Transcript The Androgen Receptor: Mechanisms of Resistance Ignacio Duran, MD UGC Oncología Integral Hospital Univ.

The Androgen Receptor:
Mechanisms of Resistance
Ignacio Duran, MD
UGC Oncología Integral
Hospital Univ. Virgen del Rocío
Sevilla
Outline
• Introduction
• The Androgen Receptor
• Mechanisms of Resistance
• Strategies to overcome resistance
• Conclusions
Basic Principles: Transcription Factor
DNA
A transcription factor:
It is a protein that binds to specific DNA sequences, thereby regulating the
transcription of genetic information from DNA to mRNA.
Transcriptions factors perform this function alone or creating a complex with
other proteins by promoting the recruitment of RNApol (enzyme that activate
the transcription of genetic information from DNA to RNA
Genes/RNA/Splicing
DNA
mRNA
mRNA
Molecular Biology
The Androgen Receptor (AR)
≈180 kb
DNA
Xq11-12
Exon 2
Exon 1
Dominio
N-Terminal
(NTD)
Exon 1
Exon 3
Exon 4
Dominio
de unión a
DNA (DBD)
Exon 2 Exon 3
Exon 5
Exon 6
Exon 7
Exon 8
Dominio
de unión a
ligando (LBD)
Región
Bisagra
Transcripcion y
“splicing” o unión del exoma
Exon 4 Exon 5 Exon 6 Exon 7 Exon 8
mRNA
codificante
3876 TGA
1116 ATG
Traducción
Proteína
Aminoácidos
1
559
672
919
Schaufele F, et al. The structural basis of androgen receptor activation: intramolecular and intermolecular amino-carboxy interactions. Proc Natl Acad Sci USA
2005; 102: 9802–9807.
Sack JS, et al. Crystallographic structures of the ligand-binding domains of the androgen receptor and its
Slide Courtesy of Dr. G. Billalabeitia
T877A mutant complexed with the natural agonist dihydrotestosterone. Proc Natl Acad Sci USA 2001; 98: 4904–4909.
How the AR works
CARM1
•
Chromatin is packed in the nucleosome and needs to
be untangle and expose in order to expose the target
genes
•
AR Target genes have some kind of “locators”
denominated Androgen Response Elements (AREs)
•
To accomplish this complicated process the AR needs
the collaboration of other proteins (Co-Activators)
TRAP220
LSD1
DHT
SRC
DHT
FoxA1
NCoR/
SMRT
CBP/
p300
pCAF
How the AR works
• The transcription induced by the AR is a complex process with multiple
players & actions:
– Some gene’s expression is induced
• Proteins in Sem. Liq (PSA)
• Proteins involved in metab
– Some gene’s expression is repressed
• Testosterone synthesis enzymes ((AKR1C3, HSD17B6)
• Androgen Receptor Genes (Self repression; negative feedback)
• Cell Cycle Progression (In physiological conditions induce differentiation)
– The AR transcription profile can vary depending on prostate cell status
(normal Vs tumoral) and undifferentiation
– TMPRSS2 is one of the target genes of the AR so in the eventual
presence of a TMPRSS2-ERG fusion gene, AR would also control ERG
•Tomlins SA, et al. Recurrent fusion of TMPRSS2 and ETS transcription factor genes in prostate cancer. Science 2005; 310: 644–648.
•Wang Q, et al. Androgen receptor regulates a distinct transcription program in androgen-independent prostate cancer. Cell 2009; 138:
245–256.
AR & CRPC
• “Owing to this new understanding,
several drugs have recently emerged for
the treatment of CRPC
• Some of these agents either suppress the
synthesis of extragonadal androgens
(adrenal and/or intratumor) or target
the androgen receptor directly
Normal prostatic tissue
CRPC tissue
8
Pmol/g
• “It is now accepted that CRPC continues
to rely on androgen signaling…”
4
Testosterone Levels in prostate tissue
Overexpression of the AR by IHC
Antonarakis ES et al. N Engl J Med 2014 371;11
The good side
The requirement for intratumoral androgen synthesis
in driving CRPC progression is most clearly
demonstrated by the survival benefit conferred by
ABIRATERONE ACETATE, (17α -hydroxylase/17,20lyase inhibitor), and ENZALUTAMIDE, (AR antagonist )
in both the pre-chemo and post-chemo setting in
patients with CRPC
De Bono J et al. NEJM 2011Scher H et al. NEJM 2012 Ryan C et al. NEJM 2013 Beer T. NEJM 2014
The bad side
• Despite the dramatic improvement in CRPC
therapeutics, the benefit is still “insufficient”
and eventually all patients develop resistance
to the currently available treatments
• Hence, there is a need to better understand
the biology of the disease and identify these
mechanisms of resistance and develop
appropriate drugs to overcome those
Molecular Mechanisms
• Two major mechanisms of resistance:
– 1.- Intratumoral synthesis of androgens?
