Vessel Size Index MRI for Evaluating the Effects of Multiple Anti-Angiogenic Therapies in Sequence

Sharon E. Ungersma¹, Glenn Pacheco², Anil Bagri¹, Shang-Fan Yu², Andrew Mcgeehan², Sarajane Ross², Richard AD Carano¹

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-NRP1^B, 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-NRP1^B before anti-VEGF.