Imaging tumor angiogenesis with contrast ultrasound and microbubbles targeted to alpha(v)beta3.
BACKGROUND
Angiogenesis is a critical determinant of tumor growth and metastasis. We hypothesized that contrast-enhanced ultrasound (CEU) with microbubbles targeted to alpha(v)-integrins expressed on the neovascular endothelium could be used to image angiogenesis.


RESULTS
Malignant gliomas were produced in 14 athymic rats by intracerebral implantation of U87MG human glioma cells. On day 14 or day 28 after implantation, CEU was performed with microbubbles targeted to alpha(v)beta3 by surface conjugation of echistatin. CEU perfusion imaging with nontargeted microbubbles was used to derive tumor microvascular blood volume and blood velocity. Vascular alpha(v)-integrin expression was assessed by immunohistochemistry, and microbubble adhesion was characterized by confocal microscopy. Mean tumor size increased markedly from 14 to 28 days (2+/-1 versus 35+/-14 mm2, P<0.001). Tumor blood volume increased by approximately 35% from day 14 to day 28, whereas microvascular blood velocity decreased, especially at the central portions of the tumors. On confocal microscopy, alpha(v)beta3-targeted but not control microbubbles were retained preferentially within the tumor microcirculation. CEU signal from alpha(v)beta3-targeted microbubbles in tumors increased significantly from 14 to 28 days (1.7+/-0.4 versus 3.3+/-1.0 relative units, P<0.05). CEU signal from alpha(v)beta3-targeted microbubbles was greatest at the periphery of tumors, where alpha(v)-integrin expression was most prominent, and correlated well with tumor microvascular blood volume (r=0.86).


CONCLUSIONS
CEU with microbubbles targeted to alpha(v)beta3 can noninvasively detect early tumor angiogenesis. This technique, when coupled with changes in blood volume and velocity, may provide insights into the biology of tumor angiogenesis and be used for diagnostic applications.
Ellegala
Dilantha B
DB
Department of Neurosurgery, University of Virginia School of Medicine, Charlottesville, USA.
Leong-Poi
Howard
H
Carpenter
Joan E
JE
Klibanov
Alexander L
AL
Kaul
Sanjiv
S
Shaffrey
Mark E
ME
Sklenar
Jiri
J
Lindner
Jonathan R
JR
D000818:Animals; D001710:Biotin / Q000737:chemistry; D001783:Blood Flow Velocity; D001932:Brain Neoplasms / Q000098:blood supply* / Q000000981:diagnostic imaging* / Q000473:pathology; D003287:Contrast Media / Q000008:administration & dosage* / Q000737:chemistry; D005909:Glioblastoma / Q000098:blood supply* / Q000000981:diagnostic imaging* / Q000473:pathology; D006801:Humans; D007150:Immunohistochemistry; D039302:Integrin alphaVbeta3 / Q000378:metabolism*; D036341:Intercellular Signaling Peptides and Proteins; D008833:Microcirculation / Q000378:metabolism / Q000473:pathology; D009368:Neoplasm Transplantation; D009389:Neovascularization, Pathologic / Q000000981:diagnostic imaging*; D010455:Peptides / Q000737:chemistry / Q000378:metabolism; D011237:Predictive Value of Tests; D051381:Rats; D011923:Rats, Nude; D012680:Sensitivity and Specificity; D014183:Transplantation, Heterologous; D014463:Ultrasonography
D003287:Contrast Media; D039302:Integrin alphaVbeta3; D036341:Intercellular Signaling Peptides and Proteins; D010455:Peptides; C057986:echistatin; D001710:Biotin