Molecular Imaging of Radiolabeled Bispecific T-cell Engager 89Zr-AMG211 Targeting CEA-positive Tumors

Background: 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 (89Zr) or fluorescent dye to evaluate the tumor targeting properties. Experimental Design: 89Zr-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 2-10 µg 89Zr-AMG211 supplemented with unlabeled AMG 211 up to 500 µg protein dose were performed. A BiTE® that does not bind CEA, 89Zr-Mec14, served as a negative control. 89Zr-AMG211 integrity was determined in tumor lysates ex vivo. Intratumoral distribution was studied with IRDye800CW-AMG211. Moreover, 89Zr-AMG211 was manufactured according to Good Manufacturing Practice (GMP) guidelines for clinical trial NCT02760199. Results: 89Zr-AMG211 demonstrated dose-dependent tumor uptake at 6 hours. The highest tumor uptake was observed with 2 μg dose, and the lowest tumor uptake was observed with 500 μg dose. After 24 hours, higher uptake of 10 μg 89Zr-AMG211 occurred in CEA-positive xenografts, compared to CEA-negative xenografts. Although the blood half-life of 89Zr-AMG211 was ~1 hour, tumor retention persisted for at least 24 hours. 89Zr-Mec14 showed no tumor accumulation beyond background level. Ex vivo autoradiography revealed time-dependent disintegration of 89Zr-AMG211. 800CW-AMG211 was specifically localized in CEA-expressing viable tumor tissue. GMP-manufactured 89Zr-AMG211 fulfilled release specifications. Conclusions: 89Zr-AMG211 showed dose-dependent CEA-specific tumor targeting and localization in viable tumor tissue. Our data enabled its use to clinically evaluate AMG 211 in vivo behavior.

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