Abstract 1324: Preclinical assessment of HWK-016, a next-generation, MUC16-targeting ADC with novel bioconjugation and linker-payload technology.

Abstract Mucin 16 (MUC16) is a cell-surface protein that plays a key role in cancer progression by facilitating tumor cell proliferation, adhesion, invasion, and immune evasion. Proteolytic cleavage of the N-terminal region of MUC16 is known to generate and shed the well-known cancer antigen and biomarker, CA125. MUC16 is highly expressed in multiple tumor types, including ovarian, endometrial, cervical, pancreatic, and lung cancers, and has relatively low expression in normal tissues, making it an attractive target for antibody-drug conjugates (ADCs), chimeric antigen receptor T-cell (CAR-T) therapy, and T-cell engagers. Early clinical trials of MUC16-targeted ADCs, DMUC5754A and DMUC4064A, showed promising efficacy but were limited by targeting an epitope within the shed extracellular domain (ECD) of MUC16, leading to off-target binding to circulating CA125, which created an antigen sink. HWK-016 is a next-generation, MUC16-targeting ADC that was designed to bind to the non-shed ECD of MUC16. HWK-016 comprises an Fc effector-attenuated IgG1 antibody that delivers a novel topoisomerase I inhibitor payload, CPT116. It contains a highly stable, cleavable linker developed using novel bioconjugation technology (carbon bridge cysteine re-pairing) designed to maximize intracellular delivery while minimizing systemic exposure of free payload. HWK-016 has a drug-to-antibody ratio of 6. The mechanism of action of HWK-016 was investigated in preclinical cancer models. Results showed that HWK-016 bound specifically to cell lines expressing the MUC16 non-shed ECD, was internalized through receptor-mediated endocytosis into lysosomes, and induced DNA damage which resulted in loss of cell viability. In contrast to DMUC5754A, addition of exogenous CA125 did not reduce HWK-016 mAb cell-surface binding and internalization, or the effect of HWK-016 on cell viability in vitro. Potent antitumor activity was observed in the high CA125-shedding OVCAR-3 xenograft tumor model at lower doses than DMUC5754A, with tumor regression observed with a 1 mg/kg single dose of HWK-016. A bystander killing effect was observed with HWK-016 in vitro, suggesting the ability to elicit activity against heterogeneous tumors. HWK-016 demonstrated a favorable pharmacokinetic profile and high stability in cynomolgus monkey and human plasma. Repeat-dose toxicology studies in non-human primates indicated a highest non-severely toxic dose (HNSTD) of 60 mg/kg. Together with preclinical efficacy studies, these data support a therapeutic index suitable for evaluation in humans. In summary, HWK-016 is a highly potent, MUC16-targeted ADC directed to the MUC16 non-shed ECD to avoid circulating CA125 binding. A phase I dose-escalation study is planned to evaluate HWK-016 in patients with advanced malignant solid tumors. Citation Format: Kathy S. Keegan, Shihe Hou, Ashwini B. Pai, Enrico Bellomo, Erik Kratzer, Victor Peykov, Bryan Ball, Yifeng Wang, Yaohua Hu, Xia Wang, Zhuozhi Wang, Siwei Nie, Yunying Chen, Jijie Gu, David J. Lennon, David Dornan. Preclinical assessment of HWK-016, a next-generation, MUC16-targeting ADC with novel bioconjugation and linker-payload technology abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 1324.