Trastuzumab (T) and pertuzumab (P)-mediated antibody-dependent cell-mediated cytotoxicity (ADCC) in tyrosine kinase inhibitor (TKI)-treated breast cancer (BC) cell lines.

643 Background: Monoclonal antibody (mAb) therapy and TKI combinations are under investigation for the treatment of HER2-positive (HER2 gene amplification/IHC 3+/2+) BC. A further ~50% of BCs can be described as HER2-low (IHC 1+/2+/non-amplified). The HER2-targeted TKI lapatinib( LAP) can modulate HER2 levels and potentiate T-mediated ADCC in pre-clinical models. This study compares the effects of three HER2-targeted TKIs, LAP, neratinib(NER) and afatinib(AFAT) on HER2 levels in HER2-positive SKBR3and HER2-low MCF-7cells and examines the associated effects on T and P-induced ADCC in vitro. Methods: MCF-7and SKBR3were treated with LAP, NER or AFAT (0.2, 1 and 2µM, 48 hr). Membrane HER2 protein levels were determined by high content analysis (HCA) using an extracellular domain (ECD)-targeted antibody. A flow cytometry-based ADCC assay utilized TKI pre-treated SKBR3and MCF-7(2µM TKI, 48 hr) and healthy volunteer CD56+ NK cells or PBMCs. Results: LAPtreatment increased HER2 in SKBR3and MCF-7. Follow...