miR-21-5p confers doxorubicin resistance in gastric cancer cells by targeting PTEN and TIMP3

Drug resistance and disease recurrence are major obstacles to the effective treatment of cancer, including gastric cancer (GC). However, the mechanisms of drug resistance remain to be fully elucidated. The present study investigated the roles of microRNA (miR)-21-5p in the doxorubicin (DOX) resistance of GC cells and the underlying mechanisms. miR-21-5p expression levels were identified to be inversely correlated with two well-known tumor suppressor genes, phosphatase and tensin homologue and tissue inhibitor of matrix metalloproteinases 3, and were upregulated in GC cell lines in proportion to their degree of resistance. Suppressing miR-21-5p expression partially sensitized SGC7901/DOX cells to DOX, suggesting that knockdown of miR-21-5p expression may be used as a therapeutic strategy to improve GC cell resistance. Importantly, increased miR-21-5p expression levels at diagnosis were correlated with clinicopathological characteristics including advanced stage and poor prognosis, further implying that a relapse of GC may be a consequence of miR-21-5p upregulation, thus providing evidence for the potential utility of miR-21-5p antagonism to sensitize GC cells to DOX chemotherapy.