Imaging Cell-Surface Glycans through Metabolic Incorporation of Bio-orthogonal Tags

In this project the student will explore ways to image cell-surface glycans through metabolic incorporation of sugars bearing bio-orthogonal tags such as azido groups or cyclopropenes. Incorporation of these tags is assessed by reaction with their bio-orthogonal reaction partners (dibenzocyclo-octynes for azido groups, tetrazines for cyclopropenes) which have attached fluorophores. Generally such tagged sugars are administered to the cells in peracetylated form to enhance cell-permeability. Initial studies will explore whether less-than-fully-acetylated sugars may give a better level of incorporation. Once the acetylation level has been optimised, the student will investigate the simultaneous use of two different bio-orthogonal tags on two different sugars. It is hoped that the ratio of the incorporation levels of the two differentially tagged sugars will prove to be a reliable indicator of the type of cell to which they are attached. In particular it is reported that more aggressive types of cancer cells incorporate more sialic acid in their cell-surface glycans than normal cells do. Therefore increased incorporation of a tagged version of N-acetylmannosamine (a precursor of sialic acid) relative to a tagged version of another sugar (e.g. N-acetylgalactosamine) would show that the tumour is aggressive. Initial studies would investigate if the incorporation ratio for a particular cell type is independent of the growth conditions. If it is then the incorporation ratios for a range of different cell-types would be measured to see how they vary and whether the ratio correlates with other factors such as levels of sialic acids and metastatic potential.