Development and qualification of an LC–MS/MS method for investigating the biological implications of micelle entrapped paclitaxel in cell culture and rats

Paclitaxel is a front-line antineoplastic drug used in chemotherapeutic modalities for treatment of various types of malignancies. However, its efficacy is limited by dose-related toxicities. In this study, we have explored two important biological aspects of entrapping paclitaxel in PEG₂₀₀₀-DSPE micelles. First, we evaluated the impact of this micellar delivery system on P-glycoprotein (P-gp)–paclitaxel interaction, and we investigated differences in plasma pharmacokinetics of free and micelle-entrapped paclitaxel. For quantification of paclitaxel, an LC–MS/MS method was developed. Paclitaxel was extracted from samples using a simple one-step protein precipitation. Chromatographic conditions included a C₁₈ column with a mobile phase consisting of 0.1% formic acid in acetonitrile–water (60:40, v/v) pumped at 1 mL/min. The lower limit of quantitation in both plasma and cell lysate was 1.0 ng/mL. The quantitative linear range was 1–1000 ng/mL. In addition, P-gp efflux studies on free and micellar paclitaxel showed the proficiency of PEG₂₀₀₀-DSPE micelles in evading P-gp-mediated efflux, thus increasing paclitaxel uptake. Furthermore, the micellar paclitaxel levels were maintained in the body for longer time as compared with taxol, which is desirable for increasing the efficacy of paclitaxel in cancer treatment.