Development of 18F-labeled positron emission tomography tracers for non-invasive assessment of isocitrate dehydrogenase (IDH) mutations in cerebral gliomas

继脑膜瘤之后，脑胶质瘤是成人最常见的原发脑肿瘤。尽管进行了积极的、多学科的治疗(切除、放疗、化疗)，尤其是像胶质母细胞瘤这样的高级别胶质瘤，预后仍然很差。因此，正在进行的密集研究工作旨在确定与肿瘤生长有关的分子，这些分子可能为这些患者的个性化治疗方法提供新的靶点。对大量胶质瘤患者的研究表明，65%的低级别胶质瘤和85%的继发性胶质母细胞瘤，但只有5%的原发胶质母细胞瘤表现出异柠檬酸脱氢酶(IDH)的突变，这与肿瘤代谢物2-羟基戊二酸的产生增加有关。由于这些突变发生在肿瘤发生的早期，并影响整个肿瘤组织，突变酶可以作为诊断生物标记物和治疗方法的潜在靶点。然而，IDH突变的检测仍然主要是通过免疫组织化学和基因组测序来实现的，这些方法需要通过活检或在手术中获取组织样本，因此不适合于疾病进展监测或纵向研究。这项工作的目的是开发IDH特异性探针，用于通过正电子发射断层扫描(PET)无创性地评估IDH在胶质瘤中的表达。我们的重点将是开发选择性地处理突变的IDH亚型的脑渗透性放射性示踪剂。为此，申请人以前开发的放射性氟化方案将被用来标记目前正在进行I期临床试验的不同特定抑制剂的氟-18，这是一种具有理想性能的放射性核素，可用于临床前和临床PET成像。除了生产足够容易获得的放射性标记前体外，还将在合成持续时间和放射化学产量方面优化放射性标记条件。同时，开发的示踪剂将通过酶和功能抑制分析、几种肿瘤细胞系的体外细胞摄取研究以及接种到胚胎鸡卵中的相同肿瘤细胞系的体外和体内研究来评估其亲和力、选择性、稳定性、脑渗透性、药代动力学和药效学特性。对于最有希望的候选者，这样获得的结果将在大鼠原位胶质母细胞瘤模型中得到验证，它们的放射合成将被转移到用于临床示踪剂生产的自动合成模块。

After meningiomas, cerebral gliomas are the most common primary brain tumors in adults. Despite aggressive, multidisciplinary treatment (resection, radiotherapy, chemotherapy), especially high-grade gliomas like glioblastomas are still associated with a poor prognosis. As a consequence, intense ongoing research efforts have been aimed at identifying molecules involved in tumor growth that could provide novel targets for personalized treatment approaches in these patients. Studies in large cohorts of glioma patients revealed that >65% of low-grade gliomas and >85% of secondary glioblastomas but only <5% of primary glioblastomas exhibit mutations in the enzyme isocitrate dehydrogenase (IDH), which are associated with increased production of the oncometabolite 2-hydroxyglutarate. As these mutations occur early during tumorigenesis and affect the whole tumor tissue, the mutant enzymes could serve as both, diagnostic biomarkers and potential targets for therapeutic approaches. However, detection of IDH mutations is still mostly achieved through immunohistochemistry and genomic sequencing, which require tissue samples retrieved by e.g. biopsy or during an operation and are thus not suitable for disease progression monitoring or longitudinal studies. Aim of this work is the development of IDH-specific probes for non-invasive assessment of IDH expression in gliomas by positron emission tomography (PET). Our focus will be on the development of brain-permeable radiotracers that selectively address the mutant IDH isoform. To this end, radiofluorination protocols previously developed by the applicants will be used to label different specific inhibitors currently undergoing phase I clinical trials with fluorine-18, a radionuclide with ideal properties for preclinical and clinical PET imaging. Apart from the production of sufficiently accessible radiolabeling precursors, the radiolabeling conditions will be optimized with regard to synthesis duration and radiochemical yields. In parallel, the developed tracers will be evaluated for their affinity, selectivity, stability, brain permeability, pharmacokinetic and pharmacodynamics properties using enzymatic and functional inhibition assays, in vitro cell uptake studies with several tumor cell lines as well as ex vivo and in vivo studies with the same tumor cell lines inoculated into embryonated chicken eggs. For the most promising candidates, the results thus obtained will be validated in an orthotopic glioblastoma model in the rat and their radiosynthesis will be transferred to an automated synthesis module for clinical tracer production.