Comment on Cancer Metabolism and on the Role of the Endocrine Pancreas

In a previous work published 4 years ago, an arrest of tumor cell proliferation was obtained with dichloroacetate, an inhibitor of pyruvate dehydrogenase kinase, aiming to dephosphorylate and activate pyruvate dehydrogenase (PDH) [1]. This observation indicates that it may be useful to act as well, on other tumor cell enzymes that change in parallel to PDH, since this leads to a “rewiring of metabolic pathways” that is specific for tumor cells. Altered signaling controls that inhibit, or activate, enzymes in tumor cells were recently reviewed [2, 3]. Schematically, in tumor cells, enzymes such as PDH and pyruvate kinase (PK) are phosphorylated and inhibited as observed for catabolism and gluconeogenesis, while other enzymes (for example, glycogen synthase) are dephosphorylated, in their anabolic configuration, associated to glycolysis. This hybrid situation rewires metabolic pathways in tumor cells and gives them a metabolic advantage, enabling them to plunder tissue reserves mobilized by catabolic hormones [4, 5]. Normally, pancreatic beta cells secrete in parallel to insulin, the transmitter GABA, which switches off neighboring alpha and delta cells releasing respectively glucagon and somatostatin. In this way, when anabolic insulin is released, catabolic glucagon is switched off by GABA [2]. A failure of this GABA mediated mechanism probably explains the hybrid catabolic/anabolic response of tumor cell; however, we also have to consider that differentiated cells in cancer, respond preferentially to catabolic hormones; this is discussed in this letter.