AKT1 and glioblastoma: However, there are some limitations in the present study: The downstream mechanism of PI3K/AKT signaling pathway in GBM cells has not been identified; also, the upstream regulatory mechanisms of circ_PTN have not been discussed; significantly, the clinical value of circ_PTN in GBM has not been analyzed; for the in vivo experiments, we have not totally simulated the process of drug resistance in the present work.