Development of novel bispecific antibodies for cancer therapy targeting the receptor tyrosine kinases HER4 and EGFR

Abstract

In this study, novel mono- and bispecific antibodies targeting the ErbB receptor family members EGFR and HER4 were investigated. Dual targeting of EGFR and HER4 by a bispecific, tetravalent antibody comprising a novel, antagonistic HER4-targeting antibody showed inhibition of proliferation and migration for a HB-EGF-stimulated ovarian cancer cell line. No inhibitory effects in a breast cancer cell line expressing EGFR and HER4 indicated that successful dual targeting does not solely rely on target expression. The complexity of HER4 with its isoforms and their different signaling properties makes HER4 a challenging cancer target that needs further in-depth research. To overcome resistances based on escape mutations located in the epitopes of clinically approved antibodies, novel antagonistic EGFR-targeting antibodies binding to a different epitope were developed. This epitope was mapped to domain III of EGFR and binding to clinically relevant EGFR ectodomain mutations resulted in inhibition of EGFR signaling in stable cell lines used as test systems. Favorable activities in comparison to clinically approved antibodies regarding inhibition of EGFR signaling and proliferation were observed for cancer cell lines expressing the EGFR wildtype. Bispecific T-cell engagers can lead to a T-cell mediated target cell killing independent of intracellular downstream signaling in the cancer cell. One challenge for the applicability of T-cell engagers in solid tumors is to keep the balance between T-cell mediated tumor cell killing and severe side-effects caused by a systemic activation of the immune system. Studies on eleven different eIg-based formats for EGFR-binding T-cell engagers showed that valency, geometry, and size influenced their activity profile. Furthermore, one bivalent and one trivalent, bispecific format were investigated for two novel EGFR-targeting moieties. As these molecules bind to clinically relevant escape mutations located in the ectodomain of EGFR, they are expected to show activity in patients with an acquired resistance to approved EGFR-targeting antibodies. These molecules led to a robust T-cell mediated cytotoxicity of cancer cells expressing EGFR. Additionally, benefits regarding an EGFR-level dependent cytotoxicity were observed for reduced binding to EGFR. An initial in vivo study using surrogate molecules in a syngeneic mouse model showed reduction of tumor growth and prolonged survival for treatment with a trivalent, bispecific T-cell engager comprising a novel EGFR-binding moiety. Taken together, beneficial effects of the novel molecules may contribute to improved therapies for patients with both pre-existing and acquired resistances to EGFR-targeting antibodies.