Abstract B133: Anti-tumor efficacy of GMF-1A3-MMAE, an antibody drug conjugate targeting cell surface cleaved Amphiregulin in endocrine-resistant breast cancer

Abstract

Abstract The Epidermal Growth Factor Receptor ligand, Amphiregulin, is a key proliferative effector of estrogen receptor signaling in breast cancer and also plays a role in other malignancies. Amphiregulin is a single-pass transmembrane protein proteolytically processed by TACE/ADAM17 to release the soluble EGFR ligand, leaving a residual transmembrane stalk that is subsequently internalized. Here, we describe the development of an antibody drug conjugate, GMF-1A3-MMAE, targeting an AREG neo-epitope revealed following ADAM17-mediated cleavage. The antibody does not interact with uncleaved Amphiregulin, providing a novel means of targeting cells with high rates of Amphiregulin shedding. Using fluorescent dye conjugation, we demonstrated that the antibody is internalized by cancer cells in a manner dependent on the presence of cell surface cleaved Amphiregulin. Antibodies conjugated with monomethyl auristatin E (MMAE) were cytotoxic in vitro and induced rapid regression of established breast tumor xenografts in immunocompromised mice. We further demonstrate that these antibodies recognize the Amphiregulin neo-epitope in formalin fixed paraffin embedded tumor tissue, suggesting their utility as a companion diagnostic for patient selection. A pan-cancer tissue microarray analysis indicates that the target is commonly detected at high levels (> 50% of cases) in breast, prostate, liver and lung cancer. In normal tissue microarrays, cleaved Amphiregulin was generally detected at moderate levels in several tissues with only 7 of 93 tissue cores having levels comparable to the high levels commonly found in tumors. These data suggest therapeutic opportunities for GMF-1A3-based ADCs in multiple malignancies, however the broad off-tumor detection of cleaved Amphiregulin suggest linker/payload optimization may be necessary for an adequate therapeutic window. Citation Format: Kristopher A Lofgren, Paraic A Kenny. Anti-tumor efficacy of GMF-1A3-MMAE, an antibody drug conjugate targeting cell surface cleaved Amphiregulin in endocrine-resistant breast cancer [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr B133.