Targeted Ultrasound Imaging of Angiogenic Receptors

描述（由申请人提供）： 这项研究计划将测试的假设，缺血心肌可以通过标记血管生成受体检测和成像，这种方法将允许血管生成的疗效评估。血管内皮生长因子-121（VEGF 121）是响应于缺氧而分泌的VEGF的非肝素结合同种型，其结合内皮细胞特异性缺氧诱导型酪氨酸激酶受体Fit-1和KDR。该小组最近表明，手术诱导的兔后肢缺血可以在体内成像为静脉注射的放射性标记的VEGF 121的选择性摄取。这些数据表明，使用受体的天然存在的配体标记缺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。因为VEGF受体（VEGFR）是内皮细胞特异性的，所以保持在血管内空间内的VEGF靶向成像剂将是理想的。因此，本发明将开发一种靶向超声成像剂，其由具有声学活性的脂质微泡组成，其中重组人VEGF 121作为泡表面上的靶向配体。根据以前的经验，预计这些微泡与缺血组织中过表达VEGFR的微血管系统的短暂粘附可以用基于谐波的超声心动图技术成像。在从体外到体内模型的逐步发展中，本提案的具体目的是解决以下问题：（1）VEGF 121缀合的微泡（VEGF-泡）是否与体外过表达VEGFR的内皮细胞结合，以及如何操作泡设计以优化结合？(2)VEGF气泡是否与体内过表达VEGFR的微血管系统结合？(3)体内VEGF-气泡结合是否可以超声成像并与VEGFR表达的大小相关？(4)血管内皮生长因子受体靶向超声心动图成像能否用于临床相关的犬进行性冠状动脉闭塞和侧支循环发展模型中的缺血和血管生成？本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具有优于现有临床方法的优势，用于检测动脉粥样硬化疾病，采用应力和休息核灌注成像，并可能提供一种敏感的方法，用于评估血管生成。

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.