Discovery of a novel aminopyrazine series as selective PI3Kα inhibitors

Article abstract of DOI:10.1016/j.bmcl.2017.05.028

We report the discovery of a novel aminopyrazine series of PI3Kα inhibitors, designed by hybridizing two known scaffolds of PI3K inhibitors. We describe the progress achieved from the first compounds plagued with poor general kinase selectivity to compounds showing high selectivity for PI3Kα over PI3Kβ and excellent general kinase selectivity. This effort culminated with the identification of compound 5 displaying high potency and selectivity, and suitable physiochemical and pharmacokinetic properties for oral administration. In vivo, compound 5 showed good inhibition of tumour growth (86% tumour growth inhibition at 50?mg/kg twice daily orally) in the MCF7 xenograft model in mice.

Full text of DOI:10.1016/j.bmcl.2017.05.028

Accepted Manuscript
Discovery of a novel aminopyrazine series as selective PI3Kα inhibitors
Bernard Barlaam, Sabina Cosulich, Martina Fitzek, Hervé Germain, Stephen
Green, Lyndsey L. Hanson, Craig S. Harris, Urs Hancox, Kevin Hudson,
Christine Lambert-van der Brempt, Maryannick Lamorlette, Françoise
Magnien, Gilles Ouvry, Ken Page, Linette Ruston, Lara Ward, Bénédicte
Delouvrié
PII:
S0960-894X(17)30509-7
DOI:
http://dx.doi.org/10.1016/j.bmcl.2017.05.028
BMCL 24973
Reference:
To appear in:
Bioorganic & Medicinal Chemistry Letters
Received Date:
Revised Date:
Accepted Date:
21 April 2017
8 May 2017
9 May 2017
Please cite this article as: Barlaam, B., Cosulich, S., Fitzek, M., Germain, H., Green, S., Hanson, L.L., Harris, C.S.,
Hancox, U., Hudson, K., Lambert-van der Brempt, C., Lamorlette, M., Magnien, F., Ouvry, G., Page, K., Ruston,
L., Ward, L., Delouvrié, B., Discovery of a novel aminopyrazine series as selective PI3Kα inhibitors, Bioorganic
&
Medicinal Chemistry Letters (2017), doi: http://dx.doi.org/10.1016/j.bmcl.2017.05.028
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Bioorganic & Medicinal Chemistry Letters
Discovery of a novel aminopyrazine series as selective PI3K inhibitors.
,
a
a
b
c
b
Bernard Barlaam,* Sabina Cosulich, Martina Fitzek, Hervé Germain, Stephen Green, Lyndsey L.
b
c,¤
b
b
c
Hanson, Craig S. Harris, Urs Hancox, Kevin Hudson, Christine Lambert-van der Brempt, Maryannick
Lamorlette, Françoise Magnien, Gilles Ouvry, Ken Page, Linette Ruston, Lara Ward, and Bénédicte
c
c
c,¤
b
b
b
,
c
Delouvrié*
a
IMED Oncology, AstraZeneca, Darwin Building, Cambridge Science Park, 319 Milton Road, Cambridge CB4 0WG, United Kingdom.
IMED Oncology, AstraZeneca, Alderley Park, Macclesfield, Cheshire SK10 4TG, United Kingdom.
AstraZeneca, Centre de Recherches, Z.I. La Pompelle, B.P. 1050, Chemin de Vrilly, 51689 Reims, Cedex 2, France
b
c
ARTICLE INFO
ABSTRACT
Article history:
Received
Revised
Accepted
Available online
We report the discovery of a novel aminopyrazine series of PI3K inhibitors, designed by
hybridizing two known scaffolds of PI3K inhibitors. We describe the progress achieved from the
first compounds plagued with poor general kinase selectivity to compounds showing high
selectivity for PI3K over PI3K and excellent general kinase selectivity. This effort culminated
with the identification of compound 5 displaying high potency and selectivity, and suitable
physiochemical and pharmacokinetic properties for oral administration. In vivo, compound 5
showed good inhibition of tumour growth (86% tumour growth inhibition at 50 mg/kg twice
daily orally) in the MCF7 xenograft model in mice.
