Antitumor activity of high-dose pulsatile gefitinib in non-small-cell lung cancer with acquired resistance to epidermal growth factor receptor tyrosine kinase inhibitors.

Epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) have demonstrated efficacy in the treatment of advanced non-small cell lung cancer (NSCLC). However, their clinical efficacy is limited by acquired resistance. Drug resistance may be mediated by EGFR transduction, and a number of clinical trials have demonstrated that high-dose pulsatile TKIs may be effective at treating patients with acquired resistance, though their underlying mechanisms of action remain unknown. The aim of the present study was to investigate the antitumor activity of high-dose pulsatile gefitinib in NSCLC model cell lines, namely the EGFR-TKI-sensitive cell line PC9, as a control group, and the EGFR-TKI-resistant cell lines H1975 and H1650. The cell lines were administered with different doses of gefitinib and cell viability was measured using an MTT assay. Cell apoptosis and cycling were also determined by flow cytometry and the expression of phospho (p)-EGFR, EGFR, p-AKT and AKT were measured by western blot analysis. It was observed that the apoptotic rate of H1975 cells treated with high-dose pulsatile gefitinib significantly increased, while levels of p-EGFR and p-AKT were decreased. However, there was no significant difference in the apoptotic rate or level of p-AKT in gefitinib-treated H1650 cells, while p-EGFR levels decreased. By contrast, the EGFR-TKI-sensitive cell line PC9 exhibited sensitivity to gefitinib. It was demonstrated that the apoptosis rates were markedly increased when treated with high dose pulsatile gefitinib in PC9 cell line, while a decrease was noted in p-EGFR and p-AKT. These data suggest that high-dose pulsatile gefitinib treatment may overcome acquired resistance in NSCLC, though its efficacy is dependent on the type of drug resistance mutation(s) present. Furthermore, high-dose pulsatile gefitinib may inhibit tumor growth and induce cell apoptosis by blocking the EGFR signaling pathway. Therefore, if the signaling pathways involved in drug resistance are not activated by the EGFR gene, high-dose pulsatile gefitinib may have little efficacy in the treatment of NSCLC.