Evaluation of Drug Resistance in the Tamoxifen-treated MKN-45 Gastric Cancer Cell Line via the Epithelial-mesenchymal Transition Signaling Pathway

One of the major challenges in gastric cancer (GC) chemotherapy is the phenomenon of multi-drug resistance (MDR). The epithelial-mesenchymal transition (EMT) and its key molecules, transforming growth factor-(3 (TGF(3) and SMAD2, play a central role in MDR occurrence. Tamoxifen (TAM), a triphenylethylene derivative, can overcome MDR in human gastric cancers. The aim of this study was to investigate the effect of TAM on 5-FU resistance of GC by suppressing the TGF(31/SMAD2 signaling pathway and EMT. The MKN-45 cell line was subjected to treatment with 5-FU, TAM and a combination of both. The MTT assay was used to investigate the cytotoxic effects of 5-FU and TAM, and the DNA laddering technique was used to assess DNA fragmentation and apoptosis. Real-time RT-PCR examined the change in gene expression in EMT-related genes (SNAI2, VIM, TGF/31 and SMAD2). The results of the present study indicated that not only TAM treatment significantly decreased the IC50 of 5-FU (P <= 0.05), but also the addition of TAM to 5-FU induced apoptosis in the MKN-45 cell line. Treatment with TAM and 5-FU significantly inhibited TGF/31 and TGF(31-induced expression of EMT markers (VIM and SNAI2) in MKN-45 cells (P <= 0.05). The reduction of TGF(31 targets downstream of the SMAD2 signaling pathway reversed the process of EMT and significantly increased the sensitivity of MKN-45 cells to 5-FU. The results of the present study suggested that reversal of EMT-mediated MDR via the TGF(31/SMAD signaling pathway using TAM may be a potential new therapeutic strategy to overcome chemoresistance to 5-FU during GC chemotherapy.