Abemaciclib (ABEMA) is the last CDKi approved for the treatment of breast cancer. Adverse reactions to this drug are not experienced in the same manner by the entire patient population but in case of severe toxicity dose reductions and therapy discontinuation are required, suggesting that a TDM-guided treatment could be beneficial for these patients. ABEMA is extensively metabolized by the liver. The most abundant active metabolites are M2 and M20. This CDKi is administered together with anti-estrogen drugs, such as letrozole (LETRO). The aim of this work was to develop and validate a LC-MS/MS method for the simultaneous quantification of ABEMA, M2, M20, and LETRO. The chromatographic separation of the analytes was obtained using a SIL-20AC XR auto-sampler coupled to LC-20AD UFLC Prominence XR pumps (Shimadzu, Tokyo, Japan). The chromatographic column employed was an XTerra MS C18, (3,5 µm, 125 Å, 50x2.1 mm) coupled with a Security Guard Cartridge (MS C18, 125 Å, 3.9x5 mm) provided by Waters. Detection was performed by an API 4000 QTrap (SCIEX) mass spectrometer. The presented analytical method was fully validated according to EMA and FDA guidelines on bioanalytical method validation. Linearity was confirmed on 10 independent tests (R² within 0.997-1.000) over the concentration ranges of 40-800 ng/mL for ABEMA, 10-200 ng/mL for M2 and M20, 20-400 ng/mL for LETRO. The method was applied to analyze plasma samples from patients enrolled in a clinical trial, collected at C_min. Incurred sample reanalysis was performed on a set of 30 samples, confirming the reproducibility of the analytical method.

Abemaciclib (ABEMA) 是最后一个获批用于治疗乳腺癌的 CDKi。整个患者群体对这种药物的不良反应并没有以相同的方式发生，但在严重毒性的情况下需要减少剂量和停止治疗，这表明 TDM 指导的治疗可能对这些患者有益。ABEMA 被肝脏广泛代谢。最丰富的活性代谢物是 M2 和 M20。该 CDKi 与抗雌激素药物（例如来曲唑 (LETRO)）一起给药。这项工作的目的是开发和验证一种用于同时定量 ABEMA、M2、M20 和 LETRO 的 LC-MS/MS 方法。使用与 LC-20AD UFLC Prominence XR 泵（Shimadzu，Tokyo，Japan）耦合的 SIL-20AC XR 自动进样器获得分析物的色谱分离。使用的色谱柱是 XTerra MS C18，（3.5 µm，125 Å，50x2.1 mm）和 Waters 提供的 Security Guard Cartridge（MS C18，125 Å，3.9x5 mm）。通过 API 4000 QTrap (SCIEX) 质谱仪进行检测。所提出的分析方法已根据 EMA 和 FDA 关于生物分析方法验证的指南进行了全面验证。线性在 10 次独立测试中得到确认（R²在 0.997-1.000 范围内）在 ABEMA 的 40-800 ng/mL、M2 和 M20 的 10-200 ng/mL、LETRO 的 20-400 ng/mL 的浓度范围内。该方法用于分析来自参加临床试验的患者的血浆样本，采集时间为 C _min。对一组 30 个样品进行了样品再分析，证实了分析方法的重现性。