Pyridyl and thiazolyl bisamide CSF-1R inhibitors for the treatment of cancer

Article abstract of DOI:10.1016/j.bmcl.2008.07.093

The bisamide class of kinase inhibitors was identified as being active against CSF-1R. The synthesis and SAR of pyridyl and thiazolyl bisamides are reported, along with the pharmacokinetic properties and in vivo activity of selected examples.

Full text of DOI:10.1016/j.bmcl.2008.07.093

Bioorganic & Medicinal Chemistry Letters 18 (2008) 4794–4797
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Pyridyl and thiazolyl bisamide CSF-1R inhibitors for the treatment of cancer
*
David A. Scott , Brian M. Aquila, Geraldine A. Bebernitz, Donald J. Cook, Les A. Dakin, Tracy L. Deegan,
Maureen M. Hattersley, Stephanos Ioannidis, Paul D. Lyne, Charles A. Omer, Minwei Ye, XiaoLan Zheng
Cancer Research, AstraZeneca R&D Boston, 35 Gatehouse Drive, Waltham, MA 02451, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
The bisamide class of kinase inhibitors was identified as being active against CSF-1R. The synthesis and
SAR of pyridyl and thiazolyl bisamides is reported, along with the pharmacokinetic properties and in vivo
activity of selected examples.
Received 19 June 2008
Revised 22 July 2008
Accepted 24 July 2008
Available online 27 July 2008
Ó 2008 Elsevier Ltd. All rights reserved.
Keywords:
CSF-1R
Kinase inhibitors
Bisamide
Thiazole
CSF-1R is a member of the class III receptor tyrosine kinases,
along with c-Kit, Flt3 and PDGFR and b. Colony stimulatory factor
compounds from this scaffold had previously been explored as
inhibitors of p38 MAP kinase.18 Other groups have found related
a
1 (CSF-1), also known as macrophage/monocyte colony stimula-
tory factor (M-CSF), binds to CSF-1R, resulting in dimerization,
autophosphorylation and activation of signal transduction.1 CSF-
1/CSF-1R signaling is essential for normal monocyte development,
trophoblastic implantation and mammary gland development dur-
ing pregnancy and lactation.2,3 In cancer, pro-tumorigenic macro-
phages have been identified and linked to poor prognosis in
breast, ovarian and prostate cancers.4,5 Elevated levels of CSF-1
and CSF-1R have been reported in several tumor types, including
breast, ovarian and endometrial cancers, and have also been linked
to invasion and metastasis.6 Inhibition of CSF-1R activity could
therefore have multiple effects on the tumor through reduction
in the levels of tumor-associated macrophages (TAMs) and direct
effects on the tumor itself.
Compounds with activity against the other class III RTKs and
KDR, such as Sutent7 and ABT-869,8 have been reported as inhibi-
tors of CSF-1R. As yet, no selective small molecule has entered clin-
ical trials, although PD0360324,9 a monoclonal antibody from
Pfizer, recently entered phase I for the treatment of rheumatoid
arthritis. Other structural types have been reported as CSF-1R
inhibitors, with some targeting inflammation rather than cancer
indications.10–17
compounds to be inhibitors of Lck and c-Kit19
.
Activity was retained when the quinoline was replaced with
other bicyclic ring systems such as quinoxaline or benzothiazole.
A variety of substituents on the left-hand side aryl ring, especially
at the 3-position, were also tolerated (data not included). Despite
good activity in both enzyme and cell assays, compounds of this
type suffered from low aqueous solubility and high plasma protein
binding. The relatively high molecular weights limited options to
improve the physical properties. The replacement of the quinoline
with a 3-pyridyl group reduced both the MW and lipophilicity, and
of the four possible configurations of the amide bonds (Fig. 2),
three compounds (2–4) demonstrated good enzyme activity, with
3 having good activity in our cell proliferation assay (Table 1).20
In our hands, Sutent had a CSF-1R enzyme IC50 of 12 nM, and cell
activity of 0.09 l
M, consistent with literature data.7,8
Replacing methyl with chloro on the central ring of pyridyl bisa-
mide 3 improved activity (Table 2, 6), with small lipophilic groups
at the 3-; 3,4- and 3,5-positions giving excellent cell potency (6,
13–16). Replacing the pyridyl ring with phenyl (17) destroyed
Subset screening of our compound collection identified diamin-
ophenyl bisamides as CSF-1R inhibitors, with 1 (Fig. 1) being the
most potent of these (CSF-1R IC50 89 nM). Within AstraZeneca,
O
O
O
N
S
N
H
N
H
O
N
1
* Corresponding author. Tel.: +1 781 839 4393.
E-mail address: david.scott@astrazeneca.com (D.A. Scott).
Figure 1. Bisamide screening hit 1.
0960-894X/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2008.07.093

