Abstract
BACKGROUND: The epidermal growth factor receptor (EGFR) represents one of the first rationally selected molecules for targeted therapy in non-small cell lung cancer (NSCLC). Gefitinib is a reversible and highly selective tyrosine kinase inhibitor that competitively blocks the binding of adenosine triphosphate to its binding site in the tyrosine kinase domain of the EGFR. It has been found that treatment with gefitinib induces cell cycle arrest and apoptosis in NSCLC cells harboring activating EGFR mutations. Despite its clinical relevance, however, the mechanism underlying gefitinib-induced apoptosis has remained largely unknown. METHODS: We used the gefitinib-sensitive NSCLC cell line HCC827, which harbors a deletion in exon 19 of the EGFR gene, to examine the effect of gefitinib on the apoptotic machinery. RESULTS: We found that gefitinib treatment caused the NSCLC cells to undergo apoptosis following activation of the caspase 8 cascade. Expression of p27, a cyclin-dependent kinase (CDK) inhibitor whose major target is the cyclin E/CDK2 complex, was found to increase during this process, and this increase was accompanied by translocation of p27 from the nucleus to the cytoplasm. Moreover, we found that cytoplasmic p27 bound to a cleaved intermediate (p43/p41) of caspase 8 and that inhibition of cytoplasmic translocation of p27 reduced gefitinib-induced cell death in HCC827 cells. CONCLUSION: Based on our results, we conclude that gefitinib-induced apoptosis is mediated by the interaction of p27 and caspase 8 in NSCLC cells carrying an activating EGFR mutation.