Discovery of 5-substituted 2-amino-4-chloro-8-((4-methoxy-3,5-dimethylpyridin-2-yl)methyl)-7,8-dihydropteridin-6(5H)-ones as potent and selective Hsp90 inhibitors

Article abstract of DOI:10.1016/j.bmcl.2009.03.074

A new series of compounds, 5-substituted 2-amino-4-chloro-8-((4-methoxy-3,5-dimethylpyridin-2-yl)methyl)-7,8-dihydropteridin-6(5H)-ones, have been designed and identified as potent and selective inhibitors of Hsp90. These compounds demonstrated nanomolar

Full text of DOI:10.1016/j.bmcl.2009.03.074

Bioorganic & Medicinal Chemistry Letters 19 (2009) 2860–2864
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Discovery of 5-substituted 2-amino-4-chloro-8-((4-methoxy-3,5-dimethylpyri-
din-2-yl)methyl)-7,8-dihydropteridin-6(5H)-ones as potent and selective Hsp90
inhibitors
*
Xiaoyuan Li, Ellyn Shocron, Aimin Song, Neela Patel, Connie L. Sun
Poniard Pharmaceuticals, Inc., 7000 Shoreline Court, South San Francisco, CA 94080, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
A new series of compounds, 5-substituted 2-amino-4-chloro-8-((4-methoxy-3,5-dimethylpyridin-2-
yl)methyl)-7,8-dihydropteridin-6(5H)-ones, have been designed and identified as potent and selective
inhibitors of Hsp90. These compounds demonstrated nanomolar potency toward both Hsp90-regulated
Her2 degradation and the growth of a panel of human tumor cell lines in cell-based assays. High selec-
tivity of these compounds toward Hsp90 was evident given that they did not inhibit a panel of 34 kinases
Received 27 February 2009
Revised 17 March 2009
Accepted 20 March 2009
Available online 24 March 2009
at 10 lM. The structure–activity relationship (SAR) of this series is reported here.
Keyword:
Hsp90 inhibitors
Ó 2009 Published by Elsevier Ltd.
Hsp90 has attracted enormous attention and has emerged as a
viable target for cancer therapy due to its critical roles in retaining
the conformation and, hence, the function of its broad range of cli-
ent proteins many of which are associated with cancer pathol-
ogy.1–3 Clinical proof of concept has been provided by a natural
product Hsp90 inhibitor, 17-AAG which is under Phase III evalua-
tion for the treatment of melanoma.4,5 However, the side effects
and poor formulability of 17-AAG restricted its potential for broad
applications.6 Small synthetic Hsp90 inhibitors emerged to address
these issues presented by this natural product. Diverse chemotypes
have been identified as potent Hsp90 inhibitors and advanced into
clinics.7–9 Most of these chemotypes bind to the N-terminal ATP
binding site. It is interesting to note that different chemotypes
have been found to induce quite unique conformational changes
in Hsp90. This was confirmed by co-crystal structures of Hsp90-
inhibitor complexes.10–12
moiety at the 2-position of 1 interacts with D93 via the critical
H-bond interaction, the pyridine ring at the 8-position interacts
Cl
H
4
N5
O
N
O
N
H2N
2
N
N8
1
Figure 1. Knowledge-based design of 2-amino-4-chloro-8-((4-methoxy-3,5-
dimethylpyridin-2-yl)methyl)-7,8-dihydropteridin-6(5H)-one (1) as an initial hit
inhibiting Hsp90.
Our knowledge-based design of Hsp90 inhibitors resulted in
identification of an initial hit, 2-amino-4-chloro-8-((4-methoxy-
3,5-dimethylpyridin-2-yl)methyl)-7,8-dihydropteridin-6(5H)-one
(compound 1 in Fig. 1). The compound inhibited Hsp90 with an
IC50 of 0.88
the degradation of Hsp90 client protein Her2 with an IC50 of
0.57 M, and inhibited the growth of human tumor cells including
MCF-7, SKBR-3, BT474, and HT-29 with GI50 values less than
1.5 M. It was anticipated that compound 1 binds to the N-termi-
lM in a fluorescence polarization (FP) assay, induced
l
l
nal ATP binding site in a similar pattern to purine-based Hsp90
Figure 2. Docking of 1 in the N-terminal ATP binding site of Hsp90a. The model
was built based on the Hsp90 structure (PDB code 3D0B). (A) 2-Amino group forms
a hydrogen bond with D93 and nitrogen atom at the 3-position interacts with D93
inhibitors.7 The modeling study suggested later that the amino
via a water molecule (red ball). The pyridine ring forms p–p stacking with F138. (B)
The 5-position directs toward the opening of the ATP binding site. The path from
the 5-position to the opening (yellow arrow) is surrounded by the hydrophobic side
chains of I96 and M98 as well as the carbon atoms of K58 and D54.
