The tyrosine kinase inhibitor ZD1839 ("Iressa") inhibits HER2-driven signaling and suppresses the growth of HER2-overexpressing tumor cells

The epidermal growth factor receptor (EGFR) is commonly overexpressed in ma ny human tumors and provides a new target for anticancer drug development. ZD1839 ("Iressa"), a quinazoline tyrosine kinase inhibitor selective for th e EGFR, has shown good activity in preclinical studies and in the early pha se of clinical trials. However, because it remains unclear which tumor type s are the best targets for treatment with this agent, the molecular charact eristics that correlate with tumor sensitivity to ZD1839 have been studied. In a panel of human breast cancer and other epithelial tumor cell lines, H ER2-overexpressing tumors were particularly sensitive to ZD1839. Growth inh ibition of these tumor cell lines was associated with the dephosphorylation of EGFR, HER2, and HER3, accompanied by the loss of association of HER3 wi th phosphatidylinositol 3-kinase, and down-regulation of Akt activity. Thes e studies suggest that HER2-overexpressing tumors are particularly suscepti ble to the inhibition of HER family tyrosine kinase signaling and suggest n ovel strategies to treat these particularly aggressive tumors.