Stabilization of Abiraterone in Human Plasma Using the Esterase Inhibitor Bis(4-nitrophenyl) Phosphate

Background: – Abiraterone, an active metabolite of abiraterone acetate, is used for the treatment of prostate cancer. Therapeutic drug monitoring (TDM) of abiraterone could improve treatment outcomes. However, its stability in plasma for only 4 hours at room temperature, is making the TDM implementation difficult in clinical practice. Stabilization experiments were performed in our laboratory using esterase inhibitors for the stabilization of abiraterone acetate in preclinical samples. The esterase inhibitor bis(4-nitrophenyl) phosphate (BNPP) stabilizes abiraterone acetate and abiraterone as well. Therefore, we investigated whether the esterase inhibitor BNPP could stabilize abiraterone in fresh human plasma.Methods: – BNPP at 1 and 10 mM were evaluated for its stabilizing effects on abiraterone in fresh human K₂EDTA plasma. The samples were analyzed using a validated liquid chromatography–mass spectrometry (LC-MS/MS) method. A partial validation assessed BNPP's impact on accuracy, precision, selectivity, and specificity within the fully validated LC-MS/MS method.Results: – BNPP at 10 mM, but not 1 mM, effectively prevented abiraterone degradation in fresh human K₂EDTA plasma, maintaining stability for at least 5 days at room temperature. Partial validation confirmed that all results met the acceptance criteria of the European Medicines Agency guidelines and the US Food and Drug Administration guidance.Conclusions: – We demonstrated that the esterase inhibitor BNPP effectively stabilizes abiraterone in fresh human K₂EDTA plasma. BNPP had no significant effect on the accuracy, precision, selectivity, or specificity of LC-MS/MS for abiraterone detection. The addition of BNPP to clinical abiraterone samples may be helpful in implementing abiraterone TDM in daily clinical practice.