ARN-509 in men with high-risk nonmetastatic castration-resistant prostate cancer (CRPC).

Abstract

7 Background: ARN-509 is a novel second-generation anti-androgen that binds directly to the ligand-binding domain of the androgen receptor, impairing nuclear translocation and DNA binding. The Phase II portion of a multicenter Phase I/II study is evaluating the activity of ARN-509 in 3 distinct patient populations of men with CRPC (high risk non-metastatic CRPC, metastatic treatment-naïve CRPC, and progressive disease after abiraterone acetate). Preliminary results for the cohort of patients with high-risk non-metastatic CRPC are presented here. Methods: All patients had CRPC, no radiographic evidence of metastases (pelvic lymph nodes <3 cm below the iliac bifurcation were allowed), and high risk for disease progression based on PSA value ≥ 8 ng/mL within 3 months of enrollment and/or PSA doubling time ≤ 10 months. Patients received ARN-509 at the recommended Phase II dose of 240 mg/day, previously established in Phase I (Rathkopf et al, GU ASCO 2012). The primary endpoint was PSA response rate at 12 weeks according to the Prostate Cancer Working Group 2 Criteria. Secondary endpoints included safety, time to PSA progression and 1-year metastasis-free survival. PSA assessments were collected every 4 weeks and tumor scans were performed every 16 weeks. Results: Forty-seven patients were enrolled between November 2011 and May 2012. The median age was 71 years (range 51 to 88) and at baseline, patients presented with ECOG performance status 0 (77%), Gleason Score 8-10 (32%), and median PSA of 10.7 ng/mL. All patients received prior treatment with a LHRH analog with or without a first-generation anti-androgen. At a median treatment duration of 20 weeks, three patients discontinued the study. The most common treatment-related adverse events (AE) were fatigue (30%), diarrhea (28%), nausea (17%), rash (13%), and abdominal pain (11%). The incidence of Grade 3 AEs was 6.4%, and no seizures have been observed to date. The 12-week PSA response was 91% and the time to PSA progression has not been reached. Conclusions: In men with high-risk non-metastatic CRPC, ARN-509 is safe and well tolerated with promising preliminary activity based on high PSA response rates. Clinical trial information: NCT01171898.