title: Phage-encoded combinatorial chemical libraries based on  bicyclic peptides.
abstract: Here we describe a phage strategy for the selection of ligands based on bicyclic or linear peptides attached covalently to an organic core. We designed peptide repertoires with three reactive cysteine residues, each spaced apart by several random amino acid residues, and we fused the repertoires to the phage gene-3-protein. Conjugation with tris-(bromomethyl)benzene via the reactive cysteines generated repertoires of peptide conjugates with two peptide loops anchored to a mesitylene core. Iterative affinity selections yielded several enzyme inhibitors; after further mutagenesis and selection, we were able to chemically synthesize a lead inhibitor (PK15; Ki =1.5 nM) specific to human plasma kallikrein that efficiently interrupted the intrinsic coagulation pathway in human plasma tested ex vivo. This approach offers a powerful means of generating and selecting bicyclic macrocycles (or if cleaved, linear derivatives thereof) as ligands poised at the interface of small-molecule drugs and biologics.
authors.affiliation: Laboratory of Molecular Biology, Medical Research Council, Cambridge, UK.
authors.forename: Christian
authors.initials: C
authors.lastname: Heinis
authors.forename: Trevor
authors.initials: T
authors.lastname: Rutherford
authors.forename: Stephan
authors.initials: S
authors.lastname: Freund
authors.forename: Greg
authors.initials: G
authors.lastname: Winter
mesh_terms: D000595:Amino Acid Sequence; D056649:Cathepsin G / Q000037:antagonists & inhibitors; D003001:Cloning, Molecular; D020650:Combinatorial Chemistry Techniques; D003545:Cysteine / Q000737:chemistry; D004791:Enzyme Inhibitors / Q000138:chemical synthesis / Q000737:chemistry* / Q000494:pharmacology; D006801:Humans; D008024:Ligands; D008969:Molecular Sequence Data; D019151:Peptide Library; D010456:Peptides, Cyclic / Q000138:chemical synthesis / Q000737:chemistry* / Q000235:genetics / Q000494:pharmacology; D020842:Plasma Kallikrein / Q000037:antagonists & inhibitors
chemical_list: D004791:Enzyme Inhibitors; D008024:Ligands; D019151:Peptide Library; D010456:Peptides, Cyclic; D056649:Cathepsin G; D020842:Plasma Kallikrein; D003545:Cysteine