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Expression of Androgen Receptor Splice Variant 7 or 9 in Whole Blood Does Not Predict Response to Androgen-Axis-targeting Agents in Metastatic Castration-resistant Prostate Cancer

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Sarah Q To
Sarah Q To
Sarah Q To
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Edmond Kwan at Monash University (Australia)
Edmond Kwan
Heidi C Fettke
Heidi C Fettke
Heidi C Fettke
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Andrew Mant
Andrew Mant
Andrew Mant
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Abstract

In 2014, a landmark study was published demonstrating that the expression of androgen receptor splice variant (AR-V) 7 was a negative predictive biomarker for response to abiraterone acetate and enzalutamide in metastatic castration-resistant prostate cancer (mCRPC) patients. However, these results were not supported by the recently reported ARMOR3-SV phase III clinical trial, which employed an identical circulating tumour cell assay to assess AR-V7 expression. Therefore, the predictive utility of AR-V7 expression in mCRPC remains uncertain, as does any potential association between other AR-Vs and treatment response. To further investigate, we designed a highly sensitive and specific whole blood assay for detecting AR-V7 and AR-V9. We then examined for a correlation between baseline AR-V7/V9 status and treatment outcome in 37 mCRPC patients commencing abiraterone or enzalutamide. Of the patients, 24% (9/37) were AR-V-positive. Notably, prostate-specific antigen (PSA) response rates did not significantly differ between AR-V-positive (6/9) and AR-V-negative (18/28) patients (66% vs 64%, p=0.9). Likewise, median PSA progression-free survival was not significantly different between AR-V-positive and AR-V-negative patients (9.2 mo vs not reached; p=0.9). These data, which support the findings of the pivotal ARMOR3-SV clinical trial, suggest that baseline AR-V expression does not predict outcomes in mCRPC patients receiving abiraterone or enzalutamide. Patient summary: Detection of androgen receptor splice variants (AR-Vs) in circulating tumour cells of advanced prostate cancer patients has been linked to resistance to abiraterone and enzalutamide. We designed a blood test to detect AR-Vs that can be performed more routinely than tests involving circulating tumour cells and found that patients with AR-Vs still benefit from these effective treatments.
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Brief
Correspondence
Expression
of
Androgen
Receptor
Splice
Variant
7
or
9
in
Whole
Blood
Does
Not
Predict
Response
to
Androgen-Axis–targeting
Agents
in
Metastatic
Castration-resistant
Prostate
Cancer
Sarah
Q.
To
a,y
,
Edmond
M.
Kwan
a,b,y
,
Heidi
C.
Fettke
a
,
Andrew
Mant
c
,
Maria
M.
Docanto
a
,
Luciano
Martelotto
a
,
Patricia
Bukczynska
a
,
Nicole
Ng
b
,
Lisa-Jane
K.
Graham
d
,
Phillip
Parente
c,e
,
Carmel
Pezaro
c,e
,
Kate
Mahon
d,f
,
Lisa
Horvath
d,f,g,h
,
Tilman
Todenho
¨fer
i
,
Arun
A.
Azad
a,b,
*
a
Department
of
Medicine,
School
of
Clinical
Sciences,
Monash
University,
Australia;
b
Department
of
Medical
Oncology,
Monash
Health,
Australia;
c
Medical
Oncology
Unit,
Eastern
Health,
Australia;
d
Medical
Oncology,
Chris
O’Brien
Lifehouse,
Australia;
e
Eastern
Health
Clinical
School,
Monash
University,
Australia;
f
Garvan
Institute
of
Medical
Research,
Australia;
g
Royal
Prince
Alfred
Hospital,
Australia;
h
University
of
Sydney,
Australia;
i
Department
of
Urology,
Eberhard-Karls-University
Tuebingen,
Germany
E
U
R
O
P
E
A
N
U
R
O
L
O
G
Y
X
X
X
(
2
0
18
)
X
X
X
–
X
X
X
ava
ilable
at
www.sciencedirect.com
journa
l
homepage:
www.europea
nurology.com
y
These
authors
contributed
equally
to
this
work.
*
Corresponding
author.
Level
7,
Translational
Research
Facility
(TRF),
Monash
Medical
Centre,
246
Clayton
Road,
Clayton
3168,
Victoria,
Australia.
Tel.
+613
857
22860;
Fax:
+613
992
88341.
E-mail
address:
arun.azad@monash.edu
(A.A.
Azad).
Article
info
Article
history:
Accepted
January
4,
2018
Associate
Editor:
Matthew
Cooperberg
Keywords:
Abiraterone
Androgen
receptor
splice
variant
Biomarker
Castration
resistant
Enzalutamide
Prostate
cancer
Abstract
In
2014,
a
landmark
study
was
published
demonstrating
that
the
expression
of
androgen
receptor
splice
variant
(AR-V)
7
was
a
negative
predictive
biomarker
for
response
to
abiraterone
acetate
and
enzalutamide
in
metastatic
castration-resistant
prostate
cancer
(mCRPC)
patients.
However,
these
results
were
not
supported
by
the
recently
reported
ARMOR3-SV
phase
III
clinical
trial,
which
employed
an
identical
circulating
tumour
cell
assay
to
assess
AR-V7
expression.
Therefore,
the
predictive
utility
of
AR-V7
expression
in
mCRPC
remains
uncertain,
as
does
any
potential
association
between
other
AR-Vs
and
treatment
response.
To
further
investigate,
we
designed
a
highly
sensitive
and
specific
whole
blood
assay
for
detecting
AR-V7
and
AR-V9.
We
then
examined
for
a
correlation
between
baseline
AR-V7/V9
status
and
treatment
outcome
in
37
mCRPC
patients
commencing
abiraterone
or
enzalutamide.
Of
the
patients,
24%
(9/37)
were
AR-V–
positive.
Notably,
prostate-specific
antigen
(PSA)
response
rates
did
not
significantly
differ
between
AR-V–positive
(6/9)
and
AR-V–negative
(18/28)
patients
(66%
vs
64%,
p
=
0.9).
Likewise,
median
PSA
progression-free
survival
was
not
significantly
different
between
AR-V–positive
and
AR-V–negative
patients
(9.2
mo
vs
not
reached;
p
=
0.9).
These
data,
which
support
the
findings
of
the
pivotal
ARMOR3-SV
clinical
trial,
suggest
that
baseline
AR-V
expression
does
not
predict
outcomes
in
mCRPC
patients
receiving
abiraterone
or
enzalutamide.
Patient
summary:
Detection
of
androgen
receptor
splice
variants
(AR-Vs)
in
circulating
tumour
cells
of
advanced
prostate
cancer
patients
has
been
linked
to
resistance
to
abiraterone
and
enzalutamide.
We
designed
a
blood
test
to
detect
AR-Vs
that
can
be
performed
more
routinely
than
tests
involving
circulating
tumour
cells
and
found
that
patients
with
AR-Vs
still
benefit
from
these
effective
treatments.
©
2018
European
Association
of
Urology.
Published
by
Elsevier
B.V.
All
rights
reserved.
EURURO-7699;
No.
of
Pages
4
Please
cite
this
article
in
press
as:
To
SQ,
et
al.
Expression
of
Androgen
Receptor
Splice
Variant
7
or
9
in
Whole
Blood
Does
Not
Predict
Response
to
Androgen-Axis–targeting
Agents
in
Metastatic
Castration-resistant
Prostate
Cancer.