Keywords:
PI3K inhibitor
rational design
Kinase selectivity
2
017 Elsevier Ltd. All rights reserved.
The phosphoinositide 3-kinase (PI3K) signalling pathway plays a crucial role in cell growth, proliferation and survival and is commonly
activated in human cancers by factors such as mutation of PI3K, overexpression of growth factor receptor tyrosine kinases or
1
inactivation of PTEN. Among this pathway, phosphoinositides (PIs), which are the substrate of PI3Ks, act as second messengers in a
wide variety of cellular contexts such as signal transduction, cell survival and death. Class I PI3Ks phosphorylate the 3’-hydroxy
position of the inositol ring of phosphoinositide-4,5-biphosphate (PIP2) to produce phosphoinositide-3,4,5-triphosphate (PIP3).
While the different class I isoforms of PI3K (4 isoforms: p110) were originally thought to be redundant in function, a
2
significant effort was initially invested in the generation of pan-class I PI3K inhibitors, with a number of compounds in early clinical
3
trials. Some of these early pan-PI3K clinical candidates also have off-target activity, especially on other members of the PI3K-related
kinase (PIKK) family such as m-TOR and DNA-PK. However, the generation of isoform selective inhibitors has started to elucidate
4
individual distinct functions for these lipid kinases. In particular, the p110 isoform of PI3K has been the most extensively studied to
5
date. The gene encoding for the p110subunit, PIK3CA, is mutated in several cancers and amplified in a variety of other cancer types.
6
Therefore selective inhibition of the PI3Kisoform is currently considered as a promising approach for cancer therapy.
During our lead generation effort, we identified a benzotriazole aminopyrazine series which gave high selectivity for PI3K over
PI3K, illustrated by compound 1 (Figure 1). However, this compound had strong activity against 13 kinases out of 76 in a ‘Dundee
7
University protein kinase’ panel (>80% inhibition at 1 M, see Figure 5). The lack of kinase selectivity was also confirmed by testing
in our internal kinase assays. The identity of some of these anti-targets (e.g. VEGFR, Aurora, FGFR1, GSK3) and their known
pharmacological effects was considered likely to lead to an unacceptable safety risk, requiring further improvement of the general
kinase selectivity for this series to be viable. We previously reported the optimisation of this series, focussing on key exploitable
8,9
differences between PI3K and those anti-targets, which resulting in the identification of a clinical candidate, AZD8835.
In this paper, we report the discovery of a new series of PI3K inhibitors from hybridization of compound 1 with competitor compound
1
0
PF-04691502 (compound 2), a pan PI3K/TOR inhibitor, and our efforts to gain selectivity for PI3K vs. PI3Kusing structural
design. Selectivity among the PI3K isoforms was routinely measured with enzyme assays and the  selectivity was also monitored in
cell assays (inhibition of AKT phosphorylation at Thr308 in PIK3CA mutant human breast ductal carcinoma BT474 cells, sensitive to
9
PI3K inhibition; and at Ser473 in PTEN null breast adenocarcinoma MDA-MB-468 cells, sensitive to PI3K inhibition .
#
¤
corresponding author: B.Barlaam. e-mail: bernard.barlaam2@astrazeneca.com
current address: Nestlé Skin Health R&D, les Templiers, 2400 route des Colles, 06410 Sophia-Antipolis, France

1
AZD8835
PI3K enz. IC : 0.016 M
5
0
PI3K enz. IC : 0.9 M
5
0
PI3K cell IC : 0.058 M
5
0
PI3K cell IC :
13 M
5
0
Figure 1. Structure of 1 and AZD8835. Activity of 1 in PI3K and PI3Kenzyme and cell assays.
A distinctive feature of the PI3K kinase related kinase (PIKK) family is the presence of a tyrosine residue (Tyr840 in PI3K) in the
ATP binding site, which is not present in other kinases. Many PI3K inhibitors have exploited this tyrosine to gain selectivity over other
1
1
kinases, usually by positioning a methyl to create a CH/π interaction with this tyrosine. This methyl is present in PF-04691502
1
0
(
compound 2), a pan PI3K/TOR inhibitor, the X-ray structure of which is available in PI3K (PDB 3ML9 ). An overlay of the structure
12
of 2 with the modelled complex of 1 docked in PI3K (pdb 3HHM ) showed that the methyl of this compound is close to the amino
group of the aminopyrazine hinge binder in our series (Figure 2).
Figure 2. Structure of compound 2 (left), PF-04691502 and overlay of compound 2 (cyan) and compound 1 (amber) in their binding conformation (right).
Compound 1 makes a double donor/acceptor interaction with the hinge residues Val851 and Glu849, but it does not interact with
Tyr840 (Figure 3, panel a). Compound 2 also displays a double donor/acceptor interaction, but this time with the hinge residue Val851.
