Abstract C119: Anti-EphA10 monoclonal antibody is a potential therapy against EphA10 positive breast cancer.

Introduction: Triple negative breast cancer (TNBC) is defined by the absence of receptors for Her2, estrogen and progesterone and is often referred to as a refractory disease, because it is resistant to treatment with anti-Her2 antibody and anti-hormone drugs. Thus, new targets for therapeutic agents are urgently required. Using a proteomic approach, we have identified EphA10, which is more highly expressed in breast cancer, including TNBC, than in normal breast tissues. Moreover, we previously revealed that EphA10 is expressed in testis, but not in other normal tissues. This suggests that EphA10 could become a promising therapeutic target in breast cancer patients. Here, we describe a novel monoclonal antibody (mAb) against the extracellular region of EphA10 showing tumor accumulation and anti-tumor effects. Materials and Methods: Characterization of anti-EphA10 mAb; Specificity of the mAb was evaluated by mAb binding to EphA family proteins (EphA1-A8, A10). Affinity of the mAb was analyzed by the surface plasmon resonance method. The kinetic parameters of the mAb against EphA10-Fc proteins were calculated using a single-cycle kinetic analysis. Tumor accumulation analysis of anti-EphA10 mAb; Alexa647-conjugated anti-EphA10 mAb or control mAb were administrated intravenously and observed daily using an in vivo imaging system. Tumor accumulation was quantified as the fluorescence intensity ratio of the tumor compared to that of the contralateral side. Anti-EphA10 mAb treatment in a mouse xenograft model; A mouse model was constructed by orthotopic transplantation of EphA10 stably expressing MDA-MB435 cells. When the tumor size reached approximately 100 mm 3 , anti-EphA10 mAb and control mAb were administrated intraperitoneally twice a week. Results and Discussion: The results showed that anti-EphA10 mAb had an affinity for EphA10 in the nanomolar range. Moreover, the mAb specifically bound to EphA10, but not to the other EphA family proteins tested. Therefore, our mAb was shown to have specificity and affinity for EphA10 equivalent to that of existing antibody drugs. Administration of the fluorescein-labeled mAb to EphA10-positive breast tumor-bearing mice showed that the mAb accumulated in tumors to a greater extent than a control mAb. Furthermore, tumor growth was significantly suppressed in the mAb-treated mice in a dose-dependent manner. These data indicate that our mAb might become a promising therapeutic tool for EphA10-positive breast cancer. We are currently analyzing the function of EphA10 to elucidate its role in cancer, and improving the antibody by humanization or drug conjugation. Conclusion: Our original anti-EphA10 mAb accumulated in EphA10-positive tumor cells and showed anti-tumor effects. We believe these findings will contribute to the development of a novel drug for refractory breast cancer patients. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):C119. Citation Format: Kazuya Nagano, Yuka Maeda, Takuya Yamashita, Masaki Inoue, Yasuhiro Abe, Yohei Mukai, Haruhiko Kamada, Kazuma Higashisaka, Yasuo Yoshioka, Yasuo Tsutsumi, Shin-ichi Tsunoda. Anti-EphA10 monoclonal antibody is a potential therapy against EphA10 positive breast cancer. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr C119.