An LC-MS/MS method for determination of the bromodomain inhibitor ZEN-3694 and its metabolite ZEN-3791 in human plasma.

We have developed and validated a novel LC-MS/MS method for the simultaneous quantification of ZEN-3694 and its active metabolite ZEN-3791 in human plasma after protein precipitation. Stable isotope-labeled versions were used as internal standards. Chromatographic separation was achieved on a Kinetex C18 column using 0.1% formic acid in H 2 O and 0.1% formic acid in MeOH as mobile phases. Detection was performed via positive electrospray ionization mode with multiple reaction monitoring. The assay exhibited linearity in the concentration range of 5-5000 ng/ml for both analytes. Intra- and inter-assay precision and accuracy were within ±11%. ZEN-3694 and ZEN-3791 recoveries were between 93 and 105%. This LC-MS/MS assay is an essential tool to study ZEN-3694 in an ongoing clinical trial (NCT04840589).