Department of Radiology, Memorial Sloan Kettering Cancer Center, New York, NY, 10065, USA.
Department of Otorhinolaryngology and Head and Neck Surgery, Federal University of São Paulo, São Paulo, SP, 04023-062, Brazil.
Mol Imaging Biol. 2021 Jun;23(3):340-349. doi: 10.1007/s11307-020-01555-z. Epub 2020 Nov 6.
Metastatic breast cancer is the second leading cause of cancer-related death in women. The 5-year survival rate for metastatic breast cancer has remained near 26.9 % for over a decade. The recruitment of hematopoietic stem cells with high expression of the vascular endothelial growth factor receptor 1 (VEGFR-1) has been implicated in early stages of metastasis formation. We propose the use of an F-labeled single-chain version of VEGF121, re-engineered to be selective for VEGFR-1 (scVR1), as a positron emission tomography (PET) imaging agent to non-invasively image early-stage metastases.
scVR1 was F-labeled via a biorthogonal click reaction between site-specifically trans-cyclooctene functionalized scVR1 and an AlF labeled tetrazine-NODA (1,4,7-triazacyclononane-1,4-diiacetic acid). The [F]AlF-NODA-scVR1 was purified using a PD10 column and subsequently analyzed on HPLC to determine radiochemical purity. Animal experiments were performed in 6-8-week-old female BALB/c mice bearing orthotopic primary 4T1 breast tumors or 4T1 metastatic lesions. The [F]AlF-NODA-scVR1 tracer was administered via tail vein injection; PET imaging and ex vivo analysis was performed 2 h post-injection.
The [F]AlF-NODA-scVR1 was prepared with a 98.2 ± 1.5 % radiochemical purity and an apparent molar activity of 7.5 ± 1.2 GBq/μmol. The specific binding of scVR1 to VEGFR-1 was confirmed via bead-based assay. The ex vivo biodistribution showed tumor uptake of 3.5 ± 0.5 % ID/g and was readily observable in PET images. Metastasis formation was detected with [F]AlF-NODA-scVR1 tracer showing colocalization with bioluminescent imaging as well as ex vivo autoradiography and immunofluorescent staining of VEGFR-1.
The diagnostic capabilities of the [F]AlF-NODA-scVR1 PET tracer was confirmed in both orthotopic and metastatic murine cancer models. These results support the potential use of [F]AlF-NODA-scVR1 as a PET tracer that could image metastases, providing clinicians with an additional tool to assess a patient's need for adjuvant therapies.
转移性乳腺癌是女性癌症相关死亡的第二大主要原因。超过十年以来，转移性乳腺癌的 5 年生存率一直保持在 26.9%左右。在转移形成的早期阶段，高表达血管内皮生长因子受体 1（VEGFR-1）的造血干细胞的募集被牵连其中。我们建议使用经过工程改造的、对 VEGFR-1 具有选择性的 F 标记的单链 VEGF121（scVR1）作为正电子发射断层扫描（PET）成像剂，以非侵入性地对早期转移进行成像。
通过特异性反式环辛烯功能化的 scVR1 与 AlF 标记的四嗪-NODA（1,4,7-三氮杂环壬烷-1,4-二乙酸）之间的生物正交点击反应对 scVR1 进行 F 标记。使用 PD10 柱对[F]AlF-NODA-scVR1 进行纯化，然后在 HPLC 上进行分析以确定放射化学纯度。在 6-8 周龄的雌性 BALB/c 小鼠中进行动物实验，这些小鼠患有原位原发性 4T1 乳腺癌或 4T1 转移性病变。通过尾静脉注射给予[F]AlF-NODA-scVR1 示踪剂，在注射后 2 小时进行 PET 成像和离体分析。
[F]AlF-NODA-scVR1 的放射化学纯度为 98.2±1.5%，表观摩尔活度为 7.5±1.2GBq/μmol。通过基于珠的测定证实了 scVR1 与 VEGFR-1 的特异性结合。离体生物分布显示肿瘤摄取率为 3.5±0.5%ID/g，在 PET 图像中可轻易观察到。使用[F]AlF-NODA-scVR1 示踪剂检测到转移形成，其与生物发光成像以及离体放射自显影和 VEGFR-1 的免疫荧光染色均具有很好的共定位。
在原位和转移性小鼠癌症模型中均证实了[F]AlF-NODA-scVR1 PET 示踪剂的诊断能力。这些结果支持使用[F]AlF-NODA-scVR1 作为 PET 示踪剂来对转移进行成像，为临床医生提供了一种评估患者辅助治疗需求的额外工具。