D. A. Scott et al. / Bioorg. Med. Chem. Lett. 18 (2008) 4794–4797
4795
O
O
O
H
N
F3C
F3C
F3C
F3C
N
H
N
H
N
H
O
O
2
4
3
5
N
N
N
N
O
H
N
H
N
H
N
N
H
O
O
Figure 2. Pyridyl bisamides 2–5.
Table 1
CSF-1R enzyme and cell activity for 2–5
Table 4
CSF-1R enzyme and cell activity—thiazolyl bisamides
R2
Compound
IC50
(
lM)
Cell (lM)
O
H
R1
2
3
4
5
0.011
0.037
0.032
6.9
2.15
0.23
1.34
ND
N
S
N
H
O
R3
N
Compound
R1
R2
R3
IC50
(
lM)
Cell (lM)
18
19
20
21
22
23
24
25
26
27
28
29
30
31
3-CF3
3-Cl
3,5-Me
3-CF3
3-CF3
Cl
Cl
Cl
Me
Cl
Me
Cl
Me
Cl
Cl
Cl
H
H
H
0.003
0.005
0.003
0.010
0.007
0.007
0.004
0.004
0.006
0.007
0.011
0.013
0.031
0.14
0.27
0.52
0.11
0.11
0.05
0.32
0.18
0.10
0.06
0.11
0.13
0.15
0.11
0.10
Table 2
CSF-1R enzyme and cell activity—pyridyl bisamides
Me
Me
Me
Me
Me
Me
Me
Me
iPr
iPr
cPr
R2
O
3-Cl
3-Cl
H
N
R1
N
H
O
3,5-Me
3,5-Me
3-CF3,5-F
3-Cl,5-F
3-CF3
X
Compound
R1
R2
X
IC50
(
lM)
Cell (lM)
Cl
Cl
Cl
3
6
7
8
3-CF3
3-CF3
3-Me
3-F
3-Cl
3-Br
3-OMe
3-NMe2
3,5-Me
3,4-Me
3,5-Cl
3,4-Cl
3-CF3
Me
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Me
N
N
N
N
N
N
N
N
N
N
N
N
CH
0.037
0.016
0.010
0.025
0.010
0.014
0.009
0.016
0.008
0.005
0.003
0.003
>50
0.23
0.14
0.24
1.64
0.33
0.26
0.94
0.77
0.05
0.15
0.13
0.09
>10
3,5-Me
3-CF3
9
10
11
12
13
14
15
16
17
cell assay than the corresponding pyridyl examples (Table 2, 6, 9
and 13). 2-Methylthiazole derivatives were more potent than the
corresponding pyridyl compounds; isopropyl and cyclopropyl
groups were also tolerated at the thiazole 2-position. The SAR
established for the pyridyl series transferred closely to the thiazol-
yl bisamides.
Compounds were prepared via the routes shown in Scheme 1,
varying the sequence of reactions to install the thiazole or the
phenyl ring at the end of the synthesis.22 (Pyridyl examples were
prepared using similar chemistry).
activity, suggesting that the pyridine N makes a key H-bond inter-
action with the protein.
Examples from this set of compounds were found to have
acceptable oral PK properties in rats, with moderate or low in vivo
clearance and good bioavailability (Table 3).
Compounds from this series were also active against another
AstraZeneca kinase target, B-Raf. Replacing the 3-pyridyl with
other six-membered heterocycles gave less potent compounds
for both CSF-1R and B-Raf.21 However, modeling studies within
our B-Raf program suggested a thiazole ring as an alternative to
the pyridine. Compounds of this type (Table 4, 18–20) also had
good in vitro potency for CSF-1R; about twofold less active in the
The aminothiazole building blocks were prepared as shown
in Scheme 2. 5-Aminothiazole was prepared by a Curtius rear-
rangement of the thiazole acid and deprotection of the Boc-pro-
tected intermediate. 2-Methyl-5-aminothiazole was prepared via
condensation and subsequent cyclization of aminoacetonitrile
and ethyl dithioacetate.23 The isopropyl and cyclopropyl thia-
zoles were prepared in a similar fashion, after first converting
the carboxylic acid to the appropriate dithioate with the Davy
reagent.24
Compound 22 was screened against a diverse panel of kinases at
1 lM (Table 5) and found to have good general kinase selectivity,
including the other class III RTKs: c-Kit, Flt3 and PDGFRb.25
Compounds with an unsubstituted thiazole (Table 6, 18, 19)
were found to have higher in vivo rat clearance than the pyridyl
analogues (Table 3, 6, 9). However, the more potent 2-methyl
thiazoles also had improved PK profiles (22, 24). In vivo clear-
ance could be reduced further with the introduction of fluorine
on the phenyl ring (27). Acceptable rat PK was also achieved
when the methyl group on the thiazole ring was replaced with
isopropyl (29).
Table 3
Rat pharmacokinetic data of pyridyl bisamides upon iv (3 mpk) and po (10 mpk)
dosing
Compound
F (%)
Cl (ml/min/kg)
Vss (L/kg)
T1/2 (h)
3
6
7
9
40
76
28
33
16
20
30
16
1
1
1
0.8
1.1
1.5
1.3
1.4

