228 - Evaluating the Efficacy of Novel MET-Targeting Camelid Derived Antibody as an Imaging Agent in Head and Neck Cancers

R. Minne¹, N. Y. Luo², C. M. Mork³, M. R. Wopat¹, K. Esbona⁴, S. Javeri¹, K. P. Nickel¹, R. Hernandez², A. M. LeBeau², R. J. Kimple¹, and A. M. Baschnagel⁵; ¹Department of Human Oncology, University of Wisconsin, Madison, WI, ²University of Wisconsin School of Medicine and Public Health, Madison, WI, ³Department of Human Oncology, University of Wisconsin, Madison, WI, Madison, WI, ⁴TRIP Laboratory University of Wisconsin, Madison, WI, ⁵Department of Human Oncology, University of Wisconsin-Madison, Madison, WI

Purpose/Objective(s): The Mesenchymal Epithelial Transition (MET) receptor tyrosine kinase is expressed on the surface of a variety of cell types. In head and neck squamous cell carcinoma (HNSCC), MET expression has been found to drive cancer growth/survival, angiogenesis, and metastasis. Despite prior investigations, clinical trials on MET directed therapies in HNSCC showed no therapeutic benefit, possibly due to inadequate patient selection based on MET expression levels. Molecular imaging may help identify patients who would respond to specific therapies including MET directed therapies. The object of this study was to evaluate a novel single-domain potent MET binding camelid antibody for the use of positron emission tomography (PET) imaging to identify MET-driven HNSCC tumors that would benefit from MET targeted therapies. Materials/

Methods: Immunostaining for MET and pan-cytokeratin was performed on a single institution TMA consisting of triplicate cores from 270 patients with HNSCC. InForm Tissue Analysis Workflow v.2.4 software was utilized for stroma and epithelium segmentation and MET expression identification. TMA samples with MET expression average >1% were considered positive. From a VHH domain phage display library, we identified a high affinity VHH clone, 1E7, for human MET. Western blotting assessed MET and p-MET expression in established head and neck cell lines. 1E7-Fc, modified to be a humanized bivalent, was evaluated for binding affinity and specificity using flow cytometry and immunofluorescence. EC50 assays measured the effects of 1E7-Fc on cell viability. Bioconjugation with ⁸⁹Zr and ¹⁷⁷Lu enabled tumor uptake imaging in xenograft models using PET/CT and SPECT imaging, respectively. The efficacy of [⁸⁹Zr]Zr-1E7-Fc as an imaging agent targeting MET expression in vivo was investigated through PET/CT imaging.
Results: Of 270 head and neck TMA analyzed, 67% of primary and 63% lymph node sites were MET positive with a median MET expression average of 33% and 30% respectively. Established cell lines Detroit 562 had significantly higher MET and p-MET expression compared to UM-SCC47 and UPCI:SCC90. In vitro, 1E7-Fc demonstrated high binding affinity and specificity to Detroit 562 but no affinity to UM-SCC47 or UPCI:SCC90. 1E7-Fc did not demonstrate cytotoxic effects on any cell lines. [⁸⁹Zr]Zr-1E7-Fc demonstrated rapid localization and high tumor uptake in Detroit 562 xenografts with 8.4 %ID/g 72 hr post injection. Rapid clearance from circulatory systems was also observed within 24 hr post injection. 1E7-Fc was successfully labeled with ¹⁷⁷Lu and imaged by SPECT.
Conclusion: MET expression is prevalent in patients with HNSCC and would be a good target for PET imaging. Our pre-clinical data suggests that camelid antibody MET-1E7-Fc would be a useful imaging agent for MET driven HSNCC. Future investigations are warranted to confirm these findings in patients as well as evaluate efficacy of 1E7-Fc as an imaging agent and possible theragnostic agent for MET driven cancers.