Cell-Free DNA Alterations in the AR Enhancer and Locus Predict Resistance to AR-Directed Therapy in Patients with Metastatic Prostate Cancer

PURPOSE:Cell-free DNA (cfDNA) and circulating tumor cell (CTC) based liquid biopsies have emerged as potential tools to predict responses to androgen receptor (AR)-directed therapy in metastatic prostate cancer. However, due to complex mechanisms and incomplete understanding of genomic events involved in metastatic prostate cancer resistance, current assays (e.g. CTC AR-V7) demonstrate low sensitivity and remain underutilized. The recent discovery of AR enhancer amplification in >80% of metastatic patients and its association with disease resistance presents an opportunity to improve upon current assays. We hypothesized that tracking AR/enhancer genomic alterations in plasma cfDNA would detect resistance with high sensitivity and specificity.METHODS:We developed a targeted sequencing and analysis method as part of a new assay called Enhancer and neighboring loci of Androgen Receptor Sequencing (EnhanceAR-Seq). We applied EnhanceAR-Seq to plasma collected from 40 patients with metastatic prostate cancer treated with AR-directed therapy to monitor AR/enhancer genomic alterations and correlate these events with therapy resistance, progression-free survival (PFS) and overall survival (OS).RESULTS:EnhanceAR-Seq identified genomic alterations in the AR/enhancer locus in 45% of cases, including a 40% rate of AR enhancer amplification. Patients with AR/enhancer alterations had significantly worse PFS and OS than those without (6-month PFS: 30% vs. 71%, P=0.0002; 6-month OS: 59% vs. 100%, P=0.0015). AR/enhancer alterations in plasma cfDNA detected 18 of 23 resistant cases (78%) and outperformed the CTC AR-V7 assay which was also run on a subset of patients.CONCLUSION:cfDNA-based AR locus alterations, including of the enhancer, are strongly associated with resistance to AR-directed therapy and significantly worse survival. cfDNA analysis using EnhanceAR-Seq may enable more precise risk stratification and personalized therapeutic approaches for metastatic prostate cancer.