GPT and breast carcinoma: A contributor to the failure of breast cancer treatment is that all breast cancer cells and their microenvironment capillary endothelial cells express asparagine linked glycoproteins with different structures, according to Banerje et al. Therefore, they tested a small biomolecule called Tunicamycin to block the catalytic activity of acetylglucosamine 1-phosphate transferase (GPT) in the protein glycosylation pathway of the endoplasmic reticulum (ER).