ACS Medicinal Chemistry Letters
Letter
We have previously shown that the cytoprotective activity
manifested by KU-32 is dependent upon expression of Hsp70,
which occurs upon Hsp90 inhibition.21 Therefore, upon
construction of the library of noviomimetics, we determined
their ability to induce Hsp70 via a luciferase reporter assay. In
this assay, an Hsp70 promoter, which contains a heat shock
binding element, is subcloned in front of a luciferase reporter
gene and the resulting vector transfected into an immortalized
sensory neuronal cell line (50B11 cells). The transformed cells
are subsequently treated with Hsp90 inhibitors, which displace
the transcription factor, heat shock factor 1 (HSF1), from the
Hsp90 complex. Upon activation, HSF1 translocates to the
nucleus, wherein it binds the Hsp70 promoter and leads to
increased luciferase activity that is easily quantified. An increase
in luciferase activity represents activation of the Hsp70
promoter.
Based on the results shown in Figure 3A, the derivatives that
closely mimicked the chair conformation of the noviose sugar,
resulted in greater Hsp70 induction. The furanose novologues
25, 26, and 27 were relatively inactive in the luciferase reporter
assay, which suggests that the conformation manifested by the
furanose derivatives does not project substituents into a
favorable region of the binding pocket and, consequently,
minimizes Hsp70 induction. Similarly cyclopentanes 33 and 34
did not result in significant induction. The novologues with
constrained rings, 29 and 30, were also relatively inactive in the
luciferase reporter assay, and do not mimic the chair
conformation exhibited by the noviose sugar. These results
collectively suggest that the novologues that mimic the chair
conformation of the noviose sugar is required for Hsp70
induction.
Novologues that contain simplified pyranose derivatives
produced varying degrees of luciferase induction. Generally, the
more simplified the pyranose, the greater the Hsp70 induction.
Compounds 36 and 37 were most active in the luciferase assay
and represent simplified pyranose derivatives. Their non-
benzylated derivatives 38 and 39 were less active but exhibit
the same trend wherein para substituents result in greater
luciferase induction when compared to the meta substituent.
These results suggest that not only is the chair conformation of
the pyranose important for activity but larger substituents
improve activity. As shown in Figure 3A, compound 37, which
contains the 4-benzyl ether on the carbocyclic ring, induced the
highest level of luciferase in the 50B11 transformed cellular
assay and, consequently, was further investigated.
the neuroprotective activity manifested by the novologue class
of compounds, such as 1, as well as the novobiocin-based
compounds (e.g., KU-32). Thus, noviomimetics may represent
a new series of synthetically simple neuroprotective compounds
for the treatment of neurodegenerative diseases.
ASSOCIATED CONTENT
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S
* Supporting Information
The Supporting Information is available free of charge on the
Preparation and evaluation of reported compounds
AUTHOR INFORMATION
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Corresponding Author
*Phone: (785) 864-2288. Fax: (785) 864-5326. E-mail:
Funding
This work was supported by grants [CA109265] to B.S.J.B.;
[DK095911] to R.T.D. and [NS075311] to B.S.J.B. and R.T.D.
from The National Institutes of Health.
Notes
The authors declare no competing financial interest.
REFERENCES
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Using nontransfected 50B11 cells, compound 37 was shown
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As depicted in Figure 4A, compound 37 is suspected to bind
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