Novel trifluoromethylated enobosarm analogues with potent antiandrogenic activity in vitro and tissue selectivity in vivo

Article abstract of DOI:10.1158/1535-7163.MCT-18-0037

Prostate cancer often develops antiandrogen resistance, possibly via androgen receptor (AR) mutations, which change antagonists to agonists. Novel therapies with increased anticancer activity, while overcoming current drug resistance are urgently needed. Enobosarm has anabolic effects on muscle and bone while having no effect on the prostate. Here, we describe the activity of novel chemically modified enobosarm analogues. The rational addition of bistrifluoromethyl groups into ring B of enobosarm, profoundly modified their activity, pharmacokinetic and tissue distribution profiles. These chemical structural modifications resulted in an improved AR binding affinity—by increasing the molecular occupational volume near helix 12 of AR. In vitro, the analogues SK33 and SK51 showed very potent antiandrogenic activity, monitored using LNCaP/ ARLuciferase cells where growth, PSA and luciferase activity were used as AR activity measurements. These compounds were 10-fold more potent than bicalutamide and 100-fold more potent than enobosarm within the LNCaP model. These compounds were also active in LNCaP/BicR cells with acquired bicalutamide resistance. In vivo, using the ARLuc reporter mice, these drugs showed potent AR inhibitory activity in the prostate and other ARexpressing tissues, e.g., testes, seminal vesicles, and brain. These compounds do not inhibit AR activity in the skeletal muscle, and spleen, thus indicating a selective tissue inhibitory profile. These compounds were also active in vivo in the Pb-Pten deletion model. SK33 and SK51 have significantly different and enhanced activity profiles compared with enobosarm and are ideal candidates for further development for prostate cancer therapy with potentially fewer side effects.

Full text of DOI:10.1158/1535-7163.MCT-18-0037

Author Manuscript Published OnlineFirst on June 12, 2018; DOI: 10.1158/1535-7163.MCT-18-0037
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Novel Trifluoromethylated Enobosarm Analogues with Potent Anti-
androgenic Activity in vitro and Tissue Selectivity in vivo.
a,c☥
b☥
c
D. Alwyn Dart
, Sahar Kandil , Serena Tommasini-Ghelfi , Gilberto Serrano de
c
c
a
b
Almeida , Charlotte L. Bevan , Wenguo Jiang , and Andrew D. Westwell
a
b
Cardiff China Medical Research Collaborative, Cardiff University School of Medicine, Cardiff, CF14 4XN, Wales, UK. School of Pharmacy and
c
Pharmaceutical Sciences, Cardiff University, Redwood Building, King Edward VII Avenue, CF10 3NB Cardiff, Wales, UK. Androgen Signalling
Laboratory, Department of Surgery & Cancer, Imperial College London, Hammersmith Hospital Campus, London, W12 0NN, UK.
☥
These authors contributed equally to this manuscript
Running title: Potent anti-androgenic enobosarm analogues for prostate cancer treatment.
Corresponding author: dartd@cardiff.ac.uk
Keywords: prostate, cancer, enobosarm, anti-androgen, therapeutics
Conflict of Interest
The authors declare that there are no conflicts of interest in relation to the work described.
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Abstract
Prostate cancer often develops anti‐androgen resistance, possibly via androgen receptor (AR)
mutations which change antagonists to agonists. Novel therapies with increased anticancer activity,
whilst overcoming current drug resistance are urgently needed. Enobosarm has anabolic effects on
muscle and bone whilst having no effect on the prostate. Here we describe the activity of novel
chemically modified enobosarm analogues. The rational addition of bis‐trifluoromethyl groups into
ring B of enobosarm, profoundly modified their activity, pharmacokinetic and tissue distribution
profiles. These chemical structural modifications resulted in an improved AR binding affinity ‐ by
increasing the molecular occupational volume near helix 12 of AR. In vitro, the analogues SK33 and
SK51 showed very potent antiandrogenic activity, monitored using LNCaP/AR‐Luciferase cells where
growth, PSA and luciferase activity were used as AR activity measurements. These compounds were
1
0-fold more potent than bicalutamide and 100-fold more potent than enobosarm within the LNCaP
model. These compounds were also active in LNCaP/BicR cells with acquired bicalutamide
resistance. In vivo, using the AR‐Luc reporter mice, these drugs showed potent AR inhibitory activity
in the prostate and other AR‐expressing tissues e.g. testes, seminal vesicles and brain. These
compounds do not inhibit AR activity in the skeletal muscle, and spleen ‐ thus indicating a selective
tissue inhibitory profile. These compounds were also active in vivo in the Pb-PTen deletion model.
SK33 and SK51 have significantly different and enhanced activity profiles compared to enobosarm,
and are ideal candidates for further development for prostate cancer therapy with potentially fewer
side effects.
2
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Introduction
Prostate cancer (PCa) is the most commonly diagnosed male cancer in the Western world (1). Tumor
growth is initially androgen dependent - driven by the androgen receptor (AR). Androgen receptor
(AR) signalling pathway remains a key driver of PCa, implicated throughout the different stages of
the disease, and as such represents an obvious therapeutic target in PCa therapy (2, 3). Androgen
receptor (AR) is a member of the family of steroid hormone receptors, which are ligand-dependent
transcriptional regulators for diverse sets of genes involved in both reproductive and anabolic
actions (4-6). The prototypical model for AR involves ligand binding that induces conformational
changes in the ligand-binding domain (LBD), revealing a co-activator dimerization surface composed
of helices 3, 5, and 12, as the LBD site is adjacent to helix 12 (H12).
Currently, the mainstays of prostate cancer treatment are androgen ablation (to castrate levels)
and/or antiandrogen treatment, which block AR signalling (2, 3). The major anti-androgens in clinical
use are bicalutamide and enzalutamide (and historically flutamide, hydroxyflutamide and
nilutamide) (Figure 1A). However, these compounds bind to AR with low affinity and can induce
escape mechanisms. Furthermore, under AR amplification or mutation conditions some of these
compounds exhibit agonist activity and fail to inhibit AR. This resistance may arise from, among
other mechanisms, mutations to several key residues in the ligand-binding domain (AR-LBD) (7, 8).
Common mutations in AR found in PCa patients include T877A, W741L, and W741C. Bicalutamide
W741L
W741C
(Figure 1A) can act as an agonist in AR
and AR
while hydroxyflutamide is an agonist in
T877A
AR
(7, 8). Gain of function mutations are common in prostate cancers and are correlated with
disease progression, the lack of therapeutic response and poor clinical outcomes. Additionally, AR
mutations may be selected for during anti-androgen therapy – reviewed in (9, 10) .
Additionally, the use of anti-androgens in patients may elicit moderate side effects e.g. muscle
wastage, bone density loss and CNS dysfunction – which are exacerbated in elderly men. Therefore,
there is a growing need for selective androgen receptor modulators (SARM) that would demonstrate
tissue-selective activity – being inhibitors of the AR in the prostate with tissue sparing effects
elsewhere (11).
TM
Enobosarm (also referred to as Ostarine , GTx-024 or S-22) is a non-steroidal selective androgen
receptor modulator (SARM) with a favourable safety and pharmacokinetic profile (Figure 1B). It
belongs to the class of arylpropionamides, which are structurally derived from the antiandrogen
bicalutamide. Enobosarm binds to and activates the AR with enantioselective affinity, potency and
efficacy similar to, but somewhat less than, that of DHT (12). Transient transfection studies indicate
that enobosarm is remarkably selective for the AR and it does not cross-react with other nuclear
hormone receptors. This receptor specificity differentiates enobosarm’s pharmacology from other
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steroidal androgens and has likely contributed to observations that the drug has generally been well
tolerated in clinical trials. It has selective anabolic effects and is under clinical development for
prevention and treatment of muscle wasting (cachexia) in cancer patients (13, 14).
