A Reliable and Effective UPLC-MS/MS Method for the Determination of Oprozomib in Rat Plasma

Oprozomib, a second-generation protease inhibitor that can be administered orally, is currently being assessed in clinical trials for its potential in treating hematological malignancies. In patients with relapsed refractory multiple myeloma, oprozomib has demonstrated promising efficacy both as a standalone treatment and in combination with other therapies.

The objective of this experiment was to establish and validate a highly sensitive and rapid method for quantifying oprozomib concentrations in rat plasma using ultraperformance liquid chromatography tandem mass spectrometry. Plasma samples were prepared by protein precipitation with acetonitrile and subsequently separated using gradient elution on a Waters Acquity UPLC BEH C18 column with dimensions of 2.1 mm × 50 mm and a particle size of 1.7 μm. Quantification was achieved using the selective reaction monitoring method, with specific ion transitions monitored at mass-to-charge ratio 533.18 to 199.01 for oprozomib and mass-to-charge ratio 493.03 to 112.03 for tepotinib, which served as the internal standard. The mobile phase consisted of acetonitrile and a 0.1% formic acid aqueous solution, delivered at a flow rate of 0.3 mL per minute.

The lower limit of quantification for this method was determined to be 1.0 ng/mL, and the method exhibited good linearity across the concentration range of 1.0 to 100 ng/mL. Furthermore, the precision of the method was evaluated at four different concentration levels, yielding values between 3.1% and 7.3%. The accuracy of the method ranged from -14.9% to 12.9%. Additionally, the recovery of oprozomib from rat plasma was found to be between 85.1% and 96.1%, and the observed matrix effects did not exceed 110.4%. The optimized ultraperformance liquid chromatography tandem mass spectrometry method was also successfully applied to a pharmacokinetic study in rats following a single oral administration of oprozomib at a dose of 21 mg/kg.