[2] Leptomycin B has been shown to be a potent and specific nuclear export inhibitor in humans[3] and the fission yeast S.

[4] Leptomycin B alkylates and inhibits CRM1 (chromosomal region maintenance)/exportin 1 (XPO1), a protein required for nuclear export of proteins containing a nuclear export sequence (NES), by glycosylating a cysteine residue (cysteine 529 in S.

[5] In addition to antifungal and antibacterial activities, leptomycin B blocks the cell cycle and is a potent anti-tumor agent.

At low nM concentrations, leptomycin B blocks the nuclear export of many proteins including HIV-1 Rev, MAPK/ERK, and NF-κB/IκB, and it inhibits the inactivation of p53.

[clarification needed] Original data copied with permission from Leptomycin B manufacturer product page (Fermentek)