Transposition of the hinge binder of compound 2 in our series required careful consideration of the SAR knowledge we had previously
generated on our series and a particular attention on the torsion of the two adjacent chains (regions highlighted in pink on Figure 3,
panel b). Indeed, our SAR knowledge suggested that significant torsion would not be tolerated on the pyrazole chain. Therefore we
decided to replace the pyrazole by a 1,2,3-triazole to force planarity with an internal H-bond. We also decided to replace the
benzotriazole by an imidazopyridine, as previous unpublished SAR from our series suggested that, when the 2-amino was replaced by a
methyl group, activity was reduced with the benzotriazole at C-3, but was somewhat restored by an imidazopyridine group.

Figure 3. (a) binding mode of 1 in PI3K; (b) transformation of 1 by hybridization with hinge binder of 2.
Compounds 3-4 were made according to Scheme 1. Starting from the commercially available chloropyrazine 3a,
dibromoaminopyrazine 3b was synthesised in a two-step sequence in good yield. Boronate 3d was formed from 3c by mesylate
1
3
displacement with 1,2,3-triazole, followed by the first example of an iridium-catalysed borylation at C-4 of the triazole ring. A Suzuki-
Miyaura cross-coupling between 3b and 3d, followed by a heteroaryl Heck coupling with imidazopyridine afforded the Boc protected
piperidine 3e. A deprotection/methylation sequence completed the synthesis of compound 3.
For the synthesis of the 1,2,4-triazole analogue 4, the sequence was as follows. Regioselective halogenations of 4a afforded the
1
4
bromochloropyrazine 4b. An iminotriphenylphosphorane (TPP) protection of the amino group previously reported by our group
8
allowed the regioselective formation and isolation of stannane 4c. A Stille coupling with 4d gave the bis-protected intermediate 4e. A
heteroaryl Heck coupling to introduce the imidazopyridine moiety, followed by deprotection and final methylation of the piperidine
yielded compound 4.
i-ii
v-vi
vii-viii
3
a
3b
3d
3e
3
iii-iv
3c
ix-x
xi-xii
xiii
xiv-xvi
4a
4b
4c
4
4e
4d
Scheme 1. Synthesis of compounds 3-4. (i) NH
3
, H
iv) bis(1,5-cyclooctadiene)di--methoxydiiridium(I), 4,4'-di- Bu-2,2'-bipyridine, 4,4,5,5-tetramethyl-1,3,2-dioxaborolane, pentane, rt, 14 h, 67%; (v)
PPh PdCl , CsF, MeOH, 130 °C, microwave, 30 min, 54%; (vi) imidazopyridine, PPh , Pd(OAc) , dioxane/EtOH, 130 °C, microwave, 60 min, 61%; (vii)
Cl , rt, 1 h, 58%; (viii) sodium triacetoxyborohydride, formaldehyde, MeOH/CH Cl , rt, 1.5 h, 75%; (ix) NCS, CHCl , rt, overnight, 57%; (x) NBS,
, rt, 10 min, 85%; (xi) PPh , perchloroethane, NEt , toluene, 90 °C, overnight, 68%; (xii) (PPh PdCl , (Me Sn) , toluene, 70 °C, 2 h, 87%; (xiii)
PdCl , CuBr, DME, 140 °C, 60 min, 45%; (xiv) imidazopyridine, PPh , Pd(OAc) , DMF/MeOH, 160 °C, microwave, 15 min; (xv) HCl, MeOH, 90 °C, 2
h, 28% for 2 steps; (xvi) sodium triacetoxyborohydride, formaldehyde, MeOH/CH Cl , rt, 1.5 h, 87%.
2 2 3
O, 180 °C, 8 h, 60%; (ii) Br , pyridine, CHCl , rt, 83%; (iii) 1,2,3-triazole, NaH, DMF, 60 °C, 5 days, 29%;
t
(
(
3
)
2
2
3
2
TFA, CH
CHCl
PPh
2
2
2
2
3
3
3
3
)
3 2
2
3
2
(
3
)
2
2
3
2
2
2
Compounds 5-7 were obtained from a common sequence highlighted in Scheme 2. From the commercially available carboxylic acids
a-6a, hydrazides 5b-6b were formed in high yields, and subjected to a cyclization with ethyl 2-amino-2-thioxoacetate to form the
5
1
5
methyl triazole ring. Bromination afforded esters 5c-6c. The imidazopyridine moiety was introduced by heteroaryl Heck coupling to
1
6
form 5d-6d, which were then directly transformed into the corresponding amides 5 and 6. Ester 5c was also transformed into amide 7a
in one step, and a Suzuki-Miyaura cross-coupling with the corresponding pyrazolopyridine boronate afforded compound 7.
