Abstract 331: Pre-clinical evaluation in endocrine resistant breast cancer of a novel antibody-drug conjugate targeting cell surface cleaved Amphiregulin

Abstract The EGFR 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 report 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 also show 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. Among ER-positive (n = 88) and ER-negative (n = 50) tumors evaluated, the proportions of tumors exhibiting medium/high intensity staining with 1A3 were essentially equivalent (69.3% v 70%, respectively). These data provide proof-of-principle that cell surface proteolytic cleavage products can represent good targets for antibody drug conjugate development and highlight the potential of using this antibody drug conjugate against tumors shedding high levels of Amphiregulin. Citation Format: Kristopher A. Lofgren, Sreeja Sreekumar, E. Charles Jenkins, Kyle J. Ernzen, Paraic A. Kenny. Pre-clinical evaluation in endocrine resistant breast cancer of a novel antibody-drug conjugate targeting cell surface cleaved Amphiregulin [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 331.