imaging was performed at 15 min, 24 h and 48 h post injection. Immunofluorescences staining of the tumor sections were performed. HT29 colorectal cancer xenografts were clearly visualized with bevacizumab-AlexaFluor 750. Results: Ex vivo analysis showed 2.1 +/- 0.4%, 37.6 +/- 6.3% and 38.5 +/- 6.2% injected dose/g accumulated in the tumors at 15 min, 24 h and 48 h respectively. Tumor uptake was significantly decreased in pretreated with excess of bevacizumab (p = 0.002). Immunofluorescence analysis showed strong staining of anti-CD 31 antibody around the blood vessels. Anti-VEGF-A and bevacizumab showed heterogeneous expression throughout the tumor. Conclusions: Current study successfully detected the VEGF expression in HT29 colorectal cancer xenografts, signifying as a potential agent for non-invasive imaging of VEGF expression, which may be applied in clinical practice.