Abstract 5441: A rapid homogeneous immunoassay for the therapeutic drug management of imatinib in plasma using a novel selective monoclonal antibody

Abstract

Abstract Objective: Imatinib is a potent and selective inhibitor of the Bcr-Abl and KIT protein tyrosine kinases. It is widely used for treatment of Philadelphia chromosome positive chronic myeloid leukemia (Ph+ CML) and KIT-positive gastrointestinal stromal tumor (GIST). Studies have shown a significant inter-patient variability in imatinib trough concentrations up to 16 fold and a correlation between systemic exposure of the drug and clinical outcome. The current physical methods for measuring imatinib require specially trained personnel, larger sample sizes, are expensive, time consuming and not amenable for widespread use. The objective of this study is to develop an automated immunoassay that provides a rapid, simple and inexpensive method to routinely measure exposure of imatinib in patients undergoing chemotherapy. Methods: A library containing five novel and highly selective antibodies to imatinib were covalently linked to carboxyl-modified nanoparticles to develop a prototype automated homogenous assay for use on the Beckman Coulter AU®400 clinical analyzer which uses a two reagent system and 2 uL of plasma to quantitate imatinib. The degree of aggregation of nanoparticles, inversely proportional to the concentration of imatinib in a sample, was monitored at 600 nm. Total imprecision and linearity of the assay were evaluated by testing normal human plasma (NHP) pools spiked with different levels of imatinib. The background of the assay was also determined by measuring >100 NHP blank samples. Immunoassay selectivity was characterized by testing metabolites including N-desmethylimatinib and other structure-related compounds of imatinib for cross-reactivity at relevant physiological concentrations. Results: With a quantitative range from 100 to 4,000 ng/mL and instrument auto-dilution, plasma samples with imatinib concentrations up to 10,000 ng/mL could be determined using this assay. Time-to-first result was 11 minutes and 400 samples per hour could be measured using a stored calibration curve. The total imprecision of NHP pools spiked with imatinib at four concentrations across the assay range was <10% CV and the assay was linear from 100 to 4,000 ng/mL. The background of the assay was <50 ng/mL. The assay cross-reactivities to N-desmethylimatinib and other cross-reactants were determined to have insignificant impact on the quantitation of imatinib. Conclusion: This immunoassay is suitable for determining imatinib concentrations in plasma with the advantages of speed, small sample size, no sample pretreatment and application on automated instrumentation, providing a tool for optimization of imatinib plasma trough levels with pharmacokinetic-guided dosing. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5441. doi:10.1158/1538-7445.AM2011-5441