A selective and potent inhibitor of RSKs (IC50 = 0.004 to 0.013 μM for RSK isoforms 1-3); reduces phosphorylation of YB1 in MDA-MB-231 cells bearing activating mutations in the MAPK signaling pathway (EC50 = 0.21 μM); reduces H358 growth in soft agar and colony forming assays. ,