Eur
Urol
(2018),
https://
doi.org/10.1016/j.eururo.2018.01.007
https://doi.org/10.1016/j.eururo.2018.01.007
0302-2838/©
2018
European
Association
of
Urology.
Published
by
Elsevier
B.V.
All
rights
reserved.
Androgen
receptor
splice
variants
(AR-Vs)
are
truncated
isoforms
of
the
androgen
receptor
(AR).
Two
of
the
most
abundantly
expressed
AR-Vs
in
metastatic
castration-
resistant
prostate
cancer
(mCRPC)
are
AR-V7
and
AR-V9.
Both
remain
constitutively
active
despite
lacking
the
ligand-
binding
domain
in
comparison
with
full-length
AR,
making
them
potentially
impervious
to
AR-axis–targeted
therapies.
Several
studies
have
concluded
that
AR-V7
expression
in
circulating
tumour
cells
(CTCs)
is
a
negative
predictive
biomarker
for
response
to
the
next-generation
hormonal
agents
abiraterone
acetate
and
enzalutamide
[1–3].
In
contrast,
two
recent
studies,
including
the
randomised
phase
III
ARMOR3-SV
clinical
trial
(which
reported
a
striking
42%
response
rate
to
enzalutamide
in
patients
with
AR-V7–positive
CTCs)
[4,5],
have
cast
doubt
about
whether
AR-V7
is
indeed
a
negative
predictive
biomarker
in
mCRPC.
AR-V9
has
also
been
previously
linked
to
abirater-
one
resistance
[6],
warranting
a
broader
investigation
incorporating
both
AR
variants.
Of
note,
no
prior
study
has
evaluated
the
predictive
utility
of
both
circulating
AR-
V7
and
AR-V9
transcripts
in
mCRPC
patients.
Despite
advances
in
the
field,
blood-based
biomarker
detection
with
CTCs
remains
limited
in
its
broader
clinical
applications
for
mCRPC
patients.
CTCs
are
more
abundant
in
patients
with
a
high
tumour
burden
[7],
which
may
present
a
source
of
selection
bias
in
biomarker
investigations.
Furthermore,
sample
processing
for
CTCs
is
time
sensitive
and
can
require
highly
specialised
equipment,
pitfalls
that
make
clinical
translation
challenging.
Accordingly,
more
recent
studies
have
sought
to
utilise
whole
blood
assays
to
detect
AR-V7
expression,
bypassing
the
need
for
CTC
enrichment
[8,9].
We
have
developed
an
assay
for
detecting
AR-V7
and
AR-
V9
that
requires
only
2.5
ml
of
whole
blood
collected
in
PAXgene
RNA
tubes.
Immediate
sample
processing
is
not
required,
and
tubes
can
be
stored
frozen
for
up
to
7
yr
without
loss
of
RNA
integrity.
RNA
is
isolated
and
subject
to
reverse
transcription
using
a
primer
specific
for
the
AR-V7
or
AR-V9
transcript
(Supplementary
material).
Quantitative
polymerase
chain
reaction
(qPCR)
is
then
performed
using
Taqman
chemistry,
and
a
probe/primer
is
set
for
specifically
targeted
unique
sequences
within
the
AR-V7
or
AR-V9
transcript
(Supplementary
Fig.
1).
Importantly,
the
combi-
nation
of
gene-specific
reverse
transcription
and
Taqman
probe
qPCR
detection
allows
for
both
high
specificity
and
sensitivity.
By
serially
diluting
RNA
from
VCaP
prostate
cancer
cells
(which
are
known
to
express
AR-V7),
we
established
that
the
lower
limit
of
detection
of
our
assay
for
AR-V7
is
0.1%
(Supplementary
material).
The
assay
also
exhibits
100%
specificity
with
neither
AR-V7
nor
AR-V9
detected
in
any
of
the
13
healthy
male
controls
(data
not
shown).
We
next
applied
our
assay
to
a
prospectively
collected
cohort
of
37
mCRPC
patients,
commencing
abiraterone
or
enzalutamide,
across
three
institutions.
Blood
samples
were
taken
immediately
before
the
commencement
of
therapy.
Patient
characteristics
are
listed
in
Supplementary
Table
1.
Clinical
outcome
data
were
collected,
including
prostate-specific
antigen
(PSA)
response
rates
(defined
as
PSA
decrease
50%,
confirmed
3
wk
later)
and
PSA
progression-free
survival
(PSA-PFS;
PCWG3
criteria).
Medi-
an
follow-up
time
of
the
cohort
was
7.3
mo
(interquartile
range
4.7–10.6
mo).
Patients
positive
for
either
AR-V7
or
AR-
V9
were
defined
as
AR-V
positive,
while
patients
negative
for
both
AR-V7
and
AR-V9
were
defined
as
AR-V
negative.
In
total,
nine
out
of
37
patients
(24%)
were
AR-V
positive,
with
seven
being
AR-V7
positive
and
two
being
AR-V9
positive
(no
patients
were
positive
for
both
AR-Vs).
The
overall
PSA
response
rate
was
65%
(24/37).
Importantly,
we
observed
similar
PSA
response
rates
in
the
AR-V7–positive
(4/7)
patients
to
those
in
the
AR-V7–negative
(20/30)
patients
(57%
vs
66%,
p
=
0.6,
chi-square
test).
When
both
AR-V7
and
AR-V9
were
analysed
together,
PSA
response
rates
to
abiraterone
or
enzalutamide
remained
similar
across
AR-V–positive
(6/9)
patients
compared
with
AR-V–
negative
(18/28)
patients
(66%
vs
64%;
p
=
0.9,
chi-square
test;
Fig.
1).
We
also
evaluated
the
probability
of
AR-V–
positive
and
AR-V–negative
patients
attaining
a
PSA
response
by
12
wk
after
starting
therapy.
We
found
no
significant
difference
in
the
proportion
of
AR-V–positive
(5/
Fig.
1
–
Waterfall
plot
of
best
prostate-specific
antigen
(PSA)
responses
for
37
patients
treated
with
abiraterone
or
enzalutamide,
according
to
AR-V7
and
AR-V9
status.
AR-V
=
androgen
receptor
splice
variant.
E
U
R
O
P
E
A
N
U
R
O
L
O
G
Y
X
X
X
(
2
0
18
)
X
X
X
–
X
X
X
2
EURURO-7699;
No.
of
Pages
4
Please
cite
this
article
in
press
as:
To
SQ,
et
al.
Expression
of
Androgen
Receptor
Splice
Variant
7
or
9
in
Whole
Blood
Does
Not
Predict
Response
to
Androgen-Axis–targeting
Agents
in
Metastatic
Castration-resistant
Prostate
Cancer.
Eur
Urol
(2018),
https://
doi.org/10.1016/j.eururo.2018.01.007
9)
and
AR-V–negative
(17/28)
patients
who
had
a
PSA
response
by
12
wk
(55%
vs
61%;
p
=
1.0,
chi-square
test).
PSA-PFS
data
were
available
for
all
37
patients
included
in
this
study.
Median
PSA-PFS
for
the
overall
cohort
was
not
reached.
Notably,
there
was
no
significant
difference
in
the
median
PSA-PFS
between
AR-V7–positive
and
AR-V7–
negative
patients
(9.2
mo
vs
not
reached;
p
=
0.4,
log-rank
test).
