Maximizing ER-α Degradation Maximizes Activity in a Tamoxifen-Resistant Breast Cancer Model: Identification of GDC-0927

Article abstract of DOI:10.1021/acsmedchemlett.8b00414

The further optimization of ER-α degradation efficacy of a series of ER modulators by refining side-chain substitution led to efficacious selective estrogen receptor degraders (SERDs). A fluoromethyl azetidine group was found to be preferred and resulted

Full text of DOI:10.1021/acsmedchemlett.8b00414

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Letter
Maximizing ER-# degradation maximizes activity in a tamoxifen-
resistant breast cancer model: Identification of GDC-0927
Mehmet Kahraman, Steven P Govek, Johnny Y Nagasawa, Andiliy Lai, Celine Bonnefous,
Karensa Douglas, John Sensintaffer, Nhin Liu, Kyoungjin Lee, Anna Aparicio, Josh
Kaufman, Jing Qian, Gang Shao, Rene Prudente, James D Joseph, Beatrice Darimont,
Dan Brigham, Richard Heyman, Peter J Rix, Jeffrey H Hager, and Nicholas D. Smith
ACS Med. Chem. Lett., Just Accepted Manuscript • DOI: 10.1021/acsmedchemlett.8b00414 • Publication Date (Web): 06 Dec 2018
Downloaded from http://pubs.acs.org on December 10, 2018
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Maximizing ER- degradation maximizes activity in a tamoxifen-
resistant breast cancer model: Identification of GDC-0927
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Mehmet Kahraman, a Steven P. Govek,a Johnny Y. Nagasawa, a Andiliy Lai,a Celine Bonnefous,a
Karensa Douglas,a John Sensintaffar, b Nhin Lu,b KyoungJin Lee,c Anna Aparicio,c Josh Kaufman,c Jing
Qian,b Gang Shao,b Rene Prudente,b James D. Joseph,b Beatrice Darimont,b Daniel Brigham,b Richard
Heyman, b Peter J. Rix,c Jeffrey H. Hager,b Nicholas D. Smith a*
Seragon Pharmaceuticals, 12780 El Camino Real, Suite 302, San Diego, California 92130.
a Department of Chemistry, b Department of Biology, c Department of Drug Safety and Disposition
KEYWORDS: Estrogen receptor, estrogen receptor degrader, SERD, antagonist, tamoxifen-resistant, breast cancer,
chromene, GDC-0927, SRN-927.
ABSTRACT: The further optimization of ER- degradation efficacy of a series of ER modulators by refining side-chain substitution,
led to efficacious selective estrogen receptor degraders (SERDs). A fluoromethyl azetidine group was found to be preferred and
resulted in the identification of bis-phenol chromene 17ha. In a tamoxifen-resistant breast cancer xenograft model, 17ha (ER-
degradation efficacy = 97%) demonstrated tumor regression, together with robust reduction of intra-tumoral ER- levels. However,
despite superior oral exposure, 5a (ER- degradation efficacy = 91%) had inferior activity. This result suggests that optimizing ER-
 degradation efficacy leads to compounds with robust effects in a model of tamoxifen-resistant breast cancer. Compound 17ha
(GDC-0927) was evaluated in clinical trials in women with metastatic estrogen receptor-positive breast cancer.
OH
The estrogen receptor ER-1 has been an important target in the
F
F
F
F
H
pharmaceutical industry for many years, with ER antagonists such
as tamoxifen (1) and aromatase inhibitors being key therapeutics
in the management of ER-positive breast cancer.2 Tamoxifen (1)
and 4-hydroxytamoxifen (active metabolite) (2) are selective
estrogen receptor modulators (SERMs), meaning they may act as
an antagonist or agonist depending on the tissue in which they
act.1 Although women with ER- positive breast cancer typically
respond well to tamoxifen, resistance can emerge.3 However ER-
 has been shown to be involved in this resistant state,4 and
fulvestrant (3), a selective estrogen receptor degrader (SERD) that
antagonizes and degrades ER-, is clinically beneficial in this
patient population.5 But fulvestrant, which was not designed
prospectively as a SERD,5 has poor pharmaceutical properties and
must be administered by an intra-muscular injection. We sought
to identify SERD’s where ER- degradation efficacy was a main
driver for structure-activity-relationship (SAR) studies and that
were orally bioavailable.