4
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Results
Rational design of novel Enobosarm analogues
Nonsteroidal anti-androgens such as bicalutamide act as AR antagonists (Figure 1A), thus preventing
androgen-dependent cell growth. In contrast, AR agonists e.g. enobosarm (Figure 1B) may act as
agonists in all the AR LBD mutants, since they will fit sterically better with the bulk-reducing AR
wt
mutations than in AR (15). The difference in activity between agonists such as enobosarm and
wt
antagonists such as bicalutamide in AR may arise from the linker oxygen’s smaller size relative to
the sulfonyl group of bicalutamide (Figure 1A&B). This bulk in AR antagonist structure, though small,
is thought to push the AR helix 12 away from the binding pocket, disturbing the agonist
conformation of the androgen receptor (16). The current theoretical key to antagonism states that
the differences observed among AR modulators (agonist or antagonist) are not because of their B-
ring size or shape but because of their linker size and orientation (17). The improved understanding
is being applied to rationally designed treatment options with novel mechanisms of action. It is
proposed that AR antagonists should have appending molecular extensions to the core structure of
AR agonists that interfere with the placement of H12, thereby disrupting co-activator recruitment
(16, 18, 19).
wt
In the enobosarm/AR co-crystal structure (PDB code; 3RLJ)(17) (Figure 2A&B), the 4-cyanophenyl
741
ether group of enobosarm is situated between residues of H12 and the indolyl side chain of Trp ,
suggesting that in the wild-type receptor (and probably the W741L mutant) the larger substitution
with the same orientation of the linker would result in a better AR antagonist by pushing against
Helix 12. We tested this hypothesis in silico by investigating whether the introduction of 3,5-Bis-
trifluoromethyl (3,5-Bis-CF ) into B ring of enobosarm would provide the geometric bulk needed to
3
keep ring B towards Helix 12 of AR. Preliminary molecular modelling studies showed that the bis-
trifluoromethyl phenyl moiety (ring B in SK33 and SK51) has significantly changed the orientation of
741
ring B so that the (3,5-Bis-CF ) groups are pointing outwards away from Trp and towards helix 12,
3
thus preventing AR from adapting the AR agonist conformation, whilst keeping the small size of the
oxygen linker. The combination of the small oxygen linker and the steric hindrance of the (3,5-Bis-
CF
conformational restriction away from Trp and towards helix 12 (Figure 2C & D). A small library of
AR antagonists having the (3,5-Bis-CF ) motif was prepared (20) among which SK33 showed the best
3
) substitution on ring B resulted in the optimum size and orientation of ring B to impose
741
3
antiproliferative and metabolic profiles, hence it was selected for further studies.
The introduction of fluorinated substituents into drug candidates can impart a unique set of
properties owing to the unique combination of electronegativity, size and lipophilicity features of
fluorinated groups (21-25). These factors can have a substantial impact on the molecular
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conformation, which in turn affect the binding affinity to the target protein (26, 27).
Chemical synthesis of SK33 and SK51
Racemic enobosarm derivatives (SK33 and SK51) were prepared by reacting methacryloyl chloride
(
2) with the corresponding substituted anilines 1a and 1b in dimethylacetamide (DMA) solvent to
obtain phenylacrylamides 3a and 4b which were converted into the corresponding epoxides 4a and
b in the presence of a large excess of hydrogen peroxide and trifluoroacetic anhydride in
dichloromethane (DCM). Opening of the epoxide rings of 4a and 4b with substituted 3,5-bis
4
(trifluoromethyl)phenol (5) in tetrahydrofuran (THF) gave the final compounds SK33 and SK51. The
1
structures of the synthesised compounds were confirmed using analytical and spectroscopic data ( H
13
19
NMR, C NMR, F NMR and mass spectrometry), which were in full accordance with their depicted
structures. SK33 and SK51 were purified (>95% as confirmed by HPLC) and tested as racemic mixture
(Figure 1C).
Cellular activity of enobosarm and the trifluoromethylated analogues SK33 and SK51
The antiproliferative and selective activities of these compounds were tested in vitro in a
panel of prostate cancer cell lines, namely LNCaP, VCaP, PC3 and Du145. LNCaP and VCaP
represent prostate cells which have retained the expression of the androgen receptor (28,
29). However, LNCaP cells overexpress a mutant AR, with a T877A mutation in the ligand
binding site. The VCaP cell line overexpresses wild type AR. Both cell lines are responsive to
androgens and cells will express androgen responsive genes. The PC3 and Du145 cells do
not express the AR nor do they express androgen responsive genes.
Cells were exposed to increasing concentrations of anti-androgens for 96 hours and cell
AR+ve
viability was analysed using the MTT assay. In LNCaP
cells the parental compound
enobosarm, showed insignificant activity with the IC50 = 40 M, however, the
trifluoromethylated enobosarm analogue, SK33, demonstrated a significantly potent activity
with IC50 = 0.2 M (Figure 3A). Moreover, when compared to the antiandrogen
bicalutamide, the novel compounds showed an increased efficacy (Figure 3B). SK51 also
displayed an increased activity compared to bicalutamide (IC50 = 0.7M) (Figure 3B).
AR-ve
In PC3
cells, enobosarm showed activity only at relatively high dose (Figure 3C), whilst
SK33 showed some moderate activity. When compared to bicalutamide, SK33 showed a
significantly increased increased activity. On the other hand, the anti-proliferative activity of
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AR+ve
AR-ve
SK33 in LNCaP
cells was over ten times higher than that of its activity against PC3
cell line (Figure 3D).
Furthermore, the panel of prostate cancer cell lines were screened for their expression of
AR+ve
AR+ve
the target androgen receptor (AR) by qPCR. As expected, LNCaP
and VCaP
cells
cells
AR-ve
AR-ve
showed robust expression of AR whilst AR was not detectable in PC3
Figure 3E).
and Du145
(
Figure 3F depicts the summary of the activity profile of the SK33 and SK51 compounds in
the four PCa cell lines where a clear activity difference (selectivity) can be observed
+ve
-ve
between the AR cell lines (LNCaP and VCaP) and the AR cell lines (PC3 and Du145).
SK33 decreases cells entering S-phase in LNCaP cells but not in PC3 cells
To further analyse the activity of these compounds in prostate cancer cell lines we treated
+ve
-ve
LNCaP (AR ) or PC3 (AR ) cells with 10M of antiandrogen (or vehicle DMSO) for 48
hours. These cell lines were collected for FACS analysis and standard cell cycle profiling
using propidium iodide staining for DNA content, was carried out.
LNCaP cells showed a decrease in the number of cells in S phase with all the anti-androgen
compounds. SK33 showed the highest reduction of the number of cells in S phase, followed
by SK51, enzalutamide and then bicalutamide, respectively. (Figure 3G). No apparent cell
toxicity could be visualised as estimated by the absence of a sub-G1 population or
fragmented necrotic cells (Figure 3G). In the PC3 cell line, no significant effect was observed
with any of the tested compound (Figure 3H). However, a small increase in G2/M phase
could be detected with SK33 in PC3 cells.
