Extracellular vesicle expansion of PMIS‐miR‐210 expression inhibits colorectal tumour growth via apoptosis and an XIST/NME1 regulatory mechanism

BACKGROUND: Colorectal cancer (CRC) has a high mortality rate, and therapeutic approaches to treat these cancers are varied and depend on the metabolic state of the tumour. Profiles of CRC tumours have identified several biomarkers, including microRNAs. microRNA‐210 (miR‐210) levels are directly correlated with CRC survival. miR‐210 expression is higher in metastatic colon cancer cells versus non‐metastatic and normal colon epithelium. Therefore, efficient methods to inhibit miR‐210 expression in CRC may provide new advances in treatments. METHODS: Expression of miRs was determined in several metastatic and non‐metastatic cell lines. miR‐210 expression was inhibited using PMIS‐miR‐210 in transduced cells, which were transplanted into xenograft mice. In separate experiments, CRC tumours were allowed to grow in xenograft mice and treated with therapeutic injections of PMIS‐miR‐210. Molecular and biochemical experiments identified several new pathways targeted by miR‐210 inhibition. RESULTS: miR‐210 inhibition can significantly reduce tumour growth of implanted colon cancer cells in xenograft mouse models. The direct administration of PMIS‐miR‐210 to existing tumours can inhibit tumour growth in both NSG and Foxn1(nu/j) mouse models and is more efficacious than capecitabine treatments. Tumour cells further transfer the PMIS‐miR‐210 inhibitor to neighbouring cells by extracellular vesicles to inhibit miR‐210 throughout the tumour. miR‐210 inhibition activates the cleaved caspase 3 apoptotic pathway to reduce tumour formation. We demonstrate that the long non‐coding transcript XIST is regulated by miR‐210 correlating with decreased XIST expression in CRC tumours. XIST acts as a competing endogenous RNA for miR‐210, which reduces XIST levels and miR‐210 inhibition increases XIST transcripts in the nucleus and cytoplasm. The increased expression of NME1 is associated with H3K4me3 and H3K27ac modifications in the NME1 proximal promoter by XIST. CONCLUSION: Direct application of the PMIS‐miR‐210 inhibitor to growing tumours may be an effective colorectal cancer therapeutic.