In vivo assessment of vascular endothelial growth factor-induced angiogenesis

To determine whether vascular endothelial growth factor (VEGF)-induced tumor microvascularity is detectable by in vivo NMR imaging, an experimental study was conducted in nude mice. Human breast cancer cells (MCF-7) and MCF-7 cells stably transfected with the cDNA for the VEGF165 isoform (MV165) were grown in nude mice and models were characterized by RT-PCR, Western blotting, ELISA, immunohistochemistry and NMR imaging using a novel synthetic protected graft copolymer (PGC) as a vascular probe. MV165 tumors showed a 1.6-fold higher microvascular density by histology. Both tumors showed identical MR signal intensities on non-contrast and Gd-DTPA enhanced images. PGC enhanced MR imaging of tumoral vascular volume fraction (VVF), however, revealed significant differences between the 2 tumor types (MV165: 8.9 +/- 2.1; MCF-7: 1.7 +/- 0.5; p < 0.003), as expected from histology. VVF changes were more heterogeneous in the MV165 model both among tumors as well as within tumors as determined 3-dimensionally at submillimeter resolutions. Our results have potential applications for non-invasive assessment of angiogenesis by in vivo imaging and for clinical monitoring during angiogenic therapies.