Leptomycin B (LepB) is a potent, specific inhibitor of nuclear export
signal (NES)-dependent protein export from the nucleus. Fukuda. M., et
al. "CRM1 is responsible for intracellular transport mediated by the
nuclear export signal." Nature390: 308-311 (1997).
The effect of LepB on the CRM1 (exportin 1) NES receptor results from
selective alkylation by LepB of a single cysteine residue. Kudo, N., et
al. "Leptomycin B inactivates CRM1/exportin 1 by covalent modification
at a cysteine residue in the central conserved region." Proc. Natl. Acad.
Sci. USA96: 9112-9117 (1999).
LepB inhibits the nucleo-cytoplasmic translocation of the HIV Rev
protein at nanomolar concentrations. Wolff, B., et al. "Leptomycin
B is an inhibitor of nuclear export: inhibition of nucleo-cytoplasmic
translocation of the human immunodeficiency virus type 1 (HIV-1) Rev protein
and Rev-dependent mRNA." Chem Biol.4: 139-147 (1997).
LepB also exhibits potent antitumor activity in vitro and in
vivo, and possesses potent antimycotic and antibiotic activity. Tunac,
J.B., et al. "Novel antitumor antibiotics, CI-940 (PD 114,720) and
PD 114,721. Taxonomy, fermentation and biological activity." J.
Antibiot.38: 460-465 (1985).
POTENCY: LepB typically exhibits IC50 values in
the 1 nM range, depending on the species, cell type, and phenomenon under
study.
Our LepB is supplied in serum bottles with teflon-lined closures
containing a solution in absolute ethanol (a better solvent than
methanol/water; see "Solvent" below).
The 100 µg size is supplied as 185 µL of a 1 mM solution (540 µg/mL).
The 500 µg size is supplied as 925 µL of a 1 mM solution.
The 1 mg size is supplied as 1.85 mL of a 1 mM solution.
Larger quantities and higher concentrations are available - please
request a quotation.
SOLVENT: Ethanol is a better solvent for LepB than methanol for at
least three reasons. First, published information indicates that LepB is
more stable in ethanol (purity unchanged after 5 months at room
temperature: US patent 4,771,070) than in methanol/water 70/30
(freezer temperatures required for storage for more than a few days: Sigma
newsletter LifeScience2, April 2001, page 11). Second,
ethanol has a significantly higher boiling point than methanol, so ethanol
solutions are expected to be less susceptible to changes in concentration
due to solvent evaporation. Third, LepB is a relatively hydrophobic
compound, and may have a tendency to stick to plastic. Being a much
stronger organic solvent than methanol/water, ethanol reduces the potential
loss of LepB when handled in plastic. NOTE: LepB is also reported to be
unstable in DMSO, so the latter solvent should not be used for dilutions.
DILUTING LepB SOLUTIONS: Dilutions of LepB for dose response studies
should be made in an organic solvent, preferably ethanol, with only the
final dilution being made into culture medium.
STABILITY WARNING: LepB in any quantity is unstable when dried down
into a film. Thus, under no circumstances should the solvent be removed
from solutions of LepB, because rapid decomposition may result.
STABILITY TESTING: To test LepB stability in ethanol, we tested LepB
dilutions under two different temperature conditions. One set of samples
was maintained at freezer temperatures after purification and dilution, and
then sent in ice to an academic laboratory in Texas. A second set of
samples was heated in an oven to 60 ºC for two hours, then shipped to the
same Texas lab, in the middle of August, without ice or refrigeration,
and the samples were assayed for inhibition of COS cell growth. No
significant differences were found between the two temperature conditions.
In another test, we refluxed a sample of our LepB in ethanol (b.p. 78.5 ºC)
for an hour; at the end of this period, HPLC analysis showed that
decomposition products amounted to less than 1%.
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