Probing the Effect of α-Helical Stapling Strategies on the Inhibition of Peptide Aggregation and Amyloid Cytotoxicity

Side chain-to-side chain peptide macrocyclization or stapling is a chemical modification that is frequently used to increase the metabolic stability, the cell permeability, and/or the binding affinity of peptide drugs. Interestingly, it was recently reported that α-helical stapling can also protect the amyloidogenic peptide hormone islet amyloid polypeptide (IAPP) from aggregation and amyloid-associated toxicity. IAPP is the major component of insoluble amyloid deposits found in diabetic patients, and its derivatives constitute potential therapeutic candidates to treat metabolic disorders. Herein, we investigated the effects of macrocyclization chemistry on amyloid formation and cytotoxicity by comparing different stapling strategies: lactamization, azide-alkyne click chemistry, and formation of thioether link. The (i, i + 4) intramolecular macrocyclization of IAPP between positions 13 and 17 imposed, or not for some derivatives, a local stability of the helical secondary structure, modulating the propensity of the peptide to self-assemble into amyloid fibrils. The helically constrained derivatives inhibited the aggregation of unmodified IAPP and showed a reduced capacity to perturb the cell plasma membrane and to induce cell death. This study offers key molecular insights into the use of stapling strategies as a chemical approach to prevent the aggregation of peptide therapeutics and to inhibit the cytotoxicity of amyloidogenic peptides associated with protein misfolding disorders.