4 Activity of galeterone in castrate-resistant prostate cancer (CRPC) with C-terminal AR loss: Results from ARMOR2

Performance comparison of two androgen receptor splice variant 7 (AR-V7) detection methods

OBJECTIVES

To compare the performance of two established androgen receptor splice variant 7 (AR-V7) mRNA detection systems, as paradoxical responses to next-generation androgen-deprivation therapy in AR-V7 mRNA-positive circulating tumour cells (CTC) of patients with castration-resistant prostate cancer (CRPC) could be related to false-positive classification using detection systems with different sensitivities.

MATERIALS AND METHODS

We compared the performance of two established mRNA-based AR-V7 detection technologies using either SYBR Green or TaqMan chemistries. We assessed in vitro performance using eight genitourinary cancer cell lines and serial dilutions in three AR-V7-positive prostate cancer cell lines, as well as in 32 blood samples from patients with CRPC.

RESULTS

Both assays performed identically in the cell lines and serial dilutions showed identical diagnostic thresholds. Performance comparison in 32 clinical patient samples showed perfect concordance between the assays. In particular, both assays determined AR-V7 mRNA-positive CTCs in three patients with unexpected responses to next-generation anti-androgen therapy. Thus, technical differences between the assays can be excluded as the underlying reason for the unexpected responses to next-generation anti-androgen therapy in a subset of AR-V7 patients.

CONCLUSIONS

Irrespective of the method used, patients with AR-V7 mRNA-positive CRPC should not be systematically precluded from an otherwise safe treatment option.

Androgen receptor splice variant 7 in castration-resistant prostate cancer: Clinical considerations

Constitutively-active ligand-independent splice variants of the androgen receptor are an adaptive response by prostate cancer cells to escape androgen deprivation therapy and novel androgen receptor-directed treatments. Androgen receptor splice variant 7 is the most common splice variant detected in clinical biospecimens, and emerging data now suggest that the presence of tumoral androgen receptor splice variant 7 might be indicative of primary and acquired resistance to next-generation androgen pathway inhibitors, such as abiraterone and enzalutamide. At the same time, taxane chemotherapy might retain its efficacy regardless of androgen receptor splice variant 7 status, thus suggesting the potential for a predictive biomarker guiding treatment selection in men with metastatic castration-resistant prostate cancer. Herein, we review the preclinical data elucidating the structure and function of androgen receptor splice variant 7, we describe the existing clinical data using this biomarker in metastatic castration-resistant prostate cancer, and we highlight potential therapeutic strategies to target androgen receptor splice variant 7-expressing prostate cancer.