Importazole is a cell-permeable inhibitor of importin-β, which transports cargo molecules bearing a nuclear localization signal into the nucleus. Importazole prevents nuclear import of GFP-tagged nuclear factor of activated T cells (NFAT-GFP) in HEK293 cells (IC50 = 15 μM), which is reversible upon importazole washout. Importazole does not interfere with transportin-mediated nuclear import or chromosomal maintenance 1 (CRM1)-mediated nuclear export. Importazole inhibits nuclear import of topoisomerase IIβ binding protein 1 (TopBP1) in Xenopus egg extracts and of NF-κB in multiple myeloma cells. It also induces defects in spindle and microtubule formation in vitro.
