Specific Interaction between a Fluoroquinolone Derivative, KG022, and RNAs with a Single Bulge

Small compounds targeting RNAs are recognized as a promising modality in drug discovery. We have found that a fluoroquinolone derivative, KG022, binds to RNAs with single-bulged residues. It has been demonstrated by ¹H NMR that KG022 binds to RNAs with a bulged G or C and a GC or AU base pair at the 3' adjacent to the bulged residues. In the present study, the effects of the base pairs at the 5' adjacent to the bulged residues on the interaction of KG022 were analyzed mainly by ¹H NMR. It was found that KG022 prefers UA and CG base pairs at the 5' adjacent to the bulged residues, indicating that a stable complex is formed by the stacking interaction among the fluoroquinolone ring and the purine bases of the 5' and 3' sides. In addition, this was confirmed by analysis of the ¹⁹F-NMR spectra. Analysis of temperature dependences of NMR spectra revealed that KG022 forms a more stable complex with RNAs having CG base pairs at the 5' adjacent position than those with UA base pairs. This work presented useful information for the development of small molecules having higher affinity to target RNAs.