Keywords:RNA structure and function RNA interactions Epitranscriptomics Small molecules RNA-based therapeutics RNA in disease Drug target A B S T R A C T The increasing appreciation for the crucial roles of RNAs in infectious and non-infectious human diseases makes them attractive therapeutic targets. Coding and non-coding RNAs frequently fold into complex conformations which, if effectively targeted, offer opportunities to therapeutically modulate numerous cellular processes, including those linked to undruggable protein targets. Despite the considerable skepticism as to whether RNAs can be targeted with small molecule therapeutics, overwhelming evidence suggests the challenges we are currently facing are not outside the realm of possibility. In this review, we highlight the most recent advances in molecular techniques that have sparked a revolution in understanding the RNA structure-to-function relationship. We bring attention to the application of these modern techniques to identify druggable RNA targets and to assess small molecule binding specificity. Finally, we discuss novel screening methodologies that support RNA drug discovery and present examples of therapeutically valuable RNA targets.
RNA as a drug targetThe vast diversity of RNAs expanding beyond coding transcripts to several classes of ncRNAs that vary in length, biogenesis, polarity, and putative functions, increases the repertoire of druggable targets. 19,20 Here, specific RNA properties contribute to its attractive, yet challenging makeup as a target molecule. RNA can form complex three-dimensional structures through canonical Watson-Crick base pairing and complex tertiary interactions that are mediated by non-canonical bonds. Such structures can be as intricate and stable as those formed by proteins and can recognize small-molecule ligands, other nucleic acids, and/or proteins with high affinity and specificity. [21][22][23][24] At the same time, the highly dynamic conformation and repetitive character of its surface presents difficulties for drug design. 25,26 In addition, many putative small molecule-binding pockets in RNA are much more polar and solvent exposed than binding sites on proteins, complicating ligand design efforts. Compounding these issues, most target RNAs are expressed at low levels, with the exception of ribosomal (rRNA) and transfer (tRNA) RNAs, which constitute 80-90% and 10-15% of total cellular RNA, respectively. 27 Other abundant RNAs, such as messenger (mRNA), small nuclear (snRNA), and small nucleolar (snoRNA) are present at levels that are about 1-2 orders of magnitude lower than rRNA and tRNA. Certain small RNAs, such as micro (miRNA) and piwi (piRNAs) can be present at very high levels; however, this appears to be cell type dependent. One should keep in mind that if the RNA has catalytic activity or if it acts as a scaffold to regulate https://doi.