PHGDH and neoplasm: Additionally, spatial compartmentalization employs BBB-penetrant nanoplatforms (e.g., transferrin receptor-functionalized siRNA lipid nanoparticles) for tumor-selective PHGDH silencing in CNS malignancies [95], or systemically restricted inhibitors (e.g., D8 derivatives) that spare neuronal serine biosynthesis [59] (Fig. 4).