New Abiraterone Formulation Shows Equivalent Efficacy at Lower Dose for Metastatic Prostate Cancer
核心洞察
A phase II study demonstrated that a new abiraterone acetate formulation (AAT[II] (搜索)) at 300 mg daily achieved equivalent testosterone suppression compared to standard 1000 mg ZYTIGA in patients with metastatic castration-resistant prostate cancer (搜索).
The improved formulation using nanocrystal technology showed comparable PSA-50 response rates exceeding 65% on Days 56 and 84, while requiring a significantly lower daily dose and having reduced food restrictions.
AAT[II] (搜索) demonstrated an improved safety profile with fewer grade ≥3 adverse events (8.8% vs 22.9%) and serious adverse events (2.9% vs 11.4%) compared to the originator formulation.
A novel formulation of abiraterone acetate has demonstrated therapeutic equivalence to the standard dose in patients with metastatic castration-resistant prostate cancer (搜索) (CRPC (搜索)), potentially offering improved convenience and safety for patients requiring long-term treatment.
The multi-center, randomized, open-label phase II study compared abiraterone acetate tablets (II) (AAT[II] (搜索)) at 300 mg daily with the originator abiraterone acetate (ZYTIGA) at 1000 mg daily, both administered with prednisone. Sixty-nine patients were enrolled across 35 sites in China, with 35 assigned to AAT[II] and 34 to the standard formulation.
Primary Efficacy Results
The study met its primary endpoint, demonstrating equivalent pharmacodynamic effects between the two formulations. The least squares mean of serum testosterone concentration on Day 9 and/or Day 10 were 1.075 ng/dL for AAT[II] (搜索) and 1.000 ng/dL for the originator formulation. The geometric mean ratio of 1.053 (90% confidence interval, 0.998 to 1.110) fell within the predefined equivalence limits of 80.0% to 125.0%.
"AAT(II) also exhibited high testosterone inhibition rate (> 90% at all visits) and PSA-50 rate (> 65% on Days 56 and 84), which were comparable to that of OAA," the researchers reported. The testosterone suppression effect was maintained throughout the 84-day study period, with both formulations achieving mean serum testosterone concentrations below 0.5 ng/dL by Day 84.
Enhanced Formulation Technology
AAT[II] (搜索) incorporates nanocrystal technology with salcaprozate sodium (搜索) as an absorption enhancer, addressing key limitations of the original formulation. The standard abiraterone acetate requires strict fasting conditions due to significant food effects, with bioavailability increasing 5- to 10-fold with meals. In contrast, AAT[II] showed only a 2-fold increase in exposure when taken with high-fat meals.
The improved bioavailability allows for dose reduction while maintaining therapeutic effect. Previous phase I studies demonstrated that 300 mg AAT[II] (搜索) provided equivalent bioavailability to 1000 mg of the originator formulation under fasting conditions.
Safety Profile Improvements
The new formulation demonstrated superior tolerability compared to standard abiraterone. Treatment-emergent adverse events occurred in 76.5% of AAT[II] (搜索) patients versus 85.7% of those receiving the originator formulation. More notably, grade ≥3 adverse events were significantly reduced (8.8% vs 22.9%), as were serious adverse events (2.9% vs 11.4%).
"In the AAT(II) group, there were no grade ≥3 hypertension, hypokalemia, or fluid retention, which are common AEs resulting from CYP17 (搜索) inhibition," the authors noted. The improved safety profile may be attributed to the lower daily dose of abiraterone (300 mg vs 1000 mg).
Clinical Implications
The median treatment duration for patients with metastatic castration-sensitive prostate cancer (搜索) approaches 24 months, making treatment convenience and compliance critical factors. The strict dietary restrictions required for standard abiraterone can significantly impact quality of life, particularly in elderly patients who comprise a large proportion of advanced prostate cancer cases.
"Strict diet restrictions can significantly lower the convenience of drug administration, thus reducing treatment compliance and quality of life," the researchers emphasized. The reduced food effect of AAT[II] (搜索) could potentially improve patient adherence and therapeutic outcomes.
Pharmacokinetic Considerations
Despite lower systemic exposure in the AAT[II] (搜索) group, therapeutic equivalence was maintained. The steady-state minimum concentration and other pharmacokinetic parameters showed reduced abiraterone exposure compared to the standard formulation, yet clinical efficacy remained comparable.
This finding aligns with the known pharmacology of abiraterone, which has high occupancy and long-lasting affinity with the CYP17A1 receptor (搜索), enabling sustained testosterone inhibition despite lower systemic exposure. Previous studies have shown no clear dose-response relationship between abiraterone trough concentration and PSA response rates.
Study Limitations and Future Directions
The phase II study utilized surrogate markers (testosterone and PSA concentrations) rather than survival endpoints due to its limited size and follow-up duration. The 84-day treatment period precluded assessment of long-term outcomes such as overall survival and disease progression.
Additionally, the study was conducted exclusively in China with predominantly Han Chinese patients, potentially limiting generalizability to other populations. Future studies will need to evaluate long-term efficacy and safety outcomes in diverse patient populations.
The results support AAT[II] (搜索) as a promising alternative to standard abiraterone acetate, offering equivalent efficacy at a reduced dose with improved safety and convenience profiles. This advancement could represent a significant improvement in the management of metastatic CRPC (搜索), particularly for patients requiring extended treatment durations.