GCLC and central nervous system cancer: We previously reported the upregulation of CBS and GCLC in IDHm gliomas, suggesting an activation of the transsulfuration pathway (Figure 1A) in these tumors,10 an important source of cysteine for GSH synthesis in astrocytes.20,21 To corroborate this at the metabolite level, we analyzed specimen from 22 glioma patients including IDHwt GBM (n = 10), IDH1m OD (n = 4), and IDH1m AS (n = 8) (Supplementary Table 1).