AKT1 and glioblastoma: However, we also observed the induction of feedback loops by the two inhibitors, indicated by elevated levels of MEK1/2 (after MEK inhibition) and Akt phosphorylation (after PI3K/mTOR inhibition) after prolonged incubation with the inhibitors, which has already been reported for NVP-BEZ235 in other glioblastoma cell lines [38, 41, 44].