LAUSR

BACKGROUND: ERY974, a modified monoclonal IgG4 bispecific antibody directed against human CD3 on T cells and glypican 3 (GPC3) on tumor cell, is currently in phase I clinical trial. The oncofetal protein GPC3 is overexpressed in several tumor types. Radiolabeling ERY974 with positron emission tomography (PET) isotope zirconium-89 (89Zr) enables non-invasive molecular imaging of tumor targeting and whole-body distribution. We aimed to evaluate 89Zr-ERY974 tumor targeting and effect of T cells on tumor uptake in mouse models, including a humanized mouse model. METHODS: ERY974 and two control molecules namely bispecific CD3xkeyhole limpet hemocyanin (KLH) and KLHxKLH antibodies were radiolabeled with 89Zr. Studies were performed in immunodeficient NOD/Shi-SCID/IL-2Rgnull (NOG) as well as human CD34+ hematopoietic stem cell engrafted NOG mice (huNOG), all subcutaneously inoculated with GPC3 overexpressing human hepatocellular carcinoma HepG2 cells. Mice received 10 µg 89Zr-ERY974, 89Zr-CD3xKLH or 89Zr-KLHxKLH intravenously, with subsequent µPET scanning at 24, 72, 120 and 168 h followed by ex vivo biodistribution. Organs of interest were quantified on µPET scans as mean standardized uptake value (SUVmean) and with ex vivo biodistribution as % injected dose/gram of tissue (%ID/g). Tumor, spleen and lymph nodes were analyzed with autoradiography and immunohistochemical CD3 staining. RESULTS: µPET imaging revealed increased tumor-to-blood ratio (TBR) of 89Zr-ERY974 in NOG over time with maximal TBR of 2.2±0.3 at 168 h post tracer injection (pi). At 168 h, tumor uptake was specific as 89Zr-CD3xKLH and 89Zr-KLHxKLH showed a TBR of only 0.6±0.2 and 0.8±0.3, respectively. In huNOG mice human CD3+ T cells were present in tumor, spleen and lymph nodes. In huNOG mice tumor uptake of 89Zr-ERY974 was higher than in NOG mice as measured on µPET scans (SUVmean at 168 h pi 6.9±2.6 vs 2.9±0.2; P CONCLUSION: 89Zr-ERY974 demonstrates specific tumor uptake in NOG and huNOG mice, while in huNOG mice tumor uptake colocalized with T cell rich infiltrate and also uptake in in spleen and lymph nodes was observed. Citation Format: Stijn J. Waaijer, Danique Giesen, Takahiro Ishiguro, Yuji Sano, Norihisa Ohishi, Athos Gianella-Borradori, Carolien P. Schroder, Elisabeth G. de Vries, Marjolijn N. Lub-de Hooge. PET imaging with the bispecific 89Zr-antibody ERY974 targeting CD3 and glypican 3 in tumor-bearing mouse models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3028.