Simultaneous determination of sutetinib and its active metabolite sutetinib N-oxide in human plasma by liquid chromatography-tandem mass spectrometry: Evaluation of plasma stability.

From the point of view of drug efficacy and safety, pharmacokinetic profiles of both parent drug and the active metabolites should be focused and evaluated. In this work, a sensitive and reliable liquid chromatographic-tandem mass spectrometric method was established for simultaneous determination of sutetinib and N-oxide metabolite (SNO) in human plasma and further applied to the pharmacokinetic study. Analytes were extracted from plasma sample (100 μL) via acetonitrile-induced protein precipitation and separated on C18 column using ammonium acetate with ammonium hydroxide and acetonitrile as the mobile phase. Positive electrospray ionization was carried out through multiple reaction monitoring with transitions of m/z 440.2→367.1 and 446.2→367.1 for sutetinib and SNO, respectively. This method was linear within the concentration range of 0.5 ~ 100 ng/mL for both analytes. The precision, accuracy, selectivity, recovery, and matrix effect of this method all met the requirements of bioanalytical guidance. Besides, plasma stability assessment demonstrated unexpected results. Sutetinib was prone to form covalent conjugates with plasma albumin in vitro. The degree of covalent binding increased with increasing temperature, resulting in a significant decrease in its plasma concentrations. However, SNO couldn't easily bind with albumin due to steric hindrance or electronegativity. Furthermore, sutetinib and SNO remained stable by keeping blood and plasma samples on wet ice. The validated method was successfully employed for the pharmacokinetic evaluation of sutetinib in patients with advanced malignant solid tumors.