Identification and Quantification of Novel Major Metabolites of the Steroidal Aromatase Inhibitor, Exemestane.

Exemestane (EXE) is an aromatase inhibitor used for the prevention and treatment of estrogen receptor-positive breast cancer. Although the known major metabolic pathway for EXE is reduction to form the active 17-dihydro-EXE (17-DHE) and subsequent glucuronidation to 17-hydroxy-EXE-17-O--D-glucuronide (17-DHE-Gluc), previous studies have suggested that other major metabolites exist for exemestane. In the present study, a liquid chromatography-mass spectrometry (LC-MS) approach was used to acquire accurate mass data in MS mode, in which precursor ion and fragment ion data were obtained simultaneously to screen novel phase II EXE metabolites in urine specimens from women taking EXE.