SK33 reduces AR transcriptional activity
We then analysed the ability of SK33 to inhibit the activity of the AR protein i.e. the ligand
activated transcription factor activity. The LNCaP/Luc cell line, has an integrated luciferase
reporter gene under the specific control of the AR transcription factor, as shown in the
schematic figure 4A (30). Growing these LNCaP/Luc cells in charcoal stripped serum for
7
2hours removes exogenous androgens and reduced the expression of AR-responsive genes
down to a baseline level, as monitored by qPCR. Adding a synthetic androgen (R1881) back
into the media (0-10nM) increased both PSA and Luciferase gene expression in a dose
dependent manner (Figure 4B). Androgen treatment does not affect G418 gene expression
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(coexpressed from the same integrated plasmid as the luciferase reporter) nor did it affect
the expression of housekeeping genes L19, -actin and GAPDH. The ability of the anti-
androgens to block this androgen-dependent gene upregulation was then further tested.
Treating hormonally starved LNCaP cells with R1881 showed a 9-fold upregulation of the
endogenous gene PSA. When treated with increasing doses of either bicalutamide or SK33 a
dose dependent inhibition of gene expression was seen. SK33 showed a greater PSA
inhibition than bicalutamide at 1 and 10M (Figure 4C). Conversely, the parental compound,
enobosarm, showed a mild stimulatory activity (Figure 4D).
We then examined the real-time activity of AR in live LNCaP/Luc cells in response to
increasing doses of SK33 compared to the parental compound enobosarm and the anti-
androgen bicalutamide. Live imaging and photon flux measurements of LNCaP/Luc cells
grown on 96 well plates in the presence of 0-100M compound for 24 hours resulted in a
strong inhibition of AR-mediated luciferase activity (Figure 4E). The AR inhibitory
concentration [50%] for both SK33 and bicalutamide were approx. 1M. Bicalutamide
showed no further inhibitory effects past this concentration. However, SK33 maintained a
dose dependent inhibition, completely inhibiting the AR-mediated luciferase activity at 50-
100M concentration (Figure 4F).
SK33 and SK51 are active in LNCaP cells with acquired bicalutamide resistance.
LNCaP cells were grown in increasing concentrations of bicalutamide for 3-6 months, until
proliferation was seen. This bicalutamide resistant cell line (LNCaP/BicR) then grew well in
20M bicalutamide, with cell cycle kinetics similar to that of the parental cell line. An
increased expression level of AR was seen in this cell line upon qPCR analysis (Figure 5A).
Treating this cell line with increasing doses of bicalutamide showed a proliferative response
–
5
5
at 20-25M, whereas the parental cell line showed sensitivity and an IC50 of 3M (Figure
B). The LNCaP/BicR cell line also showed a partial cross-resistance to enzalutamide (IC50
M approx.), Figure 5C. We then analysed if the mechanism of the acquired resistance to
=
bicalutamide extended to the novel agents SK33 and SK51. Treatment of LNCaP/BicR cells
with increasing concentrations of SK33 and SK51 for 96hours resulted in a dose-dependent
response and an inhibition of cell growth, rather than being proliferative agents as
bicalutamide (Figure 5D), with IC50 of approximately 2M for SK51 and 5M for SK33.
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Although not as active as in the parental sensitive cell line, SK51 did show an improved
activity over enzalutamide (& bicalutamide).
In vitro aqueous solubility and microsomal metabolic stability
Subsequently, an early in vitro pharmacokinetic study of the most promising compound,
SK33, was performed. The metabolic stability of SK33 was tested in human liver
microsomes, where compounds were incubated for 45 min with pooled liver microsomes
and the intrinsic clearance (CLint) and half-life (t1/2) values were calculated based on 5 time
points. Compound SK33 is characterised by an increased metabolic stability in comparison
with the standard – bicalutamide (see Table 1). SK33 has microsomal half-life (t1/2) of 32 hr,
which compares to that of standard drugs (bicalutamide and enzalutamide) and represents
a good starting point for optimisation towards a weekly or twice-weekly administrable
product. No observed in vitro cardiotoxicity was observed in our preliminary studies (7.6 %
inhibition of hERG at 25M concentration) (http://cyprotex.com). Because of these
promising in vitro properties and the potent anti-proliferative profile in prostate-cancer cell
lines, SK33 was selected for more detailed pre-clinical in vitro and in vivo studies.
SK33 is a potent inhibitor of AR in the ARE-Luc reporter mouse – and shows tissue
specificity
The transgenic ARE-Luc mouse model shows AR-driven luciferase activity in all tissues in
response to androgen action and activity can be monitored in live animals in real time (31).
Using age-matched male mice (littermates) we analysed the basal AR-driven luciferase
levels in mice prior to treatment. ARE-Luc mice were injected with D-luciferin and imaged
using an IVIS CCD camera in order to obtain baseline visualisation and measurements of
androgen receptor tissue activity. ARE-Luc mice were then injected sub-cutaneously with
5
0mg/kg bicalutamide, SK33 or vehicle (DMSO) control and left for 24 hours (n=3 for each
treatment), after which the mice were imaged again under the exact same conditions. Post
treatment mice were imaged again for luciferase activity (Figure 6A). Luciferase activity was
measured from three regions of interest (ROI), including the head, abdominal and gonadal
region (Figure 6B). Bicalutamide and SK33 treatment resulted in a decreased luciferase
activity in all areas. However, mice treated with SK33 showed a greater reduction of
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luciferase activity in these areas when compared to bicalutamide. DMSO vehicle did not
significantly affect luciferase activity in any region (Figure 6C).
Tissues were then removed from sacrificed animals, and RNA was extracted and analysed by
q-PCR for luciferase transcripts in each individual tissue. Bicalutamide and SK33 showed
strong reduction in luciferase transcripts compared to vehicle or untreated mouse tissues.
Although similar, SK33 reduced luciferase transcripts to a greater extent than bicalutamide
–
with significantly greater effects in the brain. Neither bicalutamide nor SK33 had
significant effects on AR activity in the spleen. However, SK33 did not reduce luciferase
activity in the leg muscle and showed a significant upregulation of luciferase transcripts in
this tissue (Figure 6D). Additionally, both bicalutamide and SK33 have reduced luciferase
enzymatic activity in the prostate, testes and brain. Both anti-androgens showed significant
inhibition compared to vehicle control. Although slightly more inhibition was seen in the
SK33 treated mice, the antiandrogens did not show statistically significant differences from
each other (Figure 6E).
ko
SK33 is a potent inhibitor of AR in the PTen mouse model for prostate intraepithelial
neoplasia (PIN).
PTen loss is one of the most frequent events in prostate cancer both at the initiation stage
and during late stage metastatic development - found in 30%+ of all human primary
prostate cancers, and 60%+ of higher grade metastatic lesions. Wang et al, established
loxp/loxp
Pten
;Pb-Cre4 mice, which have conditional Pten alleles deleted by a Probasin (Pb)
promoter-driven Cre recombinase, limiting Pten deletion to the prostatic epithelial layer
32). The mouse model of prostate-specific probasin-mediated Pten deletion leads to
(
prostate intraepithelial neoplasia (PIN) leading to adenocarcinoma thereafter. Although the
mouse prostate structure is different to human, there are several points of commonality –
specifically with the glandular epithelial AR-driven structure.
loxp/loxp
Pten
;Pb-Cre4 mice with an integrated androgen reporter were injected sub-
cutaneously with 50mg/kg bicalutamide, SK33 or vehicle (DMSO) control and left for
4hours (n=3 for each treatment). Prostate tissues were collected for qPCR and luciferase
2
assay analysis. Upon q-PCR for luciferase transcripts both anti-androgens showed significant
inhibition compared to vehicle control with more inhibition in the SK33 treated mice than
bicalutamide, but the anti-androgens did not show statistically significant difference from
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each other (Figure 6F).
+ve
ko
In AR mouse Pten cells growing in culture (PTEN-CaP8 -ATCC CRL-3033), SK33 showed a
stronger activity than enzalutamide or bicalutamide (Figure 6G).
