Monitoring hypoxia and vasculature during bevacizumab treatment in a murine colorectal cancer model

The purpose of this study was to assess the effect of bevacizumab on vasculature and hypoxia in a colorectal tumor model. Nude mice with subcutaneous LS174T tumors were treated with bevacizumab or saline. To assess tumor properties, separate groups of mice were imaged using 18 F‐Fluoromisonidazole (FMISO) and 18 F‐Fluorodeoxyglucose (FDG) positron emission tomography or magnetic resonance imaging before and 2, 6 and 10 days after the start of treatment. Tumors were harvested after imaging to determine hypoxia and vascular density immunohistochemically. The T 2 * time increased significantly less in the bevacizumab group. FMISO uptake increased more over time in the control group. Vessel density significantly decreased in the bevacizumab‐treated group. The Carbonic anhydrase 9 (CAIX) and glucose uptake transporter 1 (GLUT1) fractions were higher in bevacizumab‐treated tumors. However, the hypoxic fraction showed no significant difference. Bevacizumab led to shorter T 2 * times and higher GLUT1 and CAIX expression, suggesting an increase in hypoxia and a higher glycolytic rate. This could be a mechanism of resistance to bevacizumab. The increase in hypoxia, however, could not be demonstrated by pimonidazole/FMISO, possibly because distribution of these tracers is hampered by bevacizumab‐induced effects on vascular permeability and perfusion. Copyright © 2014 John Wiley & Sons, Ltd.