High-grade gliomas accumulate guanidinoacetate (GAA) to ~100-fold higher levels than non-malignant brain through imbalanced upregulation of AGAT and downregulation of GAMT enzymes, creating a creatine synthesis pathway bottleneck that causes tumor cells to secrete GAA rather than produce creatine. This secreted GAA acts as a GABAA receptor agonist that drives neuronal hyperexcitability in the tumor microenvironment through depolarizing GABA currents enabled by glioma-induced chloride dysregulation, thereby promoting neuron-glioma interactions and tumor growth that can be therapeutically targeted through genetic or dietary inhibition of AGAT activity.

The metabolic hallmarks of high-grade glioma (HGG) are not fully understood. Human brain tissue metabolomics revealed that the creatine synthesis pathway intermediate guanidinoacetate (GAA) accumulated ∼100-fold in HGGs relative to controls, which was caused by imbalanced activities of enzymes in this pathway. Glioma cells secreted GAA rather than using it to produce creatine, implicating an unexpected function. GAA accumulates in GAMT deficiency, an inborn error of metabolism, and elevates neuronal excitability. Neuronal excitability is also increased in glioma and drives tumor growth through neuron-glioma interactions. We hypothesized that glioma-generated GAA excites surrounding neurons. Indeed, GAA induced neuronal hyperactivity by activating GABAA receptors and causing depolarizing GABA currents in glioma-associated neurons with dysregulated chloride homeostasis. Depleting tumoral GAA decreased electrochemical activity, neuron-glioma interactions, and tumor aggressiveness. Our findings unveil a new mechanism linking cancer metabolism with cancer neuroscience and leverage human genetics to nominate GAA synthesis as a target in gliomas.