Tumor microvascular changes in antiangiogenic treatment: Assessment by magnetic resonance contrast media of different molecular weights

Purpose: To test magnetic resonance (MR) contrast media of different molecular weights (MWs) for their potential to characterize noninvasively microvascular changes in an experimental tumor treatment model. Materials and Methods: MD-MBA-435, a poorly differentiated human breast cancer cell line, was implanted into 31 female homozygous athymic rats. Animals were assigned randomly to a control (saline) or drug treatment (monoclonal antibody vascular endothelial growth factor (MabVEGF) antibody) group. In both groups, dynamic MR imaging (MRI) was performed in each animal using up to three different contrast media on sequential days at baseline and follow-up examination. The MWs of the contrast media used ranged from 557 Da to 92 kDa. Using a bidirectional kinetic model, tumor microvessel characteristics, including the fractional plasma volume (fPV) and transendothelial permeability K-PS, were estimated for each contrast medium. These microvascular characteristics were compared between drug and control groups and between contrast media of different MWs. Results: Tumors grew significantly slower (P <0.0005) in the drug treatment group than in the control group. Mean K-PS and fPV values decreased significantly (P