F
H
H
HO
S
N
O
R
O
1:
2:
R = H: Tamoxifen
R = OH: 4-Hydroxytamoxifen
3:
Fulvestrant
Cl
F
HO
OH
O
*
N
N
OH
N
O
H
O
4:
GDC-0810 (ARN-810)
5:
Mixture of (R)- and (S)- at chromene core
5a:
(S)-Stereoisomer at chromene core
Much of the previous work on estrogen receptor ligands provides
an understanding of the structural motifs required for potent ER-
antagonists, but there has been less disclosure on what is required
to maximize ER- degradation efficacy (i.e. SERD activity). To
drive ER- degradation SAR, we used an in-cell western assay
that measured ER- levels in MCF-7 breast cancer cells. This
assay was used to develop the SAR of two chemical series on the
program, including the clinical compound GDC-0810/ARN-810
(4),6 a carboxylic acid, as well as an early lead from an amine-
based series (5).7 This paper describes the further optimization of
ER- degradation efficacy of the amine-based chromene series
represented by 5, leading to the clinical compound GDC-0927
(SRN-927). Following the completion of this work, other
publications have been released that report SERDs.8,9
Figure 1: Estrogen receptor ligands
The compounds described in this paper consist of a central
chromene core to which an amine-based side chain is appended.
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The side-chain was installed on the core by two methods: i)
fluoromethyl-substituted pyrrolidine group was incorporated
(17e), a substantial increase in ER- degradation efficacy over
17b was observed (89%→97%). It was apparent that the mono-
fluoromethyl at the 3-position of the pyrrolidine was optimal, as
17f and 17g had inferior ER- degradation efficacy compared to
17e. Addition of the fluoromethyl substituent to either the
azetidine (17h) or piperidine (17i) side-chains, again led to an
increase in ER- degradation efficacy compared to previously
described, non-fluorinated methyl-substituted parent compounds7
(for azetidine 17h: 86%→97%; for piperidine 17i: 63%→80%).
Previously we found that a (S)-methyl group on the linker ethyl
chain led to a boost in ER- degradation efficacy compared to the
unsubstituted system,7 and so we installed a methyl in the linker
of azetidine 17h and pyrrolidine 17e, resulting in 17j and 17k
respectively. However, no further increases in ER- degradation
efficacy were obtained, although 17k was found to be another
potent, high efficacy ER- degrader compared to its non-
fluorinated parent compound 5 (98% ER- degradation efficacy
versus 91% respectively). Lead compounds 17e, 17h and 17k all
displayed an MCF-7 proliferation IC50 ≤ 0.2 nM.
1
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3
4
5
6
7
8
Ullmann coupling between an amino alcohol side-chain and an
aryl iodide on the chromene core (General Method 1, Scheme 1),
or ii) alkylation with the desired cyclic amine of a previous
installed ethyl mesylate on the chromene core (General Method 2,
Scheme 1). See Supplementary information for preparation of the
amino alcohol side-chains 10a-c, and cyclic amines 6a-g.
Intermediate 15 was prepared in an eight step sequence from 2-(3-
methoxyphenyl)acetic acid (12), while mesylate 16 was prepared
from 15 in two additional steps. Chromene intermediate 15 was
prepared from 2-(3-methoxyphenyl)acetic acid 12.7 Intermediate
16 was prepared from 15 via Ullmann coupling with ethylene
glycol, followed by mesylation to afford 16 in 51% over two
steps. The final compounds 17h and 17j-k were prepared from 15
using an Ullmann coupling with side-chains 10a-c followed by
deprotection of the THP groups using acetic acid. In turn, final
compounds 17c-g and 17i were prepared by SN2 displacement of
mesylate 16 with the cyclic secondary amines 6a-g, followed by
THP deprotection.
