Azaindole-based inhibitors of Cdc7 kinase: Impact of the Pre-DFG residue, Val 195

Article abstract of DOI:10.1021/ml300348c

To investigate the role played by the unique pre-DFG residue Val 195 of Cdc7 kinase on the potency of azaindole-chloropyridines (1), a series of novel analogues with various chloro replacements were synthesized and evaluated for their inhibitory activity

Full text of DOI:10.1021/ml300348c

Letter
pubs.acs.org/acsmedchemlett
Azaindole-Based Inhibitors of Cdc7 Kinase: Impact of the Pre-DFG
Residue, Val 195
Yunsong Tong,*,† Kent D. Stewart,*,‡ Alan S. Florjancic,† John E. Harlan,∥ Philip J. Merta,§
Magdalena Przytulinska,† Nirupama Soni,† Kerren K. Swinger,‡ Haizhong Zhu,∥ Eric F. Johnson,†
Alexander R. Shoemaker,† and Thomas D. Penning†
‡
§
∥
†Cancer Research, Structural Biology, Lead Discovery, and Protein Biochemistry, Global Pharmaceutical Research and
Development, Abbott Laboratories, 100 Abbott Park Road, Abbott Park, Illinois 60064, United States
S
* Supporting Information
ABSTRACT: To investigate the role played by the unique pre-
DFG residue Val 195 of Cdc7 kinase on the potency of
azaindole-chloropyridines (1), a series of novel analogues with
various chloro replacements were synthesized and evaluated for
their inhibitory activity against Cdc7. X-ray cocrystallization
using a surrogate protein, GSK3β, and modeling studies
confirmed the azaindole motif as the hinge binder. Weaker
hydrophobic interactions with Met 134 and Val 195 by certain
chloro replacements (e.g., H, methyl) led to reduced Cdc7
inhibition. Meanwhile, data from other replacements (e.g., F,
O) indicated that loss of such hydrophobic interaction could be compensated by enhanced hydrogen bonding to Lys 90. Our
findings not only provide an in-depth understanding of the pre-DFG residue as another viable position impacting kinase
inhibition, they also expand the existing knowledge of ligand-Cdc7 binding.
KEYWORDS: pre-DFG residue, Cdc7 kinase, azaindole
rotein kinases are bisubstrate enzymes, possessing both a
structurally well-defined ATP-binding site and a far more
inhibitor chemotypes, but its impact has previously not been
well-documented.
P
structurally variable substrate-binding site. Practically all
medicinal chemistry efforts in the last 15 years have focused
on ATP site-directed inhibitors because of the potential
opportunity for the discovery of potent and selective inhibitors.
While inhibitor selectivity can result from conformational
plasticity of the catalytic domain, during the early stage of a
kinase research program, detailed knowledge is typically limited
to a far more simplistic analysis of residue variation without an
advanced understanding of protein structural dynamics. The
ATP site of a protein kinase is comprised of approximately 25
residues.1 Some of these residues, such as the conserved Lys or
P-loop (also termed “gly-rich loop”) Gly residues, are nearly
fully conserved for all kinases (95−99% conserved). At the
other extreme, some residues, most notably the so-called
gatekeeper, exhibit higher variation. While there is an upper
limit of 20 amino acid possibilities at any one residue, no ATP
site residue of any naturally occurring human protein kinase
exhibits that extreme degree of variation. For example, the
gatekeeper is typically found to be one of approximately eight
residues1 with Met found most often for the Ser/Thr kinases
and Thr found most often for the Tyr kinases. In this paper, we
describe a chemical series that allowed us to probe potency at
another variable position in the ATP site: the “pre-DFG”
residue. This residue immediately precedes the well-known
“DFG” motif in the catalytic domain of protein kinases. Its side
chain makes van der Waals (VdW) contact with many kinase
Cdc7 (cell division cycle 7) is a serine/threonine kinase that
is essential for activating the DNA replicative complex at the
origins of replication.2−5 Cdc7 functions through binding to
Dbf4 or Drf1, a regulatory subunit.3,5,6 The Cdc7/Dbf4
complex promotes S-phase entry by phosphorylating the
minichromosome maintenance complex 2−7 (MCM2−7)
protein, preferably MCM2, at multiple sites (e.g., Ser 40 and
Ser 53).7−9 Cdc7/Dbf4 has been found to be overexpressed in
various tumor cell lines as well as in human cancers including
breast, colon, lung, leukemia, etc.10,11 Because Cdc7 over-
expression promotes proliferation and survival of certain tumor
cells, knockdown of Cdc7 by siRNA has led to p53-
independent apoptosis in cancer cell lines.12,13 Tumor cells
with the often impaired S-phase checkpoints progress to
mitosis without DNA repair. Meanwhile, upon Cdc7 depletion,
normal cells are able to arrest in the G1 phase of the cell cycle
and resume normal divisions once an initiation process is
restored.12 This differential regulation in tumor versus normal
cells presents a potential opportunity to develop novel agents
targeting Cdc7 inhibition as anticancer therapeutics.
