Detecting predictive androgen receptor modifications in circulating prostate cancer cells

// Julie Steinestel 1,2,* , Manuel Luedeke 1,* , Annette Arndt 3,* , Thomas J. Schnoeller 1 , Jochen K. Lennerz 4 , Carina Wurm 1 , Christiane Maier 1 , Marcus V. Cronauer 1 , Konrad Steinestel 5 and Andres J. Schrader 1,2 1 Clinic of Urology, University Hospital Ulm, Ulm, Germany 2 Clinic of Urology, University Hospital Muenster, Muenster, Germany 3 Institute of Pathology and Molecular Pathology, Bundeswehrkrankenhaus Ulm, Ulm, Germany 4 Massachusetts General Hospital/Harvard Medical School, Boston, MA, USA 5 Gerhard-Domagk Institute of Pathology, University of Muenster, Muenster, Germany * These authors have contributed equally to the work Correspondence to: Julie Steinestel, email: julie@steinestel.com Keywords : castration-resistant prostate cancer, androgen receptor modification, splice variants, circulating tumor cells Received: March 20, 2015     Accepted: April 07, 2015     Epub: April 23, 2015     Published: June 25, 2019 Abstract Molecular modifications of the androgen receptor (AR) can cause resistance to androgen deprivation therapy (ADT) in prostate cancer patients. Since lack of representative tumor samples hinders therapy adjustments according to emerging AR-modifications, we evaluated simultaneous detection of the two most common AR modifications (AR-V7 splice variant and AR point mutations) in circulating tumor cells (CTCs). We devised a single-tube assay to detect AR-V7 splice variants and AR point mutations in CTCs using immunomagnetic cell isolation, followed by quantitative real-time PCR and DNA pyrosequencing. We prospectively investigated 47 patients with PSA progression awaiting therapy switch. Comparison of response to newly administered therapy and CTC-AR-status allowed effect size estimation. Nineteen (51%) of 37 patients with detectable CTCs carried AR-modifications. Seventeen patients carried the AR-V7 splice variant, one harbored a p.T878A point mutation and one harbored both AR-V7 and a p.H875Y mutation. We estimated a positive predictive value for response and non-response to therapy by AR status in CTCs of ~94%. Based on a conservative calculation, we estimated the effect size for molecularly-informed therapy switches for prospective clinical trial planning to ~27%. In summary, the ability to determine key resistance-mediating AR modifications in CTCs has the potential to considerably improve prostate cancer treatment.