Chronic nicotine exposure affects programmed death-ligand 1 expression and sensitivity to epidermal growth factor receptor-tyrosine kinase inhibitor in lung cancer

BACKGROUND: Smoking histories are independently associated with poor response to epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitors (TKIs) in non-small cell lung cancer (NSCLC) patients with activating EGFR mutations. The aim of the present study was to determine the effect of nicotine exposure on programmed death-ligand 1 (PD-L1) expression in EGFR mutant lung cancer cells. METHODS: Human lung adenocarcinoma PC9 cells were exposed to 1 µM nicotine for 3 months designated as PC9/N, and cells were stimulated with gefitinib (0, 0.1, or 1 µM) for 48 hrs. Cell viability by the MTT assay and morphological changes by immunofluorescence staining were assessed. The protein expression of EGFR, mTOR, AKT, α1-nicotine acetylcholine receptor (nAchR) and PD-L1 were measured by Western blot. Gene expression of α1-nAchR and PD-L1 were examined by RT-PCR. Intratumoral levels of PD-L1 expression were compared according to the burden of smoking dosage in 54 EGFR mutant lung cancer patients. RESULTS: Cellular growth was inhibited by treatment with gefitinib, and PC9 cells were significantly more sensitive to gefitinib than PC9/N cells. Pleomorphic appearance with atypical nuclei and to be detached and shrunken with condensed nuclei in PC9 than PC9/N cells. The gene expression level of α1-nAchR and PD-L1 gene were higher in PC9/N cells compared to those in PC9 cells after treatment with gefitinib. Phosphorylation levels of EGFR, mTOR, AKT and PD-L1 level were decreased by gefitinib in PC9/N cells, which was to a lesser extent than that in PC9 cells. In tumors, heavy smokers (≥30 PY) showed 28.5% of ≥50% PD-L1 tumor proportion score (TPS) while light smoker and never smokers had 12.5% and 9.7% of ≥50% PD-L1 TPS, respectively. However, there was no statistical significance (P value =0.628). CONCLUSIONS: Chronic nicotine exposure could increase PD-L1 expression related to intrinsic resistance to EGFR-TKI in NSCLC patients harboring activating EGFR mutation. Considering the clinical importance of inevitable EGFR resistance, further studies regarding the role of anti-PD-1/PD-L1 treatment are needed, especially in EGFR mutant smokers.