PKM and glioblastoma: In addition, treating tumorspheres derived from GBM patients with inhibitors of nicotinamide phosphoribosyl transferase (NAMPT), a NAD+ salvage enzyme, resulted in c-Myc overexpression, which mediated cytotoxicity by apoptosis in tumorspheres, inhibiting glycolysis in the NAD+-dependent GA3PDH step, decreasing the enzymatic activity of HX2, PKM2, and LDHA, as well as the levels of NAD+, pyruvate, and lactate [311].