Abstract 6063: ROSE12, a novel anti-CTLA-4 Switch antibody™ with FcγR affinity-enhanced Fc, evokes tumor-selective anti-tumor immune activation by extracellular ATP without systemic immune activation

Abstract Background: Tregs are considered potential target in cancer immunotherapy, as tumor-infiltrating Tregs express higher levels of CTLA-4. A promising way to evoke effective anti-tumor immunity is to use FcγR affinity-enhanced anti-CTLA-4 antibody to deplete Tregs via ADCC activity. Although anti-CTLA-4 antibodies with non-fucosylated Fc (NF) are being clinically developed, the number of NKs and macrophages that can be activated is limited, resulting in limited efficacy. Therefore, stronger FcγR affinity-enhanced Fc is needed to show efficacy across all tumors. Moreover, systemic Treg depletion can potentially cause autoimmune side effects. Aiming to enhance anti-tumor activity and avoid systemic Treg depletion, we generated ROSE12, a novel FcγR affinity-enhanced anti-CTLA-4 Switch™ antibody. ROSE12 uses our proprietary antibody engineering technology, Switch-Ig™, allowing it to bind to CTLA-4 only in the presence of extracellular ATP, which is well known to be elevated in tumor tissue but tightly regulated in non-tumor tissue. ROSE12 is also utilized ART-Fc® technology that strongly enhances FcγR affinity. Due to this novel engineering, ROSE12 is expected to selectively deplete Tregs in tumor tissue without affecting non-tumor tissues. Methods: We evaluated ROSE12’s in vitro FcγR-affinity, ATP-dependent binding affinity to human CTLA-4, ADCC activity, and selective CTLA-4+ Treg depletion. We assessed in vivo anti-tumor efficacy in human CTLA-4 knock-in (hCTLA-4KI) mice treated with mROSE12, which has the same variable region as ROSE12 with FcγR affinity-enhanced mouse surrogate Fc. We also evaluated mROSE12 and FcγR affinity-enhanced ipilimumab (Ipi-ART)’s intratumoral Treg depletion and T cell activation in non-tumor tissues using flow cytometry. Results: ROSE12 showed ATP-dependent binding to CTLA-4 and stronger FcγRIIIa-affinity than ipilimumab-NF. Consistent with the binding profile, ROSE12 showed stronger ATP-dependent selective CTLA-4+ Treg depletion among CTLA-4+ T cells than ipilimumab-NF. mROSE12 demonstrated anti-tumor efficacy in a MC38 and PD-L1 therapy-resistant Hepa1-6 bearing mouse model. Moreover, Ipi-ART, but not mROSE12, induced systemic T-cell activation in normal tissue. Consistent with its anti-tumor efficacy, mROSE12 also depleted intratumoral Tregs. Furthermore, ROSE12 was well tolerated in cynomolgus monkeys in a repeated-dose toxicity study. Conclusion: ROSE12 is a novel FcγR affinity-enhanced anti-CTLA-4 Switch antibody™ with potent anti-tumor efficacy and a wide therapeutic window due to tumor-selective activity. These results strongly support the clinical testing of ROSE12 in the treatment of solid tumors. Currently, ROSE12 is undergoing a phase 1 clinical study (NCT05907980). Citation Format: Hiroki Hayashi, Kanako Tatsumi, Hitoshi Katada, Yutaka Matsuda, Toshiaki Tsunenari, Masaki Honda, Takayuki Nemoto, Shun Shimizu, Momoko Miura-Okuda, Yuri Ikuta, Ami Ito, Chika Ogami, Chie Kato, Masaki Kamimura, Tatsuya Kibayashi, Chiyomi Kubo, Shunichiro Komatsu, Yasunori Komori, Junko Shinozuka, Hiroaki Susumu, Honoka Tanno, Yasushi Tomii, Kenji Nakagawa, Hiroaki Nagano, Masahiko Nanami, Yukari Nishito, Nozomi Fujisawa, Tomochika Matsushita, Saki Michisaka, Moe Yoshimoto, Hiroaki Wakatsuki, Tetsuya Wakabayashi, Naoko Wada, Otoya Ueda, Hiroko Konishi, Kenji Kashima, Hiroshi Tanaka, Mika Endo, Takehisa Kitazawa, Shimon Sakaguchi, Mika Kamata-Sakurai, Tomoyuki Igawa. ROSE12, a novel anti-CTLA-4 Switch antibody™ with FcγR affinity-enhanced Fc, evokes tumor-selective anti-tumor immune activation by extracellular ATP without systemic immune activation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 6063.