Medical Isotopes Research Center and Department of Radiation Medicine, School of Basic Medical Sciences, Peking University, Beijing, 100191, China.
Key Laboratory of Carcinogenesis and Translational Research (Ministry of Education/Beijing), Department of Nuclear Medicine, Peking University Cancer Hospital & Institute, Beijing 100142, China.
Theranostics. 2022 Jul 18;12(12):5551-5563. doi: 10.7150/thno.74154. eCollection 2022.
The decreased HER2-accessibility by epitope masking is a primary trastuzumab-resistance mechanism. In this study, we developed a HER2-targeted dual radiotracer approach to predict the HER2-trastuzumab engagement noninvasively. Two novel HER2-specific VHHs, MIRC208 and MIRC213, were acquired by immunizing alpaca with human HER2 protein, and were site-specifically labeled with Tc. Biodistribution and SPECT/CT imaging studies were performed in mice bearing HER2-positive and HER2-negative tumors. The HER2 binding sites of Tc-MIRC208 and Tc-MIRC213 were investigated by cell binding and SPECT/CT imaging studies. We evaluated the therapeutic predictive ability of our dual-radiotracer imaging approach for trastuzumab treatment in mice bearing MUC4-positive tumors (trastuzumab-resistant JIMT-1 and 87MUC4) and MUC4-negative tumors (trastuzumab-sensitive 7HER2 and NCI-N87). The preliminary clinical studies of Tc-MIRC208 were performed in two patients with HER2-positive breast tumors. Tc-MIRC208 and Tc-MIRC213 clearly visualized HER2-positive tumors, but not HER2-negative tumors. Tc-MIRC208 competes with trastuzumab for HER2-binding while Tc-MIRC213 recognizes HER2 on an epitope that is not masked by MUC4. The SPECT/CT studies with Tc-MIRC208 and Tc-MIRC213 clearly showed that the MUC4-negative and trastuzumab-sensitive 7HER2 and NCI-N87 tumors had very similar tumor uptake with the SUV/SUV (2 h) ratios of 1.11 ± 0.17 in 7HER2 and 1.25 ± 0.22 in NCI-N87. However, the MUC4-positive JIMT-1 tumors showed the decreased SUV/SUV (2 h) ratio (0.63 ± 0.07), which correlated well with the low response rate to trastuzumab therapy. The SUV/SUV (2 h) ratio was reduced to 0.72 ± 0.02 in MUC4-expressing NCI-N87 cells, and resulting in the decreased trastuzumab sensitivity, further supporting the correlation between the SUV/SUV (2 h) ratio and trastuzumab-sensitivity. The primary and metastatic HER2-positive lesions of patients were clearly visualized by Tc-MIRC208 SPECT at 2 h post injection. Overall, we demonstrated that the dual radiotracer imaging strategy is a valid noninvasive approach for the cancer patient selection before trastuzumab therapy. Tc-MIRC213 SPECT is utilized to quantify the tumor HER2 expression and screen HER2-positive cancer patients, while Tc-MIRC208 SPECT is used to determine the HER2-accessibility of trastuzumab. The SUV/SUV (2 h) ratio is an important biomarker to determine the responsiveness of trastuzumab therapy.
HER2 表位掩蔽导致 HER2 可及性降低是曲妥珠单抗耐药的主要机制。本研究开发了一种 HER2 靶向的双放射性示踪剂方法，旨在无创性预测 HER2-曲妥珠单抗的结合。我们通过用人类 HER2 蛋白免疫羊驼获得了两种新型的 HER2 特异性 VHH，MIRC208 和 MIRC213，并通过放射性核素标记 Tc。在携带 HER2 阳性和 HER2 阴性肿瘤的小鼠中进行了生物分布和 SPECT/CT 成像研究。通过细胞结合和 SPECT/CT 成像研究研究了 Tc-MIRC208 和 Tc-MIRC213 的 HER2 结合位点。我们评估了我们的双放射性示踪剂成像方法在携带 MUC4 阳性肿瘤（曲妥珠单抗耐药 JIMT-1 和 87MUC4）和 MUC4 阴性肿瘤（曲妥珠单抗敏感 7HER2 和 NCI-N87）的小鼠中对曲妥珠单抗治疗的治疗预测能力。在两名 HER2 阳性乳腺癌患者中进行了 Tc-MIRC208 的初步临床研究。Tc-MIRC208 和 Tc-MIRC213 可清晰显示 HER2 阳性肿瘤，但不能显示 HER2 阴性肿瘤。Tc-MIRC208 与曲妥珠单抗竞争 HER2 结合，而 Tc-MIRC213 识别的 HER2 表位不受 MUC4 掩蔽。Tc-MIRC208 和 Tc-MIRC213 的 SPECT/CT 研究清楚地表明，MUC4 阴性和曲妥珠单抗敏感的 7HER2 和 NCI-N87 肿瘤具有非常相似的肿瘤摄取，SUV/SUV（2 h）比值在 7HER2 中为 1.11±0.17，在 NCI-N87 中为 1.25±0.22。然而，MUC4 阳性的 JIMT-1 肿瘤显示出降低的 SUV/SUV（2 h）比值（0.63±0.07），这与曲妥珠单抗治疗的低反应率密切相关。在表达 MUC4 的 NCI-N87 细胞中，SUV/SUV（2 h）比值降低至 0.72±0.02，导致曲妥珠单抗敏感性降低，进一步支持 SUV/SUV（2 h）比值与曲妥珠单抗敏感性之间的相关性。Tc-MIRC208 SPECT 在注射后 2 小时即可清晰显示患者的原发性和转移性 HER2 阳性病变。总之，我们证明了双放射性示踪剂成像策略是一种有效的无创方法，可以在曲妥珠单抗治疗前对癌症患者进行选择。Tc-MIRC213 SPECT 用于定量肿瘤 HER2 表达并筛选 HER2 阳性癌症患者，而 Tc-MIRC208 SPECT 用于确定曲妥珠单抗的 HER2 可及性。SUV/SUV（2 h）比值是确定曲妥珠单抗治疗反应的重要生物标志物。
