Ultra-Responsive "ON/OFF" Fluorescent Nanoprobes for Cancer Molecular Imaging

描述(由申请人提供)：血管生成成像在癌症的早期发现以及许多新的分子靶向抗血管生成疗法的治疗后评估方面具有相当大的前景。新的对比剂探针，如小分子放射性示踪剂，光学探针，以及基于脂质和聚合物的纳米颗粒被广泛研究，以靶向不同的血管生成生物标志物。然而，生物标志物的组织浓度低，缺乏增加信号输出的放大策略，以及高背景信号是阻碍这些分子成像技术进步的几个主要限制因素。这一应用的长期目标是开发一套基于同向荧光共振能量转移(HomoFRET)和光诱导电子转移(PET)机制的强大的可调荧光纳米探针。胶束纳米探头在正常生理条件下(例如血液循环)将保持沉默(或处于关闭状态)，背景信号最少。在特异性靶向血管生成靶点(如avb3)后，这些纳米探针可以在受体介导的内吞作用后被内体/溶酶体内的pH激活(pH 5.0-7.2)打开。我们的中心假设是，肿瘤内皮细胞信号放大、血液背景抑制和pH可激活胶束(Pham)纳米探针的协同策略将能够提高血管生成生物标志物在体内血管生成肿瘤中的成像敏感性和特异性。为了验证这一假说，我们将实施以下具体目标：(1)建立一系列过渡pH(PHT)可调的近红外(NIR)Pham纳米探针；(2)评估非靶向Pham在酸性肿瘤微环境中的激活情况；(3)建立血管靶向Pham，并研究这些纳米探针在肿瘤内皮细胞中的激活情况；(4)评价靶向Pham在荷瘤小鼠体内血管生成标志物(即VEGFR2、avb3)成像中的特异性和有效性。这项研究的成功实施将使Pham成为一个有价值的成像平台，在体内成像肿瘤内皮上的血管生成特异性生物标记物。这些纳米探针可能对于分子靶向抗血管生成治疗的疗效评估特别有用，其中可以直接测量治疗靶点(例如VEGFR2、avb3)的表达水平。 公共卫生相关性：本申请描述了超响应荧光纳米颗粒的开发，用于临床前肿瘤模型中血管生成生物标记物的分子成像。

DESCRIPTION (provided by applicant): Angiogenesis imaging holds considerable promise for early detection of cancer, as well as post-therapy assessment of many new molecular-targeted antiangiogenic therapies. New contrast probes such as small molecular radiotracers, optical probes, and lipid- and polymer-based nanoparticles are intensively investigated to target different biomarkers of angiogenesis. However, low tissue concentrations of intended biomarkers, lack of an amplification strategy to increase signal output, and high background signals are several major limiting factors that hamper the advances of these molecular imaging techniques. The long-term goal of this application is to develop a robust set of tunable fluorescent nanoprobes based on the homo fluorescent resonance energy transfer (homoFRET) and photo-induced electron transfer (PET) mechanisms. The micelle nanoprobes will stay silent (or in the OFF state) with minimum background signals under normal physiological conditions (e.g. blood circulation). Upon specific targeting to angiogenic target (e.g. avb3), these nanoprobes can be turned ON by pH activation (pH 5.0-7.2) inside endosomes/lysosomes after receptor-mediated endocytosis. Our central hypothesis is that a synergized strategy of signal amplification in tumor endothelium and background suppression in blood and pH-activatable micelle (pHAM) nanoprobes will be able to improve the imaging sensitivity and specificity of angiogenesis biomarkers in vascularized tumors in vivo. To test this hypothesis, we will carry out the following specific aims: (1) establish a series of near infrared (NIR) pHAM nanoprobes with tunable transition pH (pHt); (2) evaluate the activation of non-targeted pHAM in acidic tumor microenvironment; (3) establish vascular-targeted pHAM and investigate the intracellular activation of these nanoprobes in tumor endothelial cells; (4) evaluate the specificity and efficacy of targeted pHAM in the imaging of distinctive angiogenesis biomarkers (i.e. VEGFR2, avb3) in tumor-bearing mice in vivo. Successful execution of this research will establish pHAM as a valuable imaging platform to image angiogenesis- specific biomarkers on the tumor endothelium in vivo. These nanoprobes may be particularly useful for the efficacy assessment of molecular-targeted antiangiogenic therapies, where the expression levels of the therapeutic targets (e.g. VEGFR2, avb3) can be directly measured. PUBLIC HEALTH RELEVANCE: This application describes the development of ultra-responsive fluorescent nanoparticles for molecular imaging of angiogenesis biomarkers in preclinical tumor models.