A Whole Blood Assay for AR-V7 and AR^v567esin Patients with Prostate Cancer

Abstract

Purpose The majority of prostate cancer mortality can be attributed to metastatic castration-resistant prostate cancer, an advanced stage which remains incurable despite recent advances. The androgen receptor (AR) signaling axis remains active in CRPC. Recent studies suggest that the expression of an AR splice variant, AR-V7, may underlie resistance to abiraterone and enzalutamide. However, controversy exists over the optimal assay. The objective of this study is to develop a fast and sensitive assay for AR splice variants (AR-Vs) in patients. Materials and Methods Two approaches were assessed in this study. The first was based on depletion of leukocytes and the second used RNA purified directly from whole blood preserved in PAXgene tubes. Transcript expression was analyzed by quantitative RT-PCR. Results Through side-by-side comparison, we concluded that the whole-blood approach was suitable for the detection of AR-Vs. The specificity of the assay was corroborated in a cancer-free cohort. Using the PAXgene assay, samples from a cohort of 46 CRPC patients were analyzed. Overall, AR-V7 and ARv567es were detected in 67.53% and 29.87% of the samples, respectively. Statistical analysis revealed a strong association of AR-V positivity with a history of second-line hormonal therapies. Conclusions To our knowledge, this study is the first to demonstrate PAXgene-preserved whole blood can be used to obtain clinically relevant information regarding the expression of two AR-Vs. The data from a CRPC cohort support a role of AR-Vs in resistance to therapies targeting the AR ligand-binding domain.

Comparative Analysis of AR Variant AR-V567es mRNA Detection Systems Reveals Eminent Variability and Questions the Role as a Clinical Biomarker in Prostate Cancer

“…Further studies revealed its expression mostly related to late-stage mCRPC, whereas expression in primary tumor was low or even absent (8,12,14,23,29). Recently, AR-V567es expression has been detected in liquid biopsy samples of patients with prostate cancer (13,22,24). However, there have been conflicting results regarding the incidence of AR-V567es, that is, a range of patients with AR-V567espositive mCRPC from 3% (14) up to over 70% (13,15,24).…”

Niclosamide and Bicalutamide Combination Treatment Overcomes Enzalutamide- and Bicalutamide-Resistant Prostate Cancer

“…Recent studies have linked AR alternative splicing, particularly AR-V7, to the development of enzalutamide, abiraterone and docetaxel resistance (21, 29, 42). Clinical studies suggest that AR-V7 in circulating tumor cells from patients with CRPC is associated with resistance to enzalutamide and abiraterone (22, 43). Several pre-clinical studies revealed that AR variants might play certain roles in taxane resistance which could be through blocking nuclear translocation via AR.…”

Androgen receptor signaling in castration-resistant prostate cancer: a lesson in persistence

“…In a seminal study, Antonarakis and coworkers showed that men with detectable expression of AR-V7 mRNA in CTCs had reduced response rates to enzalutamide and abiraterone (Antonarakis et al 2014). More recent work has revealed that AR-V7 transcript is also detectable in whole blood (Liu et al 2016) and predicts poor response to abiraterone (Todenhofer et al 2016). The predictive value of AR-V7 is not limited to transcript expression as a recently developed CTC-based immunofluorescence assay demonstrated that nuclear expression of AR-V7 predicts worse survival after treatment with AR-targeted therapies (Scher et al 2016).…”