Development of a fluorescence polarization immunoassay (FPIA) for the quantitative determination of paclitaxel.

We have developed a fluorescence polarization immunoassay (FPIA) for the quantitative determination of paclitaxel in serum, crude Taxus extracts and Erwinia taxi culture medium. To achieve this, we used an antipaclitaxel monoclonal antibody and an FITC-labeled paclitaxel. Paclitaxel was chemically modified by introducing an amino function to enable coupling with fluorescein isothiocyanate. Paclitaxel competitively inhibited the binding of the monoclonal antibody with FITC-paclitaxel causing a decrease in polarization. We were able to detect paclitaxel in a concentration as low as 2 nM. Fluorescence polarization immunoassay requires only the addition of the fluorescent probe to the antibody, followed by an incubation and measurement of polarization. Both the simplicity and the sensitivity of this method make it useful for estimating the paclitaxel content in yew tree crude extracts and culture medium of paclitaxel producing micro-organisms and a possible assay for monitoring paclitaxel level in patients under treatment.