First-in-human Study of a 99mTc-Labeled Single-Domain Antibody for SPECT/CT Assessment of HER2 Expression in Breast Cancer

Background: Accurate determination of human epidermal growth factor receptor 2 (HER2) expression is essential for HER2-targeted therapy. HER2 expression in a complex environment, such as in a heterogenous tumor, makes precise assessment difficult using current methods. Therefore, we developed a novel 99mTc-labeled anti-HER2-single domain antibody (99mTc-NM-02) as a molecular imaging tracer for non-invasive detection of HER2 expression and investigated its safety, radiation dosimetry, biodistribution, and tumor-targeting potential in breast cancer patients.Methods: A lead compound (NM-02) was screened from a library of hexahistidine-tagged anti-HER2-single domain antibodies and labeled with 99mTc for the preparation of 99mTc-NM-02 tracer. Ten women with breast cancer were administered 99mTc-NM-02 at a mean dose of 458 ± 37 MBq (406−510 MBq), corresponding to 100 μg of NM-02. Whole-body and local SPECT/CT images were acquired at 1 and 2 h post-administration to investigate the tumor-targeting potential in primary and metastatic lesions. Additional images were acquired at 10 min, 3 h, and 24 h in three patients to calculate radiation dosimetry. Physical evaluation and blood analysis were performed for safety assessment.Results: No drug-related adverse reactions occurred. The tracer mainly accumulated in the kidneys and liver with mild uptake in the spleen, intestines, and thyroid, but only background levels were observed in other organs where primary tumors and metastases typically occurred. The mean effective dose was 6.56 × 10−3 mSv/MBq, and tracer uptake was visually observed in primary tumors and metastases. Owing to the fast clearance of the tracer, we were able to sufficiently discern uptake over normal background in both primary lesions and metastases within 2 h after injection. A maximal standard uptake value of 1.5 could be a reasonable cutoff for determining HER2 positivity using SPECT/CT imaging.Conclusions: Our 99mTc-NM-02 tracer can be safely used for imaging in breast cancer patients with reasonable radiation doses, favorable biodistribution and imaging characteristics. 99mTc-NM-02 SPECT imaging may provide an accurate and non-invasive method to detect HER2 status in breast cancer patients.Trial registration: ClinicalTrials.gov, NCT04040686. Registered 30 July 2019. https://clinicaltrials.gov/ct2/show/NCT04040686.