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Scheme 1. Preparation of chromene ER ligands
Table 1: Importance of a mono-fluoromethyl substituent to ER-
O
O
3'
OH
5
THPO
HO
degradation efficacy
d, e
O
a, b, c
*
*
OTHP
I
3
O
HO
O
OH
12
13
14
HO
OH
THPO
THPO
i, j
f, g, h
OTHP
O
OTHP
I
O
*
*
O
R1
*
O
OMs
16
O
15
k, l
m, l
General Method 2
HO
General Method 1
HO
ER Degradationa
Proliferationb
IC50 (nM)
0.2
10a-c
6a-g
IC50
Efficacyc
91
R1
OH
O
OH
O
Cpd
5d
(nM)
*
*
O
O
0.2
N
N
17h, 17j-k
17c-g, 17i
F
F
N
N
N
17ad
17bd
17c
17d
17e
17f
0.4
0.4
0.3
0.8
0.1
0.2
0.2
0.3
0.1
0.2
0.2
75
89
64
79
97
90
68
97
80
92
98
0.3
0.2
0.4
3.6
0.2
0.4
1.4
0.2
0.1
0.3
0.2
N
N
O
CN
17d
17c
17j
17h
N
N
N
F
N
F
F
17f
17e
F
17k
OMe
F
N
N
17g
17i
F
Reagents and conditions
: (a) SOCl2, DMF, DCM, 0 ºC; (b) 1,4-dimethoxybenzene, AlCl3, DCM, 0 ºC,
CN
F
N
55%; (c) BBr3, DCM, -78 ºC-0 ºC, 57%; (d) DHP, PPTS, DCM, 70%; (e) 4-iodobenzaldehyde,
piperidine, DBU, s-butanol, reflux, 75%; (f) MeMgCl, THF, 0 ºC-rt, 98%; (g) 80% AcOH/water, 90 ºC,
67%; (h) DHP, PPTS, DCM, 55%; (i) ethane-1,2-diol, CuI, 1,10-phenantroline, K2CO3, butyronitrile,
17h, 17j-k
: CuI, K2CO3,
17c-g, 17i
: K2CO3, acetonitrile, 60 ºC-reflux, 62-76%;
125 ºC, 58%; (j) methanesulfonyl chloride, TEA, DCM, 0 ºC, 88%; (k)
butyronitrile, 125-135 ºC, 2-4 d, 75-82%; (m)
(l) 80% AcOH/water, rt, 27-85%.
N
F
F
N
N
The mono-phenol analogs 20c and 20d (Table 2) were prepared
from the corresponding chromene intermediate using an Ullmann
coupling with the appropriate amino-alcohol side chains.
17g
17h
17i
F
F
F
N
Previously we demonstrated that subtle structural changes to the
side-chain of the chromene scaffold could lead to large changes in
ER- degradation efficacy.7 For example, installation of an (R)-3-
methyl-substituent on the pyrrolidine of 17a, giving 17b, led to a
large increase in ER- degradation efficacy (75%→89%, Table
1). We continued to optimize ER- degradation efficacy while
maintaining potency by further exploring the substituent at this 3-
position on the pyrrolidine, but found that the methoxymethyl
(17c) and nitrile (17d) derivatives, although potent ER-
N
F
F
17j
N
17k
N
degraders, lost ER- degradation efficacy. However when a
2
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a: ER- in-cell western in MCF-7 cells (n ≥ 4). b: MCF-7
a: ER- in-cell western in MCF-7 cells (n ≥ 4). b: MCF-7
proliferation assay (n ≥ 3) c: Efficacy recorded as percent of
efficacy of fulvestrant control d: See ref 7
1
2
proliferation assay (n ≥ 3) c: Efficacy recorded as percent of
efficacy of fulvestrant control d: See ref 7
3
4
5
6
7
8
9
Of the side-chains shown in Table 1, pyrrolidine 17e was found to
have inferior mouse PK compared to azetidine 17h, and was
deprioritized as a lead side-chain (AUC at 10 mg/Kg PO: 0.04
g∙hr/mL for 17e, versus 0.16 g∙hr/mL for 17h). 17h, 17k, and
their single active stereoisomers (see below) were profiled further;
the fluoromethyl azetidine side-chain of 17h was ultimately
selected over the fluoromethyl pyrrolidine of 17k as the lead side-
chain due to: i) reduced number of stereo-centers (1 versus 3), and
ii) improved performance of the single stereosiomer in a
Compounds were synthesized and tested in assays as a 50/50
mixture of stereosiomers at the chromene core. For the lead
compounds 17h, 17k, and 20c (and 5) we confirmed that SERD
activity was in one stereoisomer by separation by chiral
supercritical fluid chromatography (SFC), and then
characterization of the stereoisomers. As shown in Table 3, the
active stereoisomers 17ha, 17ka and 20ca (from 17h, 17k, and
20c respectively), all had high potency (IC50 = 0.1 nM) in the ER-
 degradation assay compared to the inactive stereoisomers 17hb,
17kb and 20cb (IC50 > 10 nM). The activity seen in 17hb, 17kb
and 20cb is likely due to residual active stereoisomer
(approximately 1% following SFC separation). Analogous results
were obtained when these pairs of compounds were tested in an
ER- binding assay and MCF-7 breast cancer cell line anti-
proliferative assay, indicating that the profiling of enantiomeric or
diastereoisomeric mixtures was acceptable during SAR studies.
