Radiolabled MAO-B Substrates for Imaging

项目描述（由申请人提供）：本项目旨在开发新的人脑单胺氧化酶B （MAO- B）放射性标记底物。在大脑中，MAO-B在星形胶质细胞中显著表达，并且MAO-B酶活性的增加已被用作神经胶质瘤的生物标志物，在许多疾病的研究中，如难治性癫痫、阿尔茨海默病、肌萎缩侧索硬化症和其他神经退行性疾病。由于反应性神经胶质瘤是一种公认的局部细胞对各种脑损伤反应的病理标志，因此对神经胶质瘤程度和模式的非侵入性测量可以广泛适用于损伤或病变组织的定位（例如癫痫的切除），相关疾病的鉴别（阿尔茨海默氏症与额颞叶痴呆（FTD）或路易体病），以及评估新的治疗方法。因此可以显著帮助许多中枢神经系统疾病的诊断和治疗。本项目提出了新的碳-11和氟-18标记底物的设计、化学和放射化学合成，以及用于MAO-B酶活性正电子发射断层扫描（PET）成像的体外和体内评价。在MAO-B成像的创新方法中，该项目将制备新型放射性标记的4-噻吩基和4-氨基甲酰- n-甲基-1,2,3,6-二氢吡啶衍生物，已知这些衍生物是无毒的MAO-B底物，可形成极性反应产物。4-噻吩基-1,2,3,6-二氢吡啶被氧化成相应的无毒二氢吡啶盐；4-氨基甲酰-1,2,3,6-二氢吡啶被氧化成相应的二氢吡啶盐，这些二氢吡啶盐自发水解释放极性胺。MAO-B酶促氧化的极性放射性标记产物将在酶作用部位积聚，因此使用代谢捕获的概念来提供可量化的PET成像数据。候选放射性示踪剂将通过体外解剖技术评估其与MAO- B （Km和kcat）的体外反应性以及在啮齿类动物体内的良好脑吸收和保留。然后通过微pet成像评估有前途的放射性示踪剂在恒河猴脑内的脑摄取、不可逆捕获和总体药代动力学。该项目的总体目标是确定适当的放射性标记基质，可以进一步评估和验证用于人体PET成像的应用。

DESCRIPTION (provided by applicant): This project aims to develop new radiolabeled substrates for the enzyme monoamine oxidase-B (MAO- B) in the human brain. In the brain, MAO-B is conspicuously expressed in astrocytes, and increased MAO-B enzymatic activity has been used as a biomarker of gliosis in numerous studies of diseases such as refractory epilepsy, Alzheimer's disease, amyotrophic lateral sclerosis, and other neurodegenerative conditions. As reactive gliosis is a recognized pathological marker of localized cellular responses to a wide variety of insults to the brain, non-invasive measurement of the extent and pattern of gliosis could have wide applicability to the localization of injured or diseased tissue (e.g., for resection in epilepsy), differentiation of related diseases (Alzheimer's versus frontal-temporal dementia (FTD) or Lewy Body disease), and evaluation of new therapeutic treatments, and thus could significantly assist in the diagnosis and management of many CNS diseases. This project proposes the design, chemical and radiochemical synthesis, and evaluation in vitro and in vivo of new carbon-11 and fluorine-18 labeled substrates for Positron Emission Tomography (PET) imaging of MAO-B enzymatic activity. In an innovative approach to MAO-B imaging, the project will prepare novel radiolabeled derivatives of 4-thiophenyl- and 4-carbamoyl-N-methyl-1,2,3,6-dihydropyridines that are known to be non-toxic MAO-B substrates that form polar reaction products. 4-Thiophenyl-1,2,3,6-dihydropyridines are oxidized to the corresponding non-toxic dihydropyridinium salts; the 4-carbamoyl-1,2,3,6- dihydropyridines are oxidized to the corresponding dihydropyridinium salts that spontaneously hydrolyze to release polar amines. The polar radiolabeled products from MAO-B enzymatic oxidation will accumulate at the site of enzyme action, thus using the concept of metabolic trapping to provide quantifiable PET imaging data. Candidate radiotracers will be evaluated for in vitro reactivity with MAO- B (Km and kcat) and good in vivo brain uptake and retention in rodents using ex vivo dissection techniques. Promising radiotracers will then be evaluated for brain uptake, irreversible trapping, and overall pharmacokinetics in rhesus monkey brain by microPET imaging. The overall goal of the project is to identify appropriate radiolabeled substrates that can be further evaluated and validated for applications in human PET imaging.