Received: October 15, 2012
Accepted: January 15, 2013
© XXXX American Chemical Society
A
dx.doi.org/10.1021/ml300348c | ACS Med. Chem. Lett. XXXX, XXX, XXX−XXX

ACS Medicinal Chemistry Letters
Letter
a
Scheme 1
In the past few years, several organizations have disclosed
small-molecule Cdc7 inhibitors.14−17,22 Among them, Nerviano
Medical Sciences has published comprehensive studies covering
pyrrolopyridine- (e.g., 218), pyrrolopyridinone- (e.g., 319,20),
and pyrrolocarboxamide21-based Cdc7 inhibitors. Some
pyrrolopyridinones, such as PHA-767491 (3, 2-pyridin-4-yl-
1,5,6,7-tetrahydro-pyrrolo[3,2,c]pyridine-4-one), have been
shown to inactivate replication origins, induce apoptosis in
cancer cells, and inhibit tumor growth in animal models.
We recently disclosed a novel class of molecules with an
azaindole-pyrimidinone scaffold as potent inhibitors for Cdc7.22
Further development in medicinal chemistry led to inhibitors
containing an azaindole-chloropyridine core (1). However,
without a lactam carbonyl as seen on 2−416 and our earlier
inhibitors, it is not obvious whether 1 binds to the hinge region
of the ATP-binding site with its pyridine or the azaindole
moiety. Meanwhile, the unique pre-DFG residue of Cdc7, Val
195, which precedes the DFG motif of Asp 196, Phe 197, and
Gly 198, warrants an elaborated SAR study to map the region
since this area has not been explored by earlier publications.
This letter will first disclose the X-ray cocrystallography and
modeling work that defines the binding mode of the
chloropyridines (1). It will then focus on the analogue studies
that illustrate exploitation of the pre-DFG residue in kinase
inhibitor discovery.
a
Reagents and conditions: (i) 1-(Phenylsulfonyl)-3-(pinacoboranyl)-
pyrrolopyridine, Pd(PPh3)2Cl2, Na2CO3, DME/EtOH/H2O, 80 °C,
quan. (ii) Amines, microwave, 160−170 °C, 30−135 min, 41−56%.
(iii) AlMe3, Pd(PPh3)4, DMF, 80 °C. (iv) NaOH, dioxane, 100 °C,
16−25% (2 steps). (v) Zn(CN)2, Zn, Pd2dba3, dppf, DMA, 120 °C,
1.5 h or microwave, 170 °C, 30 min, 44−67%. (vi) NaOH, dioxane,
100 °C, 1.7−30%.
a
Scheme 2
The synthesis of 6−8 and 12−14 is shown in Scheme 1. The
commercially available pyridine derivative 18 was subjected to a
Suzuki reaction to yield the bis-chloro intermediate 19. The
following SNAr reaction with an amine replaced one of the two
chloro groups. The initial Suzuki couplings between 20 and
methylboronic acid only led to desulfonylated starting
materials. However, reactions in the presence of AlMe3 and a
Pd catalyst replaced the targeted chloro on 20 with a methyl.
Subsequent removal of the phenylsulfonyl protecting group
under basic conditions completed the synthesis of 6−8.
Compound 20 could also react with Zn(CN)2 catalyzed by
Pd2dba3 to give 21. The standard basic deprotection resulted in
analogues 12−15.23 A similar deprotection of 20a afforded 16.
