Assessment of the Molecular Mechanism of Action of SB3, a Trastuzumab Biosimilar

BACKGROUND: SB3, a biosimilar of Herceptin(®) (trastuzumab, hereinafter referred to as reference product) is currently approved in the EU, Korea, Australia, the USA, and Brazil for the treatment of human epidermal growth factor receptor (HER) 2-positive early and metastatic breast cancer and HER2-positive metastatic gastric cancer. Previously, the biological similarity of SB3 to EU- or US-sourced reference product was assessed using various cell-based and binding assays. OBJECTIVE: In this paper, as a part of its similarity assessment, SB3 was evaluated for additional characteristics related to its molecular mechanism of action (MoA). METHODS: For extracellular effects of SB3, HER2-overexpressing cancer cell lines were used to assess expression of surface HER2, shedding of the extracellular domain of HER2, and antibody-dependent cell-mediated phagocytosis (ADCP) activity. For intracellular effects, Akt phosphorylation and vascular endothelial growth factor (VEGF) release were assessed. Additionally, in vitro docetaxel or pertuzumab combination experiments were performed for further characterization; anti-proliferation, HER2/HER3 dimerization inhibition, apoptosis, and antibody-dependent cell-mediated cytotoxicity (ADCC) assays were used. RESULTS: It was confirmed that SB3 is highly similar to the reference products on quality attributes related to extracellular/intracellular efficacy. This similarity was also confirmed during combination studies with docetaxel and pertuzumab. CONCLUSION: Overall, the equivalence of SB3 with reference product in MoA-related qualities in in vitro mono- and combination therapy experiments may support clinical bioequivalence of the two substances.