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tamoxifen-resistant breast cancer xenograft model (see below).
Previously we showed that replacement of one of the phenols of
5, to give mono-phenol derivatives such as 20a and 20b led to a
loss of ER- degradation efficacy (91%→82-84%), and in the
case of 20a, resulted in loss of anti-tumor activity in a tamoxifen-
resistant breast cancer xenograft model (Table 2).7 Having
selected the fluoromethyl azetidine as the preferred side-chain to
maximize ER- degradation on the bis-phenol chromene core, we
revisited these mono-phenol chromenes, and prepared 20c and
20d. In contrast to the methyl pyrrolidine mono-phenols 20a and
20b, fluoromethyl azetidines 20c and 20d have robust levels of
ER- degradation efficacy (98%) equal to that of the bis-phenol
chromene 17h. Hence the fluoromethyl azetidine side-chain not
only increases the degradation efficacy of bis-phenol chromenes
(compare 5 to 17h), it also maintains that level of ER-
degradation potency and efficacy for mono-phenol systems
(compare 17h to 20c and 20d). As noted for the derivatives in
Table 1, 20c and 20d are also potent in the MCF-7 proliferation
assay (IC50 < 0.5 nM).
Table 3: SERD activity resides in one chromene stereoisomer
ER- Degradationa IC50 (Efficacy)b
4'
R2
3'
4'
R2
3'
R1
R2
HO
HO
O
O
R1
R1
O
O
5a: 0.1 nM (91%)
5b: 9.7 nM (90%)c
3’-
OH
N
N
3’-
OH
17ha: 0.1 nM
17hb: 13 nM
F
(97%)
(96%)c
F
3’-
OH
17ka: 0.1 nM
17kb: 11 nM
N
(97%)
(97%)c
Table 2: The fluoromethyl azetidine side-chain significantly
improves ER- degradation efficacy
20 cb: 15 nM
F
4’-F
20ca: 0.1 nM (97%)
N
(98%)c
4'
a: ER- in-cell western in MCF-7 cells (n ≥ 4). b: Efficacy recorded as percent of
efficacy of fulvestrant control c: Activity likely due to residual active stereoisomer
(approximately 1% following SFC separation)
R2
3'
HO
O
*
R1
Previously we described the use of the rat uterine wet weight
assay to efficiently triage ER-based pharmacodynamics, and to
determine tissue-selectivity (breast versus uterine).6-7 Compounds
17ha and 20ca were examined in this assay in agonist mode (no
added ethynyl estradiol) and like 5a, displayed an inverse agonist
profile, reducing uterine weights below that of the vehicle treated
animals (Figure 2). This is in contrast to tamoxifen (1), which
showed partial agonist activity, increasing uterine weights above
vehicle in the absence of added estradiol.1
O
ER Degradationa
Proliferationb
IC50 (nM)
0.2
Cpd
R1
R2
IC50
Efficacyc
(nM)
3’-
OH
5
0.2
0.4
1.5
0.3
0.4
0.2
91
82
84
97
98
98
N
N
20ad
20bd
17h
20c
20d
4’-F
0.4
10
Figure 2: 17ha and 20ca are inverse agonists in a rat uterine wet
4’-
CN
weight assaya
N
N
N
3’-
OH
F
0.2
0.4
0.3
F
4’-F
4’-
CN
F
N
3
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The inferior profile of 5a compared to 17ha and 20ca is not due to
3
2
1
0
1
2
3
4
5
6
7
8
potency against the estrogen receptor (ER- degradation IC50: 5a
= 0.1 nM versus 17ha = 0.1 nM, 20ca = 0.1 nM; MCF-7
proliferation IC50: 5a = 0.1 nM versus 17ha = 0.1 nM, 20ca = 0.2
nM) or pharmacokinetics (day 28 xenograft free AUC = 0.19
g∙hr/mL for 5a versus 0.13 g∙hr/mL and 0.08 g∙hr/mL for
17ha and 20ca respectively). Importantly 5a is a less efficacious
ER- degrader in-vitro than 17ha and 20ca (ER- degradation
efficacy: 5a = 91% versus 17ha and 20ca: 97%). As shown in