– 2.- AR aberrant signalling
• AR amplification/ Splice variants/ AR mutants
• AR post transcriptional modifications
• AR activation NO ligand dependent
The characterisation of potential driving genomic alterations
in CRPC may provide the opportunity for a better
understanding of mechanisms of resistance to targeted
therapies and stimulate a molecularly driven clinical research
Mechanism 1: Intratumoral
synthesis of DHT
Mechanism 1: Intratumoral
synthesis of DHT
Intratumoral synthesis of DHT from precursors that are secreted
from the adrenal gland occurs through a pathway that
circumvents T
Chang et al., 2011; Knudsen and Penning, 2010
This DHT synthesis requires three enzymes:
1.3β -hydroxysteroid dehydrogenase (3β HSD)
2.Steroid-5α -reductase (SRD5A)
3.17β -hydroxysteroid dehydrogenase (17βHSD)
HSD3281 (3BHSD1)
HSD3B1 encodes for the peripherally
expressed isoenzyme (3βHSD1) and
has a germline single nucleotide
polymorphism (SNP) at position 1245
of HSD3B1, converting A → C, which
exchanges an asparagine (N) for a
threonine (T) at 3βHSD1 amino acid
position 367.
Chang KH, Li R, Kuri B et al. A gain-of-function mutation in DHT synthesis in
castration-resistant prostate cancer. Cell 2013; 154: 1074–1084.
HSD3281-367T
• CRPC sometimes expresses the 367T form of 3β
HSD1 (3β HSD1(367T)), which increases
metabolic flux from dehydroepiandrosterone
(DHEA) via the 5α -androstanedione (5α -dione)
pathway to DHT
• This happens by protein resistance to
ubiquitination and degradation rather than
increased catalytic activity.
Chang KH, Li R, Kuri B et al. A gain-of-function mutation in DHT synthesis in
castration-resistant prostate cancer. Cell 2013; 154: 1074–1084.
Mechanisms 2. AR aberrant
signalling
• The role of AR gene amplification
• Somatic mutations of AR as mechanisms of resistance
• AR gene rearrangement (Splice Variants)
• AR signalling ligand-independent
Dillard PR,. Androgen-independent prostate cancer cells acquire the complete steroidogenic potential of synthesizing testosterone from cholesterol.Mol Cell
Endocrinol 2008; 295: 115–120
Edwards J, et al. Androgen receptor gene amplification and protein expression in hormone refractory prostate cancer. Br J Cancer 2003; 89:552–556..
Taplin ME, et al. Androgen receptor mutations in androgen-independent prostate cancer: cancer and Leukemia Group B Study 9663. J Clin Oncol 2003; 21:
2673–2678.
Steinkamp MP, et al. Treatment-dependent androgenreceptor mutations in prostate cancer exploit multiple mechanisms to evade therapy. Cancer Res
2009; 69: 4434–4442.
1.-AR gene amplification
West Coast Prostate Cancer Dream Team
Androgen receptor (AR) amplification in patients with metastatic castration-resistant
prostate cancer (mCRPC) refractory to therapy with abiraterone acetate or enzalutamide:
Preliminary results from the SU2C/PCF/AACR West Coast Prostate Cancer Dream Team
(WCDT). J Clin Oncol 32:5s, 2014 (suppl; abstr 5020) Author(s): Eric Jay Small et al.
Background: ...As part of the WCDT project which aims to identify genetic pathways
underlying primary and acquired resistance to Abi and Enz, AR+ was assessed in
mCRPC biopsies.
Methods: Following central radiologic review, eligible mCRPC pts underwent biopsy at one
of 5 WCDT clinical sites, using a uniform biopsy protocol. Tissue was both frozen, and
formalin fixed/paraffin embedded (FFPE). FFPE tissue underwent a CLIA-certified assessment
of a mutational panel, IHC for PTEN, and fluorescence in situ hybridization (FISH) for AR+.
