Analytical Validation and Clinical Qualification of a New Immunohistochemical Assay for Androgen Receptor Splice Variant-7 Protein Expression in Metastatic Castration-resistant Prostate Cancer.
The androgen receptor splice variant-7 (AR-V7) has been implicated in the development of castration-resistant prostate cancer (CRPC) and resistance to abiraterone and enzalutamide.



To develop a validated assay for detection of AR-V7 protein in tumour tissue and determine its expression and clinical significance as patients progress from hormone-sensitive prostate cancer (HSPC) to CRPC.



Following monoclonal antibody generation and validation, we retrospectively identified patients who had HSPC and CRPC tissue available for AR-V7 immunohistochemical (IHC) analysis.



Nuclear AR-V7 expression was determined using IHC H score (HS) data. The change in nuclear AR-V7 expression from HSPC to CRPC and the association between nuclear AR-V7 expression and overall survival (OS) was determined.



Nuclear AR-V7 expression was significantly lower in HSPC (median HS 50, interquartile range [IQR] 17.5-90) compared to CRPC (HS 135, IQR 80-157.5; p<0.0001), and in biopsy tissue taken before (HS 80, IQR 30-136.3) compared to after (HS 140, IQR 105-167.5; p=0.007) abiraterone or enzalutamide treatment. Lower nuclear AR-V7 expression at CRPC biopsy was associated with longer OS (hazard ratio 1.012, 95% confidence interval 1.004-1.020; p=0.003). While this monoclonal antibody primarily binds to AR-V7 in PC biopsy tissue, it may also bind to other proteins.



We provide the first evidence that nuclear AR-V7 expression increases with emerging CRPC and is prognostic for OS, unlike antibody staining for the AR N-terminal domain. These data indicate that AR-V7 is important in CRPC disease biology; agents targeting AR splice variants are needed to test this hypothesis and further improve patient outcome from CRPC.



In this study we found that levels of the protein AR-V7 were higher in patients with advanced prostate cancer. A higher level of AR-V7 identifies a group of patients who respond less well to certain prostate cancer treatments and live for a shorter period of time.
Prostate Cancer Targeted Therapy Group, Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, Sutton, UK.
Jonathan
J
Welti
Prostate Cancer Targeted Therapy Group, Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, Sutton, UK.
Daniel Nava
DN
Rodrigues
Prostate Cancer Targeted Therapy Group, Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, Sutton, UK.
Adam
A
Sharp
Department of Medicine, University of Washington School of Medicine and VAPSHCS-GRECC, Seattle, WA, USA.
Shihua
S
Sun
Prostate Cancer Targeted Therapy Group, Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, Sutton, UK; Medical Oncology Department, Hospital Universitario La Fe, Valencia, Spain.
David
D
Lorente
Prostate Cancer Targeted Therapy Group, Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, Sutton, UK.
Ruth
R
Riisnaes
Prostate Cancer Targeted Therapy Group, Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, Sutton, UK.
Ines
I
Figueiredo
Prostate Cancer Targeted Therapy Group, Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, Sutton, UK.
Zafeiris
Z
Zafeiriou
Prostate Cancer Targeted Therapy Group, Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, Sutton, UK.
Pasquale
P
Rescigno
Prostate Cancer Targeted Therapy Group, Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, Sutton, UK. Electronic address: johann.de-bono@icr.ac.uk.
Johann S
JS
de Bono
Department of Medicine, University of Washington School of Medicine and VAPSHCS-GRECC, Seattle, WA, USA. Electronic address: splymate@uw.edu.
Stephen R
SR
Plymate
D000368:Aged; D000736:Androstenes / Q000627:therapeutic use; D000911:Antibodies, Monoclonal; D000970:Antineoplastic Agents / Q000627:therapeutic use; D001549:Benzamides; D001706:Biopsy; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D019008:Drug Resistance, Neoplasm; D006801:Humans; D007150:Immunohistochemistry / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009570:Nitriles; D010669:Phenylthiohydantoin / Q000031:analogs & derivatives / Q000627:therapeutic use; D011379:Prognosis; D011467:Prostate / Q000473:pathology; D064129:Prostatic Neoplasms, Castration-Resistant / Q000188:drug therapy* / Q000378:metabolism* / Q000473:pathology; D020033:Protein Isoforms / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D011944:Receptors, Androgen / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D012189:Retrospective Studies; D015996:Survival Rate; D013997:Time Factors
D000736:Androstenes; D000911:Antibodies, Monoclonal; D000970:Antineoplastic Agents; D001549:Benzamides; D009570:Nitriles; D020033:Protein Isoforms; D011944:Receptors, Androgen; D010669:Phenylthiohydantoin; C540278:enzalutamide; C089740:abiraterone
Androgen receptor; Androgen receptor variant-7; Castration-resistant prostate cancer; Metastatic biopsy; Predictor of outcome; Treatment resistance