Androgen Receptor Variant AR-V9 Is Coexpressed with AR-V7 in Prostate Cancer Metastases and Predicts Abiraterone Resistance

Abstract

Purpose Androgen receptor (AR) variant AR-V7 is a ligand-independent transcription factor that promotes prostate cancer resistance to AR-targeted therapies. Accordingly, efforts are underway to develop strategies for monitoring and inhibiting AR-V7 in castration-resistant prostate cancer (CRPC). The purpose of this study was to understand whether other AR variants may be co-expressed with AR-V7 and promote resistance to AR-targeted therapies. Experimental Design We utilized complementary short- and long-read sequencing of intact AR mRNA isoforms to characterize AR expression in CRPC models. Co-expression of AR-V7 and AR-V9 mRNA in CRPC metastases and circulating tumor cells was assessed by RNA-seq and RT-PCR, respectively. Expression of AR-V9 protein in CRPC models was evaluated with polyclonal antisera. Multivariate analysis was performed to test whether AR variant mRNA expression in metastatic tissues was associated with a 12-week progression-free survival endpoint in a prospective clinical trial of 78 CRPC-stage patients initiating therapy with the androgen synthesis inhibitor, abiraterone acetate. Results AR-V9 was frequently co-expressed with AR-V7. Both AR variant species were found to share a common 3’ terminal cryptic exon, which rendered AR-V9 susceptible to experimental manipulations that were previously-thought to target AR-V7 uniquely. AR-V9 promoted ligand-independent growth of prostate cancer cells. High AR-V9 mRNA expression in CRPC metastases was predictive of primary resistance to abiraterone acetate (HR = 4.0, 95% CI = 1.31–12.2, P = 0.02). Conclusions AR-V9 may be an important component of therapeutic resistance in CRPC.

In Situ Detection and Quantification of AR-V7, AR-FL, PSA, and KRAS Point Mutations in Circulating Tumor Cells

“…A recent publication showed that another splice variant may also play an important role in the NHT resistance mechanism. Kohli et al stated that initial annotation of the splice variant AR-V9 needs to be reevaluated, as they revealed by short-and long-read sequencing that the sequences of the 3Ј-UTR of AR-V7 and AR-V9 overlap (34 ). This implies that our AR-V7 assay may partially also detect AR-V9.…”

“…This implies that our AR-V7 assay may partially also detect AR-V9. Nevertheless, the authors also found that AR-V9-expressing cells had similar therapeutic resistance toward the NHT drug enzalutamide as the AR-V7-expressing cells (34 ). The patients we enrolled in our study were selected for establishing the in situ assay, rather than an evaluation of patient outcome.…”

Therapies Targeted to Androgen Receptor Signaling Axis in Prostate Cancer: Progress, Challenges, and Hope

“…Furthermore, several AR splice variants (AR-V1, -V7, and -V9) lacking LBD are also commonly reported ( Figure 2). Another splice variant, AR-V567es is also reported in prostate tumor [34][35][36][37]. Studies have documented that even though some AR variants lack LBD, they retain their ability to bind to DNA and promote constitutive gene transcription in the absence of androgens [38,39].…”

“…Clinical trials assessing the efficacy of cabazitaxel in patients with AR-V7-positive cases have shown promising results [65]. These variants can act independent of ligand-binding and hence confer resistance to ADT, enzalutamide, and abiraterone [36,[66][67][68][69].…”

The landscape of SNCA transcripts across synucleinopathies: New insights from long reads sequencing analysis

“…The availability of third generation long read technologies provides an unprecedented and nearly complete picture of isoform structures. However, existing long read transcript sequencing for human disease genes have used an amplicon-based approach (Treutlein et al 2014;Tseng et al 2017;Kohli 2017). While this approach has been successful in identifying complex alternative splicing in human disease genes, it is limited to the PCR primer design and will not uncover alternative start and end sites.…”