Results: 60 of 300 planned mCRPC pts have undergone a metastasis biopsy. To date, 33 pts have had
biopsies successfully evaluated by AR FISH, including 12 from bone, 11 from lymph nodes, 8 from
liver and 2 from other soft tissues. Of 16 Abi and Enz naive pts, 13 (81%) were AR+. By contrast,
only 1/11 Abi resistant pts (9%) was AR+. 4/6 Enz resistant pts (67%) were AR+. Of 6 AR+ patients
that went on to receive Abi or Enz, 3 (50%) had a response (PCWG2 criteria), whereas of 5 pts
without AR+ who went on to receive Abi/Enz, just 1 (20%) had a response.
Conclusions: AR amplification can be evaluated by FISH in small
biopsies of mCRPC, including bone, and it was observed in 18/33
samples (55%). AR+ was common in mCRPC patients prior to
therapy with Abi or Enz (81%). However, once resistance
developed, Abi resistant pts had a far lower likelihood of AR+ (9%)
than Enz resistant pts (67%).
These data support the hypothesis that treatment with
Abiraterone selects for non-AR amplified cells, whereas
Enzalutamide does not. In this relatively small cohort, mCRPC pts
with AR+ are more likely to respond to subsequent AR targeted
therapeutics than pts without AR+.
2.-AR Mutant
A novel AR mutant (AR F876L) was
recently identified in enzalutamidesensitive cell lines, as well as
xenograft models with prolonged
exposure to enzalutamide.
Acquisition of AR F876L mutation
converts enzalutamide and ARN-509
into AR agonist, and induces
treatment resistance in vitro as well
as in vivo.
Balbas MDet al. Overcoming mutation-based resistance to antiandrogens with rational drug design. Elife 2013; 2: e00499.
Joseph JD,et al. A clinically relevant androgen receptor mutation confers resistance to second-generation antiandrogens enzalutamide and
ARN-509. Cancer Discov 2013; 3: 1020–1029.
Korpal M, et al. An F876L mutation in androgen receptor confers genetic and phenotypic resistance to MDV3100 \Cancer Discov 2013; 3:
1030–1043.
AR F876L
• AR F876L allows the repositioning
of the helix in AR (helix 12) to an
agonist-like conformation that
permits coactivation recruitment
when tumor cells are treated with
enzalutamide.
• Interestingly,
bicalutamide
remained an antagonist in these
AR-mutant cells.
3.- Splice Variants
• One emerging mechanism is AR gene rearrangement, resulting in constitutively active
truncated AR splice variants (AR-Vs W with lack of LBD
• The expression of some exons is lost and some others that were cryptic in between
the introns become expressed
• The most frequent splicing variants are AR-V7, V9, V5, V1 and V3
Exon 1
Exon 2
E2b
Exon 3
Exon 1
Exon 2 Exon 3
AR-V7
Exon 1
Exon 2 Exon 3
AR-V9
Exon 1
Exon 2 Exon 3
AR-V5
Exon 1
Exon 2 Exon 3
AR-V1
Exon 1
Exon 2 Exon 3
AR-V3
Exon 1
Exon 2
E2b
E3c
E3d E3e
Exon 4
Exon 5
Exon 6 Exon 7
Exon 8
Exon 4 Exon 5 Exon 6 Exon 7 Exon 8
E3e
E3d
E3c
E3b
RAEx1/2/2b
RA4
RA3
AR ΔHR- DBD
AR
E3b
AR Δ Ex3-HR- DBD
CRYPTIC EXONS
•
Simon Haile and Marianne D. Sadar. Androgen receptor and its splice variants in prostate cancer. Cell Mol Life Sci, 2011 ;68(24):
3971–3981.
Slide Courtesy of Dr. G. Billalabeitia
Splice Variants
• AR-Vs determined in CTCs have been recently associated with
resistance to both enzalutamide and abiraterone acetate
N Engl J Med 371;11 September 11, 2014
4. Ligand Independent AR signaling
• Through different mechanisms
ligand independent aberrant AR
signalling might occur
• These include some of the posttranslational modifications of the
AR [i.e. Phosphorilation of AR
through HER expression]
as well as the loss of expression of
some key tumour suppressor
genes such as pTEN [loss of pTEN is
a common event in CRPC]
•
•
•
Gioeli D and Paschal BM. Post-translational modification of the androgen receptor. Molecular and Cellular Endocrinology 2012; 352: 70–78.
van der Steen T, Tindall DJ and Huang H. Posttranslational Modification of the Androgen Receptor in Prostate Cancer. Int. J. Mol. Sci. 2013, 14,
14833-14859
Carver B., et al. Reciprocal Feedback Regulation of PI3K and Androgen Receptor Signaling in PTEN-Deficient Prostate Cancer. Cancer Cell 2011, 19,
575–586
Another mechanisms of resistance
“Although targeting the androgen axis has a clear terapeutic benefit, its effectiveness is temporary as prostate tumor
cells adapt to survive and grow. Androgen deprivation might activate EMT and neuroendocrine transdifferentiation
Nouri M et al. Androgen-targeted therapy-induced epithelial mesenchymal plasticity and neuroendocrine transdifferentiation in prostate cancer.
