Abstract 6066: Preclinical evaluation of toxicity reduction for ROSE12, a novel ATP-dependent anti-CTLA-4 Switch antibody™ with FcγR affinity-enhanced Fc

Abstract Introduction: Cytotoxic T-lymphocyte associated protein 4 (CTLA-4) is highly expressed on tumor-infiltrating regulatory T cells (Tregs), which are known to suppress immune activation. To enhance anti-tumor efficacy via antibody-dependent cellular cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis (ADCP) activity, numerous Treg depletion antibodies with FcγR affinity-enhanced Fc are currently being developed. However, FcγR affinity-enhanced anti-CTLA-4 antibody may cause autoimmune toxicity due to systemic Treg depletion. In fact, it was reported that anti-CTLA-4 antibody with non-fucosylated Fc, a common FcγR affinity-enhancing Fc, causes autoimmune adverse events, such as colitis. Aiming to enhance anti-tumor activity without inducing systemic Treg depletion, we generated ROSE12, a novel anti-CTLA-4 Switch antibody™ with FcγR affinity-enhanced Fc. ROSE12 applies our proprietary antibody engineering technology, called Switch-Ig™, allowing it to bind to CTLA-4 only in the presence of high extracellular ATP. ROSE12 also utilizes a technology called ART-Fc® to strongly enhance FcγR affinity. Our results here show that ROSE12 avoids toxicity due to its ATP dependency. Methods: We evaluated CTLA-4 binding affinity and ADCC activity of ROSE12 at varying ATP concentrations in vitro. To evaluate the efficacy and toxicity of ROSE12 in syngeneic mouse models, we established a mouse ROSE12 surrogate Switch antibody™ (mSW-ART) and a conventional mouse anti-CTLA-4 antibody (mCTLA-4-ART), which binds to CTLA-4 in an ATP-independent manner and has the same Fc as mSW-ART. We assessed the anti-tumor efficacy of mSW-ART by measuring the tumor volume in several tumor-bearing syngeneic mouse models. To investigate colonic toxicity, we evaluated diarrhea, colon weight, and colon length in a FM3A-bearing C3H mouse model. The frequency of Tregs in colon lamina propria was also measured using flow cytometry. Results: ROSE12 both bound to CTLA-4 and exhibited ADCC activity in an ATP dependent manner. In vivo studies revealed that mSW-ART exhibited anti-tumor efficacy against several types of cancers. In the FM3A-bearing C3H mouse model, it was demonstrated that mSW-ART did not cause symptoms of colitis, while mCTLA4-ART did. Further, colonic Treg depletion was not induced by mSW-ART, in contrast to mCTLA4-ART. These results showed that mSW-ART avoids the colitis induced by anti-CTLA-4 Treg depletion antibodies which lack tumor selectivity. Conclusions: Our study suggests that ROSE12, which has ATP dependency, may mitigate colonic toxicity by avoiding the depletion of Tregs in colon lamina propria. Thus, ROSE12 may show a wide therapeutic window. A phase I clinical trial for patients with solid tumors is ongoing (NCT05907980). Citation Format: Moe Yoshimoto, Hiroki Hayashi, Kanako Tatsumi, Hitoshi Katada, Toshiaki Tsunenari, Hiroaki Susumu, Kenji Nakagawa, Hiroaki Nagano, Saki Michisaka, Chie Kato, Junko Shinozuka, Hiroshi Tanaka, Takehisa Kitazawa, Mika Kamata-Sakurai, Tomoyuki Igawa. Preclinical evaluation of toxicity reduction for ROSE12, a novel ATP-dependent anti-CTLA-4 Switch antibody™ with FcγR affinity-enhanced Fc [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 6066.