Potent inhibitor of ErbB receptor family tyrosine kinases (IC50 values are 0.008, 49 and 52 nM for EGFR, ErbB2 and ErbB2/ErbB4 respectively) that does not inhibit FGF or PDGF-mediated tyrosine phosphorylation. Induces G1 cell cycle arrest in MCF10A cells and is antiproliferative in A431 human epidermal carcinoma cells.