i
ii-iii
iv
v
R=Me 5a
R=H 6a
R=Me 5b
R=H 6b
R=Me 5c
R=H 6c
R=Me 5d
R=H 6d
R=Me 5
R=H
6
vi
vii
7
7
a
Scheme 2. Synthesis of compounds 5-7. (i) pentafluorophenol, N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride, CH
0%; (ii) ethyl 2-amino-2-thioxoacetate, dioxane/AcOH, 100 °C, overnight, 32-79%; (iii) NBS, CHCl , rt, 2 h, 69-95%; (iv) imidazopyridine, PPh
potassium acetate, DMF, 145 °C, 3 h, 82-96%; (v) MeNH , EtOH, 70 °C, overnight, 57-97%; (vi) MeNH , EtOH, 70 °C, overnight, 100 %; (vii) 3-(4,4,5,5-
tetramethyl-1,3,2-dioxaborolan-2-yl)pyrazolo[1,5-a]pyridine, (PPh PdCl , CsF, MeOH, 130 °C, microwave, 50 min, 52%.
CN/CH Cl
3 2 2
, rt, 3 h, 64-
9
3
3
, Pd(OAc)
2
,
2
2
)
3 2
2
Gratifyingly, compound 3 showed good activity against PI3K. However, it exhibited only limited selectivity vs. the PI3K isoform in
enzyme and cell assays (Table 1). The other 1,2,4-triazole analogue 4 showed a very similar profile to 3. The difference resided in the

broader chemical scope that can be explored at the 3-position of the 1,2,4-triazole scaffold compared to the 1,2,3-triazole. We used the
-position to increase / selectivity by exploiting a potential stronger interaction with Gln859, a residue unique to PI3K. The
3
equivalent residue in PI3K is an aspartic acid (Asp861). Docking of the secondary amide 5 suggested a double interaction between the
triazolocarboxamide moiety and Gln859 (Figure 4). It is worth noting that we and others previously reported taking advantage of
hydrogen bond interactions with Gln859 in order to gain PI3K selectivity vs. the other PI3K isoforms, in the work leading to the
8
,9
17
discovery of clinical candidates AZD8835, a selective dual PIK3Kinhibitor, and NVP-BYL719, a selective PI3K inhibitor.
Indeed, 5 showed high activity against PI3Kenzyme, and a ~100 fold selectivity versus PI3K in the cell assays. Moreover, excellent
protein kinase selectivity was displayed by compound 5 in the ‘Dundee University protein kinase’ panel, as illustrated in Figure 5
1
8
(
compound 5 vs. compound 1). At this stage, we checked the importance of the methyl on the pyrazine for activity and selectivity.
Compound 5 was found to be ~4 fold more potent than its des-methyl analogue 6 against PI3K in cells.
Figure 4. Docking of compound 5 in PI3K. Two different orientations illustrating on (4a) the key interactions with the hinge region and with Tyr840, and on
(
4b) the potential interactions of the triazolocarboxamide moiety with Gln859. Additional potential interactions with His855 are also shown. Potential H-bond
interactions of the imidazopyridine nitrogen with Asp933 and a conserved water molecule (red dot) are represented on (4c).
Figure 5. Heat map showing the inhibitory activity of compounds 1 (on top) and 5 (below) against a panel of kinases (‘Dundee University kinase panel’) at 1
M. The percentage of inhibition is coloured from green (0%) to yellow (60%) to red (90%)
Table 1. Biological activity of compounds 1, 3-7 in PI3K and PI3K enzyme and cell assays
PI3K
enz. IC50
PI3K
enz. IC50
PI3K
cell IC50
PI3K
a
Cpd
a
a
a
cell IC50
1
0.016
0.008
0.9
0.058
0.100
13
3
0.076
0.55

4
0.005
0.006
0.020
0.032
0.54
1.3
0.049
0.087
0.38
0.20
8.4
21
5
(R=Me)
6
(R=H)
7
<0.010
0.18
0.024
1.5
a
M; numbers are a geometric mean of 2 or more values.
Compound 5 was selected as the best compromise between potency and overall physicochemical properties. Its profile is detailed in
Table 2. We hypothesized that the limited permeability of 5 is in part due to the basicity of the imidazopyridine moiety (pKa 6.2).
