Real time imaging of immune cells and glutamate dynamics by PET and metabolic MRI

摘要 免疫细胞的激活在多发性硬化症（MS）的发生和发展中起着关键作用， 中枢神经系统（CNS）的进行性神经变性。虽然谷氨酸盐的不平衡 在MS脑中描述，并已被提出有助于轴突损伤和组织破坏， 疾病进展期间谷氨酸动力学和免疫激活之间的关系仍不清楚。 目前，缺乏临床上可用的非侵入性成像方法来检测免疫细胞和谷氨酸， 代谢限制了我们对MS发病机制的理解和对治疗反应的监测。 用于正电子发射断层扫描（PET）的放射性示踪剂的最新发展已经显示出巨大的潜力， 免疫系统细胞的检测和星形胶质细胞兴奋性氨基酸的谷氨酸再摄取成像 酸性转运蛋白2（EAAT 2）。具体地，2 '-脱氧-2'-[18F]氟-9-β-D-阿拉伯呋喃糖基鸟嘌呤（[18F]F-AraG） 能够检测炎性疾病和癌症模型中的活化T细胞。[18F]氟- 芴基乙酰胺（[18F]FFAA）已经证明能够测量CNS中的EAAT 2活性。 超极化~（13）C磁共振波谱成像（HP ~（13）C MRSI）是一种新兴的成像技术 其实时测量体内的酶反应。HP 13 C丙酮酸已被证明可以高度检测 在外周和CNS炎症模型中，来自先天免疫系统的糖酵解细胞。最近，丙酮酸 标记在第二个碳位置，[2- 13 C]丙酮酸，提供了一种新的方法来监测谷氨酸的生产， 人类的大脑 本项目旨在验证这些创新的非侵入性PET和MR方法，以提供一种新的方法 研究先天性和适应性免疫反应与谷氨酸动力学之间的关系， 临床前MS模型。该项目的指导阶段将开发和验证新的神经成像 技术：目标1将研究[18 F]F-AraG和[18 F]FFAA PET成像可视化激活的 疾病进展过程中的T细胞和谷氨酸再摄取。目标2将开发和验证HP [2- 13 C]丙酮酸盐 作为一种方法，同时检测促炎性先天免疫细胞和确定实时脑 谷氨酸生产。该项目的独立阶段将以这些初步成果为基础，目标3将 评估这种多模式PET和MRI方法监测免疫反应、谷氨酸 生产和治疗后的星形胶质细胞功能。这项提案成功的关键是，古列尔梅蒂博士 我将得到神经成像专家组的支持和指导，特别是HP 13 C MR技术（Myriam Chaumeil博士和Peder Larson博士）和PET成像（亨利VanBrocklin博士） 如神经免疫学和MS（Ari绿色博士和Zamvil博士），为她提供必要的技能， 作为一名独立的科学家开始自己的职业生涯。

ABSTRACT Activation of immune cells plays a critical role in initiation and progression of multiple sclerosis (MS), leading to progressive neurodegeneration of the central nervous system (CNS). While glutamate imbalance has been described in MS brains and has been proposed to contribute to axonal damage and tissue destruction, the relationships between glutamate dynamics and immune activation during disease progression remain unclear. Presently, the lack of clinically available noninvasive imaging methods to detect immune cells and glutamate metabolism limits our understanding of MS pathogenesis and monitoring of responses to therapies. Recent development of radiotracers for positron emission tomography (PET) have shown great potential for detection of cells from the immune system and for imaging glutamate reuptake by astroglial excitatory amino acid transporter-2 (EAAT2). Specifically, 2'-deoxy-2'-[18F]fluoro-9-β-D-arabinofuranosylguanine ([18F]F-AraG) enables the detection of activated T-cells in inflammatory diseases and cancer models. [18F]Fluoro- fluorenylaspartyl amide ([18F]FFAA) has demonstrated the ability to measure EAAT2 activity in the CNS. Hyperpolarized 13C magnetic resonance spectroscopic imaging (HP 13C MRSI) is an emerging imaging technique which measures enzymatic reactions in vivo in real-time. HP 13C pyruvate has been shown to detect highly glycolytic cells from the innate immune system in peripheral and CNS inflammation models. Recently, pyruvate labelled on the second carbon position, [2-13C]pyruvate, provided a new way to monitor glutamate production in the human brain. This project proposes to validate these innovative noninvasive PET and MR methods to provide a new way to investigate the relationships between innate and adaptive immune responses and glutamate dynamics in preclinical MS models. The mentored phase of this project will develop and validate new neuroimaging technologies: Aim 1 will investigate the potential of [18F]F-AraG and [18F]FFAA PET imaging to visualize activated T-cells and glutamate reuptake during disease progression. Aim 2 will develop and validate HP [2-13C]pyruvate as a method to simultaneously detect pro-inflammatory innate immune cells and determine real-time brain glutamate production. The independent phase of this project will build on these initial results and Aim 3 will evaluate the potential of this multimodal PET and MRI approach to monitor immune responses, glutamate production, and astrocyte functions following therapy. Central to the success of this proposal, Dr. Guglielmetti will have the support and guidance from an established group of experts in neuroimaging, particularly HP 13C MR technology (Dr. Myriam Chaumeil and Dr. Peder Larson) and PET imaging (Dr. Henry VanBrocklin) as well as in neuroimmunology and MS (Dr. Ari Green and Dr. Zamvil), providing her with the necessary skillsets to embark on a career as an independent scientist.