* Corresponding author. Tel.: +1 650 251 9202; fax: +1 650 583 3789.
E-mail address: connie_sun@yahoo.com (C.L. Sun).
0960-894X/$ - see front matter Ó 2009 Published by Elsevier Ltd.
doi:10.1016/j.bmcl.2009.03.074

X. Li et al. / Bioorg. Med. Chem. Lett. 19 (2009) 2860–2864
2861
with F138 via
p
–
p
stacking, and the 7,8-dihydropteridin-6(5H)-
acid in toluene or with ethyl oxalyl chloride in acetone followed
by refluxing in ethanol afforded 2-amino-4-chloro-8-((4-
methoxy-3,5-dimethylpyridin-2-yl)methyl)pteridin-7(8H)-one (5)
and 2-amino-4-chloro-8-((4-methoxy-3,5-dimethylpyridin-2-yl)-
methyl)-pteridine-6,7(5H,8H)-dione (6), respectively. 4-Chloro-
8-((4-methoxy-3,5-dimethylpyridin-2-yl)methyl)-5,6,7,8-tetrahy-
dropteridin-2-amine (7) was prepared by reduction of 5 with lith-
ium aluminum hydride (LAH).
one core interacts with M98 via hydrophobic interaction
(Fig. 2A). The assessment of the pharmaceutical properties for 1
indicated that it has good aqueous solubility (381 lM at pH 3)
and metabolic stability in human, rat, and mouse microsomes
(t1/2 > 60 min). Most importantly, compound 1 demonstrated
60% bioavailability in vivo (rat). Compound 1 proved to be a viable
hit for further structure elaboration to improve biological potency
toward Hsp90. Here, we report the results of structure–activity
relationship (SAR) studies on this new chemotype as a Hsp90
inhibitor.
Guided by the published co-crystal structure information and
the modeling study, our medicinal chemistry efforts were focused
on several positions of the core structure, 2-amino-7,8-dihydrop-
teridin-6(5H)-one: (i) modification of the pteridinone ring, (ii)
incorporation of diverse substitution, particularly solubilizing
groups, at the 5-position, (iii) replacing the 4-Cl with other small
moieties including methoxy, methyl, or other halogens, (iv) intro-
duction of substitutions at the 7-position, (v) elaboration of aryl
or heteroaryl rings at the 8-position.
The initial modification was focused on the pteridinone ring. It
was found from the molecular modeling study that the carbonyl
moiety at the 6-position was not found to be involved in any crit-
ical interaction (Fig. 2B). It was instead, directed toward the open-
ing of the ATP binding site. Hence, various analogs with 7-carbonyl,
6,7-dicarbonyl or no substitution at either 6- or 7- position were
prepared (Scheme 1).13–16 The key intermediate, 6-chloro-N4-((4-
methoxy-3,5-dimethylpyridin-2-yl)methyl)-pyrimidine-2,4,5-tri-
amine (4), was prepared via condensation of 4,6-dichloropyrimi-
Based on the SAR results from the structural modifications of
the pteridinone structure (compound 5–7), the efforts were re-di-
rected to 1 analog retaining 6-carbonyl group while functional
groups at other positions were explored. From the modeling study,
the substitution at the 5-position of 1 is directed toward the open-
ing of the binding site and can be used as a handle to improve the
pharmaceutical properties as well as potency. There is a hydropho-
bic environment between the 5-position and the opening of the
binding site (Fig. 2B). Accordingly, various alkyl substitutions were
first incorporated to explore the hydrophobic space around this po-
sition (Scheme 2). Solubilizing groups were then attached to some
of the alkyl substitutions for improving pharmaceutical properties
of these compounds. Compound 1 was prepared by condensation
of 4,6-dichloropyrimidine-2,5-diamine with methyl 2-((4-meth-
oxy-3,5-dimethylpyridin-2-yl)methylamino)-acetate (8) which
was obtained by amination of 2 with methyl 2-aminoacetate
hydrochloride in ethanol. Alkylation of 1 with alkyl halides affor-
ded the major N-alkylated product Ia–i and minor O-alkylated
product IIa.17 The ratio of the two products varied depending on
the alkylating agents. Both I and II analogs were evaluated for their
inhibitory potency toward Hsp90.
