Leptomycin B

Leptomycin B is a potent and specific nuclear export inhibitor. Leptomycin B alkylates and inhibits CRM1 (chromosomal region maintenance)/exportin 1, a protein required for nuclear export of proteins containing a nuclear export sequence (NES). 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 stabilizes the expression of p53. Leptomycin B also inhibits the export and translation of many RNAs, including COX-2 and c-Fos mRNAs, by inhibiting export of ribonucleoproteins.

Leptomycin B effects: Human papillomavirus (HPV) infection is strongly associated with the development of anogenital neoplasia, particularly cervical cancer. It has been estimated that 99.7% of all cervical carcinomas are attributable to infection with HPV, and types 16 and 18 account for the vast majority of such cases. Both of these 'high risk' HPV types encode the oncoproteins E6 and E7, which exert multiple effects on many proteins involved in cell-cycle regulation, including p53. The nuclear export protein inhibitor leptomycin B has been shown to cause the nuclear sequestration of p53 in cervical carcinoma cells. We demonstrate that LPB   induces apoptosis selectively at nanomolar concentrations in primary human keratinocytes (PHKs) expressing HPV oncogenes. Both monolayer and organotypic raft cultures of transduced PHKs were highly susceptible to treatment with LPB  . By contrast, although LPB   stimulated p53 accumulation in normal PHKs, no significant induction of apoptosis was detected on Western blots or immunostained monolayer/raft cells, or following pulsed exposure to the drug. Furthermore, topical application of microM concentrations of LPB   to mouse skin was non-toxic. These data suggest that the topical application of LPB   to HPV-infected intra-epithelial lesions may represent a specific and effective therapeutic strategy against HPV-associated anogenital neoplasia.

Overexpression of inducible nitric oxide synthase (iNOS) and the resultant overproduction of NO has been implicated in neuronal inflammatory diseases. LPB  , a metabolite of Streptomyces, has been identified as a specific inhibitor of CRM1 nuclear export receptor. In this study, we evaluated the effect of LPB   on lipopolysaccharide (LPS)-induced iNOS expression in BV2 cells, a murine microglial cells and the associated mechanisms. LPB   strongly inhibited LPS-induced iNOS protein and mRNA expressions in BV2 cells in which 10 ng/ml of LPB   (18 nM) was sufficient to greatly down-regulate iNOS by LPS, suggesting the potency of LPB   to inhibit iNOS. The data of iNOS promoter-driven luciferase assay further suggested that the Leptomycin B  inhibitory effect was in part due to inhibition of iNOS transcription. However, LPS-induced activation of various intracellular signaling proteins, such as nuclear factor-kappaB (NF-kappaB), extracellular signal-regulated kinases (ERKs), p38s, and c-Jun N-terminal kinases (JNKs), whose activations are known to be important for iNOS expression by LPS in BV2 cells, were not affected in the presence of Leptomycin B . Together, these results suggest that Leptomycin B  inhibits iNOS expression in response to LPS in BV2 microglia, and the inhibition seems to be associated with blockage of CRM1-mediated iNOS mRNA nuclear export and also in part transcriptional down-regulation of iNOS, but not through modulation of NF-kappaB and the mitogen-activated protein kinase signaling pathways.