⁸⁹Zr-DFO-AMG102 Immuno-PET to Determine Local Hepatocyte Growth Factor Protein Levels in Tumors for Enhanced Patient Selection

Abstract

The hepatocyte growth factor (HGF) binding antibody rilotumumab (AMG102) was modified for use as a 89 Zr-based immuno-PET imaging agent to noninvasively determine the local levels of HGF protein in tumors. Because 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 89 Zr-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 89 Zr 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 on murine xenografts of U87MG (HGF-positive, MET-positive) and MKN45 (HGF-negative, MET-positive) and 4 patient-derived xenografts (MET-positive, HGF unknown). Results: Tumor uptake of 89 Zr-DFO-AMG102 at 120 h after injection in U87MG xenografts (HGF-positive) was high (36.8 6 7.8 percentage injected dose per gram [%ID/g]), whereas uptake in MKN45 xenografts (HGF-negative) was 5.0 6 1.3 %ID/g and a control of nonspecific human IgG 89 Zr-DFO-IgG in U87MG tumors was 11.5 6 3.3 %ID/g, demonstrating selective uptake in HGF-positive tumors. Similar experiments performed in 4 different gastric cancer patient-derived xenograft models showed low uptake of 89 Zr-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 present only in U87MG tumors and that 89 Zr-DFO-AMG102 uptake was closely correlated with HGF protein levels in tumors. Conclusion: The new immuno-PET imaging agent 89 Zr-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 89 Zr-DFO-AMG102 would be a valuable companion diagnostic tool for the noninvasive selection of patients with elevated local concentrations of HGF in tumors for planning any HGF-targeted therapy, with the potential to improve clinical outcomes.

Tumor-Specific Zr-89 Immuno-PET Imaging in a Human Bladder Cancer Model

“…HuMab-5B1 was produced and provided by MabVax Therapeutics (San Diego, CA) Preparation of Zr-89-labeled HuMab-5B1 ([ 89 Zr]DFO-HuMab-5B1 or MVT-2163) was achieved in accordance with previously described methods, including conjugation of p -SCN-Bn-DFO, purification, and subsequent radiolabeling [ 13 ]. Briefly, Zr-89 oxalate in oxalic acid (1 M) was neutralized to pH 7.0–7.2, using Na 2 CO 3 (1 M) followed by addition of the appropriate construct in PBS (pH 7.4).…”

Antibody-Targeted Imaging of Gastric Cancer

“…ImmunoPET and immunoSPECT have been used for the non-invasive imaging of gastric cancer in both preclinical and clinical studies. The first section of the review will discuss the use of immunoPET in GC targeting the antigens carcinoma-associated antigen (MG7) [ 14 ], programmed death-1 (PD-1) [ 16 ], cadherin-17 (CDH17) [ 15 ], human epidermal growth factor receptors 2 and 3 (HER2 [ 5 , 9 , 21 , 22 , 23 , 24 ] and HER3 [ 12 ]), hepatocyte growth factor (HGF [ 11 ]), and the mesenchymal-epithelial transition factor (MET) [ 10 ]. As shown in Table 1 , FDA-approved or newly developed antibodies targeting membrane antigens were radiolabeled with gallium-68 ( 68 Ga), technetium-99m ( 99m Tc), indium-111 ( 111 In), copper-64 ( 64 Cu), zirconium-89 ( 89 Zr), and bromine-76 ( 76 Br) and used for PET or SPECT imaging of gastric tumors.…”

“…Activation of MET by HGF leads to tumorigenic properties including increased cell scattering, migration, invasion, and proliferation. Preclinical studies have attempted to use HGF- and MET-targeted antibodies as imaging agents in GC [ 10 , 11 ].…”

“…HGF is inhibited with the HGF monoclonal antibody rilotumumab (AMG102) [ 38 ]. Preclinical studies demonstrated that 89 Zr-DFO-AMG102 can noninvasively visualize HGF overexpression in murine xenografts [ 11 ]. 89 Zr-DFO-AMG102 demonstrated high accumulation in HGF-expressing gastric xenografts and PDXs when compared with low-expressing GC.…”

“…The use of FDG-PET is associated with false-negative and false-positive images that could misdirect therapy planning and decrease diagnostic accuracy. In this context, PET has evolved into immunoPET, wherein antibodies with high specificity for antigens overexpressed or uniquely expressed in tumor cells are labeled with PET radiometals [ 5 , 9 , 10 , 11 , 12 , 13 , 14 ]. In addition to PET, antibodies radiolabeled with single photon emission computed tomography (SPECT) radiometals allow noninvasive, highly sensitive imaging of GC [ 15 , 16 ].…”