Potent inhibitor of the ErbB receptor family (IC50 values are 0.3, 0.5 and 1.1 nM for ErbB1 (EGFR), ErbB4 and ErbB2 respectively). Inhibits EGF-induced erbB1 autophosphorylation in NIH3T3 cells and heregulin-stimulated ErbB autophosphorylation in MDA-MB-453 human breast carcinoma cells (IC50 values are 2.5 and 24 nM respectively).