Abiraterone acetate is administered as a prodrug to metastatic, castration-resistant prostate cancer (mCRPC) patients to prolong their survival. Abiraterone acetate is readily metabolized into potent Androgen Receptor inhibitors Abiraterone and Abiraterone D4A (D4A). Due to reported pharmacokinetic (PK) variability of Abiraterone, it is a potential candidate for therapeutic drug monitoring (TDM). Here, we developed and validated a bioanalytical method as per the US FDA guidelines for the absolute quantitation of Abiraterone and D4A in patient plasma using ultra-high performance liquid chromatography (UHPLC) coupled with high-resolution accurate mass (HRAM) mass spectrometer (MS). The quantitation was linear for the range of 0.074–509.6 ng/mL for Abiraterone and 0.075–59.9 ng/mL for D4A. Steady-state trough level plasma samples from two-time points of seventeen mCRPC patients were quantified using the assay.
We explored using this assay with paper spray ionization (PSI) and dried plasma spot (DPS) techniques. In these techniques, a small volume (6 µL in PSI and 20 µL in DPS) of patient plasma was spotted on a paper substrate and was dried for 2 hours under ambient conditions. In case of PSI technique, the samples were introduced directly into HRAM MS for quantitative analysis by applying voltage and solvent on the paper substrate. For DPS technique, the samples were processed to recover the drug and then were quantitatively analyzed by LC-MS. The range of quantitative values reported for Abiraterone and D4A in mCRPC patient samples analyzed by conventional liquid plasma method were from 2.8–26.2 ng/mL and 0.26–2.6 ng/mL respectively whereas the corresponding values from PSI technique were 4–5 times higher. The artificially high levels of quantitative values in PSI technique can be attributed to high background interfering ions. The DPS technique needs further exploration given the inherent advantage of low sample volumes involved, ease of sample collection, convenient storage, simple handling and transportation.