Solubility of 5 is moderate despite its low lipophilicity (log D : 1.8), presumably driven by the planarity of the molecule and its
7
.4
potential to form a network of hydrogen bonds in the crystal packing. As an illustration of the potential strong interactions in the crystal
lattice, the melting point of a crystalline form of 5 was measured at 297-298 °C. We explored a number of bicyclic systems to replace
the imidazopyridine, with one of the requirements being the retention of a strong hydrogen bond acceptor capability (because of its
involvement in the hydrogen bond network with Tyr840 and a conserved water molecule, see Figure 4, panel c). The pyrazolopyridine 7
was the most interesting result of this exploration, having much reduced basicity but retaining a strong H-bond acceptor. Compound 7
-
6
-6
was much more permeable (Caco-2 P : 36 x10 cm/s for 7 vs. 6 x10 cm/s for 5) and, satisfyingly, showed excellent potency and
app
1
9
selectivity (Tables 1 and 2). However its aqueous solubility was significantly reduced, possibly due to an increase in lipophilicity.
Compound 7 showed low oral bioavailability in the rat, presumably because of low solubility combined with medium clearance.
Therefore compound 5 was preferred for further preclinical characterization.
Table 2. Biological activity and other properties of compounds 5 and 7.
5
7
<0.010
0.024
2.3
PI3K enzyme IC50 (M)
PI3K cell IC50 (M)
0.006
0.087
1.8
a
Log D7.4
pKa
6.2
2.3
b
Aqueous solubility at pH 7.4 (M)
26
7
-
6
c
Caco-2 Papp A to B (10 cm/s)
6
36
d
Rat PK CL / V
Dog PK CL / V
D
/ F%
/ F%
11 / 0.9 / 46%
19 / 0.8 / 60%
27 / 0.8 / 9%
-
d
D
a
b
c
d
Measured using shake-flask methodology with a buffer:octanol volume ratio of 100:1.
Solubility in aqueous phosphate buffer (pH 7.4); from crystalline material for 5.
Permeability in Caco-2 cell line, A pH 6.5, B pH 7.4.
From blood concentrations in male Han Wistar rats, compound administered at 4 mol/kg i.v. and 10 mol/kg p.o.; from blood concentrations in Beagle dogs,
compound administered orally at a dose around 1 mol/kg. Intravenous parameters calculated from an intravenous bolus; bioavailability, from oral and i.v. AUC.
CL in mL/min/kg; V in L/kg for both species.
D
A range of secondary amides derived from this triazolocarboxamide subseries were explored and are not reported individually in this
Letter. Figure 6, left panel gives an overall picture of the exquisite level of potency and  selectivity obtained in this subseries. If
some amides were more potent and selective than 5 affording single digit nanomolar inhibitors in cells, they suffered from low-
moderate permeability as measured in a Caco-2 permeability assay and/or low solubility. As an illustration, representative structures of
these most active and selective compounds are provided (right panel).

O
N
N
N
N
N
N
N
N
H
N
H N
2
PI3K cell IC50 0.006 M
PI3K cell IC50 1.5 M
O
N
N
N
N
N
N
N
O
N
H
H N
2
PI3K cell IC50 0.022 M
PI3K cell IC50 16 M
Figure 6. PI3K versus PI3Kcell potency (pIC50) of all amide triazole compounds (left panel) and representative structures of the most potent and selective
compounds (right panel)
With the potential for making salts if its solubility was limiting, compound 5 was further selected for additional studies. It showed good
pharmacokinetic parameters in rat and dog as reported in Table 2 and, despite its moderate solubility, showed good exposure in mouse
following oral administration at high dose (e.g. AUC: 36.2 M.h and Cmax: 18 M after 100 mg/kg dose). In vivo activity was
evaluated in the mutant PIK3CA E545K human breast cancer MCF7 xenograft model in mouse after oral administration, where it
showed good inhibition (86% tumour growth inhibition at 50 mg/kg twice daily after 21 days of dosing) with evidence of a dose-
2
0
response (see Figure 7).
In conclusion, starting from a compound with poor general kinase selectivity, we have identified a novel series of PI3K inhibitors by
hybridization of this compound with competitor pan PI3K/TOR inhibitor PF-04691502. This new series displays excellent general
kinase selectivity and PI3K selectivity over PI3Kwas further built into this series. This culminated in the discovery of compound 5,
which has a good overall profile, i.e. good potency and excellent selectivity associated with adequate physiochemical and
pharmacokinetic properties.