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Discussion
Prostate cancer (PCa), like the prostate gland from which it is derived, is androgen
dependent – at least in the initial stages. The inhibition of the androgen receptor activity
either by anti-androgen therapy or by androgen ablation remains the mainstay of treatment
choices. Recently, there has been a movement away from classical anti-androgens due in
part to the development of resistance to these compounds and the advantages of more
novel agents e.g. the anti-testosterone synthesis agent abiraterone. Resistance has been
historically linked to the development of AR mutations especially in the ligand binding site.
For example, AR T887A, W741L and W741C have been found to arise in patients relapsing
under flutamide or bicalutamide therapy (7, 8).
However, even in apparent castrate resistant prostate cancer the AR may still be a key
molecule to cell growth, and as such remains a viable target for therapeutic intervention.
The current clinically used AR antagonists bind the receptor ligand binding site, but with far
less efficiency and affinity than natural agonists. The mechanism of the difference between
the structure of AR antagonists and partial AR agonists, such as enobosarm, has been
associated with the sulfonyl group on the antagonist being larger than the oxygen linker
group of the agonist, thus causing a better steric fit. The larger size of the antagonist then
pushes away helix 12, inhibiting the folding of the activated AR.
Here we describe the chemical modification of an AR partial agonist – enobosarm.
Enobosarm has been shown to have anabolic activity in the body e.g. on bone and muscle
mass, but to have minimal effects on the gonadal tissues i.e. an agent with selective AR
modulating effects (SARM). The introduction of the 3,5-Bis-trifluoromethyl groups was
theorized to give bulkier sides to the B ring thus inhibiting helix 12 folding. In essence
changing a high affinity agonist to a high affinity antagonist. Two bis-trifluoromethyl-
containing enobosarm analogs named SK33 and SK51 were the focus of this study.
Initial screening in prostate cancer cell lines indicated that the parental compound,
enobosarm, was inactive in all of them, whereas the SK33 and SK51, modified enobosarm
+ve
analogues showed higher activity (200 fold) in AR cell lines and modest or low activity in
-
ve
AR cell lines. SK33 showed the highest activity, being more active than the current
clinically used anti-androgen – bicalutamide. Treating LNCaP cells with SK33, resulted in the
inhibition of cell cycle progression, with cells arresting in G1. No apoptotic response or
cellular fragmentation was observed. AR inhibition has been associated with the inability of
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cells to enter the cell cycle, as the AR may act as a replication licensing protein in prostate
cells (33, 34).
The LNCaP cell line is an androgen sensitive cell line with a T877A mutation in the LBD of the
AR. Treating this cell line in culture for an extensive period with bicalutamide gave rise to a
resistant subclone (LNCaP/BicR) which proliferated in the presence of high doses of
bicalutamide, and showed an enhanced expression of AR. This switch to AR agonism is
indicative of clinical prostate cancer as it progresses, and this work has been previously
reviewed (35, 36). We did not detect other LBD mutations in this cell line. Although not as
active as in the parental cell line SK33 and especially SK51 showed moderate activity. At this
stage it is unclear if the concentration of SK33 (&SK51) required to inhibit the acquired
resistance phenotype may be achievable in vivo, but their increased metabolic stability,
resistance to oxidative metabolism and detoxification together with increased solubility may
translate to high levels of drug in circulation. Additionally and of clinical importance, SK51
showed increased activity over enzalutamide in the LNCaP/BicR cells.
It is rare that an inhibitor compound such as an anti-androgen can be tested in a biological
system where there is a highly specific real-time reporter for its target protein activity -
integrated into the host genome. Utilizing an LNCaP cell line with an integrated AR-driven
luciferase reporter (30) we analyzed the effect of these compounds directly on the
transactivation function of the AR. SK33 resulted in a stronger inhibition of AR-mediated
gene activation of both the endogenous gene PSA and the transgene luciferase, than that
mediated by bicalutamide. SK33 could also competitively inhibit the AR in the presence of a
strong synthetic androgen (R1881), whilst enobosarm itself had a mildly stimulating effect.
Further testing in vivo using unique AR-reporter mice, developed by the authors (31),
showed the anti-androgen activity of these compounds in the target tissue i.e. prostate, as
well as in peripheral tissues, in real time within the same animal. Here, side effects, and
bystander effects could be monitored. SK33 showed a stronger or equal anti-androgen
effect in most tissues, when compared to bicalutamide at the same dosage concentration.
But, interestingly we observed that the effects of SK33 upon leg muscle AR activity was
stimulatory, and the effects in the spleen were minimal.
The anabolic effects of enobosarm have been well documented, although its mechanism of
action in specifically stimulating skeletal muscle AR and not prostate or gonadal AR remains
elusive. Since SK33 is a modified analog of enobosarm the effects on skeletal muscle was
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interesting to observe, especially given its simultaneous high inhibitory activity in the
prostate and other tissues. The rational addition of bis-trifluoromethyl groups into ring B of
enobosarm seems to have successfully exaggerated the SARM activity of enobosarm. The
mechanism of SARM-like compounds remain relatively unknown but locally expressed AR
tissue-specific cofactors have been postulated to govern the activity of AR modulating
compounds such as SARMs. Although our results are limited to the mouse leg skeletal
muscle, the use of such a compound in prostate cancer patients may ease side effects such
as muscle wastage and fatigue, whilst maintaining prostate AR inhibition. The effects on
other muscle tissues e.g. the AR-responsive levator ani muscle, in the mouse was
unavailable.
It should also be noted that SK33 showed very potent inhibitory effects in the brain - this
may reflect the increased lipophilicity of the fluorinated compounds in traversing the blood-
brain barrier or in fact their increased anti-androgen potential. The CNS-specific effects
could not be determined in the mouse model, but no deleterious effects on motor function
or behavior was observed. The effects in humans could well correlate with CNS-related side
effects.
Finally, within a developing hyperplasia / adenocarcinoma in situ in mice with homozygous
PTEN deletion we observed that SK33 was equal to or better than bicalutamide in reducing
AR activity.
Conclusions
We demonstrate that structure-based design can efficiently engineer second-generation AR
antagonists that have clinical potential to circumvent anti-androgen resistance by complementing
receptor mutations at the molecular level. In principle, there is a limited number of mutations that
can cause an AR antagonist to function as an AR agonist, therefore, it is conceivable that such
approaches may ultimately lead to the development of anti-androgens that resist mutations that
cause anti-androgen withdrawal syndrome.
Utilising novel in vitro and in vivo screening techniques and models, ideally suited to analyze and
evaluate novel antiandrogens, we have identified a novel anti-androgen candidate SK33. This bis-
trifluoromethyl-containing enobosarm analog, displays better activity than bicalutamide in vitro with
increased efficacy against acquired anti-androgen resistance. Importantly, SK33 has comparable
activity in vivo, but maintains a degree of tissue selectivity associated with its SARM – enobosarm
parental molecule. The increased stability and potential differential side effect profile of these
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molecules may make them useful drugs for prostate cancer treatment.
