# Designing small molecules that target a cryptic RNA binding site via base displacement

## TL;DR

Researchers designed small molecules that target a hidden RNA site by attaching them to a host molecule, improving solubility and specificity for drug development.

## Contribution

A novel approach using a host-guest framework to enhance RNA-targeting small molecules with improved affinity and specificity.

## Key findings

- A cryptic RNA binding site was identified and exploited using a host-guest strategy.
- Compounds with higher affinity than the native ligand were discovered.
- A biphenyl-like scaffold was shown to optimize π-stacking interactions for RNA targeting.

## Abstract

Most RNA-binding small molecules have limited solubility, weak affinity, and/or lack of specificity, restricting the medicinal chemistry often required for lead compound discovery. We reasoned that conjugation of these unfavorable ligands to a suitable “host” molecule can solubilize the “guest” and deliver it site-specifically to an RNA of interest to resolve these issues. Using this framework, we designed a small molecule library that was hosted by cobalamin (Cbl) to interact with the Cbl riboswitch through a common base displacement mechanism. Combining in vitro binding, cell-based assays, chemoinformatic modeling, and structure-based design, we unmasked a cryptic binding site within the riboswitch that was exploited to discover compounds that have affinity exceeding the native ligand, antagonize riboswitch function, or bear no resemblance to Cbl. These data demonstrate how a privileged biphenyl-like scaffold effectively targets RNA by optimizing π-stacking interactions within the binding pocket.