Gefitinib-induced epidermal growth factor receptor-independent keratinocyte apoptosis is mediated by the JNK activation pathway

BACKGROUND: Gefitinib (ZD1839) is a selective epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor with a significant antitumour effect on various cancers. Skin toxicity induced by gefitinib is common, and has been shown to be related to the inhibition of EGFR signalling pathways. However, other mechanisms may be involved in gefitinib-induced skin toxicity. OBJECTIVES: To study the possible EGFR-independent mechanisms of gefitinib-induced skin toxicity. METHODS: The human immortalized keratinocyte cell line HaCaT and human lung adenocarcinoma cell lines (A549 and PC9) were treated with different concentrations of gefitinib for 24, 48 and 72 h. Cell viability was measured by MTT assay [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] after EGFR gene silencing. The signalling pathways were investigated by immunoblot analysis. Keratinocyte apoptosis was evaluated by nuclear condensation and flow cytometric analysis. RESULTS: Gefitinib maintained its cytotoxicity to HaCaT cells after EGFR gene silencing, indicating that an EGFR-independent mechanism exists. Increased phosphorylation of p38 mitogen-activated protein kinase and JNK by gefitinib was observed in a dose-dependent manner in HaCaT cells. The JNK inhibitor, SP600125, attenuated the gefitinib-induced cytotoxicity and apoptosis of HaCaT cells. Immunohistochemical examination of patient specimens showed an increased expression of phosphorylated JNK in lesional epidermis compared with nonlesional epidermis. CONCLUSIONS: Gefitinib can induce keratinocyte apoptosis through an EGFR-independent JNK activation pathway.