Figure 4, this difference in in-vitro ER- degradation efficacy is
reflected in the pharmacodynamic readout of tumor ER- protein
levels on day 28 of the xenograft study. Thus while compound 5a
reduced ER- levels to those of the vehicle plus estradiol
cohort,11 both 17ha and 20ca reduced levels substantially below
that of 5a. It is noteworthy that mono-phenol 20ca had robust
activity in this tamoxifen-resistant setting (equal to that of bis-
phenol 17ha) since as we previously described, mono-phenol 20a
was inferior to bis-phenol 5 in this same model.7 This result again
demonstrates the effectiveness of the optimized fluoromethyl
side-chain in maximizing in-vitro ER- degradation efficacy and
in-vivo xenograft performance.
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Veh Veh
+EE
1
5a 17ha 20ca
a: Compounds administered orally for 3 days (5a, 17ha and 20ca
at 10 mg/kg po; tamoxifen (1) at 60 mg/kg).
As with other ER ligands that also contain two phenol groups, the
mouse pharmacokinetics of 5a and 17ha are characterized by high
clearance (Cl > 60 mL/min/kg) and low bioavailability (%F < 15).
In contrast to 17ha, the mono-phenol 20ca had improved
clearance (Cl = 36 mL/min/kg) and bioavailability (42% F versus
10% F), leading to improved exposure following oral dosing (po
AUC = 1.9 g.hr/mL versus 0.16 g.hr/mL). Compounds 17ha,
20ca and the previous lead compound from the chromene series,
5a, were profiled in a MCF-7 based tamoxifen-resistant xenograft
model of breast cancer using sub-cutaneous estradiol pellets to
deliver sufficient levels of estradiol to drive tumor growth (Figure
3).10 Importantly, 17ha and 20ca demonstrated superior activity to
5a with 5 of 8 animals in each cohort showing tumor regressions.
In contrast, only 1 of 8 animals showed tumor shrinkage in the
cohort treated with 5a.
Figure 4: Compared to 5a, ER- levels are lower in tumors of
animals treated with 17ha and 20ca
100
50
*
*
Figure 3: 17ha and 20ca demonstrate superior activity to 5a in an
0
MCF-7 tamoxifen-resistant breast cancer xenograft modela
Veh+E2
1
5a 17ha 20ca
*: P<0.01 (t-test) versus 5a
Vehicle
1 120mg/kg po
500
The robust performance of 17ha and 20ca in this and other pre-
clinical xenograft models of breast cancer led to consideration of
both compounds as potential clinical candidates. 17ha was
ultimately selected in part due to results from an assay probing the
conformation of ER- induced by these ligands. In this assay,
ligand-induced ER-α conformation was monitored by the
interaction of ligand-selective peptide probes with the ligand-
bound receptor.12 The peptide probes utilized in this study interact
differentially with protein surfaces exposed on ER-α in response
to estradiol, 4-hydroxytamoxifen or fulvestrant binding.13,14 It was
found that 17ha and 20ca induce ER-α conformations distinct
from fulvestrant and 4-hydroxytamoxifen (see supplementary
information). However, 20ca-bound ER- interacted with the III
peptide probe, suggesting that aspects of the 20ca induced ER-
conformation are shared with that induced by the SERM 4-
hydroxytamoxifen. In contrast, the ER- conformations in
response to 17ha did not show appreciable interaction with III
(see supplementary information). As we were looking to identify
a candidate with a profile distinct from tamoxifen, we selected
17ha for development.