dine-2,5-diamine
and
(4-methoxy-3,5-dimethylpyridin-2-
Modification at the 4-position was quite limited based on the
modeling study indicating that the small space around this posi-
tion may only accommodate substitutions like halogen, methyl,
or methoxyl group. Compound IIIa and IIIb were prepared from
If via direct displacement of the 4-Cl with a methoxyl and methyl
group, respectively, under the condition described in Scheme 3.
The effect of adding a substituent at the 7-position was also
elaborated by introducing various alkyl moieties (compounds
IVa–h in Scheme 4). Compound IVa was synthesized via replacing
the 4-Cl in 4,6-dichloropyrimidine-2,5-diamine with (S)-3-((4-
methoxy-3,5-dimethylpyridin-2-yl)methylamino)-dihydrofuran-2
(3H)-one (9) which was prepared via reductive amination using
4-methoxy-3,5-dimethyl-picolinaldehyde and (S)-3-aminodi-
hydrofuran-2(3H)-one hydrochloride. Using the similar protocol,
compound IVb–e (Scheme 4) were prepared with various substitu-
tions at the 7-poisition. Alkylation of IVc and IVd at the 5-position
using the same protocol as for the synthesis of Ia–i afforded
compound IVf–h.
yl)methan-amine (3) which was obtained via amination of 2-(chlo-
romethyl)-4-methoxy-3,5-dimethylpyridine hydrochloride (2).
Condensation of 4 with ethyl 2-oxoacetate in the presence of acetic
HCl
N
N
Cl
NH2
a
b
O
O
2
3
Cl
N
N
N
N
N
c
H2N
O
N
Cl
N
NH2
NH
N
H2N
O
5
N
Cl
4
O
H
N
d
O
H2N
N
N
O
N
Cl
HCl
N
H
N
O
N
O
N
O
O
N
Cl
N
H
6
a
b
O
N
H2N
N
O
O
2
8
1
Cl
H
Cl
N
N
N
Cl
N
R
N
N
e
O
N
O
N
OR
N
N
5
H2N
N
c
N
N
H2N
H2N
N
+
N
7
O
Ia - i
IIa
O
Scheme 1. Diversification of the pteridinone core. Reagents and conditons: (a) (i)
K2CO3, DMF, isoindole-1,3-dione, room temperature, 24 h; (ii) NH2NH2, 50 °C, 1 h;
48% yield; (b) Et3N, BuOH, 4,6-dichloropyrimidine-2,5-diamine, reflux, 3 h; 50%
yield; (c) ethyl 2-oxoacetate, acetic acid, toluene, reflux, 4 h; 54% yield; (d) (i) ethyl
oxalyl chloride, K2CO3, acetone, room temperature, overnight; (ii) Et3N, EtOH,
reflux, 4 h; 90% yield; (e) LAH, THF, room temperature for 60 min; 90% yield.
Scheme 2. Synthesis of 5-substituted-2-amino-4-chloro-8-((4-methoxy-3,5-dim-
ethylpyridin-2-yl)methyl)-7,8-dihydropteridin-6(5H)-ones. Reagents and condi-
tions: (a) methyl 2-aminoacetate hydrochloride, K2CO3, EtOH, reflux, 1 day; 43%
yield; (b) Et3N, BuOH, 4,6-dichloropyrimidine-2,5-diamine, reflux, 18 h; 50% yield;
(c) NaH, DMF, RX, room temperature, overnight.

