Alzheimer's disease is imposing a growing social and economic burden worldwide, and effective therapies are urgently required. One possible approach to modulation of the disease outcome is to use small molecules to limit the conversion of monomeric amyloid (Aβ42) to cytotoxic amyloid oligomers and fibrils. We have synthesized modulators of amyloid assembly that are unlike others studied to date: these compounds act primarily by sequestering the Aβ42 monomer. We provide kinetic and nuclear magnetic resonance data showing that these perphenazine conjugates divert the Aβ42 monomer into amorphous aggregates that are not cytotoxic. Rapid monomer sequestration by the compounds reduces fibril assembly, even in the presence of pre-formed fibrillar seeds. The compounds are therefore also able to disrupt monomer-dependent secondary nucleation, the autocatalytic process that generates the majority of toxic oligomers. The inhibitors have a modular design that is easily varied, aiding future exploration and use of these tools to probe the impact of distinct Aβ42 species populated during amyloid assembly.

The amyloid-β peptide, the main protein component of amyloid plaques in Alzheimer’s disease, plays a key role in the neurotoxicity associated with the condition through the formation of small toxic oligomer species which mediate the disruption of calcium and glutamate homeostasis. The lack of therapeutic benefit associated with removal of mature amyloid-β fibrils has focused attention on the toxic oligomeric species formed during the process of fibril assembly. Here, we present the design and synthesis of a family of perphenazine-macrocyle conjugates. We find that two-armed perphenazine-cyclam conjugates divert the monomeric form of the amyloid-β peptide away from the amyloidogenic pathway into amorphous aggregates that are not toxic to differentiated SH-SY5Y cells in vitro. This strategy prevents the formation of damaging amyloid oligomers. Kinetic analysis of the effects of these compounds on the assembly pathway, together with NMR spectroscopy, identifies rapid monomer sequestration as the underlying neuroprotective mechanism. The ability to specifically target the monomeric form of amyloid-β allows for further understanding of the impact of the multiple species formed between peptide biogenesis and plaque deposition. The modular, three-dimensional structure of these compounds provides a starting point for the design of more potent modulators of this amyloid-forming peptide, and can be adapted to probe the protein self-assembly pathways associated with other proteinopathies.Significance statementThe aggregation pathway of the amyloid-β (Aβ) peptide in Alzheimer’s disease is complex and involves multiple different species. An inability to isolate and study the impact of distinct Aβ species has undermined efforts to develop effective therapies. To address this issue, we have developed a series of molecules that specifically sequester the monomeric form of the highly aggregation-prone Aβ42 peptide. Interaction with these molecules diverts Aβ42 from the amyloidogenic pathway and prevents formation of toxic oligomeric species. We use kinetic analysis and NMR spectroscopy to identify rapid monomer sequestration as the underlying neuroprotective mechanism. Future rational development of these molecules and characterisation of their interactions with Aβ will delineate the impact of different Aβ oligomers on neurobiology and pathology.