Having established an in vivo reporter system and observed efficient depletion of serum arginine in mice, we next proceeded to test the effect of ADI-PEG20 on the intracranial growth of ASS1 negative (LN229/GFP-Luc) and ASS1 positive (U87/GFP-Luc) GBM cells. This evidence concerns the gene ASS1 and glioblastoma.