Acknowledgments
We would like to acknowledge the following scientists for their contribution in characterization of the compounds: Christian Delvare,
Delphine Dorison Duval, and the members of the SAR Screening Groups for generating the cell and biochemical data.
Figure 7. Tumour growth inhibition of compound 5 in a mouse MCF-7 xenograft model following oral administration.
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Delouvrié, B.; Dorison-Duval, D.; Germain, H.; Harris, C. S.; Magnien, F.; Ouvry, G.; Tricotet, T. Tetrahedron Lett. 2012, 53, 6849.
Delouvrié, B.; Germain, H.; Harris, C. S. ; Lamorlette, M. ; Lebraud, H. ; Nguyen, H. T. H.; Noisier, A.; Ouvry, G. Tetrahedron Lett. 2012, 53, 5380.
Degorce, S.; Delouvrié, B.; Davey, P. R. J.; Didelot, M. ; Germain, H.; Harris, C. S.; Lambert-van der Brempt, C.; Lebraud, H.; Ouvry, G. Tetrahedron Lett.
2
012, 53, 6078.
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6
Characterization of compound 5: after evaporation of the reaction mixture in vacuo, the crude product was purified by flash silica chromatography, eluting
with a gradient of 0% to 4% methanol in DCM. The resulting product was triturated with MeCN, filtered and dried under vacuum overnight at 45 °C to give
1
5
8
1
(12.10 g, 97 %) as a yellow solid. H NMR ( DMSO-d
6
): 2.53 (3H, s), 2.81 (3H, d), 4.16 (3H, s), 6.95 (1H, td), 7.32 (1H, ddd), 7.66 (1H, dt), 7.92 (3H, s),
1
3
.72 (1H, dt), 8.89 (1H, q); C NMR (DMSO-d
51.46, 152.66, 153.65, 158.76; HRMS-ESI m/z: 364.1626 [MH ] C17
6
): 22.28, 25.57, 40.04, 112.34, 117.14, 121.14, 121.26, 124.93, 125.86, 129.42, 134.15, 145.07, 149.93,
+
9
H18ON requires 364.1629.
1
1
7
8
Furet, P., Guagnano, V., Fairhurst, R.A., Imbach-Weese, P., Bruce, I., Knapp, M., Fritsch, C., Blasco, F., Blanz, J., Aichholz, R., Hamon, J., Fabbro, D.,
Caravatti, G. Bioorg. Med. Chem. Lett. 2013, 23, 3741.
It should be noted that compounds 1 and 5 showed some activity vs. the PI3Kand PI3K isoforms (enzyme assays): for 1, IC50 0.28 M and 0.020 M, for
5
, IC50 0.043 M and 0.016 M, resp. on PI3K and PI3K One possible explanation is that this is a consequence of the strong three point attachment hinge
binder moiety that can be accommodated in those three isoforms. Compound 5 showed excellent selectivity outside of the class I PI3K family: in a panel of
5 lipid kinases (‘Dundee University lipid kinase panel’), 5 was inactive against all kinases at 50 M, except PIP5K2A IC50 38 M; PI4KB 2.8 M;
1
PI4KCA 2.6 M and VPS15 VPS35 16 M; it showed very modest activity in a bespoke m-TOR enzyme assay IC50 29 M.
For an analysis of the properties of pyrazolopyridine vs. imidazopyridine matched pairs, see: Degorce S. L.; Boyd S.; Curwen, J. O.; Ducray, R.; Halsall, C.
T.; Jones, C. D.; Lach, F.; Lenz, E. M.; Pass, M.; Pass, S.; Trigwell, C. J. Med. Chem. 2016, 59, 4859.
The doses of 5 for the tumour growth inhibition experiment in the murine MCF7 xenograft model were chosen based on our understanding of the PK/PD and
efficacy of AZD8835 in this same model: Hudson K.; Hancox, U. J.; Trigwell, C.; McEwen, R.; Polanska, U. M.; Nikolaou, M.; Morentin Gutierrez, P.;
Avivar-Valderas, A.; Delpuech, O.; Dudley, P.; Hanson, L.; Ellston, R.; Jones, A.; Cumberbatch, M.; Cosulich, S. C.; Ward, L.; Cruzalegui, F.; Green, S.
Mol. Cancer Ther. 2016, 15, 877.
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Graphical Abstract