Targeted Ultrasound Imaging of Angiogenic Receptors

描述(由申请人提供)： 这项研究计划将检验这样一种假设，即通过标记血管生成受体可以检测和成像缺血心肌，并且这种方法将允许评估血管生成的有效性。血管内皮生长因子121(VEGF121)是低氧下分泌的一种非肝素结合的血管内皮生长因子亚型，与内皮细胞特异的低氧诱导酪氨酸激酶受体FIT-1和KDR结合。该研究小组最近发现，手术诱导的兔后肢缺血可以在体内被成像为选择性摄取静脉注射的放射性标记的VEGF121。这些数据表明，使用受体的天然配体标记低氧特异性血管生成受体可能是检测缺血应激组织的有用方法。由于血管内皮生长因子受体(VEGFR)是内皮细胞特异性的，以VEGFR为靶点的显像剂留在血管内将是理想的。因此，这项提议将开发一种靶向超声显像剂，该显像剂由具有声学活性的脂质微泡组成，该微泡以重组人VEGF121为靶向配体。根据以往的经验，基于谐波的超声心动图技术有望在缺血组织中检测到这些微泡与过度表达VEGFR的微血管的瞬时粘连。在从体外到体内模型的逐步发展中，这项建议的具体目标是解决以下问题：(1)VEGF121结合的微泡(VEGFR)是否在体外与过度表达VEGFR的内皮细胞结合，以及如何通过泡泡设计来优化结合？(2)在体内，VEGF121结合的微泡是否与过度表达VEGFR的微血管结合？(3)体内的VEGFR结合能否通过超声成像进行，并与VEGFR表达的大小相关？(4)在进行性冠状动脉闭塞和侧支循环发展的临床相关模型中，能否使用以VEGFR为靶点的超声心动图成像来识别缺血和血管生成？这项研究的最终目标是开发一种非侵入性的、容易获得的、高分辨率的方法来量化组织的缺血负荷。这种非同位素方法可能比现有的使用负荷和静息核灌注成像检测动脉粥样硬化性疾病的临床方法更具优势，并可能为评估血管生成提供一种敏感的方法。

DESCRIPTION (provided by applicant): This research program will test the hypothesis that ischemic myocardium can be detected and imaged by labeling angiogenic receptors, and that such an approach will permit assessment of the efficacy of angiogenesis. Vascular endothelial growth factor-121 (VEGF121) is a non-heparin binding isoform of VEGF secreted in response to hypoxia that binds to endothelial cell-specific hypoxia-inducible tyrosine kinase receptors Fit-1 and KDR. This group has recently shown that surgically induced hindlimb ischemia in rabbits can be imaged in vivo as selective uptake of intravenously injected radiolabeled VEGF121. These data suggest that labeling of hypoxia-specific angiogenic receptors using the receptors' naturally occurring ligand may be a useful approach to detect ischemically stressed tissue. Because VEGF receptors (VEGFR) are endothelial-cell specific, a VEGFR-targeted imaging agent that remains within the intravascular space would be ideal. Accordingly, this proposal will develop a targeted ultrasound imaging agent comprised of an acoustically active lipid microbubble with recombinant human VEGF121 as the targeting ligand on the bubble surface. Based on previous experience, it is expected that transient adhesion of these microbubbles to microvasculature overexpressing VEGFR in ischemic tissue can be imaged with harmonic-based echocardiographic techniques. In stepwise fashion progressing from in vitro to in vivo models, the Specific Aims of this proposal are to address the following questions: (1) Do VEGF121-conjugated microbubbles (VEGF-bubbles) bind to endothelial cells overexpressing VEGFR in vitro, and how can bubble design be manipulated to optimize binding? (2) Do VEGF-bubbles bind to microvasculature overexpressing VEGFR in vivo? (3) Can in vivo VEGF-bubble binding be ultrasonically imaged and related to the magnitude of VEGFR expression? (4) Can VEGFR-targeted echocardiographic imaging be used to identify ischemia and angiogenesis in a clinically relevant canine model of progressive coronary occlusion and collateral development? The ultimate goal of this study is to develop a non-invasive, easily available, high-resolution method for quantifying the ischemic burden of tissue. Such a non-isotope approach could have advantages over existing clinical methods for detecting atherosclerotic disease employing stress and rest nuclear perfusion imaging, and may offer a sensitive method for assessing angiogenesis.