Abstract
Objectives: The hepatocyte growth factor (HGF) binding antibody rilotumumab (AMG102) was modified for use as an 89Zr-based immuno-PET (positron emission tomography) imaging agent to non-invasively determine the local levels of HGF protein in tumors. As recent clinical trials of HGF targeting therapies have been largely unsuccessful in several different cancers (e.g., gastric, brain, lung), we have synthesized and validated 89Zr-DFO-AMG102 as a companion diagnostic for improved identification and selection of patients having high local levels of HGF in tumors. To date, patient selection has not been performed using the local levels of HGF protein in tumors. Methods: The chelator p-SCN-Bn-DFO was conjugated to AMG102, radiolabeling with 89Zr was performed in high radiochemical yields and purity (>99%), and binding affinity of the modified antibody was confirmed using an enzyme-linked immunosorbent assay (ELISA) type binding assay. PET imaging, biodistribution, autoradiography and immunohistochemistry, and ex vivo HGF-ELISA experiments were performed in murine xenografts of U87MG (HGF positive (+), MET positive (+)), MKN45 (HGF negative (-), MET +), and 4 patient-derived xenografts (PDX, MET+, HGF unknown). Results: Tumor uptake of 89Zr-DFO-AMG102 at 120 h p.i. in U87MG xenografts (HGF+) was high (36.8 ± 7.8 % injected dose per gram (ID/g)), while uptake in MKN45 xenografts (HGF-) was 5.0 ± 1.3 %ID/g, and a control of non-specific human IgG 89Zr-DFO-IgG in U87MG tumors was 11.5 ± 3.3 %ID/g, demonstrating selective uptake in HGF+ tumors. Similar experiments performed in 4 different gastric cancer PDX models showed low uptake of 89Zr-DFO-AMG102 (~4-7 %ID/g), which corresponded with low HGF levels in these tumors (ex vivo ELISA). Autoradiography, immunohistochemical staining, and HGF-ELISA assays confirmed that elevated levels of HGF protein were only present in U87MG tumors, and that 89Zr-DFO-AMG102 uptake was closely correlated with HGF protein levels in tumors. Conclusions: The new immuno-PET imaging agent 89Zr-DFO-AMG102 was successfully synthesized, radiolabeled, and validated in vitro and in vivo to selectively accumulate in tumors with high local levels of HGF protein. These results suggest that 89Zr-DFO-AMG102 would be a valuable companion diagnostic tool for the non-invasive selection of patients with elevated local concentrations of HGF in tumors for planning any HGF-targeted therapy, with the potential to improve clinical outcomes.
- Copyright © 2017 by the Society of Nuclear Medicine and Molecular Imaging, Inc.