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X. Li et al. / Bioorg. Med. Chem. Lett. 19 (2009) 2860–2864
Table 1
In vitro biological activity toward Hsp90 in a FP and Her2 degradation assay
O
N
O
N
O
N
N
N
Cl
Cl
R
N
5
O
N
O
N
N
OR
N
H2N
N
a
b
6
Cl
N
H2N
N
N
H2N
N
O
N
O
N
N
N
IIIa
H2N
N
O
Ia-i
IIa
O
N
N
a
a
N
ID
R
FP assay IC50
M)
Her2 degradation IC50
(lM)
If
(
l
H2N
N
N
O
1
5
6
7
H
—
—
—
0.88 0.16
nt
nt
0.57 0.26
>10
>5
IIIb
>5
>5
Ia
Ib
Ic
Id
Ie
If
CH3
0.96 0.17
0.90 0.17
0.66 0.48
nt
0.07 0.04
0.05 0.01
nt
0.93 0.23
1.91 0.58
0.51 0.29
1.55 0.34
0.05 0.03
0.04 0.01
0.11 0.03
0.10 0.02
0.01 0.01
>10
Scheme 3. Synthesis of 4-substituted-2-amino-5-isobutyl-8-((4-methoxy-3,5-dim-
ethylpyridin-2-yl)methyl)-7,8-dihydropteridin-6(5H)-ones. Reagents and condi-
tions: (a) NaOH, CH3OH–H2O (6:1), reflux, 48 h; 70% yield; (b) Pd(PPh3)4, AlMe3,
THF, reflux, overnight; 50% yield.
(CH3)2CH(CH2)3–
(Pyrrolidin-1-yl)-(CH2)2–
(Morpholino-1-yl)-(CH2)3–
(CH3)2CH–
(CH3)2CHCH2-
Cyclopentyl
Ig
Ih
(CH3)2N(CH2)2NHCOCH(CH3)- nt
Finally, the SAR study on the substituent at the 8-position was
also elaborated by replacing substituted pyridines with other aro-
matic or heteroaromatic ring. The preparation of this series (V) fol-
lowed the same procedure described for series I with aryl- or
heteroaryl-methanamine replacing (4-methoxy-3,5-dimethylpyri-
din-2-yl)methan-amine.
IIa Cyclopentyl
Ii
nt
nt
(Morpholin-1-
yl)(CH2)2NHCO-
a
The IC50 values are means of three independent experiments (nt = not tested).
All the analogs were first evaluated for their ability to induce
degradation of the Hsp90 client protein Her2 in SKBR-3 cells. Se-
lected compounds were then evaluated in a FP assay for their affin-
compounds with dramatically decreased potency in the Her2 deg-
radation assay compared to the original compound 1 (Table 1). It is
likely that the 6-carbonyl plays an important role (sterically or
electronically) in the binding of these compounds to Hsp90. Fur-
ther SAR was then focused on the modification at different posi-
tions of 1.
Based on the modeling study, the path from the 5-position of 1
to solvent exposure at the opening of the ATP binding site of Hsp90
is surrounded by hydrophobic amino acid side chains of I96 and
M98 as well as the carbon atoms of K58 and D54 (Figure 2B). Hence
diverse alkyl (i.e., branched or straight chain) functionalities were
introduced at the 5-position with the objective of increasing the
affinity to Hsp90 via extra hydrophobic interactions. The solubiliz-
ing moiety was then attached to the alkyl groups at the 5-position
ity to Hsp90. Compounds with IC50 values less than 2.0 lM in the
Her2 degradation assay were then further evaluated for their
inhibitory activity against the growth of several human tumor cell
lines in culture, including MCF-7, BT474, SKBR-3, and HT29. To
examine the selectivity at the cellular level, selected analogs were
also assessed for cytotoxicity using a normal human mammary
epithelial cell line (hMEpiC). The results are summarized in Tables
1–4.
