Imaging Tumor Angiogenesis With Contrast Ultrasound and Microbubbles Targeted to α _v β ₃

Abstract

Background— Angiogenesis is a critical determinant of tumor growth and metastasis. We hypothesized that contrast-enhanced ultrasound (CEU) with microbubbles targeted to α v -integrins expressed on the neovascular endothelium could be used to image angiogenesis. Methods and 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 α v β 3 by surface conjugation of echistatin. CEU perfusion imaging with nontargeted microbubbles was used to derive tumor microvascular blood volume and blood velocity. Vascular α 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 mm 2 , P <0.001). Tumor blood volume increased by ≈35% from day 14 to day 28, whereas microvascular blood velocity decreased, especially at the central portions of the tumors. On confocal microscopy, α v β 3 -targeted but not control microbubbles were retained preferentially within the tumor microcirculation. CEU signal from α v β 3 -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 α v β 3 -targeted microbubbles was greatest at the periphery of tumors, where α v -integrin expression was most prominent, and correlated well with tumor microvascular blood volume ( r =0.86). Conclusions— CEU with microbubbles targeted to α v β 3 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.

Molecular profiling of angiogenesis with targeted ultrasound imaging: early assessment of antiangiogenic therapy effects

“…Ultrasound has proven to be highly sensitive for the identification of molecular structures when using targeted contrast agents (10 -13). In this context, antibody-coated, gas-filled microbubbles with diameters of 1 to 5 Am were used as specific contrast agents (11,12) and have been applied to characterize arteriosclerotic disease (14), vascular thrombosis (15), neovasculature (16), lymph nodes (17) as well as cerebral encephalitis and other inflammations (18,19).…”

Detection of T2 changes in an early mouse brain tumor

“…The U87MG implants grow as solid, nonencapsulated spheroidal tumors. The tumor displays a dense vascular network, with many characteristics of glioblastoma vessels [4], including tortuous vessels with abnormal vascular basement membrane and increased permeability. U87MG cells were cultured in DMEM solution supplemented with 10% fetal calf serum and maintained in a humidified 5% CO 2 atmosphere at 37°C.…”

“…Conventional MRI methods, including T 1 -, T 2 -weighted and Gd-enhanced MRI, have been used in glioma diagnosis [4], therapy monitoring [5] and even predicting glioma grades [6]. In particular, T 2 methods are among the most frequently used techniques [7], but the changes in T 2 associated with tumor growth remain poorly understood.…”

How molecular imaging is speeding up antiangiogenic drug development

“…4B; ref. 38). Because acoustic destruction of ''payload-bearing'' microbubbles can be used to deliver drugs or to augment gene transfection (39), integrin a v h 3 -targeted microbubbles may have applications in site-specific cancer therapy.…”