RPS6KB1 and cancer: In pOS-1 primary cancer cells, treatment with IMT1 (1 μM) potently inhibited phosphorylation of Akt (Ser-473), ribosomal protein S6 kinase 1 (S6K, Thr-389) and S6 (Ser-235/236) (Fig. 5A), indicating Akt-mTOR inactivation.