MicroRNA-122 Is More Effective than Rapamycin in Inhibition of Epithelial-mesenchymal Transition and mTOR Signaling Pathway in Triple Negative Breast Cancer

The fundamental mechanism responsible for the aggressiveness of metastatic cancers such as triple-negative breast cancer (TNBC) is the epithelial-mesenchymal transition (EMT). In cancer microenvironments, the Phosphoinositide 3-kinases (PI3K)-Akt- mammalian target of rapamycin (mTOR) signaling pathway plays a critical role in regulating the EMT mechanism. The current study focuses on the impacts of rapamycin, a newly retargeted chemotherapeutic agent against mTOR, and MicroRNA (miR)-122 on the aggressive behavior of TNBC.  The half-maximal inhibitory concentration (IC50) of rapamycin on 4T1 cells was determined using an MTT assay. Also, miR-122 was transiently transfected into 4T1 cells to study its effect on the pathway. Quantitative real-time polymerase chain reaction (qRT-PCR) was conducted to assess the expression level of central mTOR and EMT-related cascade genes. Moreover, cell mobility and migration were evaluated using scratch and migration assays, respectively. Both rapamycin and miR-122 significantly decreased the expression levels of PI3K, AKT, and mTOR, as well as ZeB1 and Snail genes. However, no significant change was observed in Twist gene expression. Furthermore, scratch and migration assays revealed that the migration of 4T1 cells was markedly reduced, especially following miR-122 induction. Our experimental findings and gene enrichment studies indicated that miR-122 mainly operates on multiple metabolic pathways, as well as EMT and mTOR, while rapamycin has restricted targets in cancer cells.  Consequently, miR-122 can be considered a potential cancer microRNA therapy option, which can be validated in the future in animal studies to demonstrate its efficacy in cancer control.