Anti-Human/Rhesus macaque/Mouse ERBB3 Monoclonal Antibody (Seribantumab)

ERBB3 (also known as HER3) is a unique member of the epidermal growth factor receptor (EGFR) family, belonging to the receptor tyrosine kinase group, yet it possesses a critical amino acid mutation within its intracellular tyrosine kinase domain that renders it almost devoid of intrinsic kinase activity, thus incapable of autophosphorylation. ERBB3 consists of an extracellular ligand-binding domain, a single transmembrane helix, and an intracellular kinase-like domain, requiring heterodimerization with other active members of the family (such as ERBB1/EGFR, ERBB2/HER2, or ERBB4/HER4) for activation, with the most classic pairing being the potent oncogenic dimer formed with ERBB2. Upon ligand binding (e.g., neuregulins NRG1 or NRG2), the intracellular domain of ERBB3 is phosphorylated by the kinase of its partner receptor, thereby providing multiple docking sites via its cytoplasmic tail rich in pYXXM motifs to efficiently recruit the p85 regulatory subunit of PI3K, leading to robust activation of the PI3K-AKT survival signaling pathway—a key functional feature that distinguishes ERBB3 from other family members. Under normal physiological conditions, ERBB3 is essential for cardiac development, nervous system function, and mammary epithelial differentiation; however, pathologically, its overexpression and aberrant activation are widely observed in various solid tumors (such as breast cancer, non-small cell lung cancer, colorectal cancer, and ovarian cancer), promoting tumor proliferation, migration, and anti-apoptosis, while also serving as a core mechanism driving resistance to EGFR- and HER2-targeted therapies. Consequently, ERBB3 has emerged as a prominent target for combinatorial therapeutic strategies in oncology, with multiple bispecific antibodies and antibody-drug conjugates currently in clinical trials.