BI-D1870 is a cell permeable, ATP-competitive inhibitor of the four isoforms of ribosomal S6 kinase (p90 RSK) (IC50′s at 100μM ATP: Rsk-1 = 31nM, Rsk-2 = 24nM, Rsk-3 = 18nM, Rsk-4 = 15nM). BI-D1870 does not significantly inhibit 10 other AGC kinases, and over 40 other protein kinases at 100X concentrations. BI-D1870 acts on the N-terminal AGC kinase domain and completely prevents PMA-induced TSC2 phosphorylation.