A novel abiraterone acetate oral suspension for patients with metastatic prostate cancer: An open-label, phase 3, randomized trial

5052 Background: Abiraterone acetate (AA) is a first-line oral hormone therapy for metastatic prostate cancer (mPC), but the licensed formulation is limited by large tablet size, requirement to take on an empty stomach, and pharmacokinetic variability. TAVT-45, a novel formulation of AA granules for oral suspension, offers improved oral bioavailability (allowing dose reduction), decreased food effect, and may provide an option for the ~20-30% of patients with dysphagia. This Phase 3, open-label global study (NCT04887506) aimed to establish therapeutic equivalence between TAVT-45 granules and reference AA tablets (R-AA). Methods: Patients with castrate-resistant or castrate-sensitive mPC (mCRPC or mCSPC) were randomized 1:1 to receive TAVT-45 (1 sachet of AA granules [250 mg] in water or juice, twice daily) or R-AA tablets (2 x 500 mg once daily ≥1 h before or ≥2 h after food), plus prednisone (5 mg once [mCSPC] or twice [mCRPC] daily) for 84 days. Efficacy (serum testosterone and prostate-specific antigen [PSA]) and safety were assessed. Average serum testosterone concentrations on Days 9 & 10 (primary endpoint, analyzed via analysis of covariance) were compared to show therapeutic equivalence. The key secondary endpoint was PSA-50 response (patients with ≥50% decrease in PSA from baseline at any time). mCRPC was the primary analysis population. Preliminary results are presented. Results: Of 107 randomized patients, 103 received TAVT-45 (n=54) or R-AA (n=49). The TAVT-45 and R-AA groups were well matched (mean [SD] age: 74.5 [8.45] and 74.9 [8.40] years; mCRPC: 61.1% and 61.2%). In mCRPC, serum testosterone concentrations fell rapidly from mean (SD) baseline of 9.7 (5.19) for TAVT-45 and 10.6 (7.32) ng/dL for R-AA, with all <1 ng/dL by Day 9. Therapeutic equivalence between TAVT-45 and R-AA at Days 9 & 10 was also shown in the full study population: Days 9 & 10 average rounded-up least-squares mean serum testosterone levels were comparable (TAVT-45 [n=52]: 1.004 ng/dL; R-AA [n=47]: 1.015 ng/dL), and the geometric mean ratio between groups was 0.990 (90% CI: 0.978-1.002), with the 90% CI falling within 80.0–125.0% equivalence limits. No statistical difference between TAVT-45 vs R-AA was demonstrated for PSA-50 (mCRPC 85% vs 70%; mCSPC 90% vs 95%). The frequency of treatment-emergent adverse events (TEAEs) was similar between groups; most were mild or moderate. Serious TEAEs occurred in 5 TAVT-45 and 3 R-AA patients. There were two deaths in treated patients due to cardiorespiratory arrest (TAVT-45) and prostate cancer (R-AA); neither was considered related to study drug. Conclusions: This Phase 3 study demonstrates that TAVT-45, a novel AA formulation with improved bioavailability, yields similar testosterone/PSA responses and a comparable safety profile to R-AA, and as an oral solution, may be suitable for mPC patients with dysphagia. Clinical trial information: NCT04887506 .