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Cancer-Chemother-Pharmacol-2005 Aug;56(2):126-37. Epub 2005 Apr 20. Related
Articles, Links
Comparison of 17-dimethylaminoethylamino-17-demethoxy-geldanamycin (17DMAG) and
17-allylamino-17-demethoxygeldanamycin (17AAG) in vitro: effects on Hsp90 and
client proteins in melanoma models.
Smith V, Sausville EA, Camalier RF, Fiebig HH, Burger AM.
Tumor Biology Center at the University of Freiburg, Breisacherstr. 117, 79106,
Freiburg, Germany.
The heat shock protein Hsp90 is a potential target for drug discovery of novel
anticancer agents. By affecting this protein, several cell signaling pathways
may be simultaneously modulated. The geldanamycin analog 17AAG has been shown to
inhibit Hsp90 and associated proteins. Its clinical use, however, is hampered by
poor solubility and thus, difficulties in formulation. Therefore, a
water-soluble derivative was desirable and
17-dimethylaminoethylamino-17-demethoxy-geldanamycin (17DMAG) is such a
derivative. Studies were carried out in order to evaluate the activity and
molecular mechanism(s) of 17DMAG in comparison with those of
17-allylamino-demethoxygeldanamycin (17AAG). 17DMAG was found to be more potent
than 17AAG in a panel of 64 different patient-derived tumor explants studied in
vitro in the clonogenic assay. The tumor types that responded best included
mammary cancers (six of eight), head and neck cancers (two of two), sarcomas
(four of four), pancreas carcinoma (two of three), colon tumors (four of eight
for 17AAG and six of eight for 17DMAG), and melanoma (two of seven).
Bioinformatic comparisons suggested that, while 17AAG and 17DMAG are likely to
share the same mode(s) of action, there was very little similarity with standard
anticancer agents. Using three permanent human melanoma cell lines with
differing sensitivities to 17AAG and 17DMAG (MEXF 276L, MEXF 462NL and MEXF
514L), we found that Hsp90 protein was reduced following treatment at a
concentration associated with total growth inhibition. The latter occurred in
MEXF 276L cells only, which are most sensitive to both compounds. The depletion
of Hsp90 was more pronounced in cells exposed to 17DMAG than in those treated
with 17AAG. The reduction in Hsp90 was associated with the expression of erbB2
and erbB3 in MEXF 276L, while erbB2 and erbB3 were absent in the more resistant
MEXF 462NL and MEXF 514L cells. Levels of known Hsp90 client proteins such as
phosphorylated AKT followed by AKT, cyclin D1 preceding cdk4, and craf-1
declined as a result of drug treatment in all three melanoma cell lines.
However, the duration of drug exposure needed to achieve these effects was
variable. All cell lines showed increased expression of Hsp70 and activated
cleavage of PARP. No change in PI3K expression was observed and all melanoma
cells were found to harbor the activating V599E BRAF kinase mutation. The
results of our in vitro studies are consistent with both 17AAG and 17DMAG acting
via the same molecular mechanism, i.e. by modulating Hsp90 function. Since
17DMAG can be formulated in physiological aqueous solutions, the data reported
here strongly support the development of 17DMAG as a more pharmaceutically
practicable congener of 17AAG.
PMID: 15841378
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