Analysis of Xanomeline, a Potential Drug for Alzheimer's Disease, by Electrospray Ionization Tandem Mass Spectrometry

Abstract

Xanomeline, (3-[4-(hexyloxy)-1, 2, 5-thiadiazol-3-yl]-1, 2, 5, 6-tetrahydro-1-methylpyridine) is a selective M 1 muscarinic agonist currently under investigation for the potential symptomatic treatment of Alzheimer's disease. The characterization of the metabolites of xanomeline has been accomplished utilizing electrospray tandem mass spectrometry (ES-MS/MS). The use of ES-MS/MS has been employed in the identification of numerous oxidative metabolites of xanomeline resulting from extensive first pass metabolism. In addition, on-line liquid chromatography (LC) coupled with ES-MS/MS has been utilized to further characterize the metabolites of xanomeline after subcutaneous dosing in rats and transdermal dosing in humans. The advantages and limitations of on-line LC/ES-MS/MS for biotransformation studies are demonstrated in this application.Electrospray (ionspray) ionization coupled with tandem mass spectrometry (ES-MS/MS) has proven to be an invaluable tool in the characterization of trace level mammalian metabolites of pharmaceutical candidates (i, 2). Furthermore, the combination of on-line LC with ES-MS/MS has become the method of choice for analysis of polar, thermolabile drug candidates and their respective metabolites in complex biological matrices (3, 4). The utilization of this methodology from the initial discovery phase of a potential drug candidate through human clinical trials and beyond can enhance a drug's rapid development (5, 6). Electrospray typically generates abundant [M+H] + species and avoids the use of high temperatures which may cause thermal degradation of metabolites (particularly polar conjugates). In addition, tandem mass spectrometry provides both the selectivity and sensitivity required for detection of trace level (ng/mL) metabolites in the presence of large concentrations of endogenous components.Identification of the metabolites from a new drug substance typically follows three steps in our laboratories. Initially animal urine, plasma or microsomal incubates are examined to tentatively identify major metabolites. Second, in vivo metabolism and balance studies are performed in different animal species utilizing radiolabeled drug substance and third, human studies are performed with