Metabolic profiling of ASS1 negative and ASS1 positive glioblastoma subtypes to identify novel targets for therapy

Glioblastoma multiforme (GBM) are the most common and most malignant brain tumours. Despite treatment advances, average survival remains unacceptably low with 15-months, hence novel therapies are desperately needed. Cellular metabolism plays a central role in cancers. Sensitivity towards arginine-deprivation via pegylated arginine deaminase (ADI-PEG20) therapy has been identified in GBM, arresting proliferation in methylated arginino-succinate-synthetase-1 (ASS1M) and not unmethylated ASS1 (ASS1U) GBM cells. Advances of biochemical techniques and analysis have facilitated therapeutic target identification as well as biomarker discovery. Complimentary gas-chromatography coupled with mass spectrometry and 1-hydrogen nuclear-magnetic-resonance spectroscopy of in vitro GBM cells identified distinct metabolic profiles in ASS1 subtypes. Intracellular and extracellular analysis of GBM cells exposed to ADI-PEG20 treatment elucidated metabolic perturbations in the arginine, creatine, glycolytic, uridine, citric acid, thymine and glutamine pathways, induced by arginine deprivation. Transcriptional analysis of perturbed pathways elucidated differentially altered enzymatic expression in ASS1 GBM subtypes upon ADI-PEG20 treatment. Significantly modulated enzymes included transcriptional down-regulation of thymidylate synthase (TYMS) in ASS1M GBM cells, whereas ASS1U remained unaltered. Significantly altered enzymatic mRNA expression also identified modulation of glutamic pyruvate transaminase 2 (GPT2) in ASS1M cells, as well as thymidine kinase 2 (TK2) and alanine-glyoxylate aminotransferase 2 (AGXT2) in ASS1U GBM. Targeting the de novo thymine and creatine metabolic pathway, demonstrated that phytic acid (IP6) arrests proliferation in GBM cells, whereas creatine supplementation boosted proliferation. IP6 arrested proliferation in a time- and dose-dependent manner, irrespective of ASS1 status. Combining IP6 and ADI-PEG20, showed arrested proliferation was enhanced, compared to either treatment alone in ASS1M GBM cells.Open Acces