Positron Emission Tomography Imaging of Endometrial Cancer Using Engineered Anti-EMP2 Antibody Fragments

Maoyong Fu,Sarah Brewer,Madhuri Wadehra,Jonathan Said,Lynn K Gordon,Tove Olafsen,Jonathan Braun,Anna M Wu

doi:10.1007/s11307-012-0558-y

Abstract

PurposeAs imaging of the cell surface tetraspan protein epithelial membrane protein-2 (EMP2) expression in malignant tumors may provide important prognostic and predictive diagnostic information, the goal of this study is to determine if antibody fragments to EMP2 may be useful for imaging EMP2 positive tumors.ProceduresThe normal tissue distribution of EMP2 protein expression was evaluated by immunohistochemistry and found to be discretely expressed in both mouse and human tissues. To detect EMP2 in tumors, a recombinant human anti-EMP2 minibody (scFv-hinge-CH3 dimer; 80 kDa) was designed to recognize a common epitope in mice and humans and characterized. In human tumor cell lines, the antibody binding induced EMP2 internalization and degradation, prompting the need for a residualizing imaging strategy. Following conjugation to DOTA (1,4,7,10-tetraazacyclododecane-N,N′,N′,N′″-tetraacetic acid), the minibody was radiolabeled with 64Cu (t 1/2 = 12.7 h) and evaluated in mice as a positron emission tomography (PET) imaging agent for human EMP2-expressing endometrial tumor xenografts.ResultsThe residualizing agent, 64Cu-DOTA anti-EMP2 minibody, achieved high uptake in endometrial cancer xenografts overexpressing EMP2 (10.2 ± 2.6, percent injected dose per gram (%ID/g) ± SD) with moderate uptake in wild-type HEC1A tumors (6.0 ± 0.1). In both cases, precise tumor delineation was observed from the PET images. In contrast, low uptake was observed with anti-EMP2 minibodies in EMP2-negative tumors (1.9 ± 0.5).ConclusionsThis new immune-PET agent may be useful for preclinical assessment of anti-EMP2 targeting in vivo. It may also have value for imaging of tumor localization and therapeutic response in patients with EMP2-positive malignancies.

Highlights

Correspondence to: Madhuri Wadehra; e-mail: mwadehra@mednet. ucla.eduApromising avenue in molecular imaging is the development of agents that detect the presence and levels of molecular biomarkers in malignant tumors
Detailed immunohistochemical analysis revealed that Epithelial membrane protein-2 (EMP2) was undetectable in many human tissues including the small and large intestines, pancreas, liver, spleen, and kidney
While EMP2 expression in human tissues has been previously studied, this has largely been evaluated at the level of messenger RNA rather than protein expression; the latter is most relevant to imaging strategies

Summary

Introduction

Apromising avenue in molecular imaging is the development of agents that detect the presence and levels of molecular biomarkers in malignant tumors. M. Fu et al.: Feasibility of Imaging EMP2 in Endometrial Cancer imaging may provide important information for patient stratification to targeted therapies, aid in restaging diseases, and be used to monitor treatment response. New biomarkers that may aid in patient management are urgently needed. A member of the growth arrest specifϊc-3/peripheral myelin protein-22 (GAS3/PMP22) family of tetraspan proteins, overexpression of EMP2 is associated with tumor progression as well as poor patient survival [1, 2]. Its expression is detected in up to 60 % of endometrial tumors and 75 % of advanced ovarian tumors [1,2,3]

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