PEG-Branch-Nitroxide Nanostructured Organic MRI Contrast Agents

描述（由申请人提供）：每年进行超过1000万次磁共振成像（MRI）手术;其中很大一部分需要使用顺磁性Gd（III）造影剂。Gd（III）药物不适用于肾功能受损的患者、新生儿或需要肝移植的患者。顺磁性有机自由基造影剂（ORCAs）可以提供合适的Gd（III）试剂的替代品，但一些技术障碍阻碍了它们的发展。我们提出了一类新的纳米结构ORCA的合成，将适合翻译到临床成像应用。这些材料将由带有聚（乙二醇）（PEG）和抗还原螺环己基氮氧化物结构域的支链大分子单体构成。这些大分子单体的平行开环易位聚合（ROMP）将产生具有受控尺寸、高水溶性、荧光标记和均质结构的新型纳米结构的分支刷ORCA的库。这些材料代表了约翰逊实验室开发的纳米结构和Rajca开发的当前最先进的树枝状ORCA之间的协同交叉。我们将在存在生物相关还原剂的情况下表征所有ORCA的氮氧猝灭动力学;将测量所有新药物的MRI弛豫率。结果将允许弛豫率与纳米结构的相关性，并将指导下一代ORCA的开发。在本研究中，将使用小鼠模型在体内研究基于低高溶解度、高弛豫率、高还原抗性和低体外毒性的顶级ORCA候选物。我们将研究毒性、生物分布和MRI对比增强。将通过整个动物荧光成像和器官匀浆的EPR光谱分析定量离体生物分布。我们将使用小鼠异种移植模型探索对具有渗漏血管的肿瘤的被动靶向。该提案的关键创新是合成方法和新的纳米结构，它们协同工作，允许快速合成具有MRI应用理想架构的ORCA。具体地，氮氧化合物在纳米结构核心附近的放置将提供足够的空间屏蔽用于长时间成像，但足够接近水用于高弛豫。重要的是，该方法是通用的;它可以扩展到双模式成像，并最终开发组合药物输送和成像平台（治疗诊断学）。作为一个整体，这一建议的结果将导致一类新的ORCA的MR成像，和新的合成概念的纳米结构的制备用于生物医学应用。

DESCRIPTION (provided by applicant): Over 10 million magnetic resonance imaging (MRI) procedures are performed each year; a significant fraction require the use of a paramagnetic Gd (III) contrast enhancement agent. Gd (III) agents are not suitable for patients with impaired kidney function, newborn children, or for patients that require liver transplants. Paramagnetic organic radical contrast agents (ORCAs) could provide suitable alternatives to Gd (III) agents, but several technological hurdles inhibit their development. We propose the synthesis of a novel class of nanostructured ORCAs that will be suitable for translation to clinical imaging applications. These materials will be constructed from branched macromonomers that carry poly (ethylene glycol) (PEG) and reduction resistant spirocyclohexyl nitroxide domains. Parallel ring opening metathesis polymerization (ROMP) of these macromonomers will yield a library of novel nanostructured branched-brush ORCAs with controlled sizes, high water solubility, fluorescent labels, and homogeneous structures. These materials represent a synergistic intersection between nanostructures developed by the Johnson lab and the current state-of-the-art dendritic ORCAs developed by Rajca. We will characterize the nitroxide quenching kinetics for all ORCAs in the presence of biologically relevant reducing agents; the MRI relaxivities will be measured for all new agents. The results will allow for correlation of relaxivity with nanostructure, and will guide the development of next generation ORCAs. In this study, the top ORCA candidates based on low high solubility, high relaxivity, high resistance to reduction, and low in vitro toxicity will be studied in vivo using mouse models. We will study the toxicity, biodistribution, and MRI contrast enhancement. Ex vivo biodistribution will be quantified by whole animal fluorescence imaging and EPR spectral analysis of organ homogenates. We will explore passive targeting to tumors with leaky vasculature using a mouse xenograft model. The key innovations of this proposal are the synthetic approach and the new nanostructures, which work synergistically to allow for rapid synthesis of ORCAs with ideal architectures for MRI applications. Specifically, the placement of nitroxides near the nanostructure core will provide adequate steric shielding for imaging at long times, but sufficient access to water for high relaxivity. Importantly, the method is versatile; it can be extended to dual-modal imaging, and ultimately development of combined drug delivery and imaging platforms (theranostics). Taken as a whole, the results of this proposal will lead to a new class of ORCAs for MR imaging, and new synthetic concepts for the preparation of nanostructures for biomedical applications.