Development of New Molecular Probes for Diagnostic Imaging of Atherosclerosis

描述(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。目前研究方案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)的氧化是动脉粥样硬化斑块发生、发展和失稳的关键因素。由于OxLDL具有免疫原性，已经从小鼠(MDA2和E06)和人类(IK17)中分离出了特异性结合氧化特异性表位的自身抗体。我们最近假设，选择性地针对oxLDL上存在的氧化特定表位的分子成像探针，可能能够在体内早期发现容易破裂的斑块。我们已经报道，oxLDL靶向Gd(Gd)胶束可用于体内MR检测动脉粥样硬化小鼠模型中的富氧化斑块。然而，研究表明，Gd的生物转化和保留程度很高，这可能会限制该技术的临床可译性。目前的提案计划通过生产含有生物相容性磁共振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(II)络合物和氧化铁颗粒作为MR肝脏的适应症，我们推测靶向锰(II)胶束的oxLDL和靶向脂质包裹的氧化铁颗粒可能为在体检测动脉粥样硬化斑块提供临床可翻译的生物相容平台。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、表征和磁共振效果。比较靶向Mn(II)胶束和氧化铁颗粒的基本原理与这两个平台相关的MR信号调制和细胞代谢/排泄的差异有关。由于可获得性，MDA2被选为靶向部分。在目标2中，将在用于目标3的小鼠品系中测试各种oxLDL靶向部分(MDA2、EO6和IK17)的药代动力学、生物分布和磁共振成像效果。由于先前的放射性示踪剂研究表明抗体摄取和oxLDL在动脉血管壁中沉积之间存在相关性，我们假设动脉MR信号将与oxLDL的含量相关(由免疫组织化学确定)，在给予oxLDL靶向的Mn(II)胶束和/或脂质包裹的氧化铁颗粒后。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是为了在动脉粥样硬化斑块进展的小鼠模型中测试最佳配方。这一目的的目的是评估该方法学在体内检测动脉壁oxLDL沉积变化的能力，以响应饮食干预。如果成功，这些MR探针可能为检测和监测脆弱的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塞是这些死亡的原因。随着人们对多种心血管疾病的分子机制有了更深入的了解，最新的研究集中在疾病的细胞和分子机制上，尤其是在高分辨率无创活体分子成像方面。靶向分子特异性造影剂与磁共振成像(MRI)的结合可以在斑块的早期检测、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.