Targeted Microbubbles for Imaging Tumor Angiogenesis: Assessment of Whole-Body Biodistribution with Dynamic Micro-PET in Mice

Abstract

Purpose:To evaluate in vivo whole-body biodistribution of microbubbles (MBs) targeted to tumor angiogenesis-related vascular endothelial growth factor (VEGF) receptor 2 (VEGFR2) by using dynamic micro-positron emission tomography (PET) in living mice. Materials and Methods:Animal protocols were approved by the Institutional Administrative Panel on Laboratory Animal Care. Lipid-shell perfluorocarbon-filled MBs, targeted to VEGFR2 via anti-VEGFR2 antibodies, were radiolabeled by conjugating the radiofluorination agent N-succinimidyl-4-[ 18 F]fluorobenzoate (SFB) to the anti-VEGFR2 antibodies. These MBs were then injected intravenously into nude mice (n ϭ 4) bearing angiosarcomas, and the whole-body biodistribution of these probes was assessed for 60 minutes by using dynamic micro-PET. Results were compared with ex vivo gamma counting (n ϭ 6) and immunofluorescence staining (n ϭ 6). Control studies in angiosarcoma-bearing mice were performed with injection of the radiolabeled antibodies alone (n ϭ 3) or free SFB (n ϭ 3). A mixed-effects regression of MB accumulation on fixed effects of time and tissue type (tumor or muscle) and random effect of animal was performed. Results:VEGFR2-targeted MBs rapidly cleared from the blood circulation (50% blood clearance after approximately 3.5 minutes) and accumulated in the liver (mean, 33.4% injected dose [ID]/g Ϯ 13.7 [standard deviation] at 60 minutes) and spleen (mean, 9.3% ID/g Ϯ 6.5 at 60 minutes) on the basis of micro-PET imaging. These findings were confirmed with ex vivo gamma counting. Uptake of targeted MBs was significantly higher (P Ͻ .0001) in tumor than in adjacent skeletal muscle tissue. Immunofluorescence staining demonstrated accumulation of the targeted MBs within hepatic Kupffer cells and splenic macrophages. Biodistribution of the radiolabeled antibodies and free SFB differed from the distribution of the targeted MBs.

A Molecular Imaging Primer: Modalities, Imaging Agents, and Applications

“…The specific in vivo binding of targeted microbubbles, and their whole body biodistribution can be evaluated by techniques like intravital microscopy (IVM) and PET, respectively (459). In the near future molecular imaging using US is expected to transition from a preclinical modality to a fully clinically useful technique through the use of different clinically translatable instrumentation, such as endoscopes (345,459), and novel US-compatible imaging agents that are able to extravasate (e.g., silica nanoparticles) (190).…”

“…In the near future molecular imaging using US is expected to transition from a preclinical modality to a fully clinically useful technique through the use of different clinically translatable instrumentation, such as endoscopes (345,459), and novel US-compatible imaging agents that are able to extravasate (e.g., silica nanoparticles) (190). C) KEY STRENGTHS AND LIMITATIONS.…”

Dual-targeted Contrast Agent for US Assessment of Tumor Angiogenesis in Vivo

“…To further obviate any bias from the order of MB injections and to minimize interactions between the MB types, the different MBs were administered in random order, and a delay of 30 minutes between the MB injections was used. We chose this delay between MB injections on the basis of our experience (20), as well as that of others (18), that most of the MBs are cleared from the mouse vasculature within 30 minutes after intravenous injection.…”

A Bridge Not Too Far: Linking Disciplines Through Molecular Imaging Probes

“…The first report of a dual-modality PET-ultrasound probe was in 2008 (43). A perfluorocarbon gas-filled microbubble surrounded by a lipid shell coated with streptavidin provides a convenient platform for attaching biotinylated antibodies.…”