MicroRNAs in cancer stem cells: current status and future directions.

The presence of stem-like cells in cancer, popularly known as cancer stem cells, have been known for a long time but it was the research of Bonnet and Dick in leukemia which got cancer researchers interested in them. Over the past few years, a lot of research has gone into the characterization of cancer stem cells (CSCs) from different tumors. CSCs have been elucidated in almost all solid tumors. The growth of this field has not been without controversies as many researchers considered CSCs to be a transient population of little consequence. The field has nevertheless progressed providing us not only a better understanding of cancer and its related facets like proliferation, EMT, and metastasis but also generating a hope for new generation therapeutics with CSCs as their targets. This search for drugs which target CSCs has also focused on miRNAs. miRNAs are small non-coding regulatory RNA molecules capable of fine-tuning the gene expression. The miRNA profile of CSCs is remarkably different from non-stem cancer cells and many miRNAs have also been shown to regulate self-renewal and differentiation properties of CSCs. The differential miRNA profile in CSCs make them probable biomarkers for the prognosis of cancer and their specificity in targeting the properties of CSCs make them potential targets for therapeutic intervention. This review critically analyzes the advancement of the miRNA research in CSC context and also explores the prospect of miRNA therapies against CSCs.