Inhibits DNA-dependent ATPase activity of XBP and induces inhibition of RNA polymerase II (RNAPII)-mediated transcription (IC50 = 200 nM). Selective for RNAPII over RNAPI and RNAPIII. Blocks RNA synthesis in HeLa cells (IC50 = 62 nM); exhibits potent antiproliferative activity in 60 cancer cell lines (average IC50 = 12 nM) and induces apoptosis by blocking TNF-α-mediated c-IAP1 and c-IAP2 induction. Also displays immunosuppressive and anti-inflammatory activity. Purity 98%. MW (observed): 360.4