Department of Immunology, Genetics and Pathology, Uppsala University, SE 75185 Uppsala, Sweden.
Molecular Immunology Laboratory, Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, 117997 Moscow, Russia.
Int J Oncol. 2019 Apr;54(4):1209-1220. doi: 10.3892/ijo.2019.4712. Epub 2019 Feb 11.
Evaluation of human epidermal growth factor receptor 2 (HER2) expression levels in breast and gastroesophageal cancer is used for the stratification of patients for HER2‑targeting therapies. The use of radionuclide molecular imaging may facilitate such evaluation in a non‑invasive way. Designed ankyrin repeat proteins (DARPins) are engineered scaffold proteins with high potential as probes for radionuclide molecular imaging. DARPin G3 binds with high affinity to HER2 and may be used to visualize this important therapeutic target. Studies on other engineered scaffold proteins have demonstrated that selection of the optimal labeling approach improves the sensitivity and specificity of radionuclide imaging. The present study compared two methods of labeling G3, direct and indirect radioiodination, to select an approach providing the best imaging contrast. G3‑H6 was labeled with iodine‑124, iodine‑125 and iodine‑131 using a direct method. A novel construct bearing a C‑terminal cysteine, G3‑GGGC, was site‑specifically labeled using [125I]I‑iodo‑[(4‑hydroxyphenyl)ethyl]maleimide (HPEM). The two radiolabeled G3 variants preserved binding specificity and high affinity to HER2‑expressing cells. The specificity of tumor targeting in vivo was demonstrated. Biodistribution comparison of [131I]I‑G3‑H6 and [125I]I‑HPEM‑G3‑GGGC in mice, bearing HER2‑expressing SKOV3 xenografts, demonstrated an appreciable contribution of hepatobiliary excretion to the clearance of [125I]I‑HPEM‑G3‑GGGC and a decreased tumor uptake compared to [131I]I‑G3‑H6. The direct label provided higher tumor‑to‑blood and tumor‑to‑organ ratios compared with the indirect label at 4 h post‑injection. The feasibility of high contrast PET/CT imaging of HER2 expression in SKOV3 xenografts in mice using [124I]I‑G3‑H6 was demonstrated. In conclusion, direct radioiodination is the preferable approach for labeling DARPin G3 with iodine‑123 and iodine‑124 for clinical single photon emission computed tomography and positron emission tomography imaging.
人表皮生长因子受体 2（HER2）表达水平的评估用于乳腺癌和胃食管交界癌患者的分层，以进行 HER2 靶向治疗。放射性核素分子成像的应用可以以非侵入性的方式促进这种评估。设计的锚蛋白重复蛋白（DARPin）是具有高潜力的工程支架蛋白，可用作放射性核素分子成像的探针。DARPin G3 与 HER2 具有高亲和力，可用于可视化这一重要的治疗靶点。对其他工程支架蛋白的研究表明，选择最佳的标记方法可提高放射性核素成像的灵敏度和特异性。本研究比较了直接和间接放射性碘标记 G3 的两种方法，以选择提供最佳成像对比度的方法。使用直接法用碘-124、碘-125 和碘-131 标记 G3-H6。一种带有 C 末端半胱氨酸的新型构建体 G3-GGGG，通过[125I]I-碘-[(4-羟基苯基)乙基]马来酰亚胺（HPEM）进行了定点标记。两种放射性标记的 G3 变体保留了与 HER2 表达细胞的结合特异性和高亲和力。体内肿瘤靶向的特异性得到了证明。在携带 HER2 表达 SKOV3 异种移植物的小鼠中比较[131I]I-G3-H6 和[125I]I-HPEM-G3-GGGG 的生物分布，结果表明，肝胆排泄对[125I]I-HPEM-G3-GGGG 的清除有明显贡献，与[131I]I-G3-H6 相比，肿瘤摄取减少。与间接标记物相比，直接标记物在注射后 4 小时提供了更高的肿瘤与血液和肿瘤与器官的比值。使用[124I]I-G3-H6 证明了在小鼠 SKOV3 异种移植瘤中进行高对比度 PET/CT 成像 HER2 表达的可行性。总之，对于用碘-123 和碘-124 进行临床单光子发射计算机断层扫描和正电子发射断层扫描成像，直接放射性碘标记是标记 DARPin G3 的首选方法。
