Simultaneous determination of temozolomide acid and its hexyl ester in plasma by LC-MS/MS: application to the first pharmacokinetic study of temozolomide hexyl ester in rats

Abstract

Temozolomide acid (TMZA) is a metabolite of temozolomide (TMZ) with demonstrable anticancer activity in vitro. As a part of preclinical development, its hexyl ester (TMZE) has been synthesized for a potential topical delivery system. In this study, an analytical method based on liquid chromatography tandem mass spectrometry (LC-MS/MS) for simultaneously determining TMZE and TMZA in rat plasma was developed and applied to a pharmacokinetic study after intravaginal administration of a suppository (0.3 g) containing TMZE (30 mg). The assay involved sample preparation by liquid–liquid extraction from acidified plasma followed by reversed phase chromatography and detection by electrospray positive ionization followed by multiple reaction monitoring. The lower limit of quantitation was 10 ng mL⁻¹ for both analytes. In the pharmacokinetic study, TMZE could not be detected in plasma whereas TMZA appeared rapidly and was slowly eliminated with an elimination half-life of 5.6 h. In all, the assay strategy could be further applied in the study of other TMZE and TMZA formulations for the treatment of cancer.