Evaluating bioanalytical capabilities of paper spray ionization for abiraterone drug quantification in patient plasma

Paper spray ionization (PSI) is a direct, fast and low‐cost ambient ionization technique which may have clinical utility for qualitative and quantitative analysis of therapeutic drugs and metabolites from patient specimens. We developed and validated a PSI‐mass spectrometry (PSI‐MS/MS) method according to the US‐FDA guidelines for bioanalytical studies to measure the prostate cancer drug abiraterone directly from patient plasma. The established linearity range was 3.1 – 156.8 ng/mL with a precision (%CV) and an accuracy (%) range of 0.5 – 10.7 and 93.5 – 103.2, respectively. The mean internal standard normalized matrix factor for abiraterone was just below 1 with highest %CV of 10.2 at the low level quality control. In benchmarking the performance of this assay against a published LC‐MS/MS assay we showed they were mostly equivalent, with the exception of accuracy with clinical samples. We found the quantitative values observed for abiraterone measured directly from patient plasma using PSI‐MS/MS showed positive bias. Upon investigation we concluded the increased values were due to summed quantitation of isomeric abiraterone conjugates and metabolites which are separable by LC‐MS/MS, but not with the current PSI‐MS/MS configuration. Despite demonstrating the utility of PSI‐MS/MS for rapid bioanalysis, this study also highlighted a limitation encountered with the direct analysis of abiraterone in clinical samples.