A randomized phase II, open-label study of sipuleucel-T with concurrent or sequential abiraterone acetate (AA) in metastatic castrate-resistant prostate cancer (mCRPC).

Abstract

114 Background: Sipuleucel-T and AA are both FDA approved for mCRPC. Given that androgen deprivation therapy is immunostimulatory, increased suppression of the androgen axis with AA could provide synergy in combination with sipuleucel-T; however, AA is given with prednisone (P), which may be immunosuppressive. In order to evaluate the impact of concurrent AA + P on product characteristics, a study of sipuleucel-T with concurrent or sequential AA + P was undertaken. Methods: Pts aged ≥18 yrs with asymptomatic or minimally symptomatic mCRPC, and ECOG PS 0/1 were randomized (1:1) to sipuleucel-T (3 infusions at approx 2-week intervals) with up to 26 weeks of AA + P (AA 1000mg QD + P 5mg BID) starting 1 day after the first sipuleucel-T infusion (concurrent arm) or at week 10 (sequential arm). The primary endpoint was cumulative CD54 upregulation (measure of antigen presenting cell activation); secondary and tertiary endpoints included CD54+cell and total nucleated cell (TNC) counts (measures of product potency), safety and efficacy. Results: 29 pts have been enrolled. 16 pts in the concurrent arm (A) and 13 pts in the sequential arm (B) have completed sipuleucel-T treatment at the time of this interim analysis (7 Sept 2012). 27/29 pts received all 3 infusions of sipuleucel-T; 2 pts (both arm A) received only 1 infusion due to insufficient TNC count (n=1) and disease progression 8 days after randomization (n=1). No significant differences in median cumulative CD54 upregulation (31.6 vs 36.6) and CD54+ count (1.9 vs 2.1 x109) were observed between arms A and B, respectively. Increased CD54 upregulation with the 2nd and 3rd treatments were indicative of a prime boost effect in both arms. Similarly, the TNC profile over time was similar for both arms. The overall incidence of adverse events (AEs) was similar in arms A (81%) and B (77%). Common all-grade AEs included muscle spasms (31% vs 23%), oral paresthesia (19% vs 31%), chills (31% vs 8%) and cough (19% vs 15%). Conclusions: These data suggest that sipuleucel-T can be manufactured during treatment with AA + P with product potency and prime boost similar to that of sipuleucel-T alone. Clinical trial information: NCT01487863.