Cellular uptake profile of paclitaxel using liquid chromatography tandem mass spectrometry

A new method for studying cellular uptake has been developed. This method is based on selected reaction monitoring liquid chromatography tandem mass spectrometry analysis of preparations from cell culture. The limit of detection for paclitaxel was approximately 0.1 microM intracellular concentration. This method has been utilized to study the uptake of paclitaxel and an analog (BMS-190616) in normal and multidrug resistant (MDR) cell lines. Paclitaxel and the analog, that had been noted to overcome MDR in animal models, were incubated with normal cells (HCT116) and MDR cells (HCT116(VM)46) at therapeutic concentrations. Intracellular drug concentrations were assayed at intervals from 0 to 1.0 h. Results show that paclitaxel accumulates to a level 12 times greater and BMS-190616 to a level 5 times greater in the normal cells as compared to MDR cells suggesting that paclitaxel is more sensitive to MDR than the analog. Furthermore, the steady state level of BMS-190616 was 4 fold greater than paclitaxel in the MDR cell line suggesting that at least part of this compound's increased therapeutic effect can be attributed to processes of uptake and efflux at the cellular level. These data show that the method is rapid, sensitive and presents a unique advantage over traditional radioisotopic methods in that it can readily be employed on a range of analogs without any additional synthetic effort.