Histological and molecular characterization of TSPO labeling

TSPO在肿瘤转化组织（包括胶质母细胞瘤）中经常上调。这可用于脑肿瘤的PET成像。IDH野生型胶质母细胞瘤中TSPO表达高于弥漫浸润性WHO II级和III级星形细胞瘤。此外，病理学上不利的间充质胶质母细胞瘤表达亚型显示出比经典或前神经亚型更高的TSPO表达。我们发现，胶质母细胞瘤中TSPO启动子甲基化的缺失可能在机制上驱动在这些肿瘤中观察到的TSPO过表达。然而，由于胶质瘤中作为TSPO-PET信号源的细胞群的异质性，成像生物标志物的解释可能具有挑战性。我们已经表明，除了骨髓细胞，神经胶质肿瘤细胞是TSPO信号的主要贡献者。然而，在脑肿瘤疾病的过程中，细胞组成发生变化，在治疗下诱导的反应性和再吸收性变化的含量增加。因此，我们计划进行一项纵向活检研究，收集原发性和复发性肿瘤的组织样本，这些肿瘤的特征是TSPO富集。然后，我们将组织学和分子解剖样品的TSPO表达，细胞组成和RNA表达谱。使用体外scRadiotracing的新技术，我们将评估TSPO的表达和富集在各自的组织样本中平行。我们还将通过在鼠SB 28模型中采用scRadiotracing进行反向翻译，以细胞分辨率解开TSPO示踪剂标记，该模型模拟人胶质母细胞瘤的肿瘤微环境。此外，将通过scRadiotracing研究移植有人原代胶质母细胞瘤细胞和SB 28的NMRI Foxn1nu/nu小鼠，以比较人和鼠模型中的单细胞TSPO富集。为了获得对人脑组织中TSPO标记的更广泛的概述，我们将对包含肿瘤和非肿瘤疾病状态的谱以及来自不同脑区域的非患病组织的组织微阵列进行染色。将该信息与来自相应患者/脑区域的TSPO-PET结合在一起将生成健康和患病脑中的TSPO表达图以供临床使用。总之，我们整合组织学、分子和成像数据的方法将为TSPO-PET富集模式提供独特的见解，并将有助于更好地理解和全面描述这种新型成像生物标志物的临床相关性。

TSPO is frequently upregulated in neoplastically transformed tissues, including glioblastomas. This may be of use for PET imaging of brain tumors. TSPO expression is higher in IDH-wildtype glioblastomas compared to diffusely infiltrating WHO grade II and III astrocytomas. Also, the prognostically unfavorable mesenchymal glioblastoma expression subtype shows a higher TSPO expression than the classical or proneural subtype. We found that a loss of TSPO promoter methylation in glioblastoma may mechanistically drive the TSPO overexpression observed in these tumors. However, due to the heterogeneity of cell populations contributing as TSPO-PET signal source in gliomas, the imaging biomarker interpretation may be challenging. We have shown that apart from myeloid cells, glial tumor cells are a major contributor to the TSPO signal. Nevertheless, in the course of the brain tumor disease cell compositions vary, with an increasing content of reactive and resorptive changes induced under therapy. We therefore plan on a longitudinal biopsy study collecting tissue samples from primary and recurrent tumors that have been characterized for TSPO enrichment. We will then histologically and molecularly dissect the samples for TSPO expression, cell composition and RNA expression profiles. Using the novel technique of in vitro scRadiotracing we will assess TSPO expression and enrichment in parallel within the respective tissue samples. We will also perform backtranslation to disentangle TSPO tracer labeling at a cellular resolution by employing scRadiotracing in the murine SB28 model, which mimics the tumor microenvironment of human glioblastoma. Furthermore, NMRI Foxn1nu/nu mice transplanted with human primary glioblastoma cells and SB28 will be investigated by scRadiotracing for comparison of single cell TSPO enrichment in human and murine models. In order to gain a broader overview on TSPO labeling in human brain tissue, we will stain tissue microarrays that contain a spectrum of neoplastic and non-neoplastic disease states as well as non-diseased tissues from different brain regions. Bringing this information together with TSPO-PETs from respective patients/brain regions will generate a map of TSPO expression in healthy and diseased brain for clinical use. Taken together, our approach of integrating histological, molecular and imaging data will provide unique insights into TSPO-PET enrichment patterns and will help to better understand and to comprehensively describe the clinical relevance of this novel imaging biomarker.