To synthesize final products 9−11 (Scheme 2), the
difluoropyridyl compound 23 was first obtained from 2,6-
difluoro-4-iodopyridine (22),24 under typical Suzuki reaction
conditions. Substituting one of the fluoro groups with a suitable
amine at 160 °C in a microwave reactor followed by
deprotection of the azaindole moiety gave 9 and 10. The
amine addition could also be accomplished on a deprotected
difluoro intermediate 24, leading to 11.
a
Reagents and conditions: (i) Pd(PPh3)2Cl2, Na2CO3, 1-(phenyl-
sulfonyl)-3-(pinacoboranyl)-pyrrolopyridine, EtOH/DME/H2O, 80
°C, 63%. (ii) NaOH, dioxane, 50 °C. (iii) Amine, EtOH, microwave,
150 °C. (iv) trans-Cyclohexane-1,4-diamine, EtOH, microwave, 170
°C, 40%.
Replacing the chloro of inhibitor class 1 may have a profound
impact on potency. As demonstrated in Table 1, the fluoro
analogues (9−11) are generally as potent as their chloro
counterparts. However, the hydrogen (5), methyl (6−8), cyano
(12−14), and carboxamide (15) substitutions led to varied
degrees of erosion on the Cdc7 inhibitory activity.
All of the inhibitors synthesized were evaluated by a
biochemical assay to measure their inhibitory activity (reported
as Ki values; see the Supporting Information for details).
B
dx.doi.org/10.1021/ml300348c | ACS Med. Chem. Lett. XXXX, XXX, XXX−XXX

ACS Medicinal Chemistry Letters
Letter
Structural consideration of the binding mode of compounds
of type 1 indicates that they contain two heterocycles (pyridine
and azaindole) known to serve as hinge binders for Cdc7 kinase
but do not have a lactam unit to interact with the conserved
Lys. Therefore, the binding mode was uncertain. A crystal
structure of compound 16 bound to GSK3β kinase,26 shown in
Figure 1, provided unambiguous evidence that the azaindole
Table 1. Effect of Cl Replacements
Figure 1. Protein crystal structure of compound 16 in GSK3β kinase.
Hinge hydrogen bonds to Asp 133 and Val 135 are shown in black
dashed lines. The gatekeeper and pre-DFG residues of GSK3β kinase
are Leu 132 and Cys 199, respectively.
unit served as the hinge-binding unit and that the pyridine
pointed toward the conserved Lys in this surrogate kinase. Also,
the twist of the pyridine ring relative to the azaindole is seen to
be flatter, at about 10°, than what would have been expected for
a biaryl system with a fused ring. The potency of compound
against GSK3β kinase was sufficient (Ki = 58 nM)27 that the
binding mode is likely to be analogous in Cdc7. Furthermore,
the presence of an ortho-chloro group would likely be sterically
confounding if the pyridyl unit were taken to be the hinge-
binding unit. Therefore, further modeling work in Cdc7 kinase
proceeded with the general binding mode assumed as observed
in GSK3β kinase.
The conserved Lys is well-precedented to donate an H-bond
to ligand acceptors in many kinase inhibitors. The surrounding
hydrophobic environment is created by the side chains of the
gatekeeper and pre-DFG residues. A model of compound 16 in
Cdc7 kinase is shown in Figure 2. The chloro substituent is
observed to make van der Waals contact with the gatekeeper
Met 134 and Val 195. The twist of the pyridine ring is observed
to be relatively low (23°) to maximize the van der Waals
interaction between the pyridine ring and the Val 195 and is
supported by the low twist angle observed in the X-ray
structure with GSK3β. While Met is a common gatekeeper
residue found in many kinases, Val is an uncommon pre-DFG
residue. Eighty-three percent of all kinases have their pre-DFG
residues as Gly, Ala, Ser, Thr, or Cys.29 Only 4% of the kinome
(20 kinases; listed in the Supporting Information) have the
sterically larger and more hydrophobic Val as the pre-DFG
residue. The potency of Cdc7 inhibitors that vary structurally in
this conserved Lys region will likely be driven by some
combination of (a) the degree and arrangement of the
hydrophobic interaction with the gatekeeper Met 134 and
pre-DFG Val 195 leading to a restricted volume relative to
other kinases with smaller pre-DFG residues and (b) the degree
of polar interaction with the conserved Lys side chain. Our
a
b
Average of two measurements. Ki ratio: each example/correspond-
c
ing Cl analogue at X. See the synthesis in ref 22.
