Quantification of docetaxel plasma concentrations using a novel nanoparticle-based immunoassay.

Abstract

e11545 Background: Docetaxel is a commonly used antineoplastic agent of the taxoid family. The pharmacokinetic profile of docetaxel has up to 10-fold inter-patient variability in total clearance and up to 7-fold in total exposure (AUC). This variability may result in severe toxicities and poor outcomes. Docetaxel AUC was shown to be a significant predictor of time to progression (TTP) and severe adverse events in non-small cell lung cancer. A new nanoparticle-based docetaxel immunoassay provides a rapid, simple and cost-effective drug concentration measurement as compared to current chromatographic methods. Methods: Novel antibodies to docetaxel were covalently linked to nanoparticles to develop a prototype automated, homogenous immunoassay. The assay was applied to the Beckman Coulter AU400 clinical analyzer. Total imprecision and linearity of the assay were evaluated by testing normal human plasma pools spiked with different levels of docetaxel. Background was determined by measuring >200 normal human plasma samples. Results: Within a quantitation range of 50 to 1000ng/mL and using instrument auto-dilution, plasma levels of docetaxel can be measured up to 10,000ng/mL with only 2µl sample size. This test range covers clinically relevant drug concentrations and can be used to calculate the systemic exposure (AUC) of docetaxel. Time-to-first result was < 9min, and 400 samples per hour could be measured. The total imprecision of plasma pools spiked with docetaxel at four concentrations across the assay range was <6% CV and the assay was linear from 50 to 1000ng/mL. Background of the assay was found to be < 10 ng/mL. The assay cross-reactivity to docetaxel hydroxy-tertbutyl carbamate, the major metabolite of docetaxel, was 20%, and <1% for 10-deacetylbaccatin, a degradation product of docetaxel. These were shown to have no significant impact on the quantitation of docetaxel. Conclusions: This rapid immunoassay is suitable for routine measurement of plasma docetaxel concentrations with only 2ul sample size and within ten minutes and could provide a tool for optimization of docetaxel blood levels for pharmacokinetic-guided dosing.