Likewise,
when
including
AR-V9
data,
there
was
no
difference
in
the
median
PSA-PFS
between
AR-V–positive
and
AR-V–negative
patients
(9.2
mo
vs
not
reached;
p
=
0.9,
log-rank
test;
Fig.
2).
We
also
examined
outcomes
at
specific
time
points
after
commencement
of
therapy
and
found
no
significant
difference
in
the
proportion
of
AR-V–positive
versus
AR-V–negative
patients
without
PSA
progression
at
3
mo
(p
=
1.0,
chi-square
test)
and
6
mo
(p
=
0.7,
chi-square
test).
In
summary,
we
found
that
positive
AR-V7
expression
using
a
novel
whole
blood
reverse
transcription
PCR
assay
was
not
linked
to
poorer
clinical
outcomes
in
mCRPC
patients
receiving
abiraterone
or
enzalutamide.
Critically,
our
results
are
in
keeping
with
the
findings
of
the
pivotal
ARMOR3-SV
clinical
trial
in
which
AR-V7
expression
was
evaluated
in
CTCs.
These
data
collectively
suggest
that
AR-V7
expression
in
either
CTCs
or
whole
blood
is
not
a
negative
predictive
biomarker
for
patients
commencing
abiraterone
or
enzalutamide,
and
therefore
testing
should
not
be
incorporated
into
routine
clinical
practice,
a
position
supported
by
recent
international
consensus
guidelines
[10].
Combining
results
for
AR-V7
and
AR-V9
confirmed
that
detection
of
either
AR-V
using
our
assay
was
not
associated
with
a
lack
of
efficacy
of
abiraterone
or
enzalutamide,
further
suggesting
that
AR-
V
expression
is
not
linked
to
treatment
outcome
in
mCRPC.
Validation
of
our
findings
in
a
larger,
more
racially
diverse
cohort
and
head-to-head
comparison
with
other
AR-V
assays
will
be
of
paramount
importance
for
future
studies.
Author
contributions:
Arun
A.
Azad
had
full
access
to
all
the
data
in
the
study
and
takes
responsibility
for
the
integrity
of
the
data
and
the
accuracy
of
the
data
analysis.
Study
concept
and
design:
Azad,
Todenhöfer.
Acquisition
of
data:
To,
Fettke,
Kwan,
Docanto,
Ng,
Mant,
Parente,
Pezaro,
Horvath,
Mahon,
Graham,
Bukczynska,
Martelotto.
Analysis
and
interpretation
of
data:
To,
Kwan,
Azad.
Drafting
of
the
manuscript:
To,
Kwan,
Azad.
Critical
revision
of
the
manuscript
for
important
intellectual
content:
Azad,
Pezaro,
Horvath,
Todenhöfer.
Statistical
analysis:
To,
Kwan,
Azad.
Obtaining
funding:
Azad.
Administrative,
technical,
or
material
support:
Docanto,
Ng.
Supervision:
Azad.
Other:
None.
Financial
disclosures:
Arun
A.
Azad
certifies
that
all
conflicts
of
interest,
including
specific
financial
interests
and
relationsh ips
and
affiliations
relevant
to
the
subject
matter
or
materials
discussed
in
the
manuscript
(eg,
employment/affiliation,
grants
or
funding,
consultancies,
honoraria,
stock
ownership
or
options,
expert
testimony,
royalties,
or
patents
filed,
received,
or
pending),
are
the
following:
Arun
Azad:
consultant—Astellas,
Janssen,
Novartis;
speakers
bureau—Astellas,
Janssen,
Novartis,
Amgen;
honoraria—Astellas,
Janssen,
Novartis,
Tolmar,
Amgen,
Pfizer;
scientific
advisory
board—Astellas,
Novartis,
Sanofi,
Astra-Zeneca,
Tolm ar,
Pfizer;
research
support—Astellas.
Tilman
Tode nhöfer:
speakers
bureau—Astellas,
Janssen;
research
support—Astellas.
Lisa
Horvath:
research
support—
Astellas.
This
work
was
funded
by
an
NHMRC
project
grant
to
Arun
Azad,
a
Cancer
Council
Victoria
Seed
Grant
to
Carmel
Pezaro,
and
Astellas
Investigator-Initiated
Grants
to
Arun
Azad
and
Lisa
Horvath.
Sarah
To
is
supported
by
an
NHMRC
fellowship,
Edmond
Kwan
is
supported
by
an
NHMRC
postgraduate
scholarship,
Arun
Azad
is
supported
by
a
Victorian
Cancer
Agency
clinical
research
fellowship.
Funding/Support
and
role
of
the
sponsor:
None.
Appendix
A.
Supplementary
data
Supplementary
data
associated
with
this
article
can
be
found,
in
the
online
version,
at
https://doi.org/10.1016/j.
eururo.2018.01.007.
Fig.
2
–
Kaplan–Meier
analysis
of
PSA
progression-free
survival
according
to
AR-V7
and
AR-V9
status.
AR-V
=
androgen
receptor
splice
variant;
PSA
=
prostate-specific
antigen.
E
U
R
O
P
E
A
N
U
R
O
L
O
G
Y
X
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(
2
0
18
)
X
X
X
–
X
X
X
3
EURURO-7699;
No.
of
Pages
4
Please
cite
this
article
in
press
as:
To
SQ,
et
al.
Expression
of
Androgen
Receptor
Splice
Variant
7
or
9
in
Whole
Blood
Does
Not
Predict
Response
to
Androgen-Axis–targeting
Agents
in
Metastatic
Castration-resistant
Prostate
Cancer.
Eur
Urol
(2018),
https://
doi.org/10.1016/j.eururo.2018.01.007
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E
U
R
O
P
E
A
N
U
R
O
L
O
G
Y
X
X
X
(
2
0
18
)
X
X
X
–
X
X
X
4
EURURO-7699;
No.
of
Pages
4
Please
cite
this
article
in
press
as:
To
SQ,
et
al.
Expression
of
Androgen
Receptor
Splice
Variant
7
or
9
in
Whole
Blood
Does
Not
Predict
Response
to
Androgen-Axis–targeting
Agents
in
Metastatic
Castration-resistant
Prostate
Cancer.
Eur
Urol
(2018),
https://
doi.org/10.1016/j.eururo.2018.01.007
... 10,11 However, this often leads to an underestimation of CTCs due to loss of certain subpopulations, as highlighted in PCa. [10][11][12][13][14][15] Whole blood RNA has been used as an attractive alternative to define gene expression profiles related to progression for diverse cancers, including PCa. [16][17][18][19][20][21] In this pilot study, we assessed the (over)expression of 14 genes representing prostate cell subtypes in whole blood RNA of 40 patients with advanced PCa and 40 healthy controls. We observed a variety of gene patterns in blood samples, also validated in PCa transcriptomic datasets. ...
... 35 Cancer-specific genes were identified in whole blood. [16][17][18][19][20][21][36][37][38][39][40][41] The sensitivity of RT-qPCR assays comparing gene expression directly in the blood of patients with PCa versus CTCs was also reported to be similar. 18,42 The central limitation remains the genes expressed in WBCs, making gene selection a key step for success. ...
