Purpose: To assess vascular remodeling in tumors during two different antiangiogenic therapies with dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) and vessel size imaging and to evaluate the vessel size index (VSI) as a novel biomarker of therapy response.
Materials and methods: In two independent experiments, nude mice bearing human skin squamous cell carcinoma xenografts were treated with a vascular endothelial growth factor (VEGF) inhibitor (bevacizumab) or a multitargeted tyrosine kinase inhibitor (SU11248). Changes in tumor vascularity were assessed by DCE-MRI and vessel size imaging. DCE-MRI data were analyzed applying a two-compartment model (Brix), calculating the parameters Amplitude and k(ep).
Results: For both experiments Amplitude decreased significantly in treated tumors while k(ep) did not change significantly. VSI showed controversial results. VSI was significantly increased in SU11248-treated A431 tumors, whereas no changes were found in bevacizumab-treated HaCaT-ras-A-5RT3 tumors. Immunohistology confirmed these results and suggest differences in the maturation of tumor vascularization as a possible explanation.
Conclusion: DCE-MRI and vessel size imaging provide reliable and supplementing biomarkers of antiangiogenic therapy response. The results of both methods are in excellent agreement with histology. Nevertheless, our results also indicate that vascular remodeling is complex and that a uniform response cannot be expected for different tumors and therapies.