LC–MS/MS bioanalytical method development for AMG 900: Resolution of an isobaric interference in rodent in vivo studies

AMG 900 is an orally available small molecule that is a highly potent and selective pan-aurora kinase inhibitor currently in development for the treatment of advanced human cancers. A co-eluting, isobaric interference was discovered in preliminary LC–MS/MS analyses of rodent in vivo pharmacokinetic samples during preclinical evaluation of AMG 900. The interference was identified as a major circulating N-oxide metabolite which partially converted to an [M+H−O]+ ion under the conditions of atmospheric pressure chemical ionization. A selective liquid chromatography–tandem mass spectrometry method for the simultaneous quantification of AMG 900 and its N-oxide metabolite in plasma was developed and successfully applied for the bioanalysis of discovery stage preclinical rodent pharmacokinetic studies.

► Isobaric interference found in LC–MS/MS analyses of AMG 900 in rodent plasma. ► Interference identified as APCI in-source conversion of N-oxide metabolite. ► LC–MS/MS method for quantitation of AMG 900 and N-oxide metabolite was developed. ► Method was successfully applied for quantitation of AMG 900 in preclinical studies.