Noninvasive Assessment of Angiogenesis by Ultrasound and Microbubbles Targeted to α v -Integrins

Abstract

Background— Noninvasive methods for characterizing neovessel formation during angiogenesis are currently lacking. We hypothesized that angiogenesis could be imaged with the use of contrast-enhanced ultrasound (CEU) with microbubbles targeted to α v -integrins. Methods and Results— Microbubbles targeted to α v -integrins were prepared by conjugating echistatin (MB E ) or monoclonal antibody against murine α v (MB α ) to their surface. Control microbubbles (MB c ) were also prepared. The microvascular behavior of these microbubbles was assessed by intravital microscopy of the cremaster muscle in mice treated for 4 days with sustained-release FGF-2. Microvascular retention was much greater ( P <0.01) for MB E (11±6 mm −3 ) and MB α (10±7 mm −3 ) than that for MB c (1±1 mm −3 ). Retained MB E and MB α attached directly to the microvascular endothelial surface. Microbubble retention in 4 control mice was minimal. Subcutaneous matrigel plugs enriched with FGF-2 were created in 12 mice and studied 10 days later. Neovessels within the matrigel stained positive for α v -integrins. CEU demonstrated greater ( P <0.01) acoustic intensity for MB E (16.0±5.9 U) and MB α (17.0±5.5 U) compared with MB c (5.8±2.6 U). The signal from targeted microbubbles (MB E and MB α ) correlated well ( r =0.90) with the matrigel blood volume determined by CEU perfusion imaging. Conclusions— CEU with microbubbles targeted for α v -integrins may provide a noninvasive method for assessing therapeutic angiogenesis.