Cancer Chemother Pharmacol. 2005
Aug;56(2):126-37. Epub 2005 Apr 20.
Comparison of 17DMAG and 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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