4796
D. A. Scott et al. / Bioorg. Med. Chem. Lett. 18 (2008) 4794–4797
Cl
Cl
O
Cl
O
O
H2N
S
H
N
a, b or c, d
R"
OH
S
N
H
N
H
e,
R"
N
R'
R'
H2N
CO2H
O
N
f, d
O
H
N
H
N
S
S
g, b
H2N
S
N
H
BocHN
R
H2N
CO2Me
O
O
e,
N
N
N
Scheme 1. Preparation of examples 18–31. Reagents and conditions: (a) SOCl2, MeOH, rt; (b) ArCO2H, HATU, iPr2NEt, DMF, rt; (c) ArCOCl, Et3N, CH2Cl2, 0 °C; (d) LiOH, THF/
i
MeOH/H2O 3:1:1, rt; (e) HATU, Pr2NEt, DMF, rt; (f) O(CO2tBu)2, K2CO3, THF/H2O 4:1, rt; (g) HCl gas, MeOH, rt.
HO2C
S
H2N
H2N
S
S
S
b
a
SEt
N
N
N
MeS
S
S
S
S
P
P
H2N
S
R = isopropyl,
cyclopropyl
S
SMe
b
R
RCO2H
R
SMe
N
c
Scheme 2. Preparation of aminothiazoles. Reagents and conditions: (a) i—DPPA, Et3N, tBuOH,
Et3N, MeOH, 0 °C, then dithioate rt, 2 h; (c) 1,2,4-trichlorobenzene, 130 °C, 10 min.
D
, 8 h; ii—4 N HCl in dioxane, MeOH, 0 °C, then rt 2 h; (b) NH2CH2CNÁH2SO4,
Table 5
model. 3T3 cells were engineered to express human mutant full
length CSF-1R (301–969) (3T3/CSF-1RMT) in which the kinase
activity was constitutively on. Female nude mice were implanted
with 5 Â 106 3T3/CSF-1RMT cells subcutaneously and grown in vivo
until tumors were >250 mm3 in size. After dosing, tumors were
analyzed for pCSF-1R levels by ELISA, and blood plasma samples
assessed for drug concentrations. Examples from the thiazolyl bisa-
mide series showed excellent inhibition of pCSF-1R in vivo at 2 and
6 h after dosing at 50 mpk (Table 6).
Kinase selectivity of thiazolyl bisamide 22
Kinase
% Kinase activity remaining
CSF-1R
EphA2
Hck
Fyn
c-Raf
Src
1
5
6
7
9
10
10
KDR
In conclusion, pyridyl and thiazolyl bisamides have excellent in
vitro activity against CSF-1R, with an example from the latter ser-
ies demonstrating good selectivity against other class III RTKs.
Members of both series have good oral PK profiles, and compounds
from within the thiazolyl class effectively inhibit CSF-1R phosphor-
ylation in an orally dosed mouse PD model. These compounds may
therefore have potential utility in the treatment of diseases driven
by the involvement of CSF-1 dependent macrophages.
PDGFRb
c-Kit
GSK3b
CDK2/cyclinA
IGF-1R
IR
Met
FGFR1
Tie2
IKKb
JAK2
Flt3
MAPK1
Pim-1
EGFR
45
57
91
95
107
108
109
111
111
112
112
114
116
116
118
Acknowledgments
The authors thank our colleagues Dominique Custeau and Srin-
ivasu Poondru for the PK studies, Kirsten Bell for the PD studies,
and Lisa Drew for help in the preparation of the manuscript.
Table 6
Rat pharmacokinetic data upon iv (3 mpk) and po (10 mpk) dosing, and PD activity, of
thiazolyl bisamides
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