Ruthenium anticancer agent KP1019 binds more tightly than NAMI-A to tRNA.

The ruthenium-based anticancer agent NAMI-A (ImH[trans-RuCl(dmso)(Im)], where Im = imidazole) has been shown to interact with RNA in vivo and in vitro. We hypothesized that the similarly structured drug KP1019 (IndH[trans-RuCl(Ind)], where Ind = indazole) binds to RNA as well. Fluorescence spectroscopy was employed to assay the interactions between either NAMI-A or KP1019 and tRNA through an intrinsic fluorophore wybutosine (Y) base and by extrinsic displacement of the intercalating agent ethidium bromide. In both the intrinsic Y-base and extrinsic ethidium bromide studies, KP1019 exhibited tighter binding to phenylalanine-specific tRNA (tRNA) than NAMI-A. In the ethidium bromide study, reducing both drugs from Ru to Ru resulted in a significant decrease in binding. Our findings suggest that the relatively large heteroaromatic indazole ligands of KP1019 intercalate in the π-stacks of tRNA within structurally complex binding pockets. In addition, NAMI-A appears to be sensitive to destabilizing electrostatic interactions with the negative phosphate backbone of tRNA. Interactions with additional tRNA molecules and other types of RNA require further evaluation to determine the role of RNA in the mechanisms of action for KP1019 and to better understand how Ru drugs fundamentally interact with biomolecules that are more structurally sophisticated than short DNA oligonucleotides. To the best of our knowledge, this is the first study to report KP1019 binding interactions with RNA.