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Materials and Methods
All chemicals were purchased from Sigma Aldrich (Gillingham, United Kingdom) or Alfa Aesar
(Heysham, United Kingdom) and were used without further purification. All reactions were
performed under a nitrogen atmosphere. H- NMR (500 MHz), C- NMR (125 MHz) and F-NMR (470
MHz) spectra were recorded on a Bruker Avance 500 MHz spectrometer at 25 C. Chemical shifts (δ)
are expressed in parts per million (ppm) and coupling constants (J) are given in hertz. The following
abbreviations are used in the assignment of NMR signals: s (singlet), bs (broad singlet), d (doublet), t
(triplet), q (quartet), m (multiplet), dd (doublet of doublet), dt (doublet of triplet), td (triple doublet),
m (multiplet). Mass spectrometry was run on a Bruker Micromass system in electrospray ionization
mode. Thin Layer Chromatography (TLC): precoated aluminium backed plates (60 F254, 0.2 mm
thickness, Merck) were visualized under both short and long wave UV light (254 and 366 nm). Flash
column chromatography was carried out using silica gel supplied by Fisher (60 A, 35-70 µm). Purity
of prepared compounds was determined by Analytical High-Performance Liquid Chromatography
(HPLC) analysis using either a ThermoScientific or a Varian Prostar system. All compounds tested in
biological assays were > 95% pure. HPLC using the eluents water (eluent A) and acetonitrile (eluent
B). Column; Varian Pursuit, 150 mm × 4.6 mm, 5.0 μm. Flow rate; 1.0 mL/min, gradient 30 min 10%
→
100% eluent B in eluent A.
General method for the preparation of intermediates (3a,b)
Methacryloyl chloride 2 (2.63 mL, 27.16 mmol) was added over the course of 10 minutes to a stirring solution
of the different aniline 1a, b (3.4 mmol) in N,N-dimethylacetamide (10 mL) at r.t. for 3 h. After the reaction
was complete, the mixture was diluted with ethyl acetate (100 mL), extracted with sat. aq. NaHCO
3
solution
(
3x25 mL) and with cold brine (4x50 mL). The organic layer was dried over Na SO and the solvent was
2
4
removed at reduced pressure. The crude residue was purified by flash column chromatography.
General method for the preparation of intermediates (4a,b)
To a stirred solution of the intermediates (3a,b) (3 mmol) in DCM (7 mL) was added 30% hydrogen peroxide
(3.6 mL, 32.03 mmol). The reaction mixture was put in a water bath at r.t. and trifluoroacetic anhydride (3.7
mL, 26.7 mmol) was added slowly to the mixture, which was then stirred for 24 h. The reaction mixture was
transferred to a separating funnel using DCM (30 mL). The organic layer was washed with distilled water (20
mL), sat. aq. Na
2 2 3 3 2 4
S O (4x20 mL), sat. aq. NaHCO (3x20 mL) and brine (20 mL), dried over Na SO and
concentrated at reduced pressure.
General method for the preparation of compounds SK33 and SK51
To a mixture of NaH (60% in mineral oil, 0.050 g, 1.23 mmol) in anhydrous THF (2 mL) at 0 °C under Ar
atmosphere was added a solution of the 3,5-bis-trifluoromethylphenol 5 (1.11 mmol) in 1 mL of anhydrous
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THF. This mixture was stirred at r.t. for 20 min. A solution of the different intermediates (4a,b) (0.74 mmol) in
anhydrous THF (3 mL) was added slowly. The reaction mixture was stirred at r.t. o.n. The mixture was then
2 4
diluted with ethyl acetate (30 mL), washed with brine (15 mL) and water (30 mL), dried over Na SO and
concentrated under vacuum. The crude residue was purified by flash column chromatography.
3
-(3,5-bis(trifluoromethyl)phenoxy)-N-(4-cyano-3-(trifluoromethyl)phenyl)-2-hydroxy-2-methylpropanamide
SK33)
Purified by flash column chromatography eluting with n-hexane/EtOAc 100:0 v/v increasing to n-hexane/EtOAc
(
9
0:10 v/v. Obtained in 85 % yield as a white solid.
1
H NMR (CDCl
3
-d
1
) δ 9.20 (bs, 1H, NH), 8.16 (d, J = 2 Hz, 1H, ArH), 8.00 (dd, J = 2, 8.5 Hz, 1H, ArH), 7.82 (d, J =
), 4.13 (d, J = 9 Hz, 1H, CH2), 3.49
8
.5 Hz, 1H, ArH), 7.53 (s, 1H, ArH), 7.36 (s, 2H, ArH), 4.59 (d, J= 9 Hz, 1H, CH
2
1
9
13
(
bs, 1H, OH), 1.67 (s, 3H, CH3); F NMR (CDCl
3
-d
1
) δ -62.24, -63.09; C NMR (CDCl
3
-d
1
) δ 172.03 (C=O), 158.28
2
2
1
(
ArC), 141.29 (ArC) , 135.92 (ArCH), 134.18 (q, JC-F = 32.6 Hz, ArC), 133.16 (q, JC-F = 33.3 Hz, ArC), 122.94 (q, JC-
1
3
3
F
= 264.5 Hz, CF
3
), 122.05 (q, JC-F = 272.6 Hz, CF
3
), 121.84 (ArCH), 117.33 (q, JC-F = 5.1 Hz, ArCH), 115.56 (q, JC-F
), 23.04
3
=
3.6 Hz, ArCH), 115.38 (ArC), 115.14 (q, JC-F = 3.8 Hz, ArCH), 104.92 (ArC), 75.83 (COH), 73.10 (CH
2
3
(CH ). MS [ESI, m/z]: 501.1 [M+H], 523.1 [M+Na]. HPLC: retention time = 25.18 min.
3
-(3,5-bis(trifluoromethyl)phenoxy)-2-hydroxy-2-methyl-N-(4-nitro-2-(trifluoromethyl)phenyl) propanamide
(
SK51)
Purified by flash column chromatography eluting with n-hexane/EtOAc 100:0 v/v increasing to n-hexane/EtOAc
9
0:10 v/v. Obtained in 78 % yield as a white solid.
1
H NMR (CDCl
3
-d
1
) δ 9.68 (bs, 1H, NH), 8.76 (d, J = 9 Hz, 1H, ArH), 8.59 (d, J = 3 Hz, 1H, ArH), 8.47 (dd, J = 2.5,
), 3.25
) δ 172.02 (C=O), 158.15
9
.5 Hz, 1H, ArH), 7.56 (s, 1H, ArH), 7.36 (s, 2H, ArH), 4.59 (d, J= 9 Hz, 1H, CH2), 4.15 (d, J = 9 Hz, 1H, CH
2
1
3
13
(bs, 1H, OH), 1.69 (s, 3H, CH
3
); F NMR (CDCl
3
-d
1
) δ -61.59, -63.06; C NMR (CDCl
3
-d
1
2
2
(
ArC), 143.17 (ArC), 140.38 (ArC), 133.16 (q, JC-F = 33.8 Hz, ArC), 133.03 (q, JC-F = 32.8 Hz, ArC), 128.38 (ArCH),
1
1
3
1
1
23.22 (q, JC-F = 268.3 Hz, CF
3
), 122.75 (q, JC-F = 271.3 Hz, CF
3
),122.62 (ArCH), 122.46 (q, JC-F = 6.3 Hz, ArCH),
3
15.67 (q, JC-F = 3.8 Hz, ArCH), 115.11 (ArCH), 75.86 (COH), 73.93 (CH
2
), 22.94 (CH
3
). MS [ESI, m/z]: 521.1
[
M+H], 543.1 [M+Na]. HPLC: retention time = 26.42 min.
Cell culture
All cell lines were purchased LGC Standards (Teddington, UK) and used within 6 passages, and
subjected to regular mycoplasma screening (Geneflow PCR test, Lichfield, UK). LNCaP cells were
o
maintained at 37 C, 5% CO
2
in RPMI medium with 10% foetal bovine serum (First Link Ltd, Brierley
Hill, U.K.). PC3, VCaP and Du145 and mouse Pten null cells were maintained in DMEM medium
Sigma) with 10% foetal bovine serum (First Link UK,). All media was supplemented with 2mM L-
(
glutamine, 100units/ml penicillin, 100mg/ml streptomycin (Sigma). For hormone depletion
experiments, 72 hours before androgen exposure, medium was replaced with ‘starvation medium’
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consisting of phenol red-free RPMI (or DMEM) medium, supplemented with 5% charcoal-stripped
foetal bovine serum (First Link UK). All cell lines were obtained from the ATCC cell bank.