... Overall, patients showed a wide phenotypic diversity in line with the clinical heterogeneity of advanced cases and reported for circulating genes in breast, colorectal, lung, and prostate cancers. [16][17][18][19][20][21][37][38][39] Among luminal genes, KLK3 expression was significantly associated with high levels of PSA in blood, suggesting that PSA reflects tumor burden, whereas circulating KLK3 would originate from CTCs or EVs. Of note, KLK3 expression in 16 of 40 (40%) of mCRPC cases is not paralleled by AR overexpression. ...
Liquid biopsy‐based targeted gene screening highlights tumor cell subtypes in patients with advanced prostate cancer
Article
Full-text available
Prostate cancer (PCa) clinical heterogeneity underscores tumor heterogeneity, which may be best defined by cell subtypes. To test if cell subtypes contributing to progression can be assessed noninvasively, we investigated whether 14 genes representing luminal, neuroendocrine, and stem cells are detectable in whole blood RNA of patients with advanced PCa. For each gene, reverse transcription quantitative polymerase chain reaction assays were first validated using RNA from PCa cell lines, and their traceability in blood was assessed in cell spiking experiments. These were next tested in blood RNA of 40 advanced PCa cases and 40 healthy controls. Expression in controls, which was low or negative, was used to define stringent thresholds for gene overexpression in patients to account for normal variation in white blood cells. Thirty‐five of 40 patients overexpressed at least one gene. Patients with more genes overexpressed had a higher risk of death (hazard ratio 1.42, range 1.12–1.77). Progression on androgen receptor inhibitors was associated with overexpression of stem (odds ratio [OR] 7.74, range 1.68–35.61) and neuroendocrine (OR 13.10, range 1.24–142.34) genes, while luminal genes were associated with taxanes (OR 2.7, range 1.07–6.82). Analyses in PCa transcriptomic datasets revealed that this gene panel was most prominent in metastases of advanced disease, with diversity among patients. Collectively, these findings support the contribution of the prostate cell subtypes to disease progression. Cell‐subtype specific genes are traceable in blood RNA of patients with advanced PCa and are associated with clinically relevant end points. This opens the door to minimally invasive liquid biopsies for better management of this deadly disease.
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... In multivariate cox regression analysis for the overall cohort, only prior abiraterone or enzalutamide (p = 0.01) was independently prognostic (Table S4). In CTC + patients, none of the parameters was independently CTC-(0) CTC+ (21) CTC- (11) AR-V7- (21) AR-V7+ (33) AR-V7- (11) AR-V7+ (0) www.nature.com/scientificreports/ prognostic (Table S5). ...
... In multivariate cox regression analysis for the overall cohort, only prior abiraterone or enzalutamide (p = 0.01) was independently prognostic (Table S4). In CTC + patients, none of the parameters was independently CTC-(0) CTC+ (21) CTC- (11) AR-V7- (21) AR-V7+ (33) AR-V7- (11) AR-V7+ (0) www.nature.com/scientificreports/ prognostic (Table S5). ...
... Most recent studies then integrated dichotomous stratification of AR-V7 + or AR-V7-patients, without previous determination of www.nature.com/scientificreports/ CTC status 6,[8][9][10][11][12] . In case of a strong predictive biomarker this stratification might be adequate. ...
Comparison of circulating tumor cells and AR-V7 as clinical biomarker in metastatic castration-resistant prostate cancer patients
Article
Full-text available
  • Jul 2022
Biomarker in metastatic castration resistant prostate cancer (mCRPC) treatment are rare. We aimed to compare the clinical value of circulating tumor cells (CTCs) and androgen receptor splice variant 7 (AR-V7) as biomarker in mCRPC patients undergoing androgen receptor-targeted agent (ARTA) treatment. Overall cohort (65 patients) was stratified regarding either CTC or AR-V7 status followed by further sub-stratification of the respective other marker. Subsequently, prostate specific antigen (PSA) response, progression free survival (PFS) and overall survival (OS)) of subgroups was compared. CTCs and AR-V7 were detected in 54 (83%) and 33 (61%) patients, respectively. All AR-V7 + were CTC +. We detected PSA response in all subgroups. For PFS and OS, biomarker stratification revealed differences between all subgroups. Interestingly, no significant differences of AR-V7 transcript copy numbers were detected between responding and non-responding patients. Additionally, multivariable analysis revealed no independent prognostic value of AR-V7 positivity. Both biomarkers show clinical value in prognosticating clinical outcome. Nonetheless, AR-V7 stratification underestimates the heterogenous subgroup of CTC − and CTC + patient, the latter requiring more intense clinical surveillance. Additionally, AR-V7 level does not correlate with clinical response. Thus, the value of AR-V7 as a clinical biomarker must be considered skeptically.
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... Twelve studies on AR mutations, amplification, or splice variants in CTCs were identified [33][34][35][36][37][38][39][40][41][42][43][44] (Table 3). Among patients with mCRPC, the presence of AR splice variant 7 (AR-V7) transcripts and the AR-V7 protein level in CTCs were associated with ARPI resistance (shorter PFS and OS) [35,37,40,43] (LOE IB) and with shorter OS after taxane chemotherapy [38,41,42] (LOE IB). ...
... Among patients with mCRPC and bone metastases, CTCnegative status was not significantly associated with prediction of enzalutamide efficacy, whereas CTC-positive/AR-V7-negative status predicted shorter PFS after enzalutamide therapy [33] (LOE IB). These results were confirmed in whole-blood assays: the presence of AR-V1 or full-length AR transcripts before and during abiraterone treatment was associated with shorter PFS [34,39] (LOE IIC). These two studies have the advantage of eliminating selection bias in biomarker investigations because CTCs were more abundant in patients with a high tumor burden [45]. ...
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... Two of the most abundantly expressed AR-Vs in mCRPC are AR-V7 and AR-V9. 43 Regarding PC a significant correlation between circulating cell-free AR CNVs and treatment response to AA and enzalutamide has been shown, indicating AR gene copy number (CN) in cfDNA may be a promising biomarker capable of predicting treatment resistance 44 Recent reports have questioned the role of CTC as a predictive biomarker given that either AR-V7 positive patients did respond to novel hormonal treatment (NHT) or AR-V7 status was not able to significantly demonstrate shorter OS compared to CTC positive yet AR-V7 negative patients 45 Initial CTC values predict the duration and magnitude of response to hormonal therapy. CTC enumeration may identify patients at risk of progression to CRPC before initiation of ADT. ...
... Both AR-V7 and AR-V9 were not associated with a lack of efficacy of abiraterone or enzalutamide in mCRPC. 43 Regarding AR-V7, there was no significant difference in PFS between the groups Treated with Enzalutamide, Abiraterone, hormone therapies, or Taxane-Based Therapies 54 While AR-V7 expression above the digital threshold of 14.7 transcripts per mL blood is highly specific for prediction of progression on first line abiraterone therapy, HOXB13 expression identifies additional non-responding patients, in whom suppression of androgen production is insufficient to achieve a sustained tumor response. 55 Moreover, patients treated with AR signalization inhibitors had the most favorable survival outcome, if they were AR-V7 negative, and had the least favorable survival outcome, if they were AR-V7 positive. ...
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... Thus, its predictive property is still under debate [9][10][11]. Other AR-Vs, e.g., AR-V3 and AR-V9, have been found to be co-expressed in clinical PC specimen of all stages [12][13][14][15][16][17][18]. ...
