Three Methods for 18F Labeling of the HER2-Binding Affibody Molecule ZHER2:2891 Including Preclinical Assessment

Human epidermal growth factor receptor (HER2)‐targeted Affibody molecules radiolabeled with 18F allow the noninvasive assessment of HER2 status in vivo through PET imaging. Such agents have the potential to improve patient management by selecting individuals for HER2-targeted therapies and allowing therapy monitoring. The aim of this study was to assess different 18 F radiolabeling strategies of the HER2-specific Affibody molecule ZHER2:2891, preclinically determine the biologic efficacy of the different radiolabel molecules, and select a preferred radiolabeling strategy to progress for automated manufacture. Methods: Cysteine was added to the C terminus of the Affibody molecule for the coupling of maleimide linkers, and 3 radiolabeling strategies were assessed: silicon-fluoride acceptor approach ( 18 F-SiFA), 18 F-AlF-NOTA, and 4- 18 F-fluorobenzaldehyde ( 18 F-FBA). The biodistributions of the radiolabeled Affibody molecules were then determined in naive CD-1 nude mice, and tumor targeting was assessed in CD-1 nude mice bearing high-HER2-expressing NCIN87 tumors and low-HER2-expressing A431 tumors. The 111 InABY-025 compound, which has demonstrable clinical utility, served as a reference tracer. Results: The non‐decay-corrected radiochemical yields based on starting 18 F-fluoride using the 18 F-FBA, 18 FSiFA, and 18F-AlF-NOTA methods were 13% 6 3% (n 5 5), 38% 6 2% (n 5 3), and 11% 6 4% (n 5 6), respectively. In naive mice, both the 18F-AlF-NOTA-ZHER2:2891 and the 111In-ABY-025 compounds