Understanding of ligand binding to Cdc7 kinase is based on
published structural studies16,18,19,25 of compounds 2−4 using
surrogates. Attempts to crystallize Cdc7 have not been
successful to date, so structural information derives from either
crystallographic studies of ligand-bound surrogate kinases, such
as PIM or GSK3β kinases, or ligand docking into homology
models of Cdc7 kinase. The high architectural conservation of
the kinase ATP site allows these surrogate and modeled
structures to be useful for SAR interpretation, even when
sequence identity of the entire catalytic domain is low. The
emerging structural understanding16,18,19,25 indicates that there
are two dominant binding features within the ATP site: (1) a
ligand heterocycle, such as pyrrolopyridine (azaindole),
pyridine, or indazole, serves as a hinge-binding unit, and (2)
a directly connected lactam functionality, such as imidazolone,
pyridone, or pyrimidone, that interacts with the conserved
lysine residue. In Cdc7 kinase, these regions are created by Pro
135 and Leu 137 within the hinge and Lys 90 with its nearby
Met 134, the “gatekeeper” residue, and Val 195, the “pre-DFG”
residue. The pre-DFG residue is the residue that immediately
precedes the well-known kinase DFG motif and has its side
chain form part of the binding surface around the conserved
Lys residue. Val 195 is of high interest as the pre-DFG residue
of Cdc7 as it is proposed to influence ligand potency, vide infra.
C
dx.doi.org/10.1021/ml300348c | ACS Med. Chem. Lett. XXXX, XXX, XXX−XXX

ACS Medicinal Chemistry Letters
Letter
around the region occupied by the gatekeeper, Met 134, and
the pre-DFG residue, Val 195, of the Cdc7 kinase. By
synthesizing a series of novel analogues with various chloro
replacements, we established the interplay among hydrogen
bonding, hydrophobic interaction, and steric influence in this
particular ATP-binding region. The reduced hydrophobic
interaction of the chloro replacements (i.e., H, Me, and CN)
with Met 134 and Val 195 led to compounds (5, 7, and 12−14)
with deteriorated Cdc7 inhibition. However, the loss of such
hydrophobic interaction could be compensated by enhanced
hydrogen bonding to Lys 90 as demonstrated by analogues
such as 9−11 and 17. The findings in this paper not only
provide an in-depth understanding of the pre-DFG residue as
another viable position impacting the kinase inhibition, they
also expand the existing knowledge of ligand-Cdc7 binding.
Figure 2. Model of chloropyridine compound 16 in Cdc7 kinase.28
Hinge hydrogen bonds to Pro 135 and Leu 137 are shown. The
gatekeeper, Met 134, and pre-DFG residue, Val 195, are highlighted to
show their proximity to the conserved Lys 90. The chlorine atom of
the inhibitor is in VdW contact with the terminal atoms of Met 134
and Val 195.
ASSOCIATED CONTENT
■
S
* Supporting Information
List of kinases having valine as the pre-DFG residue, X-ray
crystallography method and statistics, GSK3β protein purifica-
tion protocol, assay protocols, and synthetic procedures. This
material is available free of charge via the Internet at http://
pubs.acs.org.
rationalization of the SAR in Table 1 invokes both binding
features. Replacement of the chloro with hydrogen (5) or
methyl (6) led to about one log potency loss, relative to 16. A
simple tabulation of calculated LogP for benzene analogues and
the corresponding inhibitors, shown in Table 2, shows that
AUTHOR INFORMATION
■
Corresponding Author
a
Table 2. ClogP Values
*Tel: 1-847-935-1252. Fax: 1-847-935-5165. E-mail: yunsong.
tong@abbott.com (Y.T.). Tel: 1-847-937-1205. E-mail: kent.d.
stewart@abbott.com (K.D.S.).
substrate
Ph-H
ClogP
inhibitor
ClogP
2.14
2.28
2.64
2.86
1.57
1.47
0.65
5
9
4.12
4.39
4.62
4.96
4.06
2.45
Notes
Ph-F
The authors declare no competing financial interest.
