Abstract 2770: Dual-targeting mesothelin/CD47 bispecific antibodies for tumor-directed blockade of CD47 in solid cancer

Mesothelin (MSLN) is a lineage restricted cell surface protein with unknown biological function, expressed at low levels on mesothelial cells in healthy tissue. MSLN is also a tumor differentiation antigen as it is highly expressed across a wide range of solid tumors with the highest prevalence in mesothelioma, pancreatic, biliary, ovarian, lung and gastric cancers. Most solid and hematological cancers also upregulate the expression of CD47, a ubiquitous innate immune checkpoint receptor. CD47 interacts with signal-regulatory protein alpha (SIRPα) on myeloid cells, which leads to the inhibition of tumor cell phagocytosis and anti-tumor immune responses. Accordingly, elevated levels of CD47 on tumor cells are associated with cancer9s immune evasion capacity and correlate with poor clinical prognosis, all of which makes CD47 a relevant target for therapeutic blockade. We generated a series of dual-targeting bispecific CD47/MSLN antibodies (biAbs) selectively binding to MSLN-positive tumor cells, but not MSLN-negative healthy cells expressing physiological levels of CD47 (e.g., all blood cells). These CD47/MSLN biAbs block CD47-SIRPα interaction in a MSLN-dependent, tumor-specific manner, thus permitting to bypass tolerability and “antigen sink” issues related to ubiquitous CD47 expression in healthy tissues. An array of CD47/MSLN biAbs with anti-MSLN arms targeting different MSLN epitopes was tested in vitro, in antibody dependent cellular phagocytosis (ADCP) and antibody dependent cellular cytotoxicity (ADCC) assays, as well as for anti-tumor activity in vivo using mouse xenograft models. With various MSLN-positive human cancer cell lines, MSLN/CD47 biAbs demonstrate significantly enhanced cancer cell killing by ADCC and ADCP as compared to the corresponding anti-MSLN monoclonal antibody format (mAbs) as well as to amatuximab, a therapeutic anti-MSLN mAb (currently in Phase II clinical trials for mesothelioma). Correspondingly, the MSLN/CD47 biAbs also display superior efficacy in controlling tumor growth in the xenograft models in vivo. Taken together, we conclude that MSLN/CD47 biAbs should allow for efficacious, yet safe, targeting of CD47 in multiple solid tumor indications in the clinic. More generally, our data support the concept of tumor-directed blockade of CD47 with biAbs as a novel way of improving the efficacy of antibody-based cancer therapies. Citation Format: Valery Moine, Lucile Broyer, Xavier Chauchet, Eric Hatterer, Stefano Majocchi, Vanessa Buatois, Limin Shang, Gerard Didelot, Giovanni Magistrelli, Yves Poitevin, Ulla Ravn, Marie H. Kosco-Vilbois, Nicolas Fiischer, Walter G. Ferlin, Krzysztof Masternak. Dual-targeting mesothelin/CD47 bispecific antibodies for tumor-directed blockade of CD47 in solid cancer [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 2770.