Progress Towards Developing a Multi-Functional Antibody-Gold Nanocluster Through Site-Specific Glycoengineering

Abstract

Gold nanoclusters (AuNCs) have tremendous therapeutic potential as photosensitizers for photodynamic therapy (PDT) due to their small size and high biocompatibility. When used in PDT, AuNCs can generate cytotoxic reactive oxygen species, but due to a hypoxic tumour microenvironment, PDT may be insufficient for cancer treatment on its own. The combination of PDT with chemotherapy can enhance therapeutic potential; however, both treatments lack target specificity and can damage healthy tissue. Targeting ligands, such as antibodies, have been conjugated to highly potent cytotoxic drugs, forming antibody-drug conjugates which can minimize off-target toxicities. Considering the existing knowledge gap on the preparation of synergistic nanomedicine therapeutics that combine both chemo- and radiotherapy properties, nanomedicines containing a photosensitizer, a cytotoxic drug payload, and a targeting ligand have yet to be developed. This thesis presents a novel chemoenzymatic strategy for preparing a bi-functional biantennary glycan, functionalized with monomethyl auristatin E (MMAE) and an azide orthogonal group, which can be ligated to antibodies using an endoglycosidase. Once conjugated to antibodies, the chemical handle can be subsequently used to ligate AuNCs, thereby preparing targeted, multi-functional nanomedicines. Using a semi-synthetic chemoenzymatic approach, a bi-antennary glycopeptide was extracted and enzymatically trimmed to afford a bis-galactosylated N-glycan substrate. One branch of the N-glycan was functionalized with an unnatural alkyne-modified sialic acid using a branch-selective sialyltransferase, which was then ligated to MMAE via “click” chemistry. Different sialyltransferases were then used to install an unnatural azide-modified sialic acid on the other branch, affording a bi-functional N-glycan for ligation to alkyne-modified AuNCs. This chemoenzymatic approach and progress to date offer a promising framework for the development of new synergistic nanomedicines for cancer treatment.