Werner Siemens Imaging Center, Department of Preclinical Imaging and Radiopharmacy, Eberhard Karls University, Tübingen, Germany.
Cluster of Excellence iFIT (EXC 2180) "Image Guided and Functionally Instructed Tumor Therapies", 72076, Tübingen, Germany.
Mol Imaging Biol. 2023 Jun;25(3):606-618. doi: 10.1007/s11307-022-01797-z. Epub 2023 Jan 4.
Resection of the tumor-draining lymph -node (TDLN) represents a standard method to identify metastasis for several malignancies. Interestingly, recent preclinical studies indicate that TDLN resection diminishes the efficacy of immune checkpoint inhibitor-based cancer immunotherapies. Thus, accurate preclinical identification of TDLNs is pivotal to uncovering the underlying immunological mechanisms. Therefore, we validated preclinically, and clinically available non-invasive in vivo imaging approaches for precise TDLN identification.
For visualization of the lymphatic drainage into the TDLNs by non-invasive in vivo optical imaging, we injected the optical imaging contrast agents Patent Blue V (582.7 g mol) and IRDye® 800CW polyethylene glycol (PEG; 25,000-60,000 g mol), subcutaneously (s.c.) in close proximity to MC38 adenocarcinomas at the right flank of experimental mice. For determination of the lymphatic drainage and the glucose metabolism in TDLNs by non-invasive in vivo PET/magnetic resonance imaging (PET/MRI), we injected the positron emission tomography (PET) tracer (2-deoxy-2[F]fluoro-D-glucose (F-FDG) [181.1 g mol]) in a similar manner. For ex vivo cross-correlation, we isolated TDLNs and contralateral nontumor-draining lymph nodes (NTDLNs) and performed optical imaging, biodistribution, and autoradiography analysis.
The clinically well-established Patent Blue V was superior for intraoperative macroscopic identification of the TDLNs compared with IRDye® 800CW PEG but was not sensitive enough for non-invasive in vivo detection by optical imaging. Ex vivo Patent Blue V biodistribution analysis clearly identified the right accessory axillary and the proper axillary lymph node (LN) as TDLNs, whereas ex vivo IRDye® 800CW PEG completely failed. In contrast, functional non-invasive in vivo F-FDG PET/MRI identified a significantly elevated uptake exclusively within the ipsilateral accessory axillary TDLN of experimental mice and was able to differentiate between the accessory axillary and the proper LN. Ex vivo biodistribution and autoradiography confirmed our in vivo F-FDG PET/MRI results.
When taken together, our results demonstrate the feasibility of F-FDG-PET/MRI as a valid method for non-invasive in vivo, intraoperative, and ex vivo identification of the lymphatic drainage and glucose metabolism within the TDLNs. In addition, using Patent Blue V provides additive value for the macroscopic localization of the lymphatic drainage both visually and by ex vivo optical imaging analysis. Thus, both methods are valuable, easy to implement, and cost-effective for preclinical identification of the TDLN.
切除肿瘤引流淋巴结（TDLN）是识别多种恶性肿瘤转移的标准方法。有趣的是，最近的临床前研究表明，TDLN 切除会降低基于免疫检查点抑制剂的癌症免疫疗法的疗效。因此，准确的临床前 TDLN 识别对于揭示潜在的免疫机制至关重要。因此，我们通过临床前和临床可用的非侵入性体内成像方法对 TDLN 进行了验证。
为了通过非侵入性体内光学成像可视化淋巴引流到 TDLN，我们将光学成像对比剂专利蓝 V（582.7 g/mol）和 IRDye® 800CW 聚乙二醇（PEG；25,000-60,000 g/mol）注射到实验小鼠右侧腹的 MC38 腺癌附近的皮下（s.c.）。为了通过非侵入性体内正电子发射断层扫描/磁共振成像（PET/MRI）确定 TDLN 的淋巴引流和葡萄糖代谢，我们以类似的方式注射正电子发射断层扫描（PET）示踪剂（2-脱氧-2[F]氟-D-葡萄糖（F-FDG）[181.1 g/mol]）。为了进行离体交叉相关，我们分离 TDLN 和对侧非肿瘤引流淋巴结（NTDLN），并进行光学成像、生物分布和放射自显影分析。
临床应用广泛的专利蓝 V 在 TDLN 的术中宏观识别方面优于 IRDye® 800CW PEG，但在光学成像的非侵入性体内检测方面不够敏感。离体专利蓝 V 生物分布分析清楚地将右副腋和固有腋淋巴结（LN）确定为 TDLN，而离体 IRDye® 800CW PEG 完全失败。相比之下，功能非侵入性体内 F-FDG PET/MRI 仅在实验小鼠的同侧副腋 TDLN 中识别到明显升高的摄取，并能够区分副腋和固有 LN。离体生物分布和放射自显影证实了我们体内 F-FDG PET/MRI 的结果。
综上所述，我们的结果证明了 F-FDG-PET/MRI 作为一种用于 TDLN 内淋巴引流和葡萄糖代谢的非侵入性体内、术中、离体识别的有效方法的可行性。此外，使用专利蓝 V 通过离体光学成像分析为淋巴引流的宏观定位提供了附加价值，无论是在视觉上还是在视觉上。因此，这两种方法对于 TDLN 的临床前识别都是有价值的、易于实施的和具有成本效益的。
