The study aims to explore the molecular basis for the poor response of epithelial growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) in EGFR mutated non-small cell lung cancer (NSCLC) patients with smoking history. Novel agent overcoming EGFR-TKI resistance had also been investigated.

The impact of cigarette smoke extract (CSE) on gefitinib sensitive PC-9 cells was evaluated using quantitative real-time PCR (qRT-PCR), western blot, CCK-8 assays, immunofluorescence staining, matrigel invasion assays and wound healing assays.

Western blot and qRT-PCR presented that CSE stimulated the up-regulation of Vimentin and down-regulation of E-cadherin in PC-9 cells in concentration-and time-dependent manners through modulating Src phosphorylation. N-acetylcysteine (NAC) was capable of decreasing Src phosphorylation, abrogating changes of epithelial to mesenchymal transition (EMT) markers instigated by CSE. Immunofluorescence staining found that PC-9 cells displayed features of mesenchymal cells after CSE exposure, while PP2 and NAC could recover these changes. CCK-8 assays showed that CSE could increase the IC50 of PC-9 cells, while PP2 and NAC could abort the elevation of IC50 caused by CSE. Matrigel invasion assays and wound healing assays showed that CSE could increase the invasion and migration ability of PC-9 cells, which could be suppressed by NAC and PP2.

CSE exposure induced EGFR-TKI resistance via mediating Src activation and EMT in NSCLC. NAC may alleviate smoking induced EGFR-TKI resistance through inhibiting Src activation and EMT reversal. NAC may be a promising adjuvant to reinforce the effect of EGFR-TKI.