The development of new therapies to combat severe infection caused by the Staphylococcus aureus (S. aureus) bacterium is a worldwide research priority. Despite the advances of modern medicine, the current morbidity and mortality rate associated with S. aureus infections still stands at 20% for patients who contract an infection. This is a direct consequence of a spike in antibiotic-resistant bacterial strains that leave septic patients with minimal or no treatment options available. Traditional antibiotic treatments invariably have a finite lifespan due to the cunning nature of this bacterium in acquiring drug resistance, necessitating the development of alternative treatment strategies, such as a preventative therapy (e.g., a vaccine).
One approach to vaccine development is directed toward mimicking poly-N-acetylglucosamine (PNAG), a long-chain polysaccharide composed of β-(1→6)-linked N-acetylglucosamine residues, which is the main constituent of the S. aureus biofilm. Previous research has demonstrated that protective antibodies against S. aureus can be generated in vivo following immunisation with T-cell independent PNAG-analogues conjugated to various T-cell dependent carrier proteins. Results from these studies have provided strong evidence toward the potential use of such constructs as a prophylactic therapy.
In this project, a series of organic macromolecules presenting clusters of PNAG-analogues were synthesised in an effort to expand on the above strategy, in an attempt to develop a new prophylactic therapy. A simple iterative method was developed for the synthesis of short-chain, azido-functionalised β-(1→6)-glucosamine oligosaccharides between two and five monosaccharide units in length. Two different molecular scaffolds designed specifically to aid in the stable and reproducible display of PNAG-analogues were then synthesised, and three target carbohydrates were attached. A ball-like cluster of carbohydrate epitopes (increasing in glycan density depending on the oligosaccharide used) was produced through the attachment of twelve copies of each oligosaccharide to a phenylene-based dendrimer scaffold. In an alternative approach, each carbohydrate was attached to a norbornene-based monomer, and subsequent polymerisation gave a more linear display of carbohydrate epitopes in which the carbohydrate moieties were pendant to the polymer backbone. Following the synthesis and characterisation of each construct, preliminary in vivo studies, with a strong focus on method development, were undertaken to determine the ability of these compounds to act as immunostimulatory agents.