The Design and Synthesis of Peptides and Small Molecules to Control Immune Checkpoints

Hayward, Deanne (2023) The Design and Synthesis of Peptides and Small Molecules to Control Immune Checkpoints. Doctoral thesis, University of East Anglia.

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Presented within this thesis is research on the identification of novel small molecule and peptide inhibitors for the immune checkpoint protein-protein interaction, programmed cell death 1 and programmed cell death ligand 1 (PD-1/PD-L1). The discovery of PD-1/PD-L1 has been invaluable to the effectiveness of immunotherapy treatment for cancer.

In chapter one the need for new inhibitors for PD-1/PD-L1 is outlined, along with the structure of this interaction and approach for inhibition with mAbs. A literature review of small molecule inhibitors designed from the interactions of peptide inhibitors of proteins is presented, outlining inspiration for the synthetic work.

Chapter two describes the design and synthesis of a light-activated peptide inhibitor of PD-1/PD-L1. A linear peptide PD-1/PD-L1 inhibitor, was analysed via an alanine scan to determine which amino acids were essential for inhibiting PD-1/PD-L1. Following this, an azobenzene photo-switch was successfully inserted into the backbone of the peptide. The light-switching capabilities of peptide were confirmed using UV-Vis spectroscopy and analytical HPLC. Following this, the inhibitory activity of the peptide was demonstrated, exhibiting the ability to selectively bind to PD-1/PD-L1 following irradiation. Biological evaluation of the photo-switchable peptide was performed in a cell-based PD-1/PD-L1 assay.

In chapter three, the application of the linear peptide to peptide-directed binding was investigated. The peptide was split in two distributing vital residues based on the information described in chapter two. The synthesis of semi-peptides is discussed, followed by the modification of the peptides with turn-mimicking motif and a library of small molecule fragments to form peptide-small molecule hybrids. The inhibitory activity of these hybrids was tested using a homologous time-resolved fluorescence assay, identifying several peptide-small molecule hybrids capable of inhibiting PD-1/PD-L1 at nanomolar concentrations.

Chapter four presents the investigation into inverse electron demand Diels-Alder reactions using 1,2,4,5-tetrazine derivatives for use as a turn mimicking motif. The successful synthesis of 1,2,4,5-tetrazine derivatives for solid phase peptide synthesis will be discussed, alongside the use of these compounds in iEDDA reactions. The synthesis of iEDDA precursors was successful, and the investigation of their utility in the generation of peptide-small molecule hybrids is discussed.

The work described in chapter five follows the synthesis of cyclic peptide inhibitors for PD-1/PD-L1, and the investigation of these conformationally restrained molecules for application in peptide directed binding.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Pharmacy
Depositing User: Chris White
Date Deposited: 12 Jun 2024 08:26
Last Modified: 12 Jun 2024 08:26

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