Rapid Homogeneous Immunoassay to Quantify Gemcitabine in Plasma for Therapeutic Drug Monitoring.

BACKGROUND: Gemcitabine (2',2'-difluoro-2'-deoxycytidine) is a nucleoside analog used as a single agent and in combination regimens for the treatment of a variety of solid tumors. Several studies have shown a relationship between gemcitabine peak plasma concentration (Cmax) and hematological toxicity. An immunoassay for gemcitabine in plasma was developed and validated to facilitate therapeutic drug monitoring (TDM) by providing an economical, robust method for automated chemistry analyzers. METHODS: A monoclonal antibody was coated on nanoparticles to develop a homogenous agglutination inhibition assay. To prevent ex vivo degradation of gemcitabine in blood, tetrahydrouridine was used as a sample stabilizer. Validation was conducted for precision, recovery, cross-reactivity, and linearity on a Beckman Coulter AU480. Verification was performed on an AU5800 in a hospital laboratory. A method comparison was performed with (LC-MS/MS) liquid chromatography tandem mass spectrometry using clinical samples. Selectivity was demonstrated by testing cross-reactivity of the major metabolite, 2',2'-difluorodeoxyuridine. RESULTS: Coefficients of variation for repeatability and within-laboratory precision were <8%. The deviation between measured and assigned values was <3%. Linear range was from 0.40 to 33.02 µ/mL (1.5-125.5 µM). Correlation with validated LC-MS/MS methods was R = 0.977. The assay was specific for gemcitabine: there was no cross-reactivity to 2',2'-difluorodeoxyuridine, chemotherapeutics, concomitant, or common medications tested. Tetrahydrouridine was packaged in single-use syringes. Gemcitabine stability in whole blood was extended to 8 hours (at room temperature) and in plasma to 8 days (2-8°C). CONCLUSIONS: The assay demonstrated the selectivity, test range, precision, and linearity to perform reliable measurements of gemcitabine in plasma. The addition of stabilizer improved the sample handling. Using general clinical chemistry analyzers, gemcitabine could be measured for TDM.

An Automated Homogeneous Immunoassay for Quantitating Imatinib Concentrations in Plasma.

BACKGROUND: Imatinib pharmacokinetic variability and the relationship of trough concentrations with clinical outcomes have been extensively reported. Although physical methods to quantitate imatinib exist, they are not widely available for routine use. An automated homogenous immunoassay for imatinib has been developed, facilitating routine imatinib testing. METHODS: Imatinib-selective monoclonal antibodies, without substantial cross-reactivity to the N-desmethyl metabolite or N-desmethyl conjugates, were produced. The antibodies were conjugated to 200 nm particles to develop immunoassay reagents on the Beckman Coulter AU480 analyzer. These reagents were analytically validated using Clinical Laboratory Standards Institute protocols. Method comparison to liquid chromatography tandem mass spectrometry (LC-MS/MS) was conducted using 77 plasma samples collected from subjects receiving imatinib. RESULTS: The assay requires 4 µL of sample without pretreatment. The nonlinear calibration curve ranges from 0 to 3000 ng/mL. With automated sample dilution, concentrations of up to 9000 ng/mL can be quantitated. The AU480 produces the first result in 10 minutes and up to 400 tests per hour. Repeatability ranged from 2.0% to 6.0% coefficient of variation, and within-laboratory reproducibility ranged from 2.9% to 7.4% coefficient of variation. Standard curve stability was 2 weeks and on-board reagent stability was 6 weeks. For clinical samples with imatinib concentrations from 438 to 2691 ng/mL, method comparison with LC-MS/MS gave a slope of 0.995 with a y-intercept of 24.3 and a correlation coefficient of 0.978. CONCLUSIONS: The immunoassay is suitable for quantitating imatinib in human plasma, demonstrating good correlation with a physical method. Testing for optimal imatinib exposure can now be performed on routine clinical analyzers.

An automated nanoparticle-based homogeneous immunoassay for determining docetaxel concentrations in plasma.

BACKGROUND: Docetaxel (Taxotere) (DTX) is a widely used chemotherapy agent used in many regimens for the treatment of solid tumors, for example breast cancer, non-small cell lung cancer, gastric, prostate, and head and neck cancers. This drug meets the criteria for therapeutic dose management, in that it is associated with high pharmacokinetic variability and dose-limiting toxicity; it has a narrow therapeutic window, and there is a significant pharmacokinetic-pharmacodynamic relationship. Measures of exposure and area under the time-concentration curve have been associated with both toxicity and outcomes, making therapeutic dose management for this drug an unmet clinical need. The current methodologies for measuring DTX are based on physical methods, making the analysis less available and costly. An automated immunoassay has been developed to provide greater access to DTX dose management. METHODS: A DTX immunoassay (MyDocetaxel) has been developed using a generic nanoparticle turbidimetric method that can be used on a wide variety of automated clinical chemistry analyzers including the Beckman Coulter AU400 and AU640 instruments, which were used in this study. The assay is based on a competitive assay format using a selective DTX monoclonal antibody. Clinical Laboratory Standards Institute protocols for establishing manufacturer's claims were used to verify performance. Testing at 3 clinical laboratories was undertaken using the same protocols for laboratory validation of precision, accuracy, and linearity. Method comparison (n = 89) was done using samples collected from patients on DTX therapy. The comparative method was LC-MS/MS validated according to Food and Drug Administration guidance on bioanalytical methods. Institutional review board approval was obtained for prospective collection of samples from patients on DTX therapy. RESULTS: The assay on the AU400 uses 2 µL of sample, provides the first result in 9.0 minutes and can generate 400 determinations per hour. Internal studies established a lower limit of detection ≤25 ng/mL and a lower limit of quantitation ≤30 ng/mL. Additional studies demonstrated no interference from coadministered drugs, major metabolites, or related compounds. Linearity from 50 to 1000 ng/mL was validated. Method comparisons between laboratories and to the physical method gave slopes: 1 ± 0.5, intercepts: < 2.0 ng/mL, R > 0.99, with the range of DTX concentrations measured by the assay 31-9754 ng/mL, with a mean of 689 ng/mL. In all 3 laboratories, the coefficient of variation percentage for repeatability ranged from 0.8% to 6.2% and the within-laboratory precision ranged from 1.4% to 10.1%. CONCLUSIONS: This immunoassay is suitable for quantifying DTX in plasma with advantages of small sample size, no sample pretreatment, and the ability to be applied to a wide range of clinical analyzers. With the validation of this method, the application of DTX testing in clinical practice may gain wider acceptance for individualizing patient DTX dosing.

