PKM and cancer: Non-glycolytic metabolites such as succinyl-5-aminoimidazole-4-carboxamide-1-ribose-5′-phosphate (SAICAR), an intermediate of the de novo purine nucleotide synthesis (NPNS) pathway, have a stimulatory effect on PKM2 activity and promote cancer cell survival in glucose-limited conditions [170,171] (figure 1).