Consistent with these results, a reduction in the expression of PHGDH, PSAT1, or PSPH inhibited the growth of brain tumors derived from intracranially injected GSCs (XO6) [25, 26] in athymic nude mice (Fig. 3E), which was accompanied by the inhibition of cell proliferation, as evidenced by the intensity of Ki-67 expression, and induction of apoptotic cells, as detected by the terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay (Fig. 3F). Here, MKI67 is linked to brain neoplasm.