Co-expression and clinical utility of AR-FL and AR splice variants AR-V3, AR-V7 and AR-V9 in prostate cancer
Article
Full-text available
  • Apr 2023
Background Androgen receptor (AR) splice variants (AR‐Vs) have been discussed as a biomarker in prostate cancer (PC). However, some reports question the predictive property of AR‐Vs. From a mechanistic perspective, the connec‐ tion between AR full length (AR‐FL) and AR‐Vs is not fully understood. Here, we aimed to investigate the depend‐ ence of AR‐FL and AR‐V expression levels on AR gene activity. Additionally, we intended to comprehensively analyze presence of AR‐FL and three clinically relevant AR‐Vs (AR‐V3, AR‐V7 and AR‐V9) in different stages of disease, especially with respect to clinical utility in PC patients undergoing AR targeted agent (ARTA) treatment. Methods AR‐FL and AR‐V levels were analyzed in PC and non‐PC cell lines upon artificial increase of AR pre‐mRNA using either drug treatment or AR gene activation. Furthermore, expression of AR‐FL and AR‐Vs was determined in PC specimen at distinct stages of disease (primary (n = 10) and metastatic tissues (n = 20), liquid biopsy samples (n = 422), mCRPC liquid biopsy samples of n = 96 patients starting novel treatment). Finally, baseline AR‐FL and AR‐V status was correlated with clinical outcome in a defined cohort of n = 65 mCRPC patients undergoing ARTA treatment. Results We revealed rising levels of AR‐FL accompanied with appearance and increase of AR‐Vs in dependence of elevated AR pre‐mRNA levels. We also noticed increase in AR‐FL and AR‐V levels throughout disease progression. AR‐V expression was always associated with high AR‐FL levels without any sample being solely AR‐V positive. In patients undergoing ARTA treatment, AR‐FL did show prognostic, yet not predictive validity. Additionally, we observed a sub‐ stantial clinical response to ARTA treatment even in AR‐V positive patients. Accordingly, multivariate analysis did not demonstrate independent significance of AR‐Vs in neither predictive nor prognostic clinical utility. Conclusion We demonstrate a correlation between AR‐FL and AR‐V expression during PC progression; with AR‐V expression being a side‐effect of elevated AR pre‐mRNA levels. Clinically, AR‐V positivity relies on high levels of AR‐FL, making cells still vulnerable to ARTA treatment, as demonstrated by AR‐FL and AR‐V positive patients responding to ARTA treatment. Thus, AR‐FL and AR‐V might be considered as a prognostic, yet not predictive biomarker in mCRPC patients.
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... AR-V7 (the most common splice variant) expression in CTCs of patients with mCRPCportends poor response to ARPI therapy[81][82][83][84] but not taxane chemotherapy.85,86 However, detection of AR-V7-positive CTCs does not completely preclude response to ARPI therapy41,87,88 and the apparent relationship between AR-V7 and disease burden and/ or prior treatment exposure may support use as a prognostic rather than predictive biomarker.41,89,90 ...
Androgen receptor genomic alterations and treatment resistance in metastatic prostate cancer
Article
  • Aug 2022
Background: Genomic alterations to the androgen receptor (AR) are common in metastatic castration-resistant prostate cancer (mCRPC). AR copy number amplifications, ligand-binding domain missense mutations, and intronic structural rearrangements can all drive resistance to approved AR pathway inhibitors and their detection via tissue or liquid biopsy is linked to clinical outcomes. With an increasingly crowded treatment landscape, there is hope that AR genomic alterations can act as prognostic and/or predictive biomarkers to guide patient management. Methods: In this review, we evaluate the current evidence for AR genomic alterations as clinical biomarkers in mCRPC, focusing on correlative studies that have used plasma circulating tumor DNA to characterize AR genotype. Results: We highlight data that demonstrates the complexity of AR genotype within individual patients, and suggest that future studies should account for cancer clonal heterogeneity and variable tumor content in liquid biopsy samples. Given the potential for cooccurrence of multiple AR genomic alterations in the same or competing subclones of a patient, it is distinctly challenging to attribute blanket clinical significance to any individual alteration. This challenge is further complicated by the varied treatment exposures in contemporary patients, and the fact that AR genotype continues to evolve in the mCRPC setting across sequential lines of systemic therapy. Conclusions: As treatment access and liquid biopsy technology continues to improve, we posit that real-time measures of AR biology are likely to play a key role in emerging precision oncology strategies for metastatic prostate cancer.
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... Moreover, AR-V7 nuclear expression in circulating tumor cells was suggested as treatment-specific biomarker for metastatic CRPC (mCRPC) patients with short survival upon enzalutamide and abiraterone treatment and increased survival benefit on taxane therapy compared to AR-targeted therapy [63,64] . However, a recent report did not support the predictive role of AR-V7 and AR-V9 detection in the circulation [65] . ...
Evolution of the prostate cancer genome towards resistance
Article
Full-text available
  • Mar 2019
The clinical behavior of prostate cancer is highly heterogeneous, with most patients diagnosed with localized disease that successfully responds to surgery or radiotherapy or that can be followed by active surveillance. However, a fraction of men will relapse after initial treatment and eventually progress to an aggressive resistant form with metastasis spreading and high mortality, a state referred to as castration resistant prostate cancer (CRPC). The technological advances in next generation sequencing have enabled the deep genomic and epigenomic characterization of both the hormone naïve and CRPC states, leading to the definition of molecular subclasses of prostate cancer that could inform the clinicians on therapeutic strategies. These studies also shed light on the mechanisms driving resistance to therapy. CRPCs adapt to androgen receptor (AR) signaling impairment - which follows first-line therapies as androgen deprivation or AR targeting - by restoring the nuclear receptor signaling by means of multiple mechanisms. Alternatively, tumor cells might become resistant to targeted therapies by exploiting lineage plasticity and activating alternative pathways. This review will discuss the main mechanisms leading to the emergence of resistance to therapy in prostate cancer patients in the context of genomic and molecular features of CRPC and on their causal role in the development of resistance.
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... Although the AR-V7 splice variant was associated with more advanced disease, 42% of men still had a significant PSA response (> 50% fall from baseline), confirming that AR-V7 is not an appropriate negative predictive biomarker for AR pathway inhibitors. 45,46 Clinical utility tests whether a biomarker used to guide clinical practice actually improves patient outcomes compared to when that biomarker is not utilized. 25 A prospective randomized controlled trial designed specifically to address the utility of the biomarker is the "gold standard" test for clinical utility. ...
From Research to the Real World: Moving Prostate Cancer Biomarkers into the Clinic
Article
  • Jan 2022
  • Crit Rev Oncog
Effective biomarkers provide the potential to significantly improve treatment decisions and outcomes in prostate cancer patients. While the literature is inundated with prostate cancer biomarkers in the early phases of testing, very few reach the clinic. Research should be focused on progressing effective biomarkers from discovery to clinical utility and implementation. Presented here is an overview of the biomarker development pathway and a discussion of the current issues impeding our efforts to deliver biomarkers that improve clinical outcomes in men with prostate cancer.
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... AR gene structural rearrangements are associated with primary resistance and shorter progression-free survival when treated with ARPIs, 15,30 but responses can still occur. 65 Conversely, the negative prognostic and predictive potential of androgen receptor splice variants (AR-Vs) does not appear to extend to patients receiving taxane chemotherapy, 66 suggesting potential predictive utility of AR-V7 when deciding upon optimal systemic therapy. ...
