MTOR and glioblastoma: This is particularly relevant for GBM, since, among several other mechanism of action recently identified, metformin was more often reported to exert antiproliferative effects through the activation of AMPK and the subsequent inhibition of mTOR, a mechanism shown to promote GBM CSC growth (Chhipa et al., 2018; Leli and Koumenis, 2018).