Synthetic macromolecular peptide-mimetics with amino acid substructure residues as protein stabilising excipients.

The clinical use of protein and peptide biotherapeutics requires fabrication of stable products. This particularly concerns stability towards aggregation of proteins or peptides. Here, we tested a hypothesis that interactions between a synthetic peptide, which is an aggregation-prone region analogue, and its homologous sequence on a protein of interest, could be exploited to design excipients which stabilise the protein against aggregation. A peptide containing the analogue of lysozyme aggregation-prone region (GILQINSRW) was conjugated to a RAFT agent and used to initiate the polymerisation of N -hydroxyethyl acrylamide, generating a GILQINSRW-HEA 90 polymer, which profoundly reduced lysozyme aggregation. Substitution of tryptophan in GILQINSR W with glycine, to form GILQINSR G , revealed that tryptophan is a critical amino acid in the protein stabilisation by GILQINSR W -HEA 90 . Accordingly, polymeric peptide-mimetics of tryptophan, phenylalanine and isoleucine, which are often present in aggregation-prone regions, were synthesized. These were based on synthetic oligomers of acrylamide derivatives of indole-3 acetic acid (IND), phenylacetic acid (PHEN), or 2-methyl butyric acid (MBA), respectively, conjugated with hydrophilic poly( N -hydroxyethyl acrylamide) blocks to form amphiphilic copolymers denoted as IND m -, PHEN m - and MTB m - b -HEA n . These materials were tested as protein stabilisers and it was shown that solution properties and the abilities of these materials to stabilise insulin and the peptide IDR 1018 towards aggregation are dependent on the chemical nature of their side groups. These data suggest a structure-activity relationship, whereby the indole-based IND m - b -HEA n peptide-mimetic displays properties of a potential stabilising excipient for protein formulations.