Genomic Alterations to Guide Treatment Selection in Metastatic Prostate Cancer
Article
  • Jan 2022
  • Crit Rev Oncog
Treatment options for men with metastatic prostate cancer have greatly expanded in the last decade. Androgen receptor pathway inhibitors, taxane cytotoxic therapy, poly(ADP-ribose) polymerase inhibitors, and radionuclide theranostics against prostate-specific membrane antigen have collectively contributed to incremental improvements in both quality and longevity of life for patients with metastatic castration-resistant prostate cancer (mCRPC). Despite these successes, few studies inform on optimal therapy selection and sequencing across this crowded treatment landscape. Genomic analysis of both tissue and liquid biopsy specimens shows promise in bridging this practice gap, with alterations in several key prostate cancer driver genes demonstrating clear associations with clinical outcomes, as well as informing use of novel precision medicine targeted therapies. In this review, we evaluate the current evidence of genomic alterations in various oncogenic signaling pathways as clinical biomarkers in mCRPC, focusing on correlative studies that analyzed outcomes based on findings in plasma cell-free DNA. We highlight the pitfalls of interpreting genomic findings in samples with substandard tumor content, and suggest pathologic and disease factors to consider when embarking upon tumor genotyping to guide treatment decisions in metastatic prostate cancer. As access to life-prolonging therapies improves, and barriers to cost-effective genotyping and reliable data interpretation are overcome, we anticipate that predictive and prognostic biomarkers that inform on disease biology, drug sensitivity, and therapy resistance will inevitably be integrated into the routine care of patients with metastatic prostate cancer.
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The positive relationship between androgen receptor splice variant-7 expression and the risk of castration-resistant prostate cancer: A cumulative analysis
Article
Full-text available
  • Feb 2023
Background At present, androgen deprivation therapy (ADT) is still the standard regimen for patients with metastatic and locally advanced prostate cancer (PCa). The level of androgen receptor splice variant-7 (AR-V7) in men with castration-resistant prostate cancer (CRPC) has been reported to be elevated compared with that in patients diagnosed with hormone-sensitive prostate cancer (HSPC). Aim Herein, we performed a systematic review and cumulative analysis to evaluate whether the expression of AR-V7 was significantly higher in patients with CRPC than in HSPC patients. Methods The commonly used databases were searched to identify the potential studies reporting the level of AR-V7 in CRPC and HSPC patients. The association between CRPC and the positive expression of AR-V7 was pooled by using the relative risk (RR) with the corresponding 95% confidence intervals (CIs) under a random-effects model. For detecting the potential bias and the heterogeneity of the included studies, sensitivity analysis and subgroup analysis were performed. Publication bias was assessed Egger’s and Begg’s tests. This study was registered on PROSPERO (ID: CRD42022297014). Results This cumulative analysis included 672 participants from seven clinical trials. The study group contained 354 CRPC patients, while the other group contained 318 HSPC patients. Pooled results from the seven eligible studies showed that the expression of positive AR-V7 was significantly higher in men with CRPC compared to those with HSPC (RR = 7.55, 95% CI: 4.61–12.35, p < 0.001). In the sensitivity analysis, the combined RRs did not change substantially, ranging from 6.85 (95% CI: 4.16–11.27, p < 0.001) to 9.84 (95% CI: 5.13–18.87, p < 0.001). In the subgroup analysis, a stronger association was detected in RNA in situ hybridization (RISH) measurement in American patients, and those studies were published before 2011 (all p < 0.001). There was no significant publication bias identified in our study. Conclusion Evidence from the seven eligible studies demonstrated that patients with CRPC had a significantly elevated positive expression of AR-V7. More investigations are still warranted to clarify the association between CRPC and AR-V7 testing. Systematic review registration https://www.crd.york.ac.uk/prospero/ , identifier CRD42022297014.
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Novel Junction-specific and Quantifiable In Situ Detection of AR-V7 and its Clinical Correlates in Metastatic Castration-resistant Prostate Cancer
Article
Full-text available
  • Sep 2017
Background: Androgen receptor splice variant 7 (AR-V7) has been implicated in resistance to abiraterone and enzalutamide treatment in men with metastatic castration-resistant prostate cancer (mCRPC). Tissue- or cell-based in situ detection of AR-V7, however, has been limited by lack of specificity. Objective: To address current limitations in precision measurement of AR-V7 by developing a novel junction-specific AR-V7 RNA in situ hybridization (RISH) assay compatible with automated quantification. Design, setting, and participants: We designed a RISH method to visualize single splice junctions in cells and tissue. Using the validated assay for junction-specific detection of the full-length AR (AR-FL) and AR-V7, we generated quantitative data, blinded to clinical data, for 63 prostate tumor biopsies. Outcome measurements and statistical analysis: We evaluated clinical correlates of AR-FL/AR-V7 measurements, including association with prostate-specific antigen progression-free survival (PSA-PFS) and clinical and radiographic progression-free survival (PFS), in a subset of patients starting treatment with abiraterone or enzalutamide following biopsy. Results and limitations: Quantitative AR-FL/AR-V7 data were generated from 56 of the 63 (88.9%) biopsy specimens examined, of which 44 were mCRPC biopsies. Positive AR-V7 signals were detected in 34.1% (15/44) mCRPC specimens, all of which also co-expressed AR-FL. The median AR-V7/AR-FL ratio was 11.9% (range 2.7-30.3%). Positive detection of AR-V7 was correlated with indicators of high disease burden at baseline. Among the 25 CRPC biopsies collected before treatment with abiraterone or enzalutamide, positive AR-V7 detection, but not higher AR-FL, was significantly associated with shorter PSA-PFS (hazard ratio 2.789, 95% confidence interval 1.12-6.95; p=0.0081). Conclusions: We report for the first time a RISH method for highly specific and quantifiable detection of splice junctions, allowing further characterization of AR-V7 and its clinical significance. Patient summary: Higher AR-V7 levels detected and quantified using a novel method were associated with poorer response to abiraterone or enzalutamide in prostate cancer.
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Management of Patients with Advanced Prostate Cancer: The Report of the Advanced Prostate Cancer Consensus Conference APCCC 2017
Article
Full-text available
  • Jun 2017
Background: In advanced prostate cancer (APC), successful drug development as well as advances in imaging and molecular characterisation have resulted in multiple areas where there is lack of evidence or low level of evidence. The Advanced Prostate Cancer Consensus Conference (APCCC) 2017 addressed some of these topics. Objective: To present the report of APCCC 2017. Design, setting, and participants: Ten important areas of controversy in APC management were identified: high-risk localised and locally advanced prostate cancer; "oligometastatic" prostate cancer; castration-naïve and castration-resistant prostate cancer; the role of imaging in APC; osteoclast-targeted therapy; molecular characterisation of blood and tissue; genetic counselling/testing; side effects of systemic treatment(s); global access to prostate cancer drugs. A panel of 60 international prostate cancer experts developed the program and the consensus questions. Outcome measurements and statistical analysis: The panel voted publicly but anonymously on 150 predefined questions, which have been developed following a modified Delphi process. Results and limitations: Voting is based on panellist opinion, and thus is not based on a standard literature review or meta-analysis. The outcomes of the voting had varying degrees of support, as reflected in the wording of this article, as well as in the detailed voting results recorded in Supplementary data. Conclusions: The presented expert voting results can be used for support in areas of management of men with APC where there is no high-level evidence, but individualised treatment decisions should as always be based on all of the data available, including disease extent and location, prior therapies regardless of type, host factors including comorbidities, as well as patient preferences, current and emerging evidence, and logistical and economic constraints. Inclusion of men with APC in clinical trials should be strongly encouraged. Importantly, APCCC 2017 again identified important areas in need of trials specifically designed to address them. Patient summary: The second Advanced Prostate Cancer Consensus Conference APCCC 2017 did provide a forum for discussion and debates on current treatment options for men with advanced prostate cancer. The aim of the conference is to bring the expertise of world experts to care givers around the world who see less patients with prostate cancer. The conference concluded with a discussion and voting of the expert panel on predefined consensus questions, targeting areas of primary clinical relevance. The results of these expert opinion votes are embedded in the clinical context of current treatment of men with advanced prostate cancer and provide a practical guide to clinicians to assist in the discussions with men with prostate cancer as part of a shared and multidisciplinary decision-making process.
