Development and validation of a novel UPLC‐MS/MS method for the simultaneous quantification of mycophenolic mofetil and its major metabolites in rat plasma and liver S9 hydrolysis assay in rats

A sensitive liquid chromatography-tandem mass spectrometry method was developed and validated for the simultaneous quantification of mycophenolic mofetil (MMF) and its major metabolites, mycophenolic acid (MPA), mycophenolic acyl glucuronide (AcMPAG), and mycophenolic glucuronide (MPAG), in rat plasma. Upon administration, mycophenolic mofetil (MMF), a prodrug, undergoes extensive metabolism in the liver. Following hydrolyzation, the active metabolite MPA is produced. MPA can then be further metabolized to produce its glucuronide conjugated metabolites, AcMPAG and MPAG. This method can simultaneously determine both the parent compound and its major metabolites within biological samples. In addition, liver S9 fraction hydrolysis studies of MMF results in the production of MPA, demonstrating that the parent drug is first hydrolyzed within the liver. A novel UPLC method was developed to simultaneously quantify both compounds following S9 liver enzyme hydrolysis. A Shimadzu UHPLC system coupled to an AB Sciex QTrap 4000 mass spectrometer was used for the analysis. Separation was achieved using an Ultra Biphenyl 5µm column (100 × 2.1mm) with acetonitrile and 0.1% formic acid as the mobile phases. Analysis was performed under positive ionization mode using the multiple reaction monitoring (MRM) approach. Additionally, to determine the hydrolysis rate, different concentrations of MMF were incubated with liver S9 fraction (0.5µg/ml final concentration) for 30 mins, after which the reaction was terminated using 6% formic acid in acetonitrile. Samples were prepared and MPA concentrations were determined in the reaction system using UPLC for detection and quantification. The method was linear in the range of 9.77nM - 5000nM with correlation coefficient values > 0.99 for all components. The method has been shown to be reproducible, with intra- and inter-day accuracy and precision ±12.3% of nominal values, for all analytes. The average extraction recovery rates for MMF, MPA, AcMPAG, and MPAG were 91.3%, 97.9%, 98.4%, and 90.5%, respectively. Matrix effect was in the acceptable range (<15%). The analytes in plasma were found to be stable under bench -top, freeze-thaw, and storage (-4°C) conditions. The metabolic studies showed that mycophenolic mofetil can be rapidly hydrolyzed by rat liver S9 fraction with Vmax and Km values of 0.66±0.78 nmol/min/µg and 80.06±123.1µM respectively. This novel UPLC-MS/MS method can comprehensively evaluate and quantify the concentration of both mycophenolic mofetil and its major metabolites, mycophenolic acid, mycophenolic acyl glucuronide, and mycophenolic glucuronide in biological samples. This method can be used as a tool to further investigate and understand the extensive metabolism of mycophenolic mofetil in clinical practice.