Etoposide (ETP), a widely used chemotherapeutic agent has an intracellular target site of action. Unfortunately, the concentration of ETP in plasma does not properly reflect the concentration in its intracellular site of action. As per our knowledge, no reported bioanalytical method is available for intracellular quantification of ETP. In this research, we developed an LC-MS/MS method to quantitate ETP in intracellular compartments of MCF-7 cells. The Abcam nuclear extraction kit was used for extracting the nuclear and cytosolic protein from MCF-7 cells. The method showed excellent linearity in the 20–1000 ng/mL range. The intra and inter-day precision (%CV) including LLOQ were found to be in the range of 2.19–16.96% and 6.71–11.21%, respectively, with an accuracy of 86.87 to 110.37% and 93.03 to 100.50%, respectively. The concentration of ETP in nuclear and cytosolic fraction was successfully quantitated using the developed method. The developed method can be applied to understand the efficacy of different formulations based on the intracellular ETP concentration in vitro. It can be considered as a model method for quantification of other similar categories of drugs in their actual intracellular site of action after required optimization in the methodology.

依托泊苷（ETP）是一种广泛使用的化学治疗剂，具有细胞内靶标作用位点。不幸的是，血浆中ETP的浓度不能正确反映其细胞内作用部位的浓度。据我们所知，尚无报道的生物分析方法可用于ETP的细胞内定量。在这项研究中，我们开发了一种LC-MS / MS方法来定量MCF-7细胞胞内区室中的ETP。Abcam核提取试剂盒用于从MCF-7细胞提取核蛋白和胞质蛋白。该方法在20–1000 ng / mL范围内显示出极好的线性。包括LLOQ在内的日内和日间精度（％CV）分别在2.19–16.96％和6.71–11.21％的范围内，精度分别为86.87至110.37％和93.03至100.50％。使用开发的方法成功定量了核和胞浆部分中ETP的浓度。所开发的方法可用于了解基于细胞内ETP浓度的不同制剂的功效体外。在方法学中需要进行优化后，可以将其视为在其实际细胞内作用部位定量其他相似类别药物的模型方法。