Thymidylate synthase confers pemetrexed resistance of non-small cell lung cancer cells by EGFR/PI3K/AKT pathway

Chemotherapy drug resistance is the main cause leading to the relapse and metastasis of non-small cell lung cancer (NSCLC) patients. Our study aimed to investigate the mechanism of pemetrexed resistance in NSCLC. Firstly, the pemetrexed (PEM)-resistant PC-9 and A549 lung adenocarcinoma cell lines (PC-9/PEM and A549/PEM) were established. The expression of thymidylate synthase (TS) in PC-9/PEM, A549/PEM, A549, and PC-9 cells were analyzed by qRT-PCR and western blot. Then, cell viability, colony formation, migration, and invasion were performed on PEM-resistant cells transfected with TS siRNA. The role of EGFR in PEM resistance of PEM-resistant cells was investigated using EGFR siRNA. The effects of gefitinib and EGFR siRNA on EGFR/PI3K/AKT pathway and downstream signaling Cyclin D1 and E2F1 in PEM-resistant cells were analyzed. Results showed that the protein level of TS was significantly increased in A549/PEM and PC-9/PEM. TS knockdown inhibited the potency of proliferation, colony-forming potential, migration, and invasion in PEM-resistant cells. EGFR knockdown abrogated the resistance to PEM of PEM-resistant cells and suppressed the migration and invasion of PEM-resistant cells. Gefitinib treatment and EGFR knockdown respectively inhibited the EGFR/PI3K/AKT pathway and downregulated Cyclin D1 and E2F1 in PEM-resistant cells. Thus, TS might be a predictive marker for PEM resistance in NSCLC. Inhibition of the EGFR pathway abrogated the resistance to PEM and inhibited the EGFR/PI3K/AKT and downstream signaling of PEMresistant NSCLC cell lines.

Automated summary

Chemotherapy drug resistance is a major factor in the relapse and metastasis of NSCLC patients. The study identified TS as a potential predictive marker for PEM resistance and demonstrated that inhibition of the EGFR pathway can overcome drug resistance and suppress signaling pathways in PEM-resistant NSCLC cell lines.