Next Generation Bicycle Scaffolds: Phage Selection With Added Functionality

The overall aim of this project is to develop a novel platform for producing and screening synthetically constrained phage encoded combinatorial peptide libraries bearing additional biological functionality.

BicycleTx Ltd have previously developed technology for screening synthetically constrained phage encoded combinatorial peptide libraries for binding to therapeutic targets. M13 phage displaying short peptide libraries (9 - 20 residues) including three Cys residues are cross-linked through reaction of the Cys-SH with reactive functional groups on a C3-symmetrical small molecule scaffold to give conformationally constrained bicyclic peptides expressed on the pIII coat protein. These Bicycle® libraries are then screened against a range of biological targets to identify peptide sequences with high affinity and selectivity. However, it is not currently possible to screen Bicycle® libraries with additional functionality on the small molecule scaffold. This would allow libraries of peptides that are already primed for localisation to their target (e.g. via cell penetration, membrane surface localisation, or uptake to Gram -ve bacteria) to be screened for biological activity.

In this project, the student will design and synthesise novel bifunctional, C3-symmetric scaffolds bearing (i) three identical alkylating groups for covalent attachment to the phage peptide under mild aqueous conditions and (ii) one or three “click” handles that allow will allow biorthogonal attachment of additional functionality (lipids, peptides and siderophores). The student will develop two types of C3-symmetric scaffolds; rigid scaffolds based on an adamantane core and symmetrical cycle hexapeptide-based scaffolds. For each type of scaffold, the student will develop a synthetic route, attach the additional functional groups through biorthogonal click chemistry, optimise the cross-linking of the scaffold to the short peptide libraries displayed at the phage surface, and then screen the resulting constrained libraries against therapeutic targets where additional functionality is required.