Ph-Me
Ph-Cl
6
16
12
17
Ph-CN
Ph-OH
Ph-CONH2
ACKNOWLEDGMENTS
■
Use of the IMCA-CAT beamline 17-ID (or 17-BM) at the
Advanced Photon Source was supported by the companies of
the Industrial Macromolecular Crystallography Association
through a contract with Hauptman-Woodward Medical
Research Institute. Use of the Advanced Photon Source was
supported by the U.S. Department of Energy, Office of Science,
Office of Basic Energy Sciences, under Contract No. DE-AC02-
06CH11357.
a
Calculated using BioByte.
because of the lower LogP, both of these analogues would be
expected to have diminished hydrophobic interaction in this
region of the active site. Replacement with the two-atom cyano
group, 12−14, or three-atom carboxamide group, 15, led to
potency losses of 5−11- and 134-fold, respectively, from a
possible net combination of factors: loss of hydrophobic
interaction (Table 2), steric clash with a constricted hydro-
phobic environment, and/or suboptimal hydrogen bonding
between the substituent and the Lys 90. In the cases of the one-
atom fluoro analogues, compounds 9−11, or oxo analogue,
pyridinone 17, inhibition strengths typically within 3× of the
corresponding chloro analogues were observed. While both
fluoro and oxo would be expected to exhibit less hydrophobic
interaction with gatekeeper and pre-DFG side chains, their
atomic positions would be expected to be approximately 3 Å
from the ε-amino group of Lys 90. Therefore, both are able to
compensate with enhanced H-bond ability with Lys 90,
resulting in little net potency difference.
REFERENCES
■
(1) Sheridan, R. P.; Nam, K.; Mairov, V. N.; McMasters, D. R.;
Cornell, W. D. QSAR Models for predicting the similarity in binding
profiles for pairs of protein kinases and the variation of models
between experimental data sets. J. Chem. Inf. Model. 2009, 49, 1974−
1985.
(2) Bousset, K.; Diffley, J. F. The Cdc7 protein kinase is required for
origin firing during S phase. Genes Dev. 1998, 12, 480−490.
(3) Jiang, W.; McDonald, D.; Hope, T. J.; Hunter, T. Mammalian
Cdc7-Dbf4 protein kinase complex is essential for initiation of DNA
replication. EMBO J. 1999, 18, 5703−5713.
(4) Kumagai, H.; Sato, N.; Yamada, M.; Mahony, D.; Seghezzi, W.;
Lees, E.; Arai, K.; Masai, H. A novel growth- and cell cycle-
regulatedprotein, ASK, activates human Cdc7-related kinase and is
essentialfor G1/S transition in mammalian cells. Mol. Cell. Biol. 1999,
19, 5083−5095.
In summary, the binding mode of the chloropyridines (1) as
potent Cdc7 inhibitors was clarified by a cocrystal X-ray
structure of 16 in a surrogate protein, GSK3β, confirming the
azaindole moiety of the molecule as the hinge-binding motif.
Meanwhile, dissecting the impact of the chloro on potency
called for a thorough understanding of the structural biology
(5) Montagnoli, A.; Bosotti, R.; Villa, F.; Rialland, M.; Brotherton,
D.; Mercurio, C.; Berthelsen, J.; Santocanale, C. Drf1, a novel
regulatory subunit for human Cdc7 kinase. EMBO J. 2002, 2, 3171−
3181.
D
dx.doi.org/10.1021/ml300348c | ACS Med. Chem. Lett. XXXX, XXX, XXX−XXX

ACS Medicinal Chemistry Letters
Letter
(6) Chapman, J. W.; Johnston, L. H. The yeast gene, DBF4, essential
for entry into S phase is cell cycle regulated. Exp. Cell Res. 1989, 180,
419−428.
(7) Cho, W.-H.; Lee, Y.-J.; Kong, S.-I.; Hurwitz, J.; Lee, J.-K. CDC7
kinase phosphorylates serine residues adjacent to acidic amino acids in
the minichromosome maintenance 2 protein. Proc. Natl. Acad. Sci.
2006, 103, 11521−11526.
(8) Montagnoli, A.; Valsasina, B.; Brotherton, D.; Troiani, S.;
Rainoldi, S.; Tenca, P.; Molinari, A.; Santocanale, C. Identification of
Mcm2 Phosphorylation Sites by S-phase-regulating Kinases. J. Biol.
