RNA is present in all living cells and is essential to biological functioning. MicroRNAs (miRNAs) are small, single-stranded RNAs involved with gene regulation. In humans, miRNAs can manipulate cancer growth by regulating oncogenes or tumor suppressor genes. MiRNAs are created through transcription of a primary miRNA, followed by subsequent cleavage to a stem-loop precursor miRNA (pre-miRNA) by an enzyme, Dicer. Further cleavage forms the miRNA that joins an RNA-induced silencing complex to target mRNA expression and therefore gene function. In some pre-miRNAs with G-rich sequences, the stem-loop can be unraveled to form a G-quadruplex (G4). However, the stem-loop structure is pertinent to the formation of mature miRNA. Finding a way to stabilize or destabilize the G4 would allow for the regulation of mature miRNA production, which could lead to the development of cancer therapies. One method by which G4s may be stabilized is through small molecule binding. Small molecules that bind to the G4 could stabilize the structure and encourage the formation of the G4 at a higher rate. This could impact the formation of the miRNA and regulate miRNA function in diseases, including cancer.
Other RNAs are also attractive targets for therapeutic development, including chemotherapeutics. One approach to cancer treatment is through the use of metal complexes that interact with nucleic acids, often DNA, though there is current interest in understanding their interaction with RNA as well. The research presented here utilizes circular dichroism (CD) spectrophotometry to develop methods to assess small molecule binding to RNAs of interest. In one project, CD is used to analyze the structures formed by specific pre-miRNAs to pinpoint whether the stem-loop, the G4, or both are formed in the presence or absence of a small molecule ligand. In the second project, changes in the structure of tRNA are observed by CD upon binding of metal complexes of interest. Various copper- and nickel-based complexes were tested to determine their impact on tRNA structure, a nucleic acid intertwined in gene regulation. Successful selective binding of small molecules to RNA structures could have implications in gene expression and regulation and be helpful in the treatment of diseases like cancer.