A recent large-scale phase III study (the ToGA trial) demonstrated the significant efficacy of trastuzumab combined with chemotherapy in patients with HER2-positive gastric cancer. Although trastuzumab has become a key drug in cancer treatment, the resistance of breast cancer to trastuzumab is a major problem in clinical practice. However, it is unclear whether similar mechanisms of trastuzumab resistance are involved in gastric cancer (GC). The aim of the current study was to identify a novel micro-RNA (miR)/gene pathway that regulates the sensitivity of HER2-positive GC cells to trastuzumab. We focused on F-box and WD repeat domain-containing 7 (FBXW7), which is one of the major causes of drug resistance. We also identified miR-223, which can regulate FBXW7, using miR quantitative reverse transcription-PCR array analysis using by resistance cell line, which we established. Overexpression of miR-223 decreased FBXW7 expression and the sensitivity of GC cells to trastuzumab, while suppression of miR-223 restored FBXW7 expression and the sensitivity of GC cells to trastuzumab. Moreover, overexpression of miR-223 significantly suppressed trastuzumab-induced apoptosis. This study is the first report to reveal that the miR-223/FBXW7 pathway regulates the sensitivity of a HER2-positive GC cell line to trastuzumab through the modulation of apoptosis. These findings suggest that this pathway can be crucial for the mechanism of trastuzumab resistance in GC, which may lead to the development of individualized treatment in clinical practice.
© 2014 UICC.