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Positron emission tomography imaging and biodistribution of vascular endothelial growth factor with 64Cu-labeled bevacizumab in colorectal cancer xenografts

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To whom correspondence should be addressed.
E-mail: paudyal@med.gunma-u.ac.jp

Abstract

Vascular endothelial growth factor (VEGF) is considered to be a major angiogenic factor responsible for the development of tumor vasculature. The aim of this study was to image VEGF expression with 64Cu-labeled anti-VEGF antibody (bevacizumab) non-invasively, and to see whether or not the expression was correlated with tumor accumulation in colorectal cancer xenografts. Bevacizumab was conjugated with the bifunctional chelator 1, 4, 7, 10-tetraazacyclododecane-1, 4, 7, 10-tetraacetic acid (DOTA) and radiolabeled with 64Cu. In vivo biodistribution studies and positron emission tomography (PET) imaging were performed on mice bearing human colorectal cancer (HT29) xenografts after injection of 64Cu-DOTA-bevacizumab, which showed clear accumulation of 64Cu-DOTA-bevacizumab in the tumor (22.7 ± 1.0 %ID/g, 24 ± 0.2 %ID/g, 19.0 ± 2.5 %ID/g at 24, 48 and 72 h, respectively). Tumor accumulation of 64Cu-DOTA-bevacizumab was significantly correlated with VEGF expression as measured by western blot (ρ = 0.81, P = 0.004). Vascular endothelial growth factor blocking with unlabeled bevacizumab significantly reduced tumor accumulation of 64Cu-DOTA- bevacizumab (9.7 ± 1.2 %ID/g, P < 0.001) at 48 h. Interestingly, the blood concentration of VEGF in the mice treated with excess fold of bevacizumab was significantly higher than those without at 48 h (25.5 ± 4.6 %ID/g vs 6.5 ± 2.1 %ID/g, P = 0.0016). Liver uptake decreased from 24 h (17.2 ± 1.7 %ID/g) to 48 h (13.0 ± 4.2 %ID/g) and 72 h (10.6 ± 1.5 %ID/g) due to hepatic clearance of the tracer. The present study successfully showed 64Cu-DOTA-bevacizumab as a potential PET tracer for non-invasive imaging of VEGF expression in colorectal cancer xenografts. (Cancer Sci 2011; 102: 117–121)

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