The epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor, gefitinib (‘Iressa’®, ZD1839) has demonstrated anti-tumor activity in non-small cell lung cancer (NSCLC) and has been approved in over 20 countries. NSCLC has been reported to express high levels of EGFR. However, gefitinib appears to be more effective against adenocarcinoma than squamous cell carcinoma, the latter expressing more EGFR. In the present study, we evaluated the effect of gefitinib against the small cell lung cancer (SCLC) cell lines NCI-H82, NCI-H209, NCI-H510, NCI-H526 and NCI-H660. SCLC has been reported to express a low to undetectable level of EGFR. We compared the effects of gefitinib between cell lines with detectable and undetectable EGFR expression. First, we evaluated expression levels of EGFR and HER2/neu by Western blotting and immunoprecipitation respectively; EGFR protein was detected in two of the five SCLC cell lines, whereas HER2/neu was not detected in any. Next, we analyzed expression levels of phosphorylated ERK1/2 and compared these results with EGFR (HER-1/ErbB1) and HER2/neu (ErbB2) expression levels, as EGFR conducts signals through Ras-Raf-MAPK pathway; gefitinib inhibited phosphorylation of ERK1/2 by EGF addition in cell lines with detectable and undetectable EGFR expression. These data suggest that gefitinib is potentially effective against cancers with low EGFR expression such as SCLC.

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