PIK3R3 and glioblastoma: Furthermore, by conducting western blot assays, we found that the impact of circ_PTN overexpression on PI3K-alpha, p-AKT and Cleaved Caspase-3 in DDP-sensitive GBM cells was countervailed by the depletion of PIK3R3 or the treatment of PI-103 (a specific PI3K/AKT inhibitor) (Figure 8C and S5B).