5a 100mg/kg po
17ha 100mg/kg po
20ca 100mg/kg po
400
300
200
100
0
7
14
21
28
Study Day
Xenograft Day 28 PK parametersb
Free AUC
Mouse
free
fraction
C
AUC
Free C
max
0-
max
0-24
Cpd
24
(µg/mL) (µg·hr/mL)
(µg/mL)
(µg·hr/mL)
0.19
5a
17ha
20ca
0.016
0.019
0.004
1.3
0.95
2.3
12
6.9
21
0.021
0.018
0.009
0.13
0.08
Selectivity of 17ha against nuclear hormone receptors was good.
In transcriptional reporter assays for the glucocorticoid,
mineralocorticoid, progesterone-A and progesterone-B receptors,
17ha had no significant agonist or antagonist activity.
a: MCF-7 tamoxifen-resistant xenograft in mice using
subcutaneous 0.72 mg estradiol pellets. b: Plasma
pharmacokinetics measured on day 28 of study during take down.
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Cytochrome P450 inhibition profiling of 17ha indicated it had
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6. Lai, A.; Kahraman, M.; Govek, S.; Nagasawa, J.; Bonnefous, C.;
Julien, J.; Douglas, K.; Sensintaffar, J.; Lu, N.; Lee, K.-J.; Aparicio, A.;
Kaufman, J.; Qian, J.; Shao, G.; Prudente, R.; Joseph, J. D.; Darimont,
B.; Brigham, D.; Grillot, K.; Heyman, R.; Rix, P.; Hager, J.; Smith, N.
D., Identification of GDC-0810 (ARN-810), an orally bioavailable
Selective Estrogen Receptor Degrader (SERD) that demonstrates
robust activity in tamoxifen-resistant breast cancer xenografts.
Journal of medicinal chemistry 2015, 58 (12), 4888-4904.
7. Nagasawa, J.; Govek, S.; Kahraman, M.; Lai, A.; Bonnefous, C.;
Douglas, K.; Sensintaffar, J.; Lu, N.; Lee, K.-J.; Aparicio, A.; Kaufman,
J.; Qian, J.; Shao, G.; Prudente, R.; Joseph, J. D.; Darimont, B.;
Brigham, D.; Grillot, K.; Heyman, R.; Rix, P.; Hager, J.; Smith, N. D.,
Identification of an orally bioavailable chromene-based Selective
Estrogen Receptor Degrader (SERD) that demonstrates robust
activity in a model of tamoxifen-resistant breast cancer. Journal of
medicinal chemistry 2018, 61 (17), 7917-7928.
8. De Savi, C.; Brdbury, R. H.; Rabow, A. A.; Norman, R. A.; de
Almeida, C.; Andrews, D. M.; Ballard, P.; Buttar, D.; Callis, R. J.;
Currie, G. S.; Curwen, J. O.; Davies, C. D.; Donald, C. S.; Feron, L. J.;
Gingell, H.; Glossop, S. C.; Hayter, B. R.; Hussain, S.; Karoutchi, G.;
Lamont, S. G.; MacFaul, P.; Moss, T. A.; Pearson, S. E.; Tonge, M.;
Walker, G. E.; Weir, H. M.; Wilson, Z. Optimization of a novel
binding motif to (E)-3-(3,5-difluoro-4-((1R,3R)-2-(2-fluoro-2-
methylpropyl)-3-methyl-2,3,4,9-tetrahydro-1H-pyrido[3,4-
b]indol-1-yl)phenyl)acrylic acid (AZD9496), a potent and orally
bioavailable selective estrogen receptor downregulator and
antagonist. J. Med. Chem. 2015, 58(20), 8128-8140.
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little to no competitive inhibitory activity against CYP1A2,
CYP2C19, CYP2D6 or CYP3A4 (IC50 > 10 M), and modest
inhibitory effect on CYP2C8 and CYP2C9 (IC50 = 3.0 M and 3.2
M respectively). In a CEREP panel of radio-ligand binding
assays for 55 targets (protein-free conditions), 17ha at 10 µM
displayed >75% binding to 6 targets. However, in follow-up, cell-
based functional assays, the interactions with most of these 6
targets were weak with IC50 values > 10 M. The only interaction
with an IC50 < 1M was with the dopamine transporter (IC50
=
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0.39 M). When tested for its effect on the hERG channel in a
patch clamp assay, 17ha was found to be a moderate inhibitor
(IC50 = 4.6 M). This activity on the dopamine transporter and
hERG channel was not considered an issue as selectivity for ER is
>1000 fold (MCF-7 proliferation = 0.1 nM; ER- degradation =
0.1 nM). Compound 17ha was negative in an Ames assay using
the TA-98 and TA-100 tester strains.