To examine the importance of the 6-carbonyl group of 1, several
analogs were prepared by moving the carbonyl group from 6- to 7-
position (5), adding an extra carbonyl at the 7-position (6), or elim-
inating this carbonyl group (7). All these modifications resulted in
O
Cl
N
H
N
O
O
N
O
NH
H2N
N
OH
N
O
O
N
O
a
b
N
O
+
H2N
HCl
O
9
IVa
O
OCH3
R
O
HN
O
N
O
N
R
c
a
OCH3
NH2 HCl
+
O
R'
N
Cl
N
Cl
H
N
O
O
N
d
H2N
N
H2N
N
N
R
N
N
R
N
IVb-e
IVf-h
O
O
Scheme 4. Synthesis of 7-substituted-2-amino-4-chloro-8-((4-methoxy-3,5-dimethylpyridin-2-yl)methyl)-7,8-dihydropteridin-6(5H)-ones. Reagents and conditions: (a)
NaBH(OAc)3, TEA, CH2Cl2, room temperature, 2 h; 57–76% yield; (b) 4,6-dichloropyrimidine-2,5-diamine, H2SO4, MeOH, reflux, overnight; 2.1% yield; (c) DIEA, nBuOH, 150 °C
in sealed tube, 48 h; 5–10% yield; (d) NaH, DMF, RX., room temperature, overnight.

X. Li et al. / Bioorg. Med. Chem. Lett. 19 (2009) 2860–2864
2863
Table 2
potency to induce Her2 degradation is not sensitive to the stereo-
chemistry at the 7-position. IVb and its S isomer (IVc) showed sim-
ilar potency. Of particular interest, introduction of the 7-alkyl
substitution on Ie bearing 5-isopropyl moiety retained potency
(IVh vs Ie) while the same modification on If with 5-isobutyl group
greatly decreased potency (IVf and IVg vs If). This is consistent
with previous SAR trend where the potency is sensitive to substi-
tution at the 5-position. Overall, substitutions at the 7-position
did not offer any advantage with regard to potency over the ones
without such substituents. However, solubilizing moiety may be
tolerable at this position with the right substituent at the 5-
position.
Finally, the SAR study was directed to the pyridine ring while
maintaining the optimal 4-Cl and 5-isopropyl or isobutyl substitu-
ents. Analogs with different substitutions on the pyridine ring or
substituted phenyl replacing the pyridine ring were prepared and
tested (Table 3). Replacing para-methoxy with Cl on the pyridine
ring caused about 15-fold decrease in potency (Va vs If). However,
a compound with a para-bromo substituent has only 2.5-fold de-
crease of potency in the Her2 degradation assay (Vb vs If). Analog
with 30,40-dimethoxyl substituents on the pyridine ring (Vc) was
found to be 4-fold less potent than If. Further more, replacing
the pyridine with substituted phenyl ring (Vd) resulted in more
than 125-fold decrease in potency in the Her2 degradation assay.
Altogether, the SAR indicated that there is little room for the diver-
sification on the aryl or heteroaryl (i.e., pyridine) ring. This is con-
sistent with our molecular modeling study as well as previous SAR
results on purine-based Hsp90 inhibitors,17 which indicated the
pyridine ring was positioned at the bottom of the ATP binding site
(Fig. 2B).
