Molecular Imaging of Radiolabeled Bispecific T-Cell Engager Zr-AMG211 Targeting CEA-Positive Tumors.

AMG 211, a bispecific T-cell engager (BiTE) antibody construct, targets carcinoembryonic antigen (CEA) and the CD3 epsilon subunit of the human T-cell receptor. AMG 211 was labeled with zirconium-89 (Zr) or fluorescent dye to evaluate the tumor-targeting properties. Zr-AMG211 was administered to mice bearing CEA-positive xenograft tumors of LS174T colorectal adenocarcinoma or BT474 breast cancer cells, as well as CEA-negative HL-60 promyelocytic leukemia xenografts. Biodistribution studies with 2- to 10-μg Zr-AMG211 supplemented with unlabeled AMG 211 up to 500-μg protein dose were performed. A BiTE that does not bind CEA, Zr-Mec14, served as a negative control. Zr-AMG211 integrity was determined in tumor lysates Intratumoral distribution was studied with IRDye800CW-AMG211. Moreover, Zr-AMG211 was manufactured according to Good Manufacturing Practice (GMP) guidelines for clinical trial NCT02760199 Zr-AMG211 demonstrated dose-dependent tumor uptake at 6 hours. The highest tumor uptake was observed with a 2-μg dose, and the lowest tumor uptake was observed with a 500-μg dose. After 24 hours, higher uptake of 10-μg Zr-AMG211 occurred in CEA-positive xenografts, compared with CEA-negative xenografts. Although the blood half-life of Zr-AMG211 was approximately 1 hour, tumor retention persisted for at least 24 hours. Zr-Mec14 showed no tumor accumulation beyond background level. autoradiography revealed time-dependent disintegration of Zr-AMG211. 800CW-AMG211 was specifically localized in CEA-expressing viable tumor tissue. GMP-manufactured Zr-AMG211 fulfilled release specifications. Zr-AMG211 showed dose-dependent CEA-specific tumor targeting and localization in viable tumor tissue. Our data enabled its use to clinically evaluate AMG 211 behavior. .