Chem. 2006, 281, 10281−10290.
(9) Forsburg, S. L. Eukaryotic MCM proteins: Beyond replication
initiation. Microbiol. Mol. Biol. Rev. 2004, 68, 109−131.
(10) Bonte, D.; Lindvall, C.; Liu, H.; Dykema, K.; Furge, K.;
Weinreich, M. Cdc7-Dbf4 kinase is overexpressed in multiple cancers
and tumor cell lines and is correlated with p53 inactivation. Neoplasia
2008, 10, 920−931.
(11) Hessa, G. F.; Dronga, R. F.; Weilanda, K. L.; Slightoma, J. L.;
Sclafanib, R. A.; Hollingsworth, R. E. A human homolog of the yeast
CDC7 gene is overexpressed in some tumors and transformed cell
lines. Gene 1998, 211, 133−140.
(12) Montagnoli, A.; Tenca, P.; Sola, F.; Carpani, D.; Brotherton, D.;
Albanese, C.; Santocanale, C. Cdc7 inhibition reveals a p53-dependent
replication checkpoint that is defective in cancer cells. Cancer Res.
2004, 64, 7110−7116.
(13) Kim, J. M.; Kakusho, N.; Yamada, M.; Kanoh, Y.; Takemoto, N.;
Masai, H. Cdc7 kinase mediates Claspin phosphorylation in DNA
replication checkpoint. Oncogene 2008, 27, 3475−3482.
Moll, J. K.; Montagnoli, A.; Orsini, P.; Orzi, F.; Pesenti, E.; Pillan, A.;
Roletto, F.; Scolaro, A.; Tato, M.; Tibolla, M.; Valsasina, B.; Varasi, M.;
̀
Vianello, P.; Volpi, D.; Santocanale, C.; Vanotti, E. Cdc7 kinase
inhibitors: 5-heteroaryl-3-carboxamido-2-aryl pyrroles as potential
antitumor agents. 1. Lead finding. J. Med. Chem. 2010, 53, 7296−7315.
(22) Woods, K. W.; Lai, C.; Miyashiro, J. M.; Tong, Y.; Florjancic, A.
S.; Han, E. K.; Soni, N.; Shi, Y.; Lasko, L.; Leverson, J. D.; Johnson, E.
F.; Shoemaker, A. R.; Penning, T. D. Aminopyrimidinone Cdc7 kinase
inhibitors. Bioorg. Med. Chem. Lett. 2012, 22, 1940−1943.
(23) Compounds 14 and 15 were formed in the same reaction. See
Table 1 for the structures of 15 and 16.
(24) Schlosser, M.; Rausis, T. The structural proliferation of 2,6-
difluoropyridine through organometallic intermediates. Eur. J. Org.
Chem. 2004, 5, 1018−1024.
(25) Menichincheri, M.; Bargiotti, A.; Berthelsen, J.; Bertrand, J. A.;
Bossi, R.; Ciavolella, A.; Cirla, A.; Cristiani, C.; Croci, V.; D’Alessio, R.;
Fasolini, M.; Fiorentini, F.; Forte, B.; Isacchi, A.; Martina, K.; Molinari,
A.; Montagnoli, A.; Orsini, P.; Orzi, F.; Pesenti, E.; Pezzetta, D.; Pillan,
A.; Poggesi, I.; Roletto, F.; Scolaro, A.; Tato, M.; Tibolla, M.;
Valsasina, B.; Varasi, M.; Volpi, D.; Santocanale, C.; Vanotti, E. First
Cdc7 Kinase Inhibitors: Pyrrolopyridinones as Potent and Orally
Active Antitumor Agents. 2. Lead Discovery. J. Med. Chem. 2009, 52,
293−307.
(26) PDB entry 4IQ6.
(27) Obtained from a similar activity assay as the one for Cdc7.
(28) A homology model of Cdc7 was created using PDB entry 1ATP
for PKA kinase as the template. The structure of 16 was docked as
observed in the GSK3β crystal structure and energy minimized.
(29) Huang, D.; Zhou, T.; Lafleur, K.; Nevado, C.; Caflisch, A.
