Abstract A85: Preclinical evaluation of the radiolabeled bispecific T-cell engager 89Zr-AMG 211 targeting CEA-positive tumors
Authors: Waaijer S.J.H. , Warnders F.J. , Lub-de Hooge M.N. , Stienen S. , Friedrich M. , Sternjak A. , Pieslor P.C. , Cheung K. , Terwisscha van Scheltinga A.G.T. , Schröder C.P. , de Vries E.G.E. 
Published: May 2016

Abstract
Background: AMG 211 is a novel, bispecific single-chain antibody of the bispecific T-cell engager (BiTE® antibody construct) class. AMG 211 targets carcinoembryonic antigen (CEA) on tumor cells and the CD3 epsilon subunit of the human T-cell receptor complex on T-cells. CEA is a glycosylated human oncofetal antigen and is abundantly expressed by a variety of tumors; especially those in the gastrointestinal tract. We radiolabeled AMG 211 with zirconium-89 (89Zr) to study the tumor targeting and tissue distribution of AMG 211 in preclinical mouse tumor xenograft models.
Material and Methods: AMG 211 was conjugated with desferal for 89Zr labeling and quality control was performed. A tracer amount of 10 μg (5 MBq) 89Zr-AMG 211 was administered to mice bearing subcutaneously-implanted CEA-expressing LS174T human colorectal adenocarcinoma. MicroPET imaging was performed at 0.5, 3, 6, 24, 48 and 72 h after tracer injection. A dose-escalation biodistribution study was performed 6 h after injection of 2, 10, 50, 100 or 500 μg 89Zr-AMG 211. 89Zr-AMG 211 was also evaluated in a CEA-negative HL60 promyelocytic leukemia xenograft. Furthermore, the non-CEA-binding BiTE® antibody construct, MEC 14, served as a negative control in LS174T tumors. Ex vivo gel electrophoresis and autoradiography was used to determine 89Zr-AMG 211 integrity in plasma and tumor lysate.
Results: In vitro analysis of desferal-conjugated AMG 211 showed similar CEA binding as unlabeled AMG 211. Radiochemical purity of 89Zr-AMG 211 exceeded 95%, with a maximum specific activity of 500 MBq/mg. Size-exclusion high-performance liquid chromatography showed no degradation products and less than 5% of aggregates. MicroPET imaging revealed time-dependent tumor uptake of 89Zr-AMG 211 in LS174T bearing mice with the highest uptake 3 h after injection and a prolonged imageable tumor retention up to 48 h. 89Zr-AMG 211 rapidly decreased in blood (T1/2 = 1 h). Dose-escalation showed a dose-dependent tumor uptake 6 hours after injection with the highest tumor uptake observed with 2 μg (7.5 ± 1.5%ID/g) and the lowest tumor uptake with 500 μg (3.9 ± 0.1%ID/g). Mice bearing CEA-positive LS174T versus CEA-negative HL60 tumors showed higher tumor uptake (6.0 ± 1.3 vs 0.5 ± 0.1%ID/g) and tumor-to-blood ratios (21.0 ± 4.0 vs 1.6 ± 0.2) after injection of 10 μg 89Zr-AMG 211. In addition, the non-specific 89Zr-MEC 14 showed low tumor (0.5 ± 0.2%ID/g) uptake and tumor-to-blood ratio (5.5 ± 2.1) that is similar to tissue background in the LS174T model. Ex vivo autoradiography showed intact 89Zr-AMG 211 in all plasma samples. Moreover, in line with biodistribution data, intact 89Zr-AMG 211 was present only in the LS174T xenograft lysates and not detected in HL60 lysate. 89Zr-MEC14 did not bind CEA and was not detected in LS174T lysates.
Conclusions: This study showed dose-dependent CEA-specific targeting of 89Zr-AMG 211. In addition, intact labeled AMG 211 was present in plasma and LS174T tumor lysates indicating in vivo tracer integrity. Our data support the use of 89Zr-ImmunoPET in the clinical setting to assess the distribution and tumor-targeting properties of AMG 211 and BiTE® antibody constructs.
Citation Format: S.J.H. Waaijer, F.J. Warnders, M.N. Lub-de Hooge, S. Stienen, M. Friedrich, A. Sternjak, P.C. Pieslor, K. Cheung, A.G.T. Terwisscha van Scheltinga, C.P. Schröder, E.G.E. de Vries. Preclinical evaluation of the radiolabeled bispecific T-cell engager 89Zr-AMG 211 targeting CEA-positive tumors. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr A85.