CyPepUTICS · Tricyclic Peptides for the Development of Therapeutics

Peptide macrocycles can bind with high affinity and selectivity to protein targets and are an attractive class of molecules for the development of therapeutics. Recently, a phage display-based strategy was developed that allowed to generate potent bicyclic peptide antagonists (Heinis, C., et al., Nat. Chem. Biol., 2009). While bicyclic peptides with nanomolar affinities to a range of protein targets could be generated, it was more difficult to obtain high-affinity binders to some proteins, particularly to those having flat surfaces and no clefts or cavities. Herein, I propose to develop rigid, tricyclic peptides that should, due to a more defined three-dimensional structure, bind to flat surfaces similar as antibodies. Two formats are envisioned for the synthesis of tricyclic peptides: in the first one, a linear peptide is anchored via four cysteine residues to a small molecule while in the second format, bicyclic peptides will be generated and their two peptide rings are connected via Huisgen cycloaddition reaction to impose an additional conformational constraint. Phage-encoded combinatorial libraries of these peptide folds will be generated and subjected to affinity selections. Tricyclic peptide binding to a variety of biological targets including (a) the well-characterized cancer-associated targets EGFR and HER2, and (b) the more challenging target of the antibiotic vancomycin, the short peptide D-Ala-D-Ala, will be developed.