19F molecular MR imaging for detection of brain tumor angiogenesis: in vivo validation using targeted PFOB nanoparticles

Molecular imaging with magnetic resonance imaging (MRI) targeted contrast agents has emerged as a promising diagnostic approach in cancer research to detect associated biomarkers. In this work, the potential of 19F MRI was investigated to detect angiogenesis with ανβ3-targeted perfluorooctylbromide nanoparticles (PFOB NP) in a U87 glioblastoma mouse model at 7 Tesla. Mice were injected intravenously with targeted or non-targeted NP and 19F images were immediately acquired for 90 min using a PFOB-dedicated MRI sequence. Mice infused with targeted NP exhibited higher concentrations in tumors than mice of the control group, despite the presence of nonspecific signal originating from the blood. Imaging results were corroborated by histology and fluorescence imaging, suggesting specific binding of targeted NP to ανβ3 integrin. Two other groups of mice were injected 24 h before imaging to allow blood clearance but no significant differences were found between both groups, probably due to a loss of specificity of PFOB NP. This is the first demonstration of the ability of 19F MRI to detect ανβ3-integrin endothelial expression in brain tumors in vivo.