Front Oncol. 2014 Dec 23;4:370.
Some Strategies Ongoing
•
New compounds are being developed/tested targetting some of these
mechanisms responsible of resistance:
– DR103 is a compound that might restore the position of helix 12 into the
antagonist form in both wild-type and F876L-mutant AR.
– EPI-001 covalently binds to the NTD, inhibits protein–protein interactions
necessary for transcriptional activity of the AR and its splice variants.
– BGB324 is a small molecule inhibitor of the AXL receptor
– Trametinib (MEK Inh) is being tested in the neoadjuvant setting
– GI-6301 is a Brachyury vaccine in Phase I
– ARN-509 is an oral novel AR antagonist that binds to AR, and blocks nuclear
translocation and binding of AR to ARE, and recruitment of co-activators.
– Galeterone, a triple mechanism of action functioning as CYP17 lyase
inhibitor, as well as an antiandrogen and as an AR-degrading agent.
Summary
• The AR is a tightly regulated key transcription factor in
both the hormone-sensitive and castration-resistant
stages of advanced prostate cancer
• The receptor and its major ligands are critical targets
and some drugs have been successfully developed in
this setting
• Mechanisms of resistance to the current treatments
have been identified and strategies to overcome them
represent an intense area of research
• Gracias por su atención !!
But things may not be so easy….
and still there is a lot to do.
Another mechanisms of resistance
“Although targeting the androgen axis has a clear terapeutic benefit, its effectiveness is temporary as prostate tumor
cells adapt to survive and grow. Androgen deprivation might activate EMT and neuroendocrine transdifferentiation
Nouri M et al. Androgen-targeted therapy-induced epithelial mesenchymal plasticity and neuroendocrine transdifferentiation in prostate cancer.
Front Oncol. 2014 Dec 23;4:370.
• ….Tenemos tiempo aun?
• BACK-UP
Search of new compounds
New Androgen Biosynthesis
Inhibitors
ORTERONEL: TAK
• Orteronel (TAK-700; Millennium
Pharmaceuticals,
The
Takeda
Oncology Company, Cambridge, MA)
is an oral, relatively selective,
nonsteroidal CYP17 17,20-lyase
inhibitor
• The selectivity of orteronel to inhibit
17,20-lyase compared with 17hydroxylase could afford it a safer
toxicity profile than agents that
inhibit both steps in the testosterone
synthesis pathway
Ferraldeschi, R Cancer J 2013;19: Yamaoka M, et al . J Steroid Biochem Mol Biol. 2012;129:.
TAK Development: The End
• Based on positive preclinical data and solid
background
• Phase I and II studies were progressively
conducted achieving good results
• However when taken to Phase III (pre & post
chemo)...
VT-464 (VIAMET)
• VT-464 (Viamet), is a novel oral CYP17
inhibitor with a higher selectivity for 17, 20lyase over 17-hydroxylase.
• In animal models, VT-464 induces androgen
suppression without a concomitant increase
of upstream steroids or cortisol suppression,
thus providing the opportunity to be
potentially used without concomitant steroids
Eisner JR, Abbott DH, Bird IM et al. VT-464: a novel, selective inhibitor of P450c17 (CYP17)-17,
20 lyase for castration-refractory prostate cancer (CRPC).J Clin Oncol 2012; 30: abstr 198.
NEW ANTIANDROGENS
ARN-509
ARN-509.
Like enzalutamide, ARN-509 is an oral novel AR
antagonist that binds to AR, and blocks nuclear
translocation of AR, binding of AR to androgen
response elements, and recruitment of coactivators by the AR.
ARN-509
In a murine xenograft model of mCRPC, ARN509 showed greater antitumor activity than
enzalutamide, for a given dose and plasma
concentration.
Furthermore, ARN-509 achieved significantly
lower steady-state brain levels than those
observed with enzalutamide, suggesting its
lower seizurogenic potential
Clegg NJ, Wongvipat J, Joseph JD et al. ARN-509: a novel antiandrogen for
prostate cancer treatment. Cancer Res 2012; 72: 1494–1503.
