Optimized UPLC-MS/MS Method for the Simultaneous Quantification of Pazopanib and GSK-1268997 and Its Application to Drug-Drug Interaction Studies.

Introduction: Pazopanib, an oral vascular endothelial growth factor receptor tyrosine kinase inhibitor (VEGFR-TKI), is approved for treating advanced renal cell carcinoma (RCC). However, pazopanib can cause hypertension, often necessitating co-administration with antihypertensives like nicardipine. Given their shared metabolic pathway via cytochrome P450 3A4 (CYP3A4), this study investigated their potential drug-drug interaction (DDI). Methods: An ultra performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) method was developed for the simultaneous quantification of pazopanib and its metabolite, GSK-1268997. This method was applied to in vitro inhibition studies using rat liver microsomes (RLM) and human liver microsomes (HLM), as well as to an in vivo pharmacokinetic study in rats, to evaluate the impact of nicardipine on pazopanib metabolism. Results: The assay was linear over the concentration ranges of 20-60,000 ng/mL for pazopanib and 10-30,000 ng/mL for GSK-1268997. The intra- and inter-day precision (relative standard deviations, RSD%) for the analytes ranged from 1.5% to 14.5%, with accuracy (relative errors, RE%) within ± 10.2%. The method also demonstrated acceptable selectivity, stability, matrix effect, and recovery. In vitro, nicardipine inhibited the metabolism of pazopanib in both RLM and HLM. In rats, co-administration of nicardipine significantly increased pazopanib exposure. The AUC Discussion: The findings demonstrated that nicardipine significantly inhibited the metabolism of pazopanib both in vitro and in vivo, leading to substantially increased systemic exposure of pazopanib. This clinically significant finding suggests that, when these two drugs are used in combination, plasma drug concentrations should be closely monitored and the need for dose adjustment should be considered.