Angiogenesis plays a major role in tumor growth and metastasis, with tumor
perfusion regarded as a marker for angiogenesis. To evaluate antiangiogenic
treatment response in vivo, we investigated arterial spin labeling (ASL) magnetic
resonance imaging (MRI) to measure tumor perfusion quantitatively.
Chronic and 24-h acute treatment responses to bevacizumab were assessed by
ASL and dynamic-contrast-enhanced (DCE) MRI in the A498 xenograft mouse
model. After the MRI, tumor vasculature was assessed by CD34 staining. After
39 days of chronic treatment, tumor perfusion decreased to 44.8 16.1 mL/
100 g/min (P < 0.05), compared to 92.6 42.9 mL/100 g/min in the control
group. In the acute treatment study, tumor perfusion in the treated group decreased from 107.2 32.7 to 73.7 27.8 mL/100 g/min (P < 0.01; two-way analysis of variance), as well as compared with control group post dosing. A significant reduction in vessel density and vessel size was observed after the chronic treatment, while only vessel size was reduced 24 h after acute treatment. The tumor perfusion correlated with vessel size (r = 0.66; P < 0.005) after chronic, but not after acute treatment. The results from DCE-MRI also detected a significant change between treated and control groups in both
chronic and acute treatment studies, but not between 0 and 24 h in the acute treatment group. These results indicate that tumor perfusion measured by MRI can detect early vascular responses to antiangiogenic treatment. With its noninvasive and quantitative nature, ASL MRI would be valuable for longitudinal assessment of tumor perfusion and in translation from animal models to human.
This study was funded by MSD, Singapore and supported in part by the grant,
CCOGA02_010_2008 from the Agency for Science Technology and Research, Singapore.