Photoactivable Ru(II) Polypyridyl Complexes as Dual Action Modulators of Amyloid-Beta Peptide Aggregation and Cu Redox Cycling

Abstract

The misfolding and aggregation of the amyloid-β (Aβ) peptide is a major hallmark of Alzheimer's disease (AD), yet therapeutic strategies targeting this process have faced long-standing challenges related to efficacy and specificity. Here, we investigate two photoactivatable Ru(II) polypyridyl complexes (RuP) that operate as dual-action modulators of AD pathology by addressing both Aβ aggregation and Cu-Aβ associated ROS generation. The RuP complexes contain an extended planar imidazo[4,5-f] [1,10]phenanthroline ligand, which is important for pre-association with the Aβ peptide via hydrophobic and π-π interactions, as well as sterically hindered ligands 6,6'-dimethyl-2,2'-bipyridyl (6,6′-dmb) for RuP1 and 2,9-dimethyl-1,10-phenanthroline (2,9-dmp) for RuP2, which cause steric strain at the metal center. Photoactivation of the RuP complexes results in loss of either a 6,6′-dmb or 2,9-dmp ligand exposing cis-exchangeable coordination sites for binding to the Aβ peptide, which immediately redirects the Aβ peptide away from its β-sheet-rich fibrillization pathway, promoting the formation of amorphous, off-pathway aggregates that exhibit increased sensitivity to proteolytic degradation. We find that the photoactivated RuP complexes are closely associated with the amorphous aggregates, and that this is a common endpoint regardless of Aβ peptide aggregation state (monomer, oligomer, or fibril). Importantly, we show that the ejected ligands also inhibit the redox cycling and ROS generation of Cu-Aβ species. Together, these results highlight the potential of photoactivatable RuP complexes as multifunctional therapeutic candidates, offering a rational approach to intercepting Aβ aggregation and Cu-mediated oxidative stress, and advancing the design of light-responsive treatments for neurodegenerative diseases.