EURURO Vol. 71 No. 4

From Lab to Clinic

The Detection of Androgen Receptor Splice Variant 7 in

Plasma-derived Exosomal RNA Strongly Predicts Resistance

to Hormonal Therapy in Metastatic Prostate Cancer Patients

Marzia Del Re

a , * ,

Elisa Biasco

b ,

Stefania Crucitta

a ,

Lisa Derosa

b , y

, Eleonora Rofi

a ,

Cinzia Orlandini

b ,

Mario Miccoli

c ,

Luca Galli

b ,

Alfredo Falcone

b ,

Guido W. Jenster

d ,

Ron H. van Schaik

[4_TD$DIFF]

Romano Danesi

Clinical Pharmacology and Pharmacogenetics Unit, Department of Clinical and Experimental Medicine, University of Pisa, Pisa, Italy;

Medical Oncology

Unit, Department of Translational Research and New Technologies in Medicine, University of Pisa, Pisa, Italy;

Department of Clinical and Experimental

Medicine, University of Pisa, Pisa, Italy;

Department of Urology, Erasmus University Medical Center, Rotterdam, The Netherlands;

Department of Clinical

Chemistry, Erasmus University Medical Center, Rotterdam, The Netherlands

E U R O P E A N U R O L O G Y 7 1 ( 2 0 1 7 ) 6 8 0 – 6 8 7

available at

www.scienced irect.com

journal homepage:

www.europeanurology.com

Article info

Article history:

Accepted August 5, 2016

Associate Editor:

James Catto

Keywords:

AR-V7

Exosomes

Digital droplet PCR

Prostate cancer

Pharmacogenetics

Resistance

Hormonal therapy

Abstract

Background:

The androgen receptor splice variant 7 (AR-V7) is associated with resis-

tance to hormonal therapy in castration-resistant prostate cancer (CRPC). Due to

limitations of the methods available for AR-V7 analysis, the identification of a reliable

detection method may facilitate the use of this biomarker in clinical practice.

Objective:

To confirm AR-V7 as a predictor of resistance to hormonal therapy and

develop a new approach to assess AR-V7 by highly sensitive digital droplet polymerase

chain reaction (ddPCR) in plasma-derived exosomal RNA.

Design, setting, and participants:

Plasma samples were collected from 36 CRPC patients

before they began second-line hormonal treatment. Exosomes were isolated and RNA

extracted for analysis of AR-V7 by ddPCR.

Outcome measurements and statistical analysis:

The absolute target gene concentration

as copies per milliliter (copies/ml) was determined by ddPCR. Statistical analyses were

performed with SPSS software (IBM Corp., Armonk, NY, USA).

Results and limitations:

A total of 26 patients received abiraterone and 10 enzalutamide;

39% of patients were found to be AR-V7 positive (AR-V7

). Median progression-free

survival was significantly longer in AR-V7 negative (AR-V7 ) versus AR-V7

patients

(20 vs 3 mo;

0.001). Overall survival was significantly shorter in AR-V7

participants

at baseline compared with AR-V7 participants (8 mo vs not reached;

0.001).

Conclusions:

This study demonstrates that plasma-derived exosomal RNA is a reliable

source of AR-V7 that can be detected sensitively by ddPCR assay. We also showed that

resistance to hormonal therapy may be predicted by AR-V7, making it a clinically

relevant biomarker.

Patient summary:

We report a first study on a method for androgen receptor splice

variant 7 (AR-V7) detection in RNA extracted from cancer cell vesicles released in blood.

Results confirmed the role of AR-V7 as a predictive biomarker of resistance to hormonal

therapy. Our assay showed that vesicles are a reliable source of AR-V7 RNA and that the

method is fast, highly sensitive, and affordable.

Current affiliation: Medical Oncology, Institut Gustave Roussy, Villejuif, France.

* Corresponding author. University of Pisa, 55, Via Roma, 56126 Pisa, Italy. Tel. +39 0502218646;

Fax: +39 0502218758.

E-mail address:

marzia.delre@gmail.com

(M. Del Re).

http://dx.doi.org/10.1016/j.eururo.2016.08.012

0302-2838/