**6.4 Small molecule inhibitors**

Several drugs may possess the ability to modulate miRNA expression, targeting signaling pathways in miRNA biogenesis, ultimate converging on the activation of transcription factors involved in the regulation of miRNA encoding genes. The first specific molecule founded to be effective for inhibition of miRNA is an azobenzene [46]. The authors have demonstrated that the azobenzene can inhibit miRNA-21 by inhibiting miRNA-21 precursor in live cells [46]. MicroRNA-21 is significantly overexpressed in many types of human cancers, thus miR-21 is a potential therapeutic target. Recently, Naro et al. [47] have reported that, using a luciferase-based reporter assay, a high-throughput screen of >300,000 compounds led to the discovery of a new aryl amide class of small-molecule miR-21 inhibitors. Their studies further found that four aryl amide derivatives were very potent and selective miR-21 inhibitors [47]. The small molecule miRNA inhibitors are currently limited by their relatively low potencies and issues with specificity to a particular miRNA, however, they are much easier to deliver and have the promise for development of therapeutics.
