Cell-permeable inhibitor of p70 ribosomal S6 kinase (S6K1 isoform) (Ki = 20 nM; IC50 = 160 nM). Suppresses the S6K1-mediated phosphorylation of S6, Rictor and mTOR in response to IGF1; displays no effect on the activity of RSK and MSK in vivo. Exhibits no significant inhibition of S6K2 or other AGC kinases (e.g. Akt, PKA and ROCK) in vitro.