Importazole is a small molecule inhibitor of the nuclear transport receptor importin-β.

Importazole specifically blocks importin-β-mediated nuclear import both in Xenopus egg extracts and cultured cells, without disrupting transportin-mediated nuclear import or CRM1-mediated nuclear export. Importazole impairs the release of an importin-β cargo FRET probe and causes both predicted and novel defects in spindle assembly[1]. Importazole displays an IC50 of approximately 15 uM for inhibition of NFAT-GFP import. Importazole has an IC50 of approximately 22.5 uM in HeLa cells following treatment over a 24-hour period[1]. Importazole induces a dose-and time-dependent inhibition of myeloma cells growth. And the IC50 values of importazole on RPMI 8226 and NCI-H929 after 48 hours incubation are (4.43±0.41) and (4.78±0.35) umol/L, respectively. Treatment of RPMI 8226 and NCI-H929 cells with 8 umol/L importazole for 24 h could inhibit NF-κB import to nucleus and reduce its DNA binding activity[2].