Compounds active in the Her2 degradation assay were further
evaluated for their ability to inhibit human tumor cell growth
in vitro (Table 4). The sensitivity of these human tumor cells to this
series of compounds is quite different. HT-29, SKBR-3, and BT474
cells were slightly more sensitive to the inhibitory activity of these
analogs than MCF-7 cells. In general, there is a good correlation be-
tween the potency for the Her2 degradation and anti-proliferative
activity. The most potent compounds in the Her2 degradation as-
say were also found to show high anti-proliferative activity with
GI50 values ranging from 5 to 90 nM comparable to the anti-prolif-
erative activity of geldenamycin. To assess the selectivity of these
compounds toward tumor over normal cell growth, we have also
tested selected compounds for their ability to inhibit growth of
normal non-tumorigenic human mammary epithelial cells, hME-
piC. Compound Ie is 5–16-fold more selective for human tumor
Inhibition of Hsp90 binding and activity by 4,5,7-substituted 2-amino-8-((4-
methoxy-3,5-dimethylpyridin-2-yl)methyl)-7,8-dihydropteridin-6(5H)-ones
R1
R2
N
N
O
N
H2N
N
7R3
N
O
IIIa-b and IVa-h
ID
R1
Cl
R2
R3
FP assay
IC50
Her2 degradation
IC50 (lM)
a
a
(lM)
If
(CH3)2CHCH2–
H
H
H
(S)-
0.05 0.01
nt
nt
0.04 0.01
1.07 0.30
0.98 0.06
0.28 0.05
IIIa OCH3 (CH3)2CHCH2–
IIIb CH3
IVa Cl
(CH3)2CHCH2–
H
0.64 0.07
CH2CH2OH
IVb Cl
IVc Cl
IVd Cl
IVe Cl
H
H
H
H
(R)-CH3–
(S)-CH3–
0.40 0.06
nt
0.35 0.04
0.43 0.30
0.65 0.31
0.37 0.14
(S)-(CH3)2CH– 2.14b
(S)-
nt
(CH3)2CHCH2–
(CH3)2CHCH2– (S)-CH3–
(CH3)2CHCH2– (S)-(CH3)2CH– nt
(CH3)2CH– (S)-(CH3)2CH– 0.08 0.01
IVf
Cl
nt
>5
>5
IVg Cl
IVh Cl
0.06 0.02
a
The IC50 values are means of three independent experiments (nt = not tested).
One experiment has been done.
b
of active compounds to improve the solubility as well as other
pharmaceutical properties. The potency of these compounds to-
ward Hsp90 in a FP assay as well as their ability to induce Her2
degradation in SKBR-3 cells depended on the nature of the alkyl
groups (Table 1). In this regard, an analog with a methyl group at
the 5- position (Ia) gave an IC50 value of 0.93 lM in Her2 degrada-
tion assay similar to the potency of 1. Compounds with a linear al-
kyl sub-unit attached to the 5-position showed comparable or
slightly decreased potency (Ib, Ic, and Id vs 1) in Her2 degradation
assay. However, 5–14-fold increase in potency was observed in the
Her2 degradation assay for compounds with an isopropyl (Ie), iso-
butyl (If), and cyclopentyl (Ig) moiety, implying the branched sub-
stitution is preferred at the 5-position. Based on the SAR
conclusion, Ih with the solubilizing moiety attached to the
branched substitution at the 5-position was prepared and demon-
strated comparable potency to Ie in Her2 degradation assay. Dur-
ing the synthesis of the 5-alkylated analog, a minor O6-alkylated
product was also isolated and screened. Of particular interest, IIa
induced Her2 degradation with an IC50 of 0.01 nM, over 11-fold
more potent than its corresponding 5-alkylated isomer, Ig, indicat-
ing that both the 5- and 6-position could tolerate large substitu-
tions which may offer additional hydrophobic interaction.
Besides the 5-alkylated analogs, a compound with 5-urea substitu-
tion (Ii) lost the potency compared to 1. There is, in general, a good
correlation between the potency in the Her2 degradation and FP
assay. Collectively, both the 5- and 6-position could tolerate di-
verse types of substitutions. Increased potency was observed for
compounds with branched alkyl groups.
A structural modification at the 4-position of one of the most
potent compound, If which has the optimal 5-isobutyl group, re-
sulted in more than 24-fold decrease in potency in the Her2 degra-
dation assay, implying that Cl is the optimal substitution at this
position (IIIa and IIIb vs If in Table 2). Further medicinal chemistry
efforts were focused on diversification at the 7-position in the
presence of the 4-Cl group. Analogs of compound 1 with various al-
kyl or substituted alkyl groups at the 7-position (Table 2) demon-
strated sub-micromolar potency comparable to 1 (i.e., IVa–e). The
Table 3
Inhibition of Hsp90 binding and activity by 8-(aryl-methyl) substituted 2-amino-4-
chloro-5-isobutyl-7,8-dihydropteridin-6(5H)-ones
Cl
N
Cl
N
N
N
O
N
N
O
O
N
N
H2N
H2N
O
O
N
2'
R1
R3
Cl
Vd
R2
Va-c
a
a
ID
R1
R2
R3
FP assay IC50
(l
M)
Her2 degradation IC50 (lM)
If
CH3
CH3
CH3
OCH3
—
OCH3
Cl
Br
OCH3
—
CH3
CH3
CH3
H
0.05 0.01
nt
0.06 0.01
nt
nt
0.04 0.01
0.59 0.19
0.10 0.02
0.16 0.14
>5
Va
Vb
Vc
Vd
—
a
The IC50 values are means of three independent experiments (nt = not tested).

