Dual targeting of EGFR and HER-2 in breast cancer cell lines

Abstract

13132 Background: ErbB2 is overexpressed in approximately 25–30% of breast cancers. Recent studies have shown that overexpression of ErbB2 is also frequently associated with expression of ErbB1 and that ErbB1 expression influences response to ErbB2 inhibition. The aim of this study was to investigate the effects of dual targeting of ErbB1 and ErbB2 in ErbB2 overexpressing breast cancer cell lines. Methods: Combinations of Trastuzumab (Herceptin), Gefitinib (Iressa) and Lapatinib (GW572016) were tested in two ErbB2 and ErbB1 positive breast cancer cell lines, SKBR3 and BT474. Proliferation assays were performed using the acid phosphatase assay and apoptosis was measured using the Cell Death Detection ELISA (Roche). The average combinations index (CI) values at ED25, ED50 and ED75 were determined using CalcuSyn. Results: With regard to inhibition of proliferation, dual targeting with Trastuzumab and Gefitinib is additive (CI=0.8) in SKBR3 cells and synergistic (CI=0.6) in BT474 cells. Combined treatment with Trastuzumab and Lapatinib is synergistic (CI=0.5) in SKBR3 cells and additive (CI=1.0) in BT474 cells. Dual targeting with Gefinitib and Lapatinib is antagonistic in both cell lines. Trastuzumab (10 nM) alone and Gefitinib (5 μM) alone did not induce significant apoptosis in SKBR3 cells whereas Lapatinib (0.75 μM) alone induced apoptosis and in combination with Trastuzumab enhanced apoptosis induction. Combined treatment with Trastuzumab (10 nM) and Gefitinib (5 μM) induced apoptosis comparable to Lapatinib alone (0.75 μM). Conclusions: Our results suggest that dual targeting of ErbB1 and ErbB2 with combinations of the monoclonal antibody, Trastuzumab and tyrosine kinase inhibitors may improve response to treatment in a sub-group of patients with ErbB2 overexpressing tumours that also express ErbB1. Interestingly, the apoptosis assays suggest that inhibition of both ErbB1 and ErbB2 is required to efficiently induce apoptosis in cells which express both receptors. [Table: see text]