In this study, we described the utilization of EMP2 as a therapeutic target in ovarian cancer. Previous studies have demonstrated the importance of EMP2 in human endometrial cancer (14
). However, to date, limited data exists on the role of EMP2 in ovarian cancer. In this study, we assessed the expression of EMP2 in an ovarian cancer TMA, and determined its suitability as a therapeutic target using anti-EMP2 recombinant antibody fragments.
Analysis of 129 ovarian carcinoma patients revealed that EMP2 expression was prevalent among serous and endometrioid tumors, although its expression was not predictive of overall survival probability. As these subtypes represent the majority (90–95%) of ovarian cancers diagnosed in North America, we further evaluated the potential of EMP2 to serve as a therapeutic target. Preliminary experiments in a panel of ovarian cancer cell lines demonstrated that EMP2 is highly expressed in the majority of cell lines. Moreover, incubation with recombinant EMP2 diabodies significantly inhibited cell growth and induced cell death both in vitro and in vivo.
EMP2 is a member of the tetraspan superfamily of proteins. The tetraspan family have been implicated in a multitude of processes including malignancy, regulation of the immune system, fertilization, and infectious disease processes (15
). Moreover, targeting of specific tetraspan proteins has been shown to induce the subsequent activation of an intracellular signal transduction cascade resulting in cell death, cell growth inhibition, antibody-dependent cellular cytotoxicity (ADCC), complement mediated cytotoxicity or activation of anti-tumor immune response (38
). Similarly, EMP2 in several cell types plays a role in growth control, invasion, metastasis and protein trafficking (20
). Biochemically, EMP2 can directly associate with integrin αvβ3 and focal adhesion kinase (FAK), and promote integrin-mediated FAK-Src activation (23
). Although the exact mechanism of EMP2 diabodies on ovarian cancer has yet to be elucidated, we predict that the diabodies dysregulate the integrin-FAK nexus, leading to apoptosis. Accordingly, it is possible that EMP2 contributes to malignant progression in part by augmenting integrin-mediated functions essential to tumor cell biology.
Human ovarian cancer cell xenografts in immune-deficient mice are useful research models for analyzing cell tumorigenicity and evaluation of therapeutics in ovarian cancer (42
). In the present study, treatment of OVCAR5 human ovarian cancer xenografts with anti-EMP2 diabody blocked tumor growth and induced tumor necrosis. These findings are similar to the effect of anti-EMP2 diabody on EMP2-positive human endometrial cancer xenografts (15
). Anti-EMP2 diabodies lack detectable toxicity to normal tissues, including the lung, which physiologically express high levels of EMP2 (15
). These findings suggest that in contrast to tumor cells, physiological expression of EMP2 is either inaccessible to anti-EMP2 antibody (perhaps due to tight junction sequestration (44
), or its ligation does not interfere with critical functions required by these normal cell types. Additional studies will be required to further delineate the in vivo
biodistribution and safety of anti-EMP2 therapy, and the efficacy of anti-EMP2 diabody (or other native or antibody fragments) for in vivo
cytotoxicity of ovarian cancer cell lines.
In conclusion, EMP2 expression is a common feature of major subtypes of human ovarian carcinoma, and treatment of human ovarian cancer cell lines with human bivalent anti-EMP2 diabodies directly induced cell death and retarded cell growth both in vitro
, and in tumor xenografts. These results suggest that EMP2 may be a potential target for ovarian cancer antibody therapy. Finally, reengineering of anti-EMP2 diabody fragments into a native antibody format may offer improved therapeutic benefits relative to pharmacokinetics, biodistribution, and effector functions (16
STATEMENT OF TRANSLATIONAL RELEVANCE
Ovarian cancer is the fifth leading cause of death from cancer in women and the leading cause of death from a gynecological cancer. Few modalities exist for its treatment, and like most cancers new treatments are needed. Epithelial membrane protein-2 (EMP2) is a tetraspan protein whose expression was previously shown to be an independent, prognostic indicator for endometrial cancer. In this study, we analyze the expression of EMP2 in ovarian cancer and determine its utility as a therapeutic target for disease. Using recombinant bivalent antibody fragments (diabody) to EMP2, we test their cytotoxic efficacy on a panel of human ovarian cancer cell lines in vitro and in xenografts in vivo. This study provides a preclinical assessment of antibody-targeting of EMP2 for treatment of ovarian cancer and further justifies its development as a treatment strategy for other EMP2-expressing cancers.