A RECEPTOR PROTEIN-BASED BIOASSAY FOR QUANTITATIVE-DETERMINATION OF PACLITAXEL

A novel receptor-based bioassay for the quantitative measurement of Ta xol was developed. The assay was based on the well-investigated and es tablished finding that Taxol, its active analogs, and active metabolit es bind reversibly to the receptor protein tubulin, a process similar to antibody and antigen interaction, The assay was performed in a comp etitive format by allowing a mixture of horseradish peroxidase-labeled Taxol and Taxol in the analyte sample to compete for the Taxol bindin g site of a polystyrene microtiter plate wall coated with purified tub ulin and subsequently measuring the tubulin-Taxol complex by determini ng the activity of the horseradish peroxidase label. Using this method , Taxol was measured very sensitively, linear range of 0.0001-1 nM, an d selectively, without interference from non-tumor-active compounds su ch as baccatin III, cephalomaninne, and 10-deacetyl taxol. The method was applied for the determination of picomolar concentrations of Taxol in human plasma.