68 Ga-Labeled Dimeric Cyclic Peptide for Nectin-4–Targeted PET Imaging: From Preclinical Evaluation to First-in-Human Imaging in Breast Cancer

Nectin-4 is an attractive target for molecular imaging and targeted therapy because of its overexpression in multiple malignancies. We developed a nectin cell adhesion molecule 4 (nectin-4)–targeted 68Ga-labeled dimeric cyclic peptide PET tracer, [68Ga]Ga-TDN1, for noninvasive imaging of nectin-4 expression. Methods: TDN1 was generated by click chemistry to conjugate 2 nectin-4–binding bicyclic peptides and was radiolabeled with 68Ga. Binding affinity was assessed by surface plasmon resonance. Target specificity and tumor-targeting ability were evaluated by cell uptake, blocking, small-animal PET/CT, and biodistribution studies in nectin-4–positive and nectin-4–negative tumor models. [68Ga]Ga-TDN1 was further compared with [68Ga]Ga-N188 in preclinical models. After preclinical evaluation, [68Ga]Ga-TDN1 PET/CT was investigated in a pilot first-in-human study in 6 patients with breast cancer and directly compared with [18F]FDG PET/CT. Results: TDN1 showed high affinity for nectin-4 (KD = 1.92 × 10−10 M). In preclinical studies, [68Ga]Ga-TDN1 showed specific uptake in nectin-4–positive cells and tumors, low uptake in nectin-4–negative models, and marked reduction in uptake under blocking conditions. Compared with [68Ga]Ga-N188, [68Ga]Ga-TDN1 showed higher tumor uptake and longer retention across multiple nectin-4–positive xenografts. In the pilot clinical study, [68Ga]Ga-TDN1 was well-tolerated and showed favorable biodistribution and dosimetry. [68Ga]Ga-TDN1 PET/CT revealed imaging performance comparable to that of [18F]FDG PET/CT for primary tumors and most nodal metastases and demonstrated higher uptake and improved lesion detection in bone and liver metastases in selected patients. [68Ga]Ga-TDN1 was a clinically translatable nectin-4–targeted PET tracer with high affinity, favorable pharmacokinetics, and specific tumor uptake. Preclinical and pilot clinical results supported further clinical evaluation of [68Ga]Ga-TDN1 for noninvasive imaging of nectin-4 expression, particularly for assessment of metastatic disease.