Development of New Molecular Probes for Diagnostic Imaging of Atherosclerosis

描述（由申请人提供）：需要改进的成像策略和靶向分子成像造影剂来识别、表征和监测动脉粥样硬化斑块。目前研究计划的主要目标是开发敏感的生物相容性分子成像探针，能够通过磁共振成像（MRI）识别和监测动脉粥样硬化斑块的进展。低密度脂蛋白（oxLDL）的氧化已被确定为动脉粥样硬化斑块起始、进展和去稳定的关键因素。由于OxLDL具有免疫原性，因此已从小鼠（MDA2和E06）和人类（IK17）中分离出特异性结合氧化特异性表位的自身抗体。我们最近假设，选择性靶向氧化特异性表位的分子成像探针，存在于oxLDL上，可能能够在体内早期检测容易破裂的斑块。我们报道了oxLDL靶向钆（Gd）胶束可用于小鼠动脉粥样硬化模型中富氧化斑块的体内MR检测。然而，研究表明，存在高度的Gd生物转化和保留，这可能限制了该技术的临床可翻译性。目前的建议计划通过生产含有生物相容性MR标签的纳米颗粒来解决这些安全问题。由于FDA已经批准使用锰（Mn(II)）螯合剂和氧化铁颗粒用于MR肝脏适应症，我们假设oxLDL靶向Mn（II）胶束和oxLDL靶向脂质涂层氧化铁颗粒可能为体内检测动脉粥样硬化斑块提供临床可翻译的生物相容性平台。Aim1将重点研究MDA2标记的Mn（II）胶束和脂质包裹的氧化铁颗粒在动脉粥样硬化小鼠中的合成、表征和MR效果。比较靶向Mn（II）胶束和氧化铁颗粒的基本原理与这两种平台相关的MR信号调制和细胞代谢/排泄的差异有关。考虑到可用性，我们选择MDA2作为目标片段。在Aim 2中，各种oxLDL靶向部分（MDA2、EO6和IK17）的药代动力学、生物分布和MR成像功效将在Aim 3中使用的小鼠品系中进行测试。由于先前的放射性示踪剂研究表明抗体摄取与动脉血管壁中oxLDL沉积之间存在相关性，我们假设在给予oxLDL靶向Mn（II）胶束和/或脂质包裹的氧化铁颗粒后，动脉MR信号将与oxLDL含量（通过免疫组织化学测定）相关。将根据生物分布和MR信号与oxLDL沉积的相关性来选择最佳配方（靶向部分和Mn（II）或铁颗粒）。目的3是在小鼠动脉粥样硬化斑块进展模型中测试最佳配方。本研究的目的是评估该方法在饮食干预下检测动脉壁oxLDL沉积在体内变化的能力。如果成功，这些MR探针可能为检测和监测易损动脉粥样硬化斑块提供一个强大的临床可翻译平台。公共卫生相关性：心血管疾病仍然是美国死亡的主要原因，动脉粥样硬化引起的心肌和脑梗死占这些死亡的主要原因。随着对众多心血管疾病分子途径的深入了解，最新的研究集中在疾病的细胞和分子机制上，特别是高分辨率无创体内分子成像。靶向分子特异性造影剂与磁共振成像（MRI）能力的结合可以在早期斑块检测，了解疾病的分子机制和监测治疗反应方面带来最佳结果。

DESCRIPTION (provided by applicant): Improved imaging strategies and targeted molecular imaging contrast agents are needed to allow for the identification, characterization, and monitoring of atherosclerotic plaque. The main objective of the current research proposal is to develop sensitive biocompatible molecular imaging probes that are capable of identifying and monitoring atherosclerotic plaque progression by magnetic resonance imaging (MRI). Oxidation of low-density lipoprotein (oxLDL) has been identified as a critical factor in atherosclerotic plaque initiation, progression and de-stabilization. Since OxLDL is immunogenic, autoantibodies that specifically bind oxidation-specific epitopes have been isolated from mice (MDA2 and E06) and humans (IK17). We recently hypothesized that molecular imaging probes that selectively target oxidization-specific epitopes, present on oxLDL, may enable early in vivo detection of plaque prone to rupture. We have reported that oxLDL targeted gadolinium (Gd) micelles may be used for in vivo MR detection of oxidation-rich plaques in murine models of atherosclerosis. However, it was shown that there is a high degree of Gd biotransformation and retention that may limit the clinical translatability of this technology. The current proposal plans to solve these safety issues by producing nanoparticles containing biocompatible MR labels. Since the FDA has already approved the use manganese (Mn(II)) chelates and iron oxide particles for MR liver indications, we hypothesize that oxLDL targeted Mn(II) micelles and oxLDL targeted lipid coated iron oxide particles may provide clinically translatable biocompatible platforms for in vivo detection of atherosclerotic plaque. Aim1 will focus on the synthesis, characterization, and MR efficacy of MDA2 labeled Mn(II) micelles and lipid coated iron oxide particles in atherosclerotic mice. The rationale for comparing targeted Mn(II) micelles and iron oxide particles is related to differences in the MR signal modulation and cellular metabolism/excretion associated with these two platforms. MDA2 was chosen as the targeting moiety due to availability. In Aim 2 the pharmacokinetics, biodistribution, and MR imaging efficacy of the various oxLDL targeting moieties (MDA2, EO6, and IK17) will be tested in the mouse strain to be used in Aim 3. Since previous radiotracer studies show a correlation between antibody uptake and oxLDL deposition in the arterial vessel wall, we hypothesize that the arterial MR signal will correlate to oxLDL content (as determined by immunohistochemistry) following administration of oxLDL targeted Mn(II) micelles and/or lipid coated iron oxide particles. The optimal formulation (targeting moiety and Mn(II) or iron particle) will be chosen based upon biodistribution and the correlation of the MR signal to oxLDL deposition. Aim 3 is designed to test the optimal formulation in murine models of atherosclerotic plaque progression. The goal of this aim is to evaluate the ability of this methodology to detect in vivo changes in arterial wall oxLDL deposition in response to dietary intervention. If successful, these MR probes may provide a powerful clinically translatable platform for the detection and monitoring of vulnerable atherosclerotic plaque. PUBLIC HEALTH RELEVANCE: Cardiovascular disease remains the primary cause of mortality in the United States with myocardial and cerebral infarction caused by atherosclerosis accounting for these deaths. With better understanding of molecular pathways of numerous cardiovascular diseases, the latest research has focused on cellular and molecular mechanism of the disease, more particularly to high resolution non-invasive in vivo molecular imaging. The combination of targeted molecule- specific contrast agents and the capabilities of magnetic resonance imaging (MRI) can bring optimal results in early plaque detection, understand the molecular mechanism of the disease and monitor response to treatment.