Determination of paclitaxel in mouse plasma and brain tissue by liquid chromatography-mass spectrometry

Paclitaxel is an anticancer agent extracted from the bark of the yew tree and is widely used in chemotherapy for solid tumors, including non-small cell lung cancer and ovarian carcinoma. Most assays to measure paclitaxel in plasma require a large amount of sample (0.4-1ml) to achieve the necessary sensitivity, and are not suitable when only small sample sizes are available. To circumvent this latter limitation, we developed a sensitive liquid chromatography-mass spectrometry (LC-MS) method for the determination of paclitaxel in plasma based on the use of small sample volumes (50μl plasma). A solid phase extraction procedure was employed that enabled the eluent to be directly injected onto a reversed phase chromatographic HPLC system using positive electrospray ionization followed by mass spectrometric detection. The extraction recoveries of paclitaxel were 98 and 83% from plasma and brain tissues, respectively. The mobile phase consisted of 50% acetonitrile in 0.1% formic acid that was pumped at 0.2ml/min to yield a retention time for paclitaxel of 6.2 and 5.4min for cephalomannine, the internal standard. The method has been validated at paclitaxel plasma concentrations from 0.036 to 9.9μg/ml, and from 0.054 to 1.96μg/ml in brain homogenates. A sensitive and specific assay for paclitaxel has been developed that has the advantages of using small sample sizes, and a single extraction step without solvent evaporation.