Abstract: Objective To investigate the effect of quercetin on epithelial-mesenchymal transdifferentiation (EMT) of non-small cell lung cancer (NSCLC) and its molecular mechanism in improving gemcitabine (Gb) resistance from the perspective of microRNA-101 (miR-101)/Zeste gene homologous protein 2 (EZH2) axis. Methods A549 and A549/Gb cells were cultured with different concentrations of quercetin, and CCK-8 method was used to screen suitable quercetin concentration for the follow-up test. A549 cells were divided into the blank group, the A549 + EMT inducer group, the A549+ quercetin group and the quercetin + EMT inducer group. A549 cells and A549/Gb were divided into the A549 group, the A549/Gb group, the A549/Gb + quercetin group, the A549/Gb + EMT inducer group, the miR-101-inhibitor group, the quercetin+miR-101-inhibitor group and the miR-NC group. Real-time fluorescence quantitative PCR (qPCR) was used to detect the expression level of miR-101 in each group. The expression of EZH2, transforming growth factor (TGF) - β1/ drosophila, mother DPP homolog 4 (SMAD4), p-SMAD4, and EMT marker proteins E-cadherin, N-cadherin and Vimentin were detected by Western blot assay. The optical density (OD) of each group was measured by CCK-8 method, and IC50 and IR were calculated. Results The IC 50 of quercetin for A549 and A549/Gb were 64 and 128 μmol/L, respectively. After EMT inducer enhanced the EMT characteristics of A549 cells (the expression levels of N-cadherin and Vimentin were increased, the expression of E-cadherin was decreased), the expression of miR-101 was decreased, EZH2, TGF-β1 and pSMAD4/SMAD4 protein expression, IC50 and IR increased (P＜0.05). Quercetin could inhibit the EMT characteristics of A549 cells, reduce IC50 and IR, up-regulate miR-101, inhibit EZH2, TGF-β1 and p-SMAD4/SMAD4 protein expression (P＜0.05). EMT inducers could reverse the above effects of quercetin (P＜0.05). Compared with A549 cells, the EMT characteristics increased in A549/Gb cells, and IC50, IR, EZH2, TGF- β1 and p-SMAD4/SMAD4 expressions were all increased (P＜0.05). The inhibition of miR-101 or treatment with EMT inducer could further increase the EMT characteristics, IC50, IR, EZH2, TGF-β1 and p-SMAD4/SMAD4 protein expression of A549/Gb cells (P＜0.05). Quercetin could inhibit the EMT process of A549/Gb cells and reduce its IC50, IR and EZH2, TGF-β1 and p-SMAD4/SMAD4 protein expression (P＜0.05). The inhibition of miR-101 expression could reverse the above effects of quercetin (P＜0.05). Conclusion Quercetin can up-regulate miR-101 and inhibit EZH2 expression, thereby inhibiting EMT process and reducing NSCLC cell drug resistance.

Key words: quercetin, carcinoma, non-small-cell lung, A549 cells, drug resistance, neoplasm, microRNAs, epithelialmesenchymal transition, enhancer of Zeste homolog 2 protein, microRNA-101, gemcitabine