Mutant IDH1 inhibitor treatment is currently in clinical trials for glioma patients. However, to date, treatment does not result in tumor shrinkage. Therefore, in vivo biomarkers are needed to assess early therapeutic response. Here we treated mutant IDH1-expressing cells with the emerging inhibitor BAY-1436032. Using 1H MRS we found a significant decrease in 2-hydroxyglutarate that was accompanied by an increase in glutamate and phosphocholine, and using 13C MRS we detected a significant increase in glutamate produced from hyperpolarized [1-13C]α-ketoglutarate.