Protein tyrosine kinase (PTK) inhibitors are potential antiproliferative agents for diseases caused by the hyperactivity of PTK. Tyrphostins are a class of antiproliferative compounds which act as PTK blockers. PTK inhibitors which preferentially inhibit the epidermal growth factor receptor (EGFR) kinase and block EGFR-dependent cell proliferation. AG-1478 is an inhibitor of EGFR kinase with an IC50 value of 3 nM. Due to its potency and selectivity, AG-1478 has been used in a broad range of studies. It reversibly inhibits rat brain Kv1.5 potassium channels (IC50 = 9.8 µM) independent of protein tyrosine kinase (PTK) activity. AG-1478 also inhibits the growth of leiomyoma and myometrium cell cultures with IC50 values of 5.6 and 5.7 µM, respectively. This inhibitor suppresses MAP kinase activation and strongly inhibits induction of fos gene expression and DNA synthesis.