Development and evaluation of a nanoparticle-based immunoassay for determining paclitaxel concentrations on routine clinical analyzers.

BACKGROUND: Paclitaxel (PTX; Taxol, Abraxane) is used in many regimens for breast cancer, non-small cell lung cancer (NSCLC), and ovarian cancer. Multiple studies have demonstrated that PTX exhibits a greater than 10-fold interpatient variability of clearance rates when patients are dosed according to body surface area (BSA). Pharmacokinetic and pharmacodynamic relationships have been elucidated from BSA-based dosing. PTX is a candidate for dose management, and studies have shown that therapeutic dose management (TDM) is feasible and may provide improved outcomes for patients undergoing treatment. METHODS: A PTX immunoassay (MyPaclitaxel) has been developed, which employs a novel PTX monoclonal antibody in a nanoparticle-based turbidimetric assay in a competitive format. Precision, accuracy, and linearity were evaluated by Clinical Laboratory Standards Institute protocols at 3 laboratories on the Olympus AU400 analyzer. Method comparison was done versus a validated high-performance liquid chromatography-tandem mass spectroscopy method using samples (n = 119) collected from patients on PTX therapy. RESULTS: The assay requires 8 µL of plasma sample and can produce 400 determinations per hour. The response curve is based on a 6-point nonlinear curve fit and has a range of 0-320 ng/mL, extended to 3200 ng/mL with 10-fold autodilution. Three controls and 4 patient pools were used in precision studies. For all samples across 3 sites, repeatability coefficient of variation percentages ranged 0.9%-4.9%, and within-laboratory coefficient of variation percentages were 1.0%-4.2% with standard curve stability up to 24 days. Linearity was demonstrated over the linear range. Lower limits of detection and quantitation were 11 and 19 ng/mL, respectively. Method comparison results were analyzed by Deming regression, demonstrating a slope = 1.002 and intercept = -3.029 and an R = 0.996. The PTX samples ranged from 24 to 3164 ng/mL with a mean of 745 ng/mL. CONCLUSIONS: The analytical performance of an automated immunoassay for PTX has been validated and may serve as a useful tool for TDM of this drug.

Multicenter evaluation of a novel nanoparticle immunoassay for 5-fluorouracil on the Olympus AU400 analyzer.

BACKGROUND: 5-Fluorouracil (5-FU) is the most widely used chemotherapy drug, primarily against gastrointestinal, head and neck, and breast cancers. 5-FU has large pharmacokinetic variability resulting in unexpected toxicity or ineffective treatment. Therapeutic drug management of 5-FU minimizes toxicity and improves outcome. A nanoparticle-based immunoassay was developed to provide oncologists with a rapid, cost-effective tool for determining 5-FU plasma concentrations. METHODS: Monoclonal antibodies, bound to nanoparticles, were used to develop an immunoassay for the Olympus AU400. Assay precision, linearity, calibration stability, and limit of detection were run at multiple centers; interference, cross-reactivity, lower limit of quantitation and recovery at 1 center. Clinical samples collected from 4 cancer centers were analyzed for 5-FU concentrations by liquid chromatography-tandem mass spectrometry and compared with the immunoassay results. RESULTS: With calibrators from 0 to 1800 ng/mL 5-FU and autodilution, concentrations up to 9000 ng/mL could be determined. Time to first result was 10 minutes, and 400 samples per hour could be quantitated from a standard curve stored for >30 days. Imprecision across all laboratories was <5%, and the assay was linear upon dilution over the entire range. Cross-reactivities for dihydro-5-FU, uracil, capecitabine, and tegafur were <1%, 9.9%, 0.05%, and 0.23%, respectively. The limit of detection was 52 ng/mL with a lower limit of quantitation of 86 ng/mL. Assay results of clinical samples (93-1774 ng/mL) correlated with liquid chromatography-tandem mass spectrometry results: (R = 0.9860, slope 1.035, intercept 10.87 ng/mL). CONCLUSIONS: This novel immunoassay is suitable for quantitating 5-FU plasma concentrations with advantages of speed, small sample size, minimal sample pretreatment, and application on automated instrumentation. These advantages enable efficient therapeutic drug management of 5-FU in clinical practice.