Purpose

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 ¹⁸F-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.

Procedures

scVR1 was ¹⁸F-labeled via a biorthogonal click reaction between site-specifically trans-cyclooctene functionalized scVR1 and an Al¹⁸F labeled tetrazine-NODA (1,4,7-triazacyclononane-1,4-diiacetic acid). The [¹⁸F]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 [¹⁸F]AlF-NODA-scVR1 tracer was administered via tail vein injection; PET imaging and ex vivo analysis was performed 2 h post-injection.

Results

The [¹⁸F]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 [¹⁸F]AlF-NODA-scVR1 tracer showing colocalization with bioluminescent imaging as well as ex vivo autoradiography and immunofluorescent staining of VEGFR-1.

Conclusions

The diagnostic capabilities of the [¹⁸F]AlF-NODA-scVR1 PET tracer was confirmed in both orthotopic and metastatic murine cancer models. These results support the potential use of [¹⁸F]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.

中文翻译：

---

使用 18 F 标记的 VEGFR-1 特异性单链 VEGF 突变体对早期转移灶进行成像

目的

转移性乳腺癌是女性癌症相关死亡的第二大原因。十多年来，转移性乳腺癌的 5 年生存率一直保持在 26.9% 附近。血管内皮生长因子受体 1 (VEGFR-1) 高表达的造血干细胞的募集与转移形成的早期阶段有关。我们建议使用¹⁸ F 标记的 VEGF121 单链版本，重新设计为对 VEGFR-1 (scVR1) 具有选择性，作为正电子发射断层扫描 (PET) 成像剂对早期转移进行非侵入性成像.

程序

scVR1通过位点特异性反式-环辛烯功能化的 scVR1 和 Al ¹⁸ F标记的四嗪-NODA（1,4,7-三氮杂环壬烷-1,4-二乙酸）之间的双正交点击反应进行^{18 F 标记。}[ ¹⁸ F]AlF-NODA-scVR1 使用 PD10 柱纯化，随后在 HPLC 上分析以确定放射化学纯度。在携带原位原发性 4T1 乳腺肿瘤或 4T1 转移性病变的 6-8 周龄雌性 BALB/c 小鼠中进行动物实验。[ ¹⁸ F]AlF-NODA-scVR1示踪剂通过尾静脉注射给药；PET 成像和离体分析在注射后 2 小时进行。

结果

[ ¹⁸ F]AlF-NODA-scVR1 的放射化学纯度为 98.2 ± 1.5 %，表观摩尔活性为 7.5 ± 1.2 GBq/μmol。scVR1 与 VEGFR-1 的特异性结合通过基于珠的测定得到证实。离体生物分布显示肿瘤摄取为 3.5 ± 0.5 % ID/g，并且在 PET 图像中很容易观察到。用[ ¹⁸ F]AlF-NODA-scVR1 示踪剂检测到转移形成，该示踪剂显示与生物发光成像以及体外放射自显影和VEGFR-1的免疫荧光染色的共定位。

结论

^{[ 18} F]AlF-NODA-scVR1 PET 示踪剂的诊断能力在原位和转移性小鼠癌症模型中都得到了证实。这些结果支持 [ ¹⁸ F]AlF-NODA-scVR1 作为可以对转移灶成像的 PET 示踪剂的潜在用途，为临床医生提供了一种额外的工具来评估患者对辅助治疗的需求。