Kinase selectivity potential for inhibitors targeting the ATP binding
site: A network analysis. Bioinformatics 2010, 26, 198−204.
(14) Lindvall, M.; McBride, C.; McKenna, M.; Gesner, T. G.;
Yabannavar, A.; Wong, K.; Lin, S.; Walter, A.; Shafer, C. M. 3D
Pharmacophore model-assisted discovery of novel CDC7 inhibitors.
ACS Med. Chem. Lett 2011, 2, 720−723.
(15) Swords, R.; Mahalingam, D.; O’Dwyer, M.; Santocanale, C.;
Kelly, K.; Carew, J.; Giles, F. Cdc7 kinase; a new target for drug
development. Eur. J. Cancer 2010, 46, 33−40.
(16) Shafer, C. M.; Lindvall, M.; Bellamacina, C.; Gesner, T. G.;
Yabannavar, A.; Jia, W.; Lin, S.; Walter, A. 4-(1H-Indazol-5-yl)-6-
phenylpyrimidin-2(1H)-one analogs as potent CDC7 inhibitors.
Bioorg. Med. Chem. Lett. 2008, 18, 4482−4485.
(17) Zhao, C.; Tovar, C.; Yin, X.; Xu, Q.; Todorov, I. T.; Vassilev, L.
T.; Chen, L. Synthesis and evaluation of pyrido-thieno-pyrimidines as
potent and selective Cdc7 kinase inhibitors. Bioorg. Med. Chem. Lett.
2009, 19, 319−323.
(18) Ermoli, A.; Bargiotti, A.; Brasca, M. G.; Ciavolella, A.; Colombo,
N.; Fachin, G.; Isacchi, A.; Menichincheri, M.; Molinari, A.;
Montagnoli, A.; Pillan, A.; Rainoldi, S.; Riccardi Sirtori, F.; Sola, F.;
Thieffine, S.; Tibolla, M.; Valsasina, B.; Volpi, D.; Santocanale, C.;
Vanotti, E. Cell Division Cycle 7 Kinase Inhibitors: 1HPyrrolo[2,3-
b]pyridines, Synthesis and Structure-Activity Relationships. J. Med.
Chem. 2009, 52, 4380−4390.
(19) Vanotti, E.; Amici, R.; Bargiotti, A.; Berthelsen, J.; Bosotti, R.;
Ciavolella, A.; Cirla, A.; Cristiani, C.; D’Alessio, R.; Forte, B.; Isacchi,
A.; Martina, K.; Menichincheri, M.; Molinari, A.; Montagnoli, A.;
Orsini, P.; Pillan, A.; Roletto, F.; Scolaro, A.; Tibolla, M.; Valsasina, B.;
Varasi, M.; Volpi, D.; Santocanale, C. Cdc7 kinase inhibitors:
Pyrrolopyridinones as potential antitumor agents. 1. Synthesis and
structure-activity relationships. J. Med. Chem. 2008, 51, 487−501.
(20) Montagnoli, A.; Valsasina, B.; Croci, V.; Menichincheri, M.;
Rainoldi, S.; Marchesi, V.; Tibolla, M.; Tenca, P.; Brotherton, D.;
Albanese, C.; Patton, V.; Alzani, R.; Ciavolella, A.; Sola, F.; Molinari,
A.; Volpi, D.; Avanzi, N.; Fiorentini, F.; Cattoni, M.; Healy, S.;
Ballinari, D.; Pesenti, E.; Isacchi, A.; Moll, J.; Bensimon, A.; Vanotti, E.;
Santocanale, C. A. Cdc7 kinase inhibitor restricts initiation of DNA
replication and has antitumor activity. Nat. Chem. Biol. 2008, 4, 357−
365.
(21) Menichincheri, M.; Albanese, C.; Alli, C.; Ballinari, D.; Bargiotti,
A.; Caldarelli, M.; Ciavolella, A.; Cirla, A.; Colombo, M.; Colotta, F.;
Croci, V.; D’Alessio, R.; D’Anello, M.; Ermoli, A.; Fiorentini, F.; Forte,
B.; Galvani, A.; Giordano, P.; Isacchi, A.; Martina, K.; Molinari, A.;
E
dx.doi.org/10.1021/ml300348c | ACS Med. Chem. Lett. XXXX, XXX, XXX−XXX