The oxathiazinane compound GP-2250 (Figure 1A) is a highly effective antineoplastic agent, as has been demonstrated for pancreatic adenocarcinoma in vitro and in vivo. 1,2 GP-2250 inhibited tumour cell proliferation and induced apoptotic cytotoxicity. In vivo, the growth of patient-derived pancreatic tumour tissue was strongly inhibited in xenograft mouse models. 1,2 GP-2250 is presently in a clinical trial for the treatment of pancreatic cancer (NCT 03854110). 3 Its molecular mechanism of action, however, has remained unclear.As GP-2250 showed comparable antineoplastic activity in pancreatic and mesothelioma tumour cell lines, 1,4 GP-2250 was expected to target a common feature of cancer cells such as aerobic glycolysis, a hallmark of cancer metabolism. [5][6][7] As the first step in glycolysis,