Abstract A29: Anti-CTLA-4 antibody scFv producing recombinant Bifidobacterium secretes CTLA-4 blocker specifically inside hypoxic tumor and suppresses tumor growth in syngeneic mice model
Authors: Shioya Koichiro , Kataoka Shiro , Wang Li , Matsumura Tomio , Shimizu Hitomi , Kanari Yasuyoshi , Seki Yuji , Shimatani Yuko , Fujimori Minoru , Taniguchi Shun'ichiro 
Published: March 2017

Abstract
Success of immune checkpoint antibody drugs has provided broad perspective in cancer immunotherapy. Anti-PD-1 antibody and anti-CTLA-4 antibody showed notable efficacy and the combination complimentarily enhanced antitumor benefit. Nevertheless, either single-agent therapy or combination therapy is facing immune-related adverse events (irAEs), which is major cause of treatment discontinuation. Also, still large fraction of cancer patients doesn't respond to the antibody immunotherapy. Since non-specific systemic activation of normal immune system by the therapy is one of major reasons to cause the above problems, approaches to target the hypoxic condition of tumors may help increasing the drug's tumor-targeting specificity, which results in minimizing the irAEs and improving the response rate in patients. In an aim to improve anti-cancer drug delivery efficacy, we have been developing in situ Delivery and Production System (i-DPS) by modifying a non-pathogenic anaerobic bacterium, Bifidobacterium, which localizes and proliferates only in the hypoxic environment like solid tumors after intravenous administration, produces anticancer proteins, enzymes or other pharmacologically active molecules selectively at the tumor site. Here we present anti-human CTLA-4 antibody scFv producing i-DPS in cancer immunotherapy, which could be specifically delivered to and amplified only at the hypoxic sites of solid tumors. A series of in vitro assays has been performed to confirm the stable expression and secretion of anti-hCTLA-4 scFv by recombinant Bifidobacterium, the binding affinity of purified anti-hCTLA-4 scFv and the IC50 competing with hCTLA-4/hCD80 or hCD86 interaction as well. Anti-murine CTLA-4 scFv producing Bifidobacterium as surrogate systemically administered to the syngeneic mice model demonstrated significant tumor growth inhibition. Moreover, the combination therapy of anti-mCTLA-4 scFv producing Bifidobacterium and anti-murine PD-1 antibody was more effective than each of monotherapy. It is noteworthy that scFv was only detected in tumor tissue but not in blood proved by immunoprecipitation assay. Altogether, i-DPS for anti-CTLA-4 antibody provide a new promising immune-therapeutic modality to target hypoxic solid tumors and also provide a unique insight for antibody drug delivery in cancer immunotherapy.
Citation Format: Koichiro Shioya, Shiro Kataoka, Li Wang, Tomio Matsumura, Hitomi Shimizu, Yasuyoshi Kanari, Yuji Seki, Yuko Shimatani, Minoru Fujimori, Shun'ichiro Taniguchi. Anti-CTLA-4 antibody scFv producing recombinant Bifidobacterium secretes CTLA-4 blocker specifically inside hypoxic tumor and suppresses tumor growth in syngeneic mice model. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2016 Oct 20-23; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2017;5(3 Suppl):Abstract nr A29.