Molecular photoacoustic imaging of angiogenesis with integrin‐targeted gold nanobeacons

Abstract

Photoacoustic tomography (PAT) combines optical and acoustic imaging to generate high-resolution images of microvasculature. Inherent sensitivity to hemoglobin permits PAT to image blood vessels but precludes discriminating neovascular from maturing microvasculature. α(v)β(3)-Gold nanobeacons (α(v)β(3)-GNBs) for neovascular molecular PAT were developed, characterized, and demonstrated in vivo using a mouse Matrigel-plug model of angiogenesis. PAT results were microscopically corroborated with fluorescent α(v)β(3)-GNB localization and supporting immunohistology in Rag1(tm1Mom) Tg(Tie-2-lacZ)182-Sato mice. α(v)β(3)-GNBs (154 nm) had 10-fold greater contrast than blood on an equivolume basis when imaged at 740 nm to 810 nm in blood. The lowest detectable concentration in buffer was 290 nM at 780 nm. Noninvasive PAT of angiogenesis using a 10-MHz ultrasound receiver with α(v)β(3)-GNBs produced a 600% increase in signal in a Matrigel-plug mouse model relative to the inherent hemoglobin contrast pretreatment. In addition to increasing the contrast of neovessels detected at baseline, α(v)β(3)-GNBs allowed visualization of numerous angiogenic sprouts and bridges that were undetectable before contrast injection. Competitive inhibition of α(v)β(3)-GNBs with α(v)β(3)-NBs (no gold particles) almost completely blocked contrast enhancement to pretreatment levels, similar to the signal from animals receiving saline only. Consistent with other studies, nontargeted GNBs passively accumulated in the tortuous neovascular but provided less than half of the contrast enhancement of the targeted agent. Microscopic studies revealed that the vascular constrained, rhodamine-labeled α(v)β(3)-GNBs homed specifically to immature neovasculature (PECAM(+), Tie-2(-)) along the immediate tumor periphery, but not to nearby mature microvasculature (PECAM(+), Tie-2(+)). The combination of PAT and α(v)β(3)-GNBs offered sensitive and specific discrimination and quantification of angiogenesis in vivo, which may be clinically applicable to a variety of highly prevalent diseases, including cancer and cardiovascular disease.

Angiopoietin-2 differentially regulates angiogenesis through TIE2 and integrin signaling

“…In contrast to the destabilizing roles of ANG-2 on resting ECs (13,14), ANG-2 has been shown to act as an antiapoptotic protective factor for stressed ECs (15), which themselves are particularly strong producers of ANG-2 (16,17). Several groups have recently reported that the ANG-2-positive tumor endothelium harbors a subpopulation of ECs that do not express its receptor TIE2 (18)(19)(20)(21)(22). These puzzling differential expression findings for ANG-2 and its receptor TIE2 raise provocative questions on pos-sible signaling roles of ANG-2 in the absence of TIE2.…”

Biomedical photoacoustics: fundamentals, instrumentation and perspectives on nanomedicine

“…52,53 The gold nanobeacons are synthesized by entrapping small spherical AuNPs within a colloidal particle and then encapsulating them with a biocompatible phospholipids coating. 54 The entrapment of small AuNPs is presumed to enhance the signals, while the AuNPs can be metabolized and eliminated through the urinary system. Moreover, the aggregation of small AuNPs will lead to the tunable absorption peaks for best in vivo PAI signals.…”

“…With the injection of αvβ3-targeted rhodaminelabeled GNB1, angiogenesis could be discriminated from the microvasculature with high sensitivity and specificity. 54 …”

Synthesis of Novel Copolymer for Selective Biomolecule Immobilization on Gold Surface

“…Among these nanoparticles, gold nanoparticles have been extensively exploited for various applications including drug delivery, 1-4 imaging agents, [5][6][7][8] biosensors, [9][10][11][12] and computed tomography (CT) contrast agents [13][14][15][16][17] because they have many advantages such as low cytotoxicity, easy size control, high x-ray absorption, unique optical and electrical properties. Stability of gold nanoparticles under physiological conditions is key step for biomedical application.…”