Molecular mechanism of chemoresistance and restoration in human gastric cancer cells.

person Hye Jung Chang Departments of Internal Medicine, National Medical Center, Seoul, South Korea info_outline Hye Jung Chang, Moon Young Choi, Min-Hee Cho, Kyoung Eun Lee, Soon-Nam Lee

Authors person Hye Jung Chang Departments of Internal Medicine, National Medical Center, Seoul, South Korea info_outline Hye Jung Chang, Moon Young Choi, Min-Hee Cho, Kyoung Eun Lee, Soon-Nam Lee Organizations Departments of Internal Medicine, National Medical Center, Seoul, South Korea, Division of Medical Oncology, Department of internal medicine, Inje University Busan Paik Hospital, Busan, South Korea, Departments of Internal Medicine, School of Medicine, Ewha Womans University, Seoul, South Korea, Department of Hematology & Oncology Ewha Womans University Hospital, Seoul, South Korea, Department of Hematology & Oncology, Ewha Womans University Hospital, Seoul, South Korea Abstract Disclosures Research Funding Other Background: Gastric cancer is characterized by a high rate of relapse and failure of chemotherapy because of the emergence of drug resistant cells. Hence, resistance to chemotherapy is a major obstacle for the management of gastric cancer. It might be related with the development of cancer stem cells (CSCs). The aim of this study is to investigate the characteristics of the 5-fluorouracil (FU) resistant gastric cancer and to study how to restore the chemosensitivity. Methods: We used the AGS gastric cancer cell line (AGS) and transformed it into a 5-FU resistant cell line (AGS-R). AGS-R was established by continuous exposure of the cells to progressively increasing concentrations of 5-FU for about 1 year and modulating mRNA expression levels of four genes associated with thymidylate synthase (TS). The research methods used were MTT assay, flow cytometry analysis, luciferase reporter assay, western blotting, and siRNA transfection. Results: 5-FU-resistant gastric cancer cell, AGS-R was established by continuous exposure to 5-FU with gradual increase of its concentration for about 1 year. Comparing with AGS, thymidylate synthase (TS) expression in AGS-R was highly increase at transcriptional and translational level. And decreased transcriptional activity of β-catenin in AGS-R was confirmed by Western blotting and luciferase assay. Even though treatment with ICG-001, an inhibitor of β-catenin, showed growth inhibition of AGS in a dose- and time-dependent manner, but it could not in AGS-R. The expression of CD44, well-known CSCs marker, was significantly higher on AGS-R compared to AGS. And the Notch pathway was remarkably up-regulated. Flow cytometry analysis revealed that CD44 expression was reduced on AGS-R transfected with specific siRNA for notch intracellular domain (NICD). Conclusions: This study suggests that chemoresistance of gastric cancer against continuous exposure to 5-FU is associated with decrease of β-catenin activity and development of stemness via the activation of Notch pathway. Therefore, the inhibition of Notch pathway might be a potential therapeutic target in 5-FU-resistant gastric cancer.