Abstract CT302: Pharmacokinetics (PK) and safety of ARN-509 with abiraterone acetate (AA) and prednisone (P) in patients (pts) with metastatic castration-resistant prostate cancer (mCRPC)

Abstract

Abstract Background: ARN-509 and AA target the androgen axis via different mechanisms and may have complementary activity in mCRPC. ARN-509, a potent and selective androgen receptor (AR) antagonist, inhibits AR nuclear translocation and DNA binding without significant AR agonist properties (Clegg et al. Cancer Res. 2012). AA is the prodrug of abiraterone, which directly inhibits androgen biosynthesis. No overlapping toxicities are expected for the combination. This ongoing phase Ib study evaluates the potential PK drug-drug interaction and safety of ARN-509 in combination with AA + P. Methods: Pts had progressive mCRPC and ECOG score ≤ 2. Pts received AA (1000 mg/d) + P (5 mg BID) beginning on Cycle 1 Day 1 (C1D1) with the addition of ARN-509 (240 mg/d) on C1D8 in 28-day treatment cycles until disease progression or toxicity. Serial blood samples for PK analysis were collected on C1D7 and C2D8 for abiraterone analysis and on C2D8 for ARN-509 analysis. Primary objective: evaluate effect of ARN-509 on abiraterone PK. Secondary objective: evaluate safety of ARN-509 in combination with AA + P. Results: As of November 21, 2014, 28 pts have been enrolled. At baseline, the median age was 70 years (range: 49-83); median prostate-specific antigen was 56.8 μg/L (range: 4.1-2597.0 μg/L); bone, nodal, and visceral disease were present in 24 (86%), 17 (61%), and 8 (29%) pts; and 13 (46%) pts were pretreated with docetaxel, 11 (39%) with AA, and 12 (43%) with enzalutamide. 9 pts thus far completed 1 cycle, 6 completed 2 cycles, and 4 completed 3 cycles. 26 pts are continuing therapy. 10 pts were evaluable for PK assessment and 28 pts were evaluable for safety assessment. Most drug-related adverse events (AEs) were grade 1-2, and included fatigue (n = 5), diarrhea (n = 3), dysgeusia (n = 3), vomiting (n = 4), abdominal pain (n = 2), anorexia (n = 3), dyspepsia (n = 2), rash (n = 2) and nausea (n = 3). Grade 3 drug-related AEs included hyponatremia (n = 1), fatigue (n = 1), and increased alanine aminotransferase (n = 1), and were managed by drug interruption and supportive measures. Interim data indicate a small reduction in abiraterone PK exposure when AA + P is coadministered with ARN-509. PK of ARN-509 were consistent with historical data when ARN-509 was given as monotherapy. Conclusions: This ongoing phase Ib study (NCT02123758) indicates no clinically significant PK interaction between ARN-509 and AA + P. The combination is well tolerated in pts with mCRPC; interim AE data were consistent with those seen in the AA + P phase III trials (Fizazi et al. Lancet Oncol. 2012; Ryan et al. NEJM. 2013). These preliminary results justify further evaluation of the safety and efficacy of ARN-509 in combination with AA + P for mCRPC. Citation Format: Edwin M. Posadas, Kim N. Chi, Ronald de Wit, Maja JA de Jonge, Gerhardt Attard, Terence Friedlander, Margaret Yu, Peter Hellemans, Caly Chien, Charlene Abrams, Martha Gonzalez, Géralyn C. Trudel, Vijay Chauhan, Fred Saad. Pharmacokinetics (PK) and safety of ARN-509 with abiraterone acetate (AA) and prednisone (P) in patients (pts) with metastatic castration-resistant prostate cancer (mCRPC). [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr CT302. doi:10.1158/1538-7445.AM2015-CT302