Abstract 1778: Preclinical characterization of the safety and antitumor activity of IMAB027-vcMMAE, an anticlaudin 6 antibody-drug conjugate
Authors: Türeci Özlem , Kreuzberg Maria , Walter Korden , Wöll Stefan , Schmitt Ramona , Yamada Tomohiro , Nakajo Ikumi , Sahin Ugur 
Published: August 2018

Abstract
Background Claudin 6 (CLDN6) is a tight junction membrane protein whose expression in normal tissue is confined to embryonic cells, but is aberrantly expressed in various human cancers. The anti-CLDN6 monoclonal antibody (mAb), IMAB027, has shown promising antitumor activity in preclinical human CLDN6-positive (CLDN6+) cancer models. Conjugation of IMAB027 with monomethyl auristatin E (MMAE) may utilize the precision tumor-targeting of the mAb to deliver a highly effective cytotoxic drug to the tumor. In this report we present the preclinical characterization of this antibody–drug conjugate, IMAB027–vcMMAE.
Methods Internalization of IMAB027 in various CLDN6+ human ovarian (OC) and testicular cancer (TC) cell lines was assessed by immunofluorescence, flow cytometry, and Fab-ZAP internalization assay. Binding characteristics of IMAB027–vcMMAE were examined by flow cytometry. Cell viability and IMAB027–vcMMAE-mediated cytotoxic effects (direct and indirect [bystander]) were assessed in cell cultures by the XTT metabolic assay. Apoptosis was evaluated by caspase 3/7, annexin V, and TUNEL assays. Xenograft mouse tumors were generated by injecting human OC cells into nude mice to assess the safety and antitumor activity of IMAB027–vcMMAE.
Results IMAB027–vcMMAE binds robustly to, and is internalized by, cell lines expressing CLDN6. IMAB027–vcMMAE reduced the viability of CLDN6+ OC and TC cells by up to 100% with EC50 values in the ng/mL order. IMAB027–vcMMAE induced apoptosis in CLDN6+ cells in a dose-dependent manner. Additionally, after conjugation, IMAB027–vcMMAE retained IMAB027's ability to induce CLDN6+ cell death via antibody-dependent cellular cytotoxicity and complement-dependent cytotoxicity. Cell lines that did not express CLDN6 were unaffected by IMAB027–vcMMAE in monocultures; however, in cocultures of CLDN6+ and CLDN6-negative cells, IMAB027–vcMMAE exerted bystander effect, resulting in the death of cocultured CLDN6-negative cells in addition to the target-bearing CLDN6+ cells. In vivo, significant antitumor effects were observed after a single intravenous administration of 16 mg/kg IMAB027–vcMMAE in mouse OC xenografts. Further, xenograft tumors with low and/or heterogeneous CLDN6 expression treated with IMAB027–vcMMAE showed efficient tumor size reduction. Repeated dosing of IMAB027–vcMMAE was well tolerated in mice, with no physical abnormalities, changes in behavior, or alterations in appearance observed.
Conclusions IMAB027–vcMMAE is a specific antibody–drug conjugate against CLDN6 that induces potent antitumor activity in CLND6+ tumor cells in vitro and in vivo. Furthermore, IMAB027–vcMMAE was able to induce antitumor effects in tumors with low and/or heterogeneous target expression, which may be driven by bystander activity.
Citation Format: Özlem Türeci, Maria Kreuzberg, Korden Walter, Stefan Wöll, Ramona Schmitt, Tomohiro Yamada, Ikumi Nakajo, Ugur Sahin. Preclinical characterization of the safety and antitumor activity of IMAB027-vcMMAE, an anticlaudin 6 antibody-drug conjugate [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1778.