A Diruthenium Metallodrug as a Potent Inhibitor of Amyloid‑β Aggregation: Synergism of Mechanisms of Action

The physical and chemical properties of paddlewheel diruthenium compounds are highly dependent on the nature of the ligands surrounding the bimetallic core. Herein, we compare the ability of two diruthenium compounds, [Ru2­Cl­(D-p-FPhF)­(O2CCH3)3]·H2O (1) (D-p-FPhF– = N,N′-bis­(4-fluorophenyl)­formamidinate) and K3[Ru2­(O2CO)4]·3H2O (2), to act as inhibitors of amyloid aggregation of the Aβ1–42 peptide and its peculiar fragments, Aβ1–16 and Aβ21–40. A wide range of biophysical techniques has been used to determine the inhibition capacity against aggregation and the possible mechanism of action of these compounds (Thioflavin T fluorescence and autofluorescence assays, UV–vis absorption spectroscopy, circular dichroism, nuclear magnetic resonance, mass spectrometry, and electron scanning microscopy). Data show that the most effective inhibitory effect is shown for compound 1. This compound inhibits fiber formation and completely abolishes the cytotoxicity of Aβ1–42. The antiaggregatory capacity of this complex can be explained by a binding mechanism of the dimetallic units to the peptide chain along with π–π interactions between the formamidinate ligand and the aromatic side chains. The results suggest the potential use of paddlewheel diruthenium complexes as neurodrugs and confirm the importance of the steric and charge effects on the properties of diruthenium compounds.