Potent inhibitor of epidermal growth factor receptor (EGFR) tyrosine kinase (IC50 = 3 nM). Displays ~ 100-fold lower potency against ErbB2 (IC50 = 290 nM) and is selective over a range of other related tyrosine kinases (IC50 > 10 μM). Blocks downstream EGFR signaling events such as MAPKK/MAPK activation. Oral administration inhibits growth of established human xenografts in athymic mice. Purity 97%. MW (observed): 516.87