PROPOSAL SUMMARY RNA-binding proteins (RBPs) regulate gene expression through binding to mRNAs, thus influencing rates of translation, mRNA subcellular location, and mRNA half-life. The specific functional outcome of an RBP-mRNA interaction is dependent on the identity of both binding partners. However, it is challenging to predict the functional consequences of a specific interaction due to the diverse combinations of RBP-mRNA interactions that occur within the cell. The RBP HuR binds has a multitude of different mRNA binding partners, allowing HuR to control many critical cellular functions. Dysregulation of the HuR-mRNA interaction network is notably implicated in cancers such as colon, lung, and pancreatic cancers, the three most deadly cancers in the United States. A recently discovered azaphilone HuR inhibitor is very potent but lacks the selectivity required for therapeutic development or to dissect the complex network of HuR mRNA binding partners. Traditional synthetic methods are a major roadblock towards enantioselective azaphilone synthesis, making it infeasible to screen analogs for more favorable bioactivity. However, recent innovation has produced a straightforward, one-pot biocatalytic route that can be used to generate large, diverse azaphilone libraries. I aim to identify novel azaphilones that act as potent and selective HuR-mRNA inhibitors using a combined biocatalytic generation and HuR binding assay platform. I will characterize and validate HuR-azaphilone interactions and identify selective azaphilone inhibitors of HuR both in vitro and in cellulo. Next, I will investigate functional implications of disrupting specific HuR-mRNA interactions in a cancer cell model. Completion of the proposed work will result in the identification and characterization of novel azaphilones that are potent and selective HuR-mRNA interactions and can be further developed as chemical probes and cancer therapeutics.