Figure 4.
Signal transducer and activator of transcription 3 (STAT3) activation mediates trastuzumab‐emtansine (T‐DM1) resistance in BT‐474/KR cells. A, Growth inhibitory effects of T‐DM1, alone or in combination with 0.3 μmol/L napabucasin, on BT‐474/KR cells. Cell growth was measured using the sulforhodamine B assay. Data shown represent mean ± SD of 3 independent experiments. B, BT‐474/KR cells were treated with napabucasin for 24 h. STAT3 activation was detected on western blotting. C, Phosphorylated and total STAT1, STAT3, and STAT5 in BT‐474 and BT‐474/KR cells on western blotting. D, BT‐474/KR cells transfected with either non‐targeting control (NTC) or STAT3 small interfering RNA (siRNA) for 48 h were exposed to T‐DM1 (1 μg/mL) for an additional 72 h. Human epidermal growth factor receptor 2 (HER2), STAT3 and cleaved caspase 3 were detected on western blotting. IC50, 50% inhibitory concentration