ARN-509
A phase I trial accrued 30 men with mCRPC and reported
promising activity of ARN-509
At 12 weeks, 42% ≥50% PSA declines & FDHT-PET imaging
demonstrated AR blockade at 4 weeks
ARN-509 was safe and exhibited linear pharmacokinetics.
A phase II showed at 12 weeks, PSA response of 91% in
therapy naïve and 60% in post-AA mCRPC patients and
89.5% in non metastatic CRPC patients
A Phase III trial in M0 is ongoing and results are pending
Rathkopf DE, Antonarakis ES, Shore ND et al. ARN-509 in men with metastatic castration-resistant prostate cancer. In ESMOSeptember
2012. Abstract 964 TIP. Smith MR, Antonarakis ES, Ryan CJ et al. ARN-509 in men with high-risk nonmetastatic castration reistant prostate
cancer. In ESMO, September 2012. Abstract 920P
ODM-201
ODM-201
•This is a novel pure oral AR antagonist that
does not penetrate the blood–brain barrier in
preclinical models.
•In a phase I/II study, treatment with ODM-201
was well tolerated and was associated with a
high activity in mCRPC, including those with
prior treatment with docetaxel and a CYP17
inhibitor
Fizazi K, Bono P, Jones RH et al. An open-label, phase I/II safety, pharmacokinetic,and proof-of concept study of ODM-201 in patients
with progressive metastatic castration-resistant prostate cancer (CRPC). In European Cancer Congress 2013,
AZD 3514
• AZD3514.
• This is an oral drug which inhibits AR signaling
through two distinct mechanisms, an inhibition
of ligand-driven nuclear translocation of AR, and
downregulation of androgen receptor levels.
• Preclinically, AZD3514 has been shown to have
antitumor activity in both androgen-sensitive and
castration resistant prostate tumors
AZD 3514
In a first-in-man phase I trial, 49 CRPC pts were treated with
escalating dose levels of AZD3514
Encouraging responses were seen, even in those with prior
disease progression on AA, including: PSA decline of ≥30% in
11 of 49 (23%), PSA decline of ≥50% in 7 of 49 (14%),and
objective soft tissue responses in 2 of 26 (8%) men with
measurable disease.
The most common toxicities were nausea and vomiting, and
were manageable with oral antiemetics.
None met the definition of dose limiting toxicity.
Loddick SA, Ross SJ, Thomason AG et al. Mol Cancer Ther 2013; 12: 1715–1727.
Omlin A, Jones RJ, van der Noll R et al. J Clin Oncol 2013; 31(suppl): abstr 4511
Galeterone: TOK-001
• Galeterone (VN/124-1, TOK-001; Tokai Pharmaceuticals, Cambridge, MA)
• It is an oral, semisynthetic, steroidal agent with a triple
mechanism of action functioning as CYP17 lyase inhibitor,
as well as an antiandrogen and as an AR-degrading agent.
• ARMOR (Androgen Receptor Modulation Optimized for
Response) clinical development program for the evaluation of
galeterone in patients with CRPC, has been completed
TOK-001
In a phase I study of chemo-naïve men with CRPC, TOK-001
was well tolerated and demonstrated clinical activity. ARMOR1
Of 49 patients,22% demonstrated a >50% PSA decline and an
additional 26% had PSA declines of 30%–50% [34]. Based on
these preliminary results
Galeterone received fast-track designation from FDA
ARMOR-2
• The most mature dataset is in metastatic
treatment naïve CRPC where interim data in
21 patients show 90% achieved a PSA30 and
81% achieved a PSA50.
• In addition, initial data in abiraterone
refractory patients shows both biochemical
activity and stable disease.
EPI-001
EPI-001 covalently binds to the NTD,
inhibits protein–protein interactions
necessary for transcriptional activity of
the AR and its splice variants, and
reduces the growth of CRPC in
xenografts.
EPI-001 has the potential to be
efficacious in CRPC progressing on
treatment with enzalutamide,where
AR-Vs are believed to play an
increasing role as driver of tumor
progression
Myung JK, Banuelos CA, Fernandez JG et al. An androgen receptor N-terminal domain antagonist for treating prostate cancer. J Clin
Invest 2013; 123:2948–2960.
Molecular Facts behind clinical
observations
• Prostate cancer is very heterogeneous
disease
• Prostate
cancer
progression
grouped into three categories:
– Endocrine-driven
is
– Microenvironment-dependent
– Tumor cell–autonomous
Cancer Discov; 3 (8): 849-61. 2013
M. Fraser et al. Urologic Oncology: Seminars and Original Investigations ] (2013) 1–10