FGL1 regulates acquired resistance to Gefitinib by inhibiting apoptosis in non-small cell lung cancer

Background: This study investigated the role of fibrinogen-like protein 1 (FGL1) in regulating gefitinib resistance of PC9/GR non-small cell lung Cancer (NSCLC).

Methods: The effect of different concentrations of gefitinib on cell proliferation were evaluated using the CCK-8 assay. FGL1 expression in the normal human bronchial epithelial cell line Beas-2B, as well as four lung tumor cell lines, H1975, A549, PC9, and PC9/GR, was investigated by using western blotting and qRT-PCR. FGL1 was knocked down using small interfering RNA to evaluate the effects of FGL1 on PC9 and PC9/GR. The correlation between FGL1 expression and gefitinib resistance was determined in vitro via CCK-8 and colony formation assays, and flow cytometry and in vivo via flow cytometry and immunohistochemistry.

Results: FGL1 expression was significantly upregulated in non-small cell lung Cancer cells with EGFR mutation and higher in the gefitinib-resistant NSCLC cell line PC9/GR than in the gefitinib-sensitive NSCLC cell line PC9. Further, FGL1 expression in PC9 and PC9/GR cells increased in response to gefitinib treatment in a dose-dependent manner. Knockdown of FGL1 suppressed cell viability, reduced the gefitinib IC50 value, and enhanced Apoptosis in PC9 and PC9/GR cells upon gefitinib treatment. Mouse xenograft experiments showed that FGL1 knockdown in PC9/GR tumor cells enhanced the inhibitory and apoptosis-inducing actions of gefitinib. The potential mechanism of gefitinib in inducing Apoptosis of PC9/GR cells involves inhibition of PARP1 and Caspase 3 expression via suppression of FGL1.

Conclusions: FGL1 confers gefitinib resistance in the NSCLC cell line PC9/GR by regulating the PARP1/Caspase 3 pathway. Hence, FGL1 is a potential therapeutic target to improve the treatment response of NSCLC patients with acquired resistance to gefitinib.

Apoptosis; Epidermal growth factor receptor; Fibrinogen-like-protein 1; Gefitinib resistance; Non-small cell lung cancer.