MicroRNAs are small noncoding RNAs with key roles in gene expression. It has been revealed that
aberrant expression of microRNAs is related to gene expression abnormality, and they have the potential to be
used as anti-cancer drugs. However, the delivery of microRNAs is limited due to barriers, such as low uptake and
insufficient endosomal release, intracellular nucleases degradation, phagocytic elimination, and renal filtration.
To overcome these issues, novel delivery systems are developed for improving the efficiency of microRNAs
therapy ranging from viral to synthetic; some are further developed with targeted ligands for active targeting
purposes. Such delivery systems provide efficient cellular uptake and endosomal release as well as low cytotoxicity
and minimum unwanted host immune response. Nevertheless, more complementary studies are warranted
before being applied in human studies. This review deals with recent updates on the challenges and achievements
of the various nanotechnology-based gene delivery vehicles with a special emphasis on the miRNA delivery in
cancer therapy. In addition, we attempted to categorize the designed delivery systems based on miRNA therapeutic
molecule. The related cellular signaling pathways and pharmacological action against cancer promotion have
also been highlighted.