MTOR and glioblastoma: Given the known existing cross-talks between the PI3K/Akt/mTOR and the Ras/extracellular signal-regulated kinase (ERK) signaling pathway, we performed Western blot analysis of the GBM cells EV5, T98G, U87 and U251 after treatment with PI3K isoform-specific inhibitors (6 h) and analyzed the phosphorylation levels of ERK.