MTT Assay
The MTT assay was used as a cell viability assay for the all the cell lines listed using the anti-
4
androgen compounds. Briefly, cells (5 × 10 cells/ml) were seeded into 96-well plates (200ul/well),
allowed to attach and grow for 24hr and subsequently treated with varying concentrations of
antiandrogens (0–100 μM) for 96 hours. Optimal seeding densities were premeasured for linear
growth over the 96hours. MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide,
o
5
mg/ml in PBS) was added to a final concentration of 0.5mg/ml for 4 h at 37 C. After four hours,
purple formazan crystals, formed by mitochondrial reduction of MTT, were solubilized in acidified
isopropanol (200μl/well) and the absorbance was read at 570 nm after 10 min incubation. Percent
inhibition of viability was calculated as a % of untreated control and the cytotoxicity / cell growth
inhibition was expressed as IC50
.
Luciferase Assays
Cells were washed and lysed in reporter lysis buffer (Promega). Lysate was mixed with D-luciferin
substrate (Promega) and light emission measured using the Promega Glomax multi luminometer.
For live cell imaging D-luciferin substrate was added directly into the cell media and plates were
imaged on a Syngene G:Box imager.
Tissue was pulverized by grinding in liquid nitrogen and then completely homogenised, using a
microfuge pestle, in reporter lysis buffer with protease inhibitors (Promega). Lysate (20µl) was mixed
with luciferin substrate (20µl) and light emission measured using the Promega Glomax multi
luminometer. Light emission was then normalised to protein content as measured by a Bradford
Assay.
RNA extraction and RT-PCR
Total RNA samples were prepared using Trizol reagent (Sigma) and converted to cDNA using the
GoScript™ Reverse Transcription System (Promega).
Q-PCR
Reactions were performed in triplicate on cDNA samples in 96-well optical plates on an ABI Prism
StepOne System (ThermoFisher, U.K.). Reactions consisted of 2 μl cDNA, 7 μl PCR-grade water, 10 μl
2
× TaqMan Universal PCR Master Mix (Applied Biosystems), 1 μl Taqman specific assay probes
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(Applied Biosystems) for PSA, TMPRSS2, KLK2, and L19. Parameters were: 50°C for 2 min, 95°C for 10
min, 40 cycles of 95°C for 15 sec and 60°C for 1 min. Data was recorded using Sequence Detector
Software (SDS version 2.3; PE Applied Biosystems). Levels were normalised to GAPDH, -actin and
RPL19.
Animal experiments
All mouse procedures were performed in accordance with the UK Animals (Scientific Procedures) Act
1
986 under Home Office license. ARE-Luc strains were made and available ‘in house’ (31), and
loxp/loxp
Pten
;Pb-Cre4 were obtained from The Jackson Laboratory.
Luciferase imaging
Anaesthetized mice (3% isofluorane with O carrier, Abbott Animal Health UK) were injected i.p. or
2
s.c. with D-luciferin (Caliper Life Sciences Ltd, Runcorn, UK) at 150 mg/kg, 10 min before imaging.
Light emission from luciferase was detected by the IVIS Imaging System 100 series (Xenogen
Corporation), and overlaid as a pseudocolour image with reference scale, upon a greyscale optical
image.
For ex vivo imaging, mice were sacrificed 10 min after luciferin injection, and immediately dissected.
Target organs were rinsed briefly in PBS and placed under the bioluminescent camera. Tissues were
then collected for luciferase assays, RNA extraction or fixed in 10% formaldehyde before wax
embedding and sectioned using standard procedures.
Cell cycle analysis (FACS)
Cells were grown on 10cm dishes for 24-96ꢀh ± treatments. Cells were then trypsinized, washed
twice in PBS, fixed in 70% ethanol at 4ꢀ°C, were stained with 5ꢀg/ml propidium iodide and RNA
removed using 50ꢀmg/ml RNase A. FACS analysis was carried out using a FACS Calibur (Beckton-
Dickinson, Oxford, UK), using linear scale representation of forward and side scatter during flow
analysis, as well as DNA content. Single cells were gated and the cell cycle profiles measured using
FCS Express4 software, using the built in kinetics & cell cycle analysis best-fit model for cell cycle
phase identification. A total of 10ꢀ000 events were measured per sample.
Acknowledgments
The authors would like to pay a tribute to Professor Christopher McGuigan (the Drug Hunter) for all
his contributions for the success of this project. Professor McGuigan was an exceptional and
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dedicated scientist who has remarkable achievements in the anticancer and antiviral drug discovery
field.
The authors would like to thank Cyprotex (U.K.) for performing the metabolic stability, PPB %
recovery, hERG inhibition assays as an outsourced service. We would also like to thank our funders -
The Welsh Government (A4B-Academic Expertise for Business grant), The Cardiff University – Peking
University Cancer Institute, Prostate Cancer UK, Cancer Research UK and the Harvey Spack memorial
Fellowship (GSA).
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References
1
.
Ferlay J, Autier P, Boniol M, Heanue M, Colombet M, Boyle P. Estimates of the cancer
incidence and mortality in Europe in 2006. Ann Oncol. 2007;18(3):581-92.
2
2
3
.
Brinkmann AO, Trapman J. Prostate cancer schemes for androgen escape. Nat Med.
000;6(6):628-9.
Brinkmann AO. Molecular mechanisms of androgen action--a historical perspective.
.
Methods Mol Biol. 2011;776:3-24.
Matsumoto T, Shiina H, Kawano H, Sato T, Kato S. Androgen receptor functions in
male and female physiology. J Steroid Biochem Mol Biol. 2008;109(3-5):236-41.
Patrão MT, Silva EJ, Avellar MC. Androgens and the male reproductive tract: an
overview of classical roles and current perspectives. Arq Bras Endocrinol Metabol.
4.
5.
2
6
2
7
009;53(8):934-45.
.
Manolagas SC, Kousteni S, Jilka RL. Sex steroids and bone. Recent Prog Horm Res.
002;57:385-409.
.
Hara T, Miyazaki J, Araki H, Yamaoka M, Kanzaki N, Kusaka M, et al. Novel mutations
of androgen receptor: a possible mechanism of bicalutamide withdrawal syndrome. Cancer
Res. 2003;63(1):149-53.
8
.
Suzuki H, Akakura K, Komiya A, Aida S, Akimoto S, Shimazaki J. Codon 877 mutation
in the androgen receptor gene in advanced prostate cancer: relation to antiandrogen
withdrawal syndrome. Prostate. 1996;29(3):153-8.
9
.
Brooke GN, Bevan CL. The role of androgen receptor mutations in prostate cancer
progression. Curr Genomics. 2009;10(1):18-25.
0. Paliouras M, Zaman N, Lumbroso R, Kapogeorgakis L, Beitel LK, Wang E, et al.
1
Dynamic rewiring of the androgen receptor protein interaction network correlates with
prostate cancer clinical outcomes. Integr Biol (Camb). 2011;3(10):1020-32.
1
1.
Future Med Chem. 2013;5(10):1109-20.
2. Jones A, Coss CC, Steiner MS, Dalton JT. An Overview on Selective Androgen
Receptor Modulators. Focus on Enobosarm.: Drugs of the Future; 2013. p. 309-16.
3. Dalton JT, Barnette KG, Bohl CE, Hancock ML, Rodriguez D, Dodson ST, et al. The
McEwan IJ. Androgen receptor modulators: a marriage of chemistry and biology.
