Sharon E. Ungersma1, Glenn Pacheco2, Anil Bagri1, Shang-Fan Yu2, Andrew Mcgeehan2, Sarajane Ross2, Richard AD Carano1
1Tumor Biology & Angiogenesis, Genentech, South San Francisco, CA, USA; 2Translational Oncology, Genentech, South San Francisco, CA, USA
In vivo imaging of tumors treated with anti-angiogenic agents can reveal information about therapeutic effects on tumor vasculature. Vessel size index (VSI) MRI uses a USPIO contrast agent to determine the blood volume, mean vessel size, and Q (a parameter related to vessel density) for each voxel. We used VSI MRI to examine the effects of two potential therapies in sequence: anti-VEGF, an antibody to vascular endothelial growth factor, and anti-NRP1B, an anti-angiogenic agent believed to inhibit vessel maturation. The VSI technique detected significant reductions in vascular parameters that indicated an advantage to dosing with anti-NRP1B before anti-VEGF.