PET Imaging of the Tumor Microenvironment for Cancer Detection

项目总结 胰腺癌(PDAC)，以其侵袭性和肿瘤内广泛的纤维化为特征 微环境(TME)，令人沮丧的5年存活率只有7%。胰腺肿瘤由丰富的 表达成纤维细胞激活蛋白α的细胞外基质和肿瘤相关成纤维细胞 (FAP)。FAP+TAFs促进胰腺肿瘤的发生和发展 细胞外基质和抑制局部CD8+T细胞在癌变过程中的反应。胰腺肿瘤 FAP+TAFs；FAP表达程度与淋巴结状况、肿瘤大小呈正相关 体积大，复发快，临床结局差。由于FAP在肿瘤组织中过表达，并具有基础 在良性组织中表达，它作为调节肿瘤间质的癌症治疗的靶点具有价值 互动。然而，用现有的分子探针在体内定量FAP的表达是困难的，也是一个关键 悬而未决的问题是，基于PET的分子显像剂是否可以检测到PDAC中的FAP+TAFs 肿瘤间质。在本应用中，我们假设靶向成纤维细胞激活蛋白α(FAP-a) 在PDAC TME中发现的肿瘤相关成纤维细胞(TAFs)上发现的独特生物标记物将使我们能够检测和 用正电子发射计算机断层扫描(PET)定量测定体内TME。为了检验这一假设，我们提出了两个具体目标。在第一个目标中，我们 将合成基于氰基吡咯烷支架的新型FAP抑制剂。这些分子将是 用平板IC50和亲和力分析评价FAP的选择性、亲脂性(LogP)和体外稳定性 使用的是人类肝脏微粒子。在目标2中，最有希望的化合物将被碳-11放射性标记。 在PDX异种移植小鼠的生物分布和小动物PET/CT研究中进行了评估 模型，该模型概括了临床上观察到的PDAC肿瘤的异质性。放射性 累积将从共同注册的肿瘤周围绘制的感兴趣区域(ROI)进行量化 PET/CT图像。最后，将对小鼠组织标本进行多光谱显微镜检查，以评估 放射性示踪剂的特异性和放射性蓄积与FAP和其他生物标志物的相关性 一种TAF表型。如果成功，这项工作将立即影响基础科学家研究FAP表达的方式 还有胰腺的TME。这项工作可能会为胰腺癌成像的新范例提供信息， 作为综合战略的一部分加以利用，以便在诊断和管理方面进行亟需的改进 胰腺癌。

PROJECT SUMMARY Pancreatic cancer (PDAC), characterized by its aggressive nature and extensive fibrosis within the tumor microenvironment (TME), has a dismal 5-year survival rate of only 7%. Pancreatic tumors consist of abundant extracellular matrix and tumor-associated fibroblasts (TAFs) that express fibroblast activation protein alpha (FAP). FAP+TAFs promote tumor development and progression in the pancreas through remodeling the extracellular matrix and suppressing local CD8+ T cell response during carcinogenesis. Pancreatic tumors contain FAP+TAFs; the degree of FAP expression positively correlates with lymph node status, larger tumor size, faster recurrence, and worse clinical outcome. Since FAP is overexpressed in tumor tissue and has basal expression in benign tissue, it has value as a target for cancer therapies that modulate tumor-stroma interactions. However, quantifying FAP expression in vivo with available molecular probes is difficult, and a key unanswered question is whether PET-based molecular imaging agents can detect FAP+TAFs in the PDAC tumor stroma. In this application we hypothesize that targeting fibroblast activation protein alpha (FAP) – a unique biomarker found on tumor-associated fibroblasts (TAFs) in the PDAC TME, will allow us to detect and quantify the TME in vivo using PET. To test this hypothesis, we propose two specific aims. In the first aim we will synthesize novel FAP inhibitors that are based upon a cyanopyrrolidine scaffold. These molecules will be assessed for FAP selectivity using plate-based IC50 and affinity assays, lipophilicity (log P) and in vitro stability using human liver microsomes. In Aim 2 the most promising compounds will be radiolabeled with carbon-11 and evaluated in biodistribution and small animal PET/CT studies using a PDX orthotopic xenograft mouse model, which recapitulates the heterogeneity of PDAC tumors observed in the clinic. Radioactivity accumulation will be quantified from regions of interest (ROIs) drawn around the tumor on the co-registered PET/CT images. Finally, multi-spectral microscopy will be conducted on murine tissue specimens to assess radiotracer specificity and correlate the radioactivity accumulation with FAP and other biomarkers that describe a TAF phenotype. If successful, this work will immediately impact how basic scientists study FAP expression and the pancreatic TME. This work could inform new paradigms for pancreatic cancer imaging that can be exploited as part of an integrated strategy for much-needed improvements in diagnosis and management of pancreatic carcinoma.