1
1
selective androgen receptor modulator GTx-024 (enobosarm) improves lean body mass and
physical function in healthy elderly men and postmenopausal women: results of a double-
blind, placebo-controlled phase II trial. J Cachexia Sarcopenia Muscle. 2011;2(3):153-61.
1
4.
Dalton JT, Taylor RP, Mohler ML, Steiner MS. Selective androgen receptor
modulators for the prevention and treatment of muscle wasting associated with cancer.
Curr Opin Support Palliat Care. 2013;7(4):345-51.
1
5.
Kim J, Wu D, Hwang DJ, Miller DD, Dalton JT. The para substituent of S-3-(phenoxy)-
is major
2-hydroxy-2-methyl-N-(4-nitro-3-trifluoromethyl-phenyl)-propionamides
a
structural determinant of in vivo disposition and activity of selective androgen receptor
modulators. J Pharmacol Exp Ther. 2005;315(1):230-9.
1
6.
folding inhibition hypothesis. Bioorg Med Chem. 2005;13(17):5080-93.
7. Duke CB, Jones A, Bohl CE, Dalton JT, Miller DD. Unexpected binding orientation of
bulky-B-ring anti-androgens and implications for future drug targets. J Med Chem.
011;54(11):3973-6.
Hashimoto Y, Miyachi H. Nuclear receptor antagonists designed based on the helix-
1
2
21
Downloaded from mct.aacrjournals.org on June 19, 2018. © 2018 American Association for Cancer Research.

Author Manuscript Published OnlineFirst on June 12, 2018; DOI: 10.1158/1535-7163.MCT-18-0037
Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited.
1
8.
Weatherman RV, Fletterick RJ, Scanlan TS. Nuclear-receptor ligands and ligand-
binding domains. Annu Rev Biochem. 1999;68:559-81.
9. McGinley PL, Koh JT. Circumventing anti-androgen resistance by molecular design. J
Am Chem Soc. 2007;129(13):3822-3.
0. Ferla S, Bassetto M, Pertusati F, Kandil S, Westwell AD, Brancale A, et al. Rational
1
2
design and synthesis of novel anti-prostate cancer agents bearing a 3,5-bis-
trifluoromethylphenyl moiety. Bioorg Med Chem Lett. 2016;26(15):3636-40.
2
1.
Purser S, Moore PR, Swallow S, Gouverneur V. Fluorine in medicinal chemistry. Chem
Soc Rev. 2008;37(2):320-30.
2
2
2
2
2.
Hagmann WK. The many roles for fluorine in medicinal chemistry. J Med Chem.
008;51(15):4359-69.
3.
4.
Swallow S. Fluorine in medicinal chemistry. Prog Med Chem. 2015;54:65-133.
Xing L, Blakemore DC, Narayanan A, Unwalla R, Lovering F, Denny RA, et al. Fluorine
in drug design: a case study with fluoroanisoles. ChemMedChem. 2015;10(4):715-26.
5. Prchalová E, Štěpánek O, Smrček S, Kotora M. Medicinal applications of
perfluoroalkylated chain-containing compounds. Future Med Chem. 2014;6(10):1201-29.
6. Kandil S, Westwell AD, McGuigan C. 7-Substituted umbelliferone derivatives as
2
2
androgen receptor antagonists for the potential treatment of prostate and breast cancer.
Bioorg Med Chem Lett. 2016;26(8):2000-4.
2
7.
Kandil S, Wymant JM, Kariuki BM, Jones AT, McGuigan C, Westwell AD. Novel cis-
selective and non-epimerisable C3 hydroxy azapodophyllotoxins targeting microtubules in
cancer cells. Eur J Med Chem. 2016;110:311-25.
2
8.
model of human prostatic carcinoma. Cancer Res. 1983;43(4):1809-18.
9. Korenchuk S, Lehr JE, MClean L, Lee YG, Whitney S, Vessella R, et al. VCaP, a cell-
based model system of human prostate cancer. In Vivo. 2001;15(2):163-8.
0. Dart DA, Spencer-Dene B, Gamble SC, Waxman J, Bevan CL. Manipulating prohibitin
Horoszewicz JS, Leong SS, Kawinski E, Karr JP, Rosenthal H, Chu TM, et al. LNCaP
2
3
levels provides evidence for an in vivo role in androgen regulation of prostate tumours.
Endocr Relat Cancer. 2009;16(4):1157-69.
3
1.
male and female mice. PLoS One. 2013;8(8):e71694.
2. Wang S, Gao J, Lei Q, Rozengurt N, Pritchard C, Jiao J, et al. Prostate-specific deletion
of the murine Pten tumor suppressor gene leads to metastatic prostate cancer. Cancer Cell.
Dart DA, Waxman J, Aboagye EO, Bevan CL. Visualising androgen receptor activity in
3
2
3
003;4(3):209-21.
3. D'Antonio JM, Vander Griend DJ, Isaacs JT. DNA licensing as a novel androgen
receptor mediated therapeutic target for prostate cancer. Endocr Relat Cancer.
2
3
009;16(2):325-32.
4. Koushyar S, Economides G, Zaat S, Jiang W, Bevan CL, Dart DA. The prohibitin-
repressive interaction with E2F1 is rapidly inhibited by androgen signalling in prostate
cancer cells. Oncogenesis. 2017;6(5):e333.
3
5.
therapies: incidence and clinical significance. Drug Saf. 2000;23(5):381-90.
6. Visakorpi T, Hyytinen E, Koivisto P, Tanner M, Keinänen R, Palmberg C, et al. In vivo
Paul R, Breul J. Antiandrogen withdrawal syndrome associated with prostate cancer
3
amplification of the androgen receptor gene and progression of human prostate cancer. Nat
Genet. 1995;9(4):401-6.
22
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Tables:
Metabolic stability
t1/2 mins)
Plasma protein
binding assay (PPB)
%
%hERG inhibition at
25μM
(
Bicalutamide
SK33
214
n.d.
96 *
7.64
1930
94.7
Table 1. t1/2 calculated in human liver microsomes; SK33 is metabolically stable with no loss
of parent compound detected for the duration of the assay. Plasma protein binding (PPB)
assay; results are expressed in terms of mean % bound from duplicate experiments.
Cardiotoxicity expressed in terms of % hERG inhibition at 25 μM compound concentration.
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Figure legends
Figure 1.
A, Chemical structure of the clinically used non-steroidal antiandrogens; flutamide,
hydroxylflutamide, nilutamide, bicalutamide and enzalutamide showing rings A and B. B,
Chemical structure of enobosarm (left), SK33 and SK51 (right). C, Chemical synthesis of SK33
and SK51 compounds, reagents and conditions: i) DMA, rt, 24h, ii) H2O2, DCM, rt, 2h, iii)
NaH, THF, rt, 24 h.
Figure 2.
(
A, B) X-ray structure of enobosarm (red-carbons) co-crystallised with (AR wt) in the agonist
conformation showing the orientation the distal ring B extending away from Helix 12 (H12)
towards Trp741. (C, D) Overlaid predicted binding modes of SK33-R (pink carbons), SK33-S
(turquoise carbons) and enobosarm (grey carbons) inside the AR-LBD showing the
orientation of ring B with the bis-CF3 groups inducing geometric bulk keeping Helix 12 in the
antagonist conformation (open) even upon the development of adaptive (resistant) bulk
reducing mutations.
Figure 3. Enobosarm analogues SK33 and SK51 show potent and selective activity in AR
positive prostate cancer cells.