2864
X. Li et al. / Bioorg. Med. Chem. Lett. 19 (2009) 2860–2864
Table 4
tumor cells over normal human cells. Efforts are currently directed
toward improving the in vivo properties of these analogs with re-
gard to their pharmacokinetic properties and efficacy.
Growth inhibition of tumor cell lines and human mammary epithelial cell in vitro
a
a
a
a
a
ID
MCF-7 IC50
M)
HT29 IC50
M)
SKBR-3 IC50
M)
BT474 IC50
M)
hMEpiC IC50
M)
(
l
(
l
(
l
(
l
(l
Acknowledgment
1
1.49 0.42
2.19 1.28
3.11 0.16
1.32 0.35
2.59 0.71
0.05 0.02
0.07 0.03
0.82 0.35
0.12 0.03
2.14
1.18 0.52
1.47 0.81
2.26 0.69
1.08 1.23
2.95 1.34
0.06 0.06
0.04 0.01
0.33 0.06
0.10 0.03
1.20
0.02 0.01
0.47 0.04
0.66 0.46
1.06 0.32
0.69 0.45
0.09 0.08
0.28 0.07
0.14 0.03
0.04 0.01
0.39 0.16
0.46 0.08
0.97 0.00
0.30 0.26
1.11 0.15
0.02 0.01
0.01 0.01
0.12 0.01
0.03 0.005
>5
0.005 0.004 0.01 0.003
0.22 0.05
0.25 0.11
0.43 0.09
0.23 0.02
0.65 0.10
0.95 0.11
1.65 0.22
0.52 0.49
1.81 0.23
0.03 0.03
0.02 0.01
0.29 0.04
0.06 0.01
>100
nt
nt
nt
nt
nt
Ia
Ib
Ic
Id
Ie
If
Ig
Ih
Iib
IIa
The authors would like to thank Drs. Gerald McMahon and Rob-
ert DeJaga from Poniard Pharmaceuticals, Inc. for discussions on
this program and Yongliang Zhu, the consultant, for providing
modeling support.
0.32 0.21
0.13 0.08
nt
nt
nt
nt
nt
nt
nt
nt
nt
nt
References and notes
0.04 0.02
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IVb 0.79 0.24
IVc 0.94 0.15
IVd 1.60 0.41
IVe 0.93 0.07
IVh 0.04 0.04
Va
Vb
Vc
0.41 0.01
0.47 0.20
0.76 0.17
0.49 0.07
0.005 0.004 0.02 0.01
0.47 0.26
0.28 0.21
0.10 0.06
0.11 0.02
0.06 0.01
0.01 0.00
0.24 0.03
0.13 0.02
0.03 0.003
0.18 0.12
0.24 0.15
a
The IC50 values are means of three independent experiments (nt = not tested).
One experiment was done.
b
8. Chandarlapaty, S.; Sawai, A.; Ye, Q.; Scott, A.; Silinski, M.; Huang, K.; Fadden, P.;
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cells tested than normal cells. Comparing to its growth inhibition
on hMEpiC, compound If is highly selective for SKBR-3 (13-fold)
and BT474 (6-fold) but less selective for MCF-7 (2-fold) and
HT29 (3-fold). The same selectivity trend was seen for compound
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quite understood. Furthermore, the implication of the cellular
selectivity in in vivo setting is still remained to be revealed.
In summary, we have reported a new series of Hsp90 inhibitors
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similar to other purine-based Hsp90 inhibitors. Both SAR and
molecular modeling studies supported this mechanism of action.
Co-crystal structures will further refine our understanding of the
molecular mechanisms by which these compounds inhibit
Hsp90. These compounds are highly selective for Hsp90 over 34
tyrosine or serine-threonine kinases (data not shown). They did
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not inhibit the activity of these kinases at 10
lM. At the cellular le-
vel, some compounds also selectively inhibit the growth of human