Detection of Androgen Receptor Splice Variant 7 in Circulating Tumor Cells for Dynamic
Treatment Decision in Prostate Cancer Patients

Introduction: 

The androgen receptor (AR) is the principal driver of prostate cancer (PC) progression and the primary therapeutic target of androgen receptor signaling inhibitors (ARSIs). Androgen receptor splice variant 7 (AR-V7) is a constitutively active splice variant of AR that lacks the ligand-binding domain targeted by ARSIs, enabling persistent AR signaling despite therapy. AR-V7 has emerged as a predictive biomarker of resistance to ARSI therapy in metastatic castration-resistant prostate cancer (mCRPC), with shorter progression-free survival (PFS) and overall survival (OS) with abiraterone or enzalutamide. Detection of AR-V7 in circulating tumour cells (CTCs) is a strong predictive biomarker for identifying patients who are less likely to benefit from ARSI therapy. Dynamic treatment decisions (DTD) based on AR-V7 expression in CTCs may have significant implications for improving clinical outcomes. We evaluated AR-V7 expression in CTCs and CTC clusters from patients with prostate cancer (PC).

Methods: 

Retrospectively, 1.5 mL of peripheral blood samples from 30 cancer patients, comprising 24 patients with advanced prostate cancer and 6 negative controls (non-PC), were processed using the CDSCO-approved OncoDiscover immunomagnetic affinity platform. CTC enrichment was performed using anti-EpCAM antibody-based immunomagnetic capture, followed by identification of CK18-positive, CD45-negative, DAPI-positive cells. CTCs and CTC clusters were immunostained with antibodies against total AR and the AR-V7 splice variant and analysed using microscopy. Individual CTCs and CTC clusters were evaluated for AR and AR-V7 expression at single-CTC resolution.

Results: 

Among 23 patients with advanced PC, CTCs and/or CTC clusters were detected in 73.9% (17/23) of patients. A total of 31 CTCs were isolated, corresponding to a mean CTC distribution of 1.35 per patient, including 61.29% (19/31) individual CTCs and 38.70% (12/31) CTC clusters. AR-V7-positive CTCs and/or CTC clusters were detected in 43.47% (10/23) of patients. Overall, 35.5% (11/31) of CTCs were AR-V7-positive, comprising 6 individual CTCs and 5 CTC clusters. Among the 12 CTC clusters, 5 (41.7%) expressed AR-V7. Seven of 10 AR-V7-positive patients (70.0%) demonstrated both AR-V7-positive and AR-V7-negative CTCs and CTC clusters, highlighting interpatient and intrapatient heterogeneity.

Conclusion: 

We detected AR-V7-positive CTCs and CTC clusters in patients with PC, demonstrating heterogeneity in AR-V7 expression. Further clinical studies correlating AR-V7 status with dynamic treatment decisions and therapeutic response outcomes are warranted.