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In summary, we have further maximized ER- degradation
efficacy of a series of ER modulators resulting in highly potent
and efficacious chromene SERDs. A fluoromethyl substituent on
either a pyrrolidine or azetidine ring at the end of the side-chain
was found to be optimal for maximizing ER- degradation.
Fluoromethyl azetidine was determined to be the preferred ring
system on the side-chain, leading to the identification of bis-
phenol chromene 17ha. In contrast to previous work, when
applied to a mono-phenol chromene core, the fluoromethyl
azetidine side-chain gave highly efficacious ER- degraders such
as 20ca. In a tamoxifen-resistant breast cancer xenograft model,
17ha and 20ca (ER- degradation efficacy = 97%) demonstrated
tumor regression, together with robust reduction intra-tumoral
ER- levels. However, despite higher drug levels, 5a (ER-
degradation efficacy = 91%) had inferior activity. This data
suggests optimizing ER- degradation in-vitro, maximizes
activity in a tamoxifen-resistant breast cancer xenograft derived
from the MCF-7 breast cancer cell line. Compound 17ha (GDC-
0927 or SRN-927) was selected for development and was
evaluated in clinical trials in women with metastatic ER-positive
breast cancer.
ASSOCIATED CONTENT
The Supporting Information is available free of charge on the ACS
Publications website.
9. Xiong, R.; Zhao, J.; Gutgesell, L. M.; Wang, Y.; Lee, S.; Karumudi,
B.; Zhao, H.; Lu, Y.; Tonetti, D. A.; Thatcher, G. R. Novel selective
estrogen receptor downregulators (SERDs) developed against
treatment-resistant breast cancer. J Med Chem. 2017, 60(4),1325-
1342.
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Experimental information for synthesis of compounds.
Ligand-induced ER- conformation
Biological assays
AUTHOR INFORMATION
10. This E2 is used to drive xenograft tumor growth in-vivo, and
leads to high E2 concentrations (300-400 pg/ml), thus requiring
more ER ligand to out-compete the native ligand (E2) and so mediate
an inhibitory effect. This is of relevance as plasma E2 levels in the
target patient population of post-menopausal women (~5 pg/mL),
are substantially lower. Thus efficacy models run in the context of
high E2 plasma concentrations potentially overestimate ER ligand
dose and plasma levels necessary to drive efficacy in a post-
menopausal setting.
Corresponding author:
*Phone: 858-369-7604. E-mail: nsmith@seragonpharm.com.
Notes: The authors declare no competing financial interest
ABBREVIATIONS
E2, estradiol; EE, ethynyl estradiol; ER, estrogen receptor; ERE,
estrogen response element; SERD, selective estrogen receptor
degrader; SERM, selective estrogen receptor modulator; UWW,
uterine wet weight;
11. Of note is that although an ER agonist, estradiol is also a strong
degrader of ER-. See: Wijayaratne, A. L.; McDonnell, D. P.; Journal
of Biological Chemistry, 2001, 276, 38, 35684-35692.
REFERENCES
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Maximizing ER- degradation maximizes activity in a
tamoxifen-resistant breast cancer model: Identification of GDC-
0927
Mehmet Kahraman, a Steven P. Govek,a Johnny Y. Nagasawa, a Andiliy Lai,a Celine
Bonnefous,a Karensa Douglas,a John Sensintaffar, b Nhin Lu,b KyoungJin Lee,c Anna
Aparicio,c Josh Kaufman,c Jing Qian,b Gang Shao,b Rene Prudente,b James D. Joseph,b
Beatrice Darimont,b Daniel Brigham,b Richard Heyman, b Peter J. Rix,c Jeffrey H. Hager,b
Nicholas D. Smith a*
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