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Androgen Receptor Variant AR-V9 Is Coexpressed with AR-V7 in Prostate Cancer Metastases and Predicts Abiraterone Resistance
Article
Full-text available
  • May 2017
Purpose: Androgen receptor (AR) variant AR-V7 is a ligand-independent transcription factor that promotes prostate cancer resistance to AR-targeted therapies. Accordingly, efforts are underway to develop strategies for monitoring and inhibiting AR-V7 in castration-resistant prostate cancer (CRPC). The purpose of this study was to understand whether other AR variants may be co-expressed with AR-V7 and promote resistance to AR-targeted therapies. Experimental Design: We utilized complementary short- and long-read sequencing of intact AR mRNA isoforms to characterize AR expression in CRPC models. Co-expression of AR-V7 and AR-V9 mRNA in CRPC metastases and circulating tumor cells was assessed by RNA-seq and RT-PCR, respectively. Expression of AR-V9 protein in CRPC models was evaluated with polyclonal antisera. Multivariate analysis was performed to test whether AR variant mRNA expression in metastatic tissues was associated with a 12-week progression-free survival endpoint in a prospective clinical trial of 78 CRPC-stage patients initiating therapy with the androgen synthesis inhibitor, abiraterone acetate. Results: AR-V9 was frequently co-expressed with AR-V7. Both AR variant species were found to share a common 3' terminal cryptic exon, which rendered AR-V9 susceptible to experimental manipulations that were previously-thought to target AR-V7 uniquely. AR-V9 promoted ligand-independent growth of prostate cancer cells. High AR-V9 mRNA expression in CRPC metastases was predictive of primary resistance to abiraterone acetate (HR = 4.0, 95% CI = 1.31-12.2, P = 0.02). Conclusions: AR-V9 may be an important component of therapeutic resistance in CRPC.
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AR-V7 and Resistance to Enzalutamide and Abiraterone in Prostate Cancer
Article
Full-text available
  • Sep 2014
Background: The androgen-receptor isoform encoded by splice variant 7 lacks the ligand-binding domain, which is the target of enzalutamide and abiraterone, but remains constitutively active as a transcription factor. We hypothesized that detection of androgen-receptor splice variant 7 messenger RNA (AR-V7) in circulating tumor cells from men with advanced prostate cancer would be associated with resistance to enzalutamide and abiraterone. Methods: We used a quantitative reverse-transcriptase-polymerase-chain-reaction assay to evaluate AR-V7 in circulating tumor cells from prospectively enrolled patients with metastatic castration-resistant prostate cancer who were initiating treatment with either enzalutamide or abiraterone. We examined associations between AR-V7 status (positive vs. negative) and prostate-specific antigen (PSA) response rates (the primary end point), freedom from PSA progression (PSA progression-free survival), clinical or radiographic progression-free survival, and overall survival. Results: A total of 31 enzalutamide-treated patients and 31 abiraterone-treated patients were enrolled, of whom 39% and 19%, respectively, had detectable AR-V7 in circulating tumor cells. Among men receiving enzalutamide, AR-V7-positive patients had lower PSA response rates than AR-V7-negative patients (0% vs. 53%, P=0.004) and shorter PSA progression-free survival (median, 1.4 months vs. 6.0 months; P<0.001), clinical or radiographic progression-free survival (median, 2.1 months vs. 6.1 months; P<0.001), and overall survival (median, 5.5 months vs. not reached; P=0.002). Similarly, among men receiving abiraterone, AR-V7-positive patients had lower PSA response rates than AR-V7-negative patients (0% vs. 68%, P=0.004) and shorter PSA progression-free survival (median, 1.3 months vs. not reached; P<0.001), clinical or radiographic progression-free survival (median, 2.3 months vs. not reached; P<0.001), and overall survival (median, 10.6 months vs. not reached, P=0.006). The association between AR-V7 detection and therapeutic resistance was maintained after adjustment for expression of full-length androgen receptor messenger RNA. Conclusions: Detection of AR-V7 in circulating tumor cells from patients with castration-resistant prostate cancer may be associated with resistance to enzalutamide and abiraterone. These findings require large-scale prospective validation. (Funded by the Prostate Cancer Foundation and others.).
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Circulating tumour cell (CTC) counts as intermediate end points in castration-resistant prostate cancer (CRPC): A single-centre experience
Article
Full-text available
  • Aug 2008
  • ANN ONCOL
The purpose of this study was to evaluate the association of circulating tumour cell (CTC) counts, before and after commencing treatment, with overall survival (OS) in patients with castration-resistant prostate cancer (CRPC). A 7.5 ml of blood was collected before and after treatment in 119 patients with CRPC. CTCs were enumerated using the CellSearchSystem. Higher CTC counts associated with baseline characteristics portending aggressive disease. Multivariate analyses indicated that a CTC >or=5 was an independent prognostic factor at all time points evaluated. Patients with baseline CTC >or=5 had shorter OS than those with <5 [median OS 19.5 versus >30 months, hazard ratio (HR) 3.25, P=0.012]; patients with CTC >50 had a poorer OS than those with CTCs 5-50 (median OS 6.3 versus 21.1 months, HR 4.1, P<0.001). Patients whose CTC counts reduced from >or=5 at baseline to <5 following treatment had a better OS compared with those who did not. CTC counts showed a similar, but earlier and independent, ability to time to disease progression to predict OS. CTC counts predict OS and provide independent prognostic information to time to disease progression; CTC dynamics following therapy need to be evaluated as an intermediate end point of outcome in randomised phase III trials.
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Clinical factors associated with AR-V7 detection in ARMOR3-SV, a randomized trial of galeterone (Gal) vs enzalutamide (Enz) in men with AR-V7+ metastatic castration-resistant prostate cancer (mCRPC).