MTT cytotoxicity assays of LNCaP cells treated with increasing doses of enobosarm or SK33
(
A) or Bicalutamide, SK33 and SK51 (B) at 0-100M. MTT cytotoxicity assays of PC3 cells
treated with increasing doses of enobosarm or SK33 (C) or Bicalutamide, SK33 and SK51 (D)
at 0-100M for 96hr. E, Q-PCR analysis of a panel of prostate cancer cells for AR expression.
Data represents the mean of three independent experiments. Data was normalised to
GAPDH, -actin and RPL19 housekeeping genes. F, Bar chart representing a summary of the
IC50 values for the 4 cell lines listed according to their AR status. G, FACS analysis of LNCaP
cells treated with 10M bicalutamide, enzalutamide, SK33, SK51 or vehicle control for
4
8hours, and analysed for S phase (left hand side). Histograms showing DNA content (PI
fluorescence) of treated LNCaP cells (right hand side). H, FACS analysis of PC3 cells treated
with 10M bicalutamide, enzalutamide, SK33, SK51 or vehicle control for 48hours, and
24
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analysed for S phase (left hand side). Histograms showing DNA content (PI fluorescence) of
treated PC3 cells (right hand side). 10,000 gated cells were measured for each experiment.
Figure 4. SK33 and SK51 inhibit AR-mediated transcriptional activity in prostate cancer
cells.
A, Schematic diagram of the activation of the synthetic androgen reporter construct
integrated into the LNCaP/ARE-Luc cell line. Ligand bound AR activates the expression of the
luciferase reporter gene which in the presence of luciferin substrate gives off
bioluminescence directly proportional to AR activity. B, Q-PCR analysis of the endogenous
androgen induced gene PSA and the transgenes luciferase and G418 (Neomycin resistance
gene - aminoglycoside 3‘-phosphotransferase) in LNCaP/ARE-Luc cells. Cells were grown for
7
2hours in charcoal stripped FCS and then treated with 0-10 nM R1881. Data represents the
mean of three independent experiments. Data was normalised to GAPDH, -actin and
RPL19 housekeeping genes. C, Q-PCR analysis of PSA gene expression in LNCaP cells grown
in charcoal stripped medium for 72hours and then treated with R1881 in the presence of
increasing concentrations of bicalutamide or SK33 (0-10 M) or enobosarm (D). Data
represents the mean of three independent experiments. Data was normalised to GAPDH, -
actin and RPL19 housekeeping genes. E, Grey scale image of bioluminescence from live
LNCaP/Luc cells treated with enobosarm, SK33 and bicalutamide (0-100 M) for 24 hours. F,
Line graph indicating bioluminescence activity measurements from LNCaP/Luc cells treated
with increasing concentrations of bicalutamide, enobosarm and SK33 for 24 hours. ** =
p>0.01.
Figure 5. SK33 is active in LNCaP cells with acquired bicalutamide resistance.
A, Bar graph indicating the relative expression levels of AR in LNCaP and LNCaP/BicR cells.
Data represents the mean of three independent experiments. Data was normalised to
GAPDH, -actin and RPL19 housekeeping genes. B&C, MTT cytotoxicity assays of LNCaP or
LNCaP/BicR cells treated with increasing concentrations of bicalutamide (B) or enzalutamide
25
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Author Manuscript Published OnlineFirst on June 12, 2018; DOI: 10.1158/1535-7163.MCT-18-0037
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(
C) for 96 hours. D, MTT cytotoxicity assays of LNCaP/Bic20 cells treated with increasing
concentrations of bicalutamide, SK33 and SK51 for 96 hours.
Figure 6. SK33 inhibits AR transcriptional activity in vivo and in prostate intraepithelial
neoplasia (PIN).
A, Bioluminescent imaging of live ARE-Luc mice pre and post treatment with bicalutamide or
SK33 (or DMSO vehicle) for 24 hours. Image represents a grey scale image overlaid with
pseudo-colour bioluminescent activity data (scale represents flux rate of photons/sec/cm2).
B, grey scale image of an ARE-Luc mouse, white circles represent the three regions of
interest measurements for each mouse. C, Bar graph representing relative bioluminescent
data emanating from the three regions of interest - head, abdomen and gonadal regions.
Data is normalised to mouse bioluminescence pre-treatment with bicalutamide, SK33 (50
mg/kg) or DMSO vehicle. D, Q-PCR analysis of luciferase expression from various body
tissues as indicated. Data is presented as luciferase / housekeeping genes (GAPDH, RPL19
and -actin). E, Bar graph indicating relative luciferase enzymatic activity from various
tissues from ARE-Luc mice treated with either bicalutamide, SK33 or DMSO. F, Q-PCR
ko
analysis of luciferase expression from the mouse PTen prostate tissues. Data is presented
as luciferase / housekeeping genes (GAPDH, RPL19 and -actin). G, MTT assay of PTen null
mouse prostate cells treated with increasing doses of bicalutamide, enzalutamide and SK33
for 96hours. *= p value 0.05, ** = p value 0.01.
26
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Figure 1.
A.
A
A
A
A
A
B
B
B.
CF 3
CN
O
B
A
F 3C
O
O
N
H
CF 3
NC
CN
HO
O
B
A
R ational Des ign
SK33
O
N
H
CF 3
CF 3
HO
NO 2
O
B
A
Enobosarm
F 3C
N
H
HO
SK51
CF3
C.
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Figure 2.
A.
B.
Helix 12
C.
D.
Helix 12
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Author Manuscript Published OnlineFirst on June 12, 2018; DOI: 10.1158/1535-7163.MCT-18-0037
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Figure 3.
A.
LNCaP
LNCaP
B.
Enobosarm
SK33
Bicalutamide
SK33
SK51
1
00
100
50
0
5
0
0
IC50
Eno = 40uM
SK33 = 0.2uM
IC50
Bic = 3.0uM
SK33 = 0.2uM
SK51 = 0.7uM
-
1
0
1
2
-1
0
1
2
Log10 concentration (µM )
Log10 concentration (µM )
PC3
D.
C.
PC3
Bicalutamide
SK51
SK33
Enobosarm
SK33
1
00
1
00
5
0
0
5
0
0
IC50
Eno = 87uM
SK33 = 3.2uM
IC50
Bic = 30uM
SK33 = 3.2uM
SK51 = 5.0uM
-
1
0
1
2
-
1
0
1
2
Log10 concentration (µM )
Log10 concentration (µM )
E.
F.
IC50
1
1
0
0
.5
.0
.5
.0
LNCaP
VCaP
Du145
PC3
0
.1
1
10
100
1000 µM
Eno
Bic
SK51
SK33
C ell L in e
G.
Untreated
SK33
2
2
1
1
5
0
5
0
5
0
t
O
c
z
3
1
n
i
3
5
S
n
U
B
E
K
K
M
S
S
D
Fluorescence (PI)
C o m p o u n d
H.
2
5
Untreated
SK33
2
1
1
0
5
0
5
0
t
O
c
z
3
1
n
i
3
5
S
n
U
B
E
K
K
M
S
S
D
Fluorescence (PI)
C o m p o u n d
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Figure 4.
A.
B.
C.
D.
*
*
0
- 10nM R1881
1
1
5
0
5
0
1
0
5
2
1
1
0
.0
.5
.0
.5
0
0 .0
D M SO
100uM
A
e
8
1
d
h
1
0.5
1
0
1
0.5
1
0
s
e
t
8
1
S
a
4
t
E
8
Enobosarm
P
r
a
1
+
e
G
r
e
R
f
i
t
c
n
+
Bic
SK33
u
U
L
T r e a tm e n t
Gene of interest
E.
F.
0
- 100µM
Enobosarm
SK33
Bicalutamide
Enobosarm
SK33
1
00
5
0
0
Bicalutamide
-
1
0
1
2
L o g1 0 co n cen tratio n (µM )
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