I. Islam et al. / Bioorg. Med. Chem. Lett. 12 (2002) 1767–1769
1769
receptor is the only NPY subtype to contain a histidine
residue in TM6. Other important interactions high-
lighted by the model, include an acid-base pair formed
with the amine of the sulfonamide amine and Glu211
and hydrophobic interactions between the aromatic
groups and hydrophobic regions of the receptor.
In summary, we have shown that a weak and non-
selective flexible molecule, benextramine, can be used as
a starting point for the design of potent and selective
ligands. Central to this improvement was the incor-
poration of a sulfonamide group that provides a bias
towards the NPY Y5 receptor. Systematic exploration
of this series led to a series of NPY Y5 antagonists of
high potency. A model for howthese ligands bind to the
receptor is presented that is consistent with the SAR
trends.
Figure 2. Model of sulfonamide 6 binding to hY5 receptor.
The sulfonamide amines were found to be very selective
for the Y5 over the other NPY receptors (Y1, Y2, and
Y4) and therefore represent excellent tools for studying
the physiological roles of the Y5 receptor.
Acknowledgements
We thank Zoya Shaposhnik and Nancy Rogacki for
their efforts in Ki determinations.
All of the sulfonamide amines in Table 1 were pharma-
cologically characterized in binding and functional
assays (n ꢀ2). Radioligand binding assays were per-
formed with membranes from COS-7 cells transiently
transfected with NPY receptor subtypes, labeled with
125I-PYY plus or minus test compounds.8 Functional
assays were conducted with HEK-293 or LMTK- cells
stably transfected with NPY receptor subtypes; intact
cells were stimulated with forskolin and NPY plus or
minus test compounds, then cAMP levels were detected
by radioimmunoassay. All sulfonamides (6 and 11–19)
are pure antagonists, in that they competitively attenu-
ate the ability of NPY to inhibit forskolin-stimulated
cAMP. These antagonists are potent inhibitors of the
functional response to NPY with Kb values very similar
to the Ki values (e.g., 11 hY5 Ki=8 nM, hY5
Kb=26 nM; 12 hY5 Ki=14 nM, hY5 Kb=6 nM). The
compounds were tested in a panel of GPCRs and found
to be selective for the NPY hY5 receptor (>100-fold for
most receptors). The main cross reactivity being with
the cloned human a2c and D2 receptors (e.g., 11
Ki=100 nM on human a2c and Ki=63 nM on human
D2). The sulfonamide series of NPY antagonists are
also potent and selective for the rat NPY Y5 subtype
(e.g., 11 Ki rY5=18 nM, Ki rY1=22,000 nM).
References and Notes
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