EGCG overcomes gefitinib resistance by inhibiting autophagy and augmenting cell death through targeting ERK phosphorylation in NSCLC

BACKGROUND: Several EGFR-tyrosine kinase inhibitors (TKIs), such as gefitinib (Gef), have been used as effective clinical therapies for patients with non-small cell lung cancer (NSCLC). However, due to acquired resistance, the efficacy of Gef treatment is severely blocked. Our preliminary study found that epigallocatechin gallate (EGCG) in combination with Gef could work synergistically to increase the sensitivity to Gef in NSCLC, but the mechanisms responsible for this have not been completely defined. PURPOSE: In our present study, we devoted to investigate the synergistic effects of combined EGCG and Gef treatment and the importance of autophagy and ERK signaling pathway in overcoming acquired drug resistance to Gef in NSCLC. METHODS: We evaluated the synergistic effects of combined EGCG and Gef treatment through in vitro cell proliferation/viability assays and in vivo xenograft studies, respectively. Autophagic flux was assessed by GFP-microtubule-associated protein 1 light chain 3 (LC3) plasmid transfection and western blot detection of autophagy-related proteins. Besides, the role of ERK on acquired resistance was validated with a ERK inhibitor. RESULTS: We discovered that EGCG can synergize with Gef to inhibit the proliferation of Gef-resistant NSCLC cells and suppress tumor growth in a xenograft mouse model. The underlying mechanisms of synergism were investigated, and the results showed that co-treatment with Gef and EGCG could inhibit Gef-induced autophagy and ERK phosphorylation. Consistently, the expression of LC3-II/I and ATG5 were inhibited, whereas the expression of p62 was enhanced in EGCG and Gef combination treatment groups. Further, inhibition of autophagy in Gef-resistant A549 cells could augment cell death. CONCLUSION: In conclusion, EGCG overcomes Gef resistance by inhibiting autophagy and augmenting cell death through targeting ERK pathway in NSCLC. Gef and EGCG combination therapy may be an effective strategy to overcome acquired resistance in NSCLC.