A rapid and sensitive LC-ESI-MS/MS method for determining vincristine in micro-volumes of plasma for pediatric cancer patients

Vincristine is a natural vinca alkaloid drug, which is widely used in pediatric cancer treatment with dose-dependent neurotoxicity. Thus far, little is known about the association between neurotoxicity and plasma vincristine concentration, which markedly varies among individuals. Routine therapeutic drug monitoring (TDM) can be seen as a reliable strategy to improve efficacy and reduce side effects. Therefore, a rapid, sensitive, and reproducible method is critical for the clinical implementation of TDM. In this study, micro-volume (50 μL) human plasma samples were prepared by a simple one-step protein precipitation method with acetonitrile. Chromatographic separation of vincristine and its internal standard vincristine-d₃ from background noise was achieved on a Kinetex C18 column (2.1 mm × 50 mm, 1.7 μm) with a gradient elution program at a flow rate of 0.3 mL min^-1 in 4 min. The mass spectrometric detection was performed in electrospray ionization multiple reaction monitoring mode using the ion transitions of 825.4 → 765.1 for vincristine, and 828.2 → 768.2 for vincristine-d₃, respectively. As a result, no matrix effect was observed. The lower limit of quantification was 0.5 ng mL^-1 with a precision of 14.6% and an accuracy of 97.4%. The calibration curve was linear from 0.5 to 100 ng mL^-1 (r² > 0.99, n = 8). The intra- and inter-batch precision and accuracy, recovery, and stability of the new method were all within the acceptable criteria. The method was successfully applied to monitor the vincristine concentration for six pediatric cancer patients. Arguably, such proactive TDM of vincristine may be helpful to manage the treatment for these cancer patients.