Toward the Mode of Action of the Clinical Stage All-D-Enantiomeric Peptide RD2 on Aβ42 Aggregation

The aggregation of amyloid-beta (A beta) into oligomers and fibrillary structures is critical for the pathogenesis of Alzheimers disease (AD). Recently, research effort has been focused on developing novel agents that can preferentially suppress A beta oligomer mediated toxicities, for example, by directly targeting these toxic assemblies. The compound RD2 has been developed and optimized for A beta 42 monomer binding and stabilization of the monomer in its native intrinsically disordered conformation. It has been demonstrated to improve and even reverse the cognitive and behavioral deficits in AD mouse models, while the detailed mechanism of action is not fully clarified. Here we focused on exploring the interaction between RD2 and A beta 42 monomers and its consequences for the fibrillation of A beta 42. RD2 binds to A beta 42 monomers with nanomolar affinities, according to microscale thermophoresis and surface plasmon resonance measurements. Complexes between RD2 and A beta 42 monomers are formed at 1:1 and other stoichiometries, as revealed by analytical ultracentrifugation. At substoichiometric levels, RD2 slows down the secondary structure conversion of A beta 42 and significantly delays the fibril formation. Our research provides experimental evidence in supporting that RD2 eliminates toxic A beta assemblies by stabilizing A beta monomers in their native intrinsically disordered conformation. The study further supports the promising application of RD2 in counteracting A beta aggregation related pathologies.