[18F]BF3标记的右旋糖苷类多模态分子影像探针的构建及在乳腺癌前哨淋巴结精准成像中的应用研究

Sentinel lymph node (SLN) plays an important role in draining metastatic cancer cells from primary tumor. In the clinical cases of breast cancer, identification or mapping of SLN is now an indispensable procedure for SLN biopsy, and subsequently determining the choices of therapy protocols and the prognosis in the staging of the patient. The rapid development of the multimodal molecular imaging provides a new strategy to improve the accuracy for the SLN mapping and precise resection during the surgery. Of the various imaging modalities, both positron emission tomography (PET) imaging and near-infrared fluorescent (NIRF) imaging are increasingly used in clinical applications. NIRF imaging has several advantages such as, high photon penetration and visualization for fluorescent-guided surgeries. As the nuclear medicine imaging, the key advantage of PET imaging is that it can provides moderate-resolution, sensitive images of the targeting radiotracer in vivo. In this research, we intend to construct a NIRF/PET multimodal molecular imaging probe for specific targeting of SLNs. The backbones of the probe in our research are based on mannosylated dextran derivatives, which is a glycoconjugated nanomolecule consisting of multiple units of mannose, attached to a 10-kDa dextran backbone. The mannose residues serve as a ligand for receptors (CD206) expressed on the surface of macrophages and dendritic cells, which are sufficiently present in tumor draining sentinel lymph nodes. Based on the presence of the mannose motif, the imaging agent will to be a progressive potential candidate for SLN specific recognition and binding. In order to construct the NIRF/PET signal component, a novel radiosynthon (18F-alkyltrifluoroborate, [18F]BF3) is designed and chemically appended to a heptamethine cyanine, a classical NIRF dyes that possess excellent optical properties and safety record. The [18F]BF3 strategy is based on 18F-19F isotope exchange (IEX) in aqueous 18F- without azeotropic drying. After designing and synthesizing the SLN targeting probes, the specificities, sensitiveness and selectiveness of radiolabeled mannosylated dextran derivatives for in vivo imaging will be examed with the NIRF/PET imaging in the model mice. In this research, the developments of this radiopharmaceutical will provide material foundation and technological support for SLNs site specific targeting and precise imaging. It will also provide a new dual-mode tracer having strong potential for bench-to-bedside translational applications.

乳腺癌前哨淋巴结（SLNs）的精准定位对乳腺腺癌患者术式及预后有着重要的临床意义。多模态显像技术为SLNs的精准成像提供了一种新思路。结合PET显像高灵敏度和NIRF成像高分辨率的优点，本项目拟构建一种靶向前哨淋巴结的NIRF/PET多模态分子影像探针。该探针分子以甘露糖化的右旋糖苷为结构骨架，甘露糖结构单元可与巨噬细胞表面甘露糖受体特异性结合，实现对SLNs的主动靶向结合；利用[18F]BF3标记方法在近红外染料的基础上构建信号组件，实现探针分子NIRF和PET信号下的双模态活体成像。在探针分子构建的基础之上，以乳腺癌荷瘤裸鼠动物模型为研究对象，依托NIRF和PET小动物活体成像技术，验证探针对SLNs双模态成像可行性，已期筛选出信号灵敏度高，显像特异性强，空间分辨率好的分子探针。该项目中分子探针的研制不仅为SLNs双模态精准成像提供物质基础，而且具有临床转化的应用潜力。

乳腺癌前哨淋巴结活检（Sentinel lymph node biopsy, SLNB）是目前临床检测乳腺癌前哨淋巴结有无转移的最准确的临床检测方法，通过对乳腺癌前哨淋巴结的病理分析来判断患者的手术方式。目前临床上常用的前哨淋巴结示踪剂主要有蓝染料和99mTc标硫胶体两大类。但在应用过程中由于特异性差，注射位点滞留时间长等诸多弊端，大大影响SLN 的定位精准度和检出率。因此，发展新型的前哨淋巴结成像技术和高特异性的分子影像探针用于乳腺癌前哨淋巴结的精准显像对乳腺癌的诊疗具有重要临床意义。. 本项目以“靶向分子影像探针的构建”这一分子影像学核心问题为切入点；以实现对SLN的快速、实时、精准定位为研究目标；以多模态分子影像技术为研究手段，发展一种基于[18F]AlF标记的NIRF探针分子用于SLN的特异性显像。发挥PET成像的灵敏度实现术前对前哨淋巴结的精准成像，同时结合NIRF成像的高组织分辨率实现对术中前哨淋巴结的准确定位。我们通过体外细胞实验，系统考察了该探针材料靶向前哨淋巴结的分子机制，发现Lymphoseek结构上甘露糖结构单元与巨噬细胞表面甘露糖受体（Mannose receptor, MR）特异性结合，实现对前哨淋巴结的主动靶向检测；建立了基于活体动态的NIRF/PET成像技术和方法，通过乳腺癌荷瘤裸鼠动物模型，实现分子探针[18F]AlF-IR790@Lymphoseek对前哨淋巴结的双模态NIRF/PET活体检测。以 [18F]AlF-IR790为双模态信号组件，不仅实现了在活体层面PET高灵敏成像功能精准定位前哨淋巴，而且在此基础上结合NIRF的荧光活体成像技术，同时实现了前哨淋巴结的快速、准确切除。. 该分子探针[18F]AlF-IR790@Lymphoseek集近红外荧光，正电子核素多模态成像于一身，构建了靶向前哨淋巴结的多模态分子探针。以小动物光学活体成像、小动物PET成像技术平台为依托，实现了对前哨淋巴结的多模态精准活体成像，为研发灵敏度高和特异性强的乳腺癌前哨淋巴结示踪剂提供了新的设计思路。该项目中分子探针的研制不仅为前哨淋巴结的精准定位提供了双模态影像学手段，而且该探针材料还具有在淋巴结清除术中实现荧光术中导航的应用潜力。