MDH1 and pancreatic ductal adenocarcinoma: Pancreatic ductal adenocarcinomas (PDACs) rely on glutamine to sustain proliferation, and malate dehydrogenase 1 (MDH1), a key enzyme in glutamine metabolism, is highly O-GlcNAcylated at Ser-189 in PDAC patients, which enhances MDH1 enzymatic activity and glutamine metabolism, thus providing an Achilles heel for the treatment of PDAC (35).