Article
  • May 2017
5005 Background: Presence of the AR-V7 splice variant may predict resistance to Enz and abiraterone in men with mCRPC. Gal is an oral agent that disrupts AR signaling via AR degradation, CYP17 lyase inhibition, and AR antagonism. ARMOR3-SV was designed to test the hypothesis that in mCRPC patients with AR-V7+ CTCs, Gal could improve radiographic progression-free survival (rPFS) versus Enz. Methods: In this randomized, open-label, multicenter phase 3 study (NCT02438007), men with treatment-naïve mCRPC were screened for CTC-specific AR-V7 (Qiagen), and AR-V7+ men were randomized 1:1 to Gal or Enz. rPFS (by independent blinded central review) was the primary endpoint. Planned sample size was 148, with 120 rPFS events to achieve 90% power to detect a hazard ratio of ≤0.55. Results: 953 patients were screened globally for AR-V7 from Sept 2015 through study closure; 73 men (8%; 95% CI 6-10%) were AR-V7+, 250 (26%) AR-V7–, and 630 (66%) had no CTCs/AR present (unevaluable). AR-V7 detection was associated with higher PSA levels ( > vs < median; P < 0.01), more bone metastases ( > 20 vs 11-20 vs 6-10 vs 0-5; P < 0.01), presence of M1 disease at diagnosis (dx) (yes vs no; P = 0.04), shorter time from dx to screening ( < vs > median; P < 0.01), higher ECOG (≥1 vs 0; P = 0.02), prior antiandrogen use (yes vs no; P < 0.01) and prior docetaxel use (yes vs no; P < 0.01). Among the AR-V7+ men, 38 were randomized (19 Gal, 19 Enz), 31 screen failed, and 4 were discontinued from screening at study halt. Baseline characteristics were balanced. On the recommendation of the DSMB, the study was closed early as it was unlikely to meet its primary endpoint. At the time of the study closure, in the Gal and Enz arms respectively, median time on therapy was 2.0 vs 2.8 mo, median time to PSA progression (PCWG1) was 3.9 vs 3.8 mo, PSA 50 response rates in evaluable patients were 2/16 (13%) and 8/19 (42%), and there were no new safety signals. Conclusions: In treatment-naïve mCRPC patients, AR-V7 detection is more common in men with higher disease burden and portends a poor prognosis. Novel study designs and alternative treatment approaches are urgently needed for AR-V7+ mCRPC patients. Clinical trial information: NCT02438007.
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AR-V7 in Peripheral Whole Blood of Patients with Castration-resistant Prostate Cancer: Association with Treatment-specific Outcome Under Abiraterone and Enzalutamide
Article
  • Aug 2017
Background: It has been demonstrated that androgen receptor splice variant 7 (AR-V7) expression in circulating tumor cells (CTCs) predicts poor treatment response in metastatic castration-resistant prostate cancer (mCRPC) patients treated with abiraterone or enzalutamide. Objective: To develop a practical and robust liquid profiling approach for direct quantification of AR-V7 in peripheral whole blood without the need for CTC capture and to determine its potential for predicting treatment response in mCRPC patients. Design, setting, and participants: Whole blood samples from a prospective biorepository of 85 mCRPC patients before treatment initiation with abiraterone (n=56) or enzalutamide (n=29) were analyzed via droplet digital polymerase chain reaction. Outcome measurements and statistical analysis: The association of AR-V7 status with prostate-specific antigen (PSA) response defined by PSA decline ≥50% and with PSA-progression-free survival (PSA-PFS), clinical PFS, and overall survival (OS) was assessed. Results and limitations: High AR-V7 expression levels in whole blood were detectable in 18% (15/85) of patients. No patient with high AR-V7 expression achieved a PSA response, and AR-V7 status was an independent predictor of PSA response in multivariable logistic regression analysis (p=0.03). High AR-V7 expression was associated with shorter PSA-PFS (median 2.4 vs 3.7 mo; p<0.001), shorter clinical PFS (median 2.7 vs 5.5 mo; p<0.001), and shorter OS (median 4.0 vs. 13.9 mo; p<0.001). On multivariable Cox regression analysis, high AR-V7 expression remained an independent predictor of shorter PSA-PFS (hazard ratio [HR] 7.0, 95% confidence interval [CI] 2.3-20.7; p<0.001), shorter clinical PFS (HR 2.3, 95% CI 1.1-4.9; p=0.02), and shorter OS (HR 3.0, 95% CI 1.4-6.3; p=0.005). Conclusions: Testing of AR-V7 mRNA levels in whole blood is a simple and promising approach to predict poor treatment outcome in mCRPC patients receiving abiraterone or enzalutamide. Patient summary: We established a method for determining AR-V7 status in whole blood. This test predicted treatment resistance in patients with metastatic castration-resistant prostate cancer undergoing treatment with abiraterone or enzalutamide. Prospective validation is needed before application to clinical practice.
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Expression of AR-V7 in Circulating Tumour Cells Does Not Preclude Response to Next Generation Androgen Deprivation Therapy in Patients with Castration Resistant Prostate Cancer
Article
  • Jul 2016
The androgen receptor splice variant AR-V7 has recently been discussed as a predictive biomarker for nonresponse to next-generation androgen deprivation therapy (ADT) in patients with castration-resistant prostate cancer. However, we recently identified one patient showing a response from abiraterone despite expression of AR-V7 in his circulating tumour cells (CTC). Therefore, we precisely assessed the response in a cohort of 21 AR-V7 positive castration-resistant prostate cancer patients who had received therapy with abiraterone or enzalutamide. We detected a subgroup of six AR-V7 positive patients showing benefit from either abiraterone or enzalutamide. Their progression free survival was 26 d (censored) to 188 d. Four patients displayed a prostate-specific antigen decrease of >50%. When analysing prior therapies, we noticed that only one of the six patients had received next-generation ADT prior to CTC collection. As a result, we conclude that AR-V7 status in CTC cannot entirely predict nonresponse to next generation ADT and AR-V7-positive patients should not be systematically denied abiraterone or enzalutamide treatment, especially as effective alternative treatment options are still limited.
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AR-V7 Transcripts in Whole Blood RNA of Patients with Metastatic Castration Resistant Prostate Cancer Correlate with Response to Abiraterone Acetate
Article
  • Jul 2016
  • J UROLOGY
Purpose: Expression of androgen receptor splice variant 7 (AR-V7) in circulating tumour cells (CTCs) has been associated with resistance to abiraterone and enzalutamide in patients with metastatic castration resistant prostate cancer (mCRPC). We used a sensitive whole blood RT-PCR assay that does not require CTC enrichment to correlate outcomes on abiraterone with whole blood expression of AR-V7 and other prostate cancer-associated transcripts. Methods: Expression of AR-V7, FOXA1, GRHL2, HOXB13, KLK2, KLK3 and TMPRSS2:ERG mRNA were assessed in 2.5 ml whole blood of 27 mCRPC patients and 33 non-cancer controls (discovery cohort). Cycle threshold (Ct) values of controls with highest gene expression were set as the threshold for a positive test. Thresholds were then applied to a validation cohort of 37 patients with mCRPC commencing abiraterone. Gene expression was correlated with PSA response rate (PSA RR) using Chi squared test; and with time to PSA progression (PSA-PFS) and overall survival (OS) using log-rank. Results: In the discovery cohort, 3/27 (11.1%) CRPC patients were AR-V7 positive vs. 4/37 (10.8%) of patients in the validation cohort. In the validation cohort, patients with an AR-V7+ test had lower PSA RR (0% vs. 42%, P=0.27) together with shorter median PSA-PFS (0.7 months vs. 4.0 months, P<0.001) and median OS (5.5 months vs. 22.1 months, P<0.001). Conclusions: RT-PCR detection of AR-V7 transcripts in whole blood was associated with inferior outcomes in patients treated with abiraterone. These results reinforce the potential utility of AR-V7 as a prognostic and predictive biomarker for mCRPC.
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