THE CHEMISTRY OF NEW IMAGING AGENTS

这个子项目是利用资源的许多研究子项目之一。 由NIH/NCRR资助的中心拨款提供。对子项目的主要支持 子项目的首席调查员可能是由其他来源提供的， 包括美国国立卫生研究院的其他来源。为子项目列出的总成本可能 表示该子项目使用的中心基础设施的估计数量， 不是由NCRR赠款提供给次级项目或次级项目工作人员的直接资金。 新陈代谢过程的分子成像的进展将在很大程度上取决于新分子作为传感器的可用性。在这个项目中，我们专注于开发化学，以建立新的，战略性设计的分子，用于核磁共振对代谢物水平和途径通量的分子成像。在目标1中，我们的重点将放在用于糖酵解和磷酸戊糖途径的超极化13C成像的新的葡萄糖衍生物上。我们提出了一种新的策略，将13C极化存储在单个长T1位，然后在代谢发生时，转移同一分子中更具下游代谢物特征的其他自旋耦合位的极化。通过这种方式，人们可以利用较短的T1质子化碳的化学位移来读出下游的代谢物。在目标2中，我们将应用新型超极化13C传感器来成像组织氧化还原和pH。目标3专注于开发一种新型的基于酶的纳米传感器，用于特定生物靶点的分子成像，而目标4专注于继续开发一种用于成像动物体内葡萄糖细胞外分布的PARACEST试剂。 第一个目标是开发长T1葡萄糖类似物，用于组织葡萄糖摄取和代谢的成像。我们已经合成了[1-13C]葡萄糖内酯，并表明它很容易超极化，被葡萄糖转运蛋白转运到细胞内，被磷酸化，进入磷酸戊糖途径(PPP)，经过两个酶催化步骤产生HP[H13C03-]。我们将继续向研发项目2供应[1-13C]葡萄糖内酯，并专注于开发新的长T1葡萄糖衍生物，用于储存足够长的极化时间，以允许代谢过程发生。在观察脉冲之前，多余的极化将被转移到葡萄糖分子中的其他自旋耦合碳，以识别葡萄糖-6-P和其他可能的下游代谢物。我们的目标是创造出能保持极化3-5分钟或更长时间的新系统。 目标2是开发Long-T1氧化还原和pH传感器，用于异常生理的超极化成像。产酸是新陈代谢的一个基本特性，因此，有一种简便的方法来成像组织的pH值，对于识别癌症和感染等高代谢组织将是非常有价值的。造血干细胞和祖细胞表达高水平的乙醛脱氢酶(ALDH1)，这已成为鉴定和纯化这些细胞的热门靶点。我们假设当肿瘤对药物治疗有反应时，基于长T1 HP-13C-醛的探针将有助于监测通过ALDH1的流量。 目标3是开发一系列能够在体内对特定生物靶点成像的纳米级MRI探测器。核磁共振被认为对体内生物靶点的分子成像过于不敏感。该项目将专注于开发单酶纳米颗粒(SENS)，用于将具有长T1碳的酶特定底物转化为仅在SENS探针所针对的区域的特定产品。这项技术将允许在活体内对特定分子靶标进行成像，其灵敏度是传统核磁共振的20倍、500倍或更高。 目的4是利用葡萄糖敏感的顺磁性CEST试剂和SWIFT成像技术对体内葡萄糖的胞外分布进行成像。使用CEST原理对葡萄糖的分布进行成像一直是一个长期目标，但之前报告的葡萄糖传感器存在两个问题，限制了该项目的成功。这些问题现在已经被发现和解决。以前限制体内检测PARACEST试剂的线宽T2exch效应现在通过使用SWIFT成像原理被绕过。这一令人兴奋的进展现在将允许在体内对具有响应性的PARACEST试剂进行成像，包括新的葡萄糖传感器。这一技术成就为新陈代谢成像传感器打开了大门。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Progress in molecular imaging of metabolic processes will depend heavily on the availability of new molecules as sensors. In this project, we focus on developing the chemistry to build new, strategically-designed molecules for molecular imaging of metabolite levels and pathway fluxes by MRI. In aim 1, our focus will be on new glucose derivatives for hyperpolarized 13C imaging of glycolysis and the pentose phosphate pathways. We propose a new strategy of storing 13C polarization in a single long T1 site then, as metabolism happens, transfer the polarization of other spin-coupled sites in the same molecule that are more characteristic of downstream metabolites. In this way, one can use the chemical shifts of shorter T1 protonated carbons to readout downstream metabolites. In aim 2, we will apply new hyperpolarized 13C sensors for imaging tissue redox and pH. Aim 3 focuses on development of a new type of enzyme-based nanosensor for molecular imaging of a specific biological target while aim 4 focuses on continued development of a PARACEST agent for imaging the extracellular distribution of glucose in animals. Aim 1 is to develop long-T1 glucose analogs for imaging tissue uptake and metabolism of glucose. We have already synthesized [1-13C]gluconolactone and shown that it is readily hyperpolarized, transported into cells by glucose transporters, phosphorylated, enters the pentose phosphate pathway (PPP) and yields HP[H13C03-] after two enzyme catalyzed steps. We will continue supplying [1-13C]gluconolactone to TR&D Project 2 and focus on developing new long T1 glucose derivatives for storing polarization long enough to allow metabolic processes to occur. Excess polarization will then be transferred to other spin-coupled carbons in the glucose molecule prior to an observation pulse to identify glucose-6-P and other possible downstream metabolites. Our goal is to create new systems that remain polarized for 3-5 minutes or longer. Aim 2 is to develop long-T1 redox and pH sensors for hyperpolarized imaging of abnormal physiology. Acid generation is a fundamental property of metabolism so having a convenient method for imaging tissue pH would be extremely valuable for identifying hypermetabolic tissues such as cancer and infection. Hematopoietic stem cells and progenitors express high levels of aldehyde dehydrogenase (ALDH1) and this has become a popular target for identifying and purifying these cells. We hypothesize that long T1 HP-13C-aldehyde-based probes will be useful for monitoring flux through ALDH1 as tumors respond to drug therapy. Aim 3 is to develop a family of nanoscale MRI detectors capable of imaging specific biological targets in vivo. MRI is considered too insensitive for molecular imaging of biological targets in vivo. This project will focus on development of single enzyme nanoparticles (SENs) for converting an enzyme-specific substrate having a long T1 carbon into specific product only in regions where SENs probes are targeted. This technology will allow imaging of specific molecular targets in vivo at a 20,OOO-fold or more sensitivity advantage over conventional MRI. Aim 4 is to image the extracellular distribution of glucose in vivo using a glucose-sensitive paramagnetic CEST agent and SWIFT imaging. Imaging the distribution of glucose using CEST principles has been a long-term goal but the glucose sensor reported previously was found to have two problems that limited success in that project. Those problems have now been identified and solved. The line broadening T2exch effects that limited detection of PARACEST agents in vivo previously are now circumvented by using of SWIFT imaging principles. This exciting advance will now allow imaging of responsive PARACEST agents in vivo, including the new glucose sensor. This technology achievement opens the door to imaging sensors of metabolism.