Ultrafast selective quantification of methotrexate in human plasma by high-throughput MALDI-isotope dilution mass spectrometry.
ABSTRACT A new analytical MS method using isotope dilution combined with MALDI-triple quadrupole MS/MS has been developed and validated for the determination of methotrexate and 7-hydroxymethotrexate in plasma. Methotrexate, methotrexate-d3, 7-hydroxymethotrexate and 7-hydroxymethotrexate-d3 were monitored by selected reaction monitoring using the transitions m/z 455.2→308.2, 458.2→311.2, 471.2→324.2 and 474.2→327.2 for methotrexate, methotrexate-d3, 7-hydroxymethotrexate and 7-hydroxymethotrexate-d3, respectively.
The LLOQ was 1 nmol/l for methotrexate and 7-hydroxymethotrexate while the limit of detection was 0.3 nmol/l for both analytes. The new developed method was cross-validated by a fluorescence polarization immunoassay and tested for its clinical feasibility by measuring plasma samples from patients suffering from acute lymphoblastic leukemia. Plasma methotrexate concentrations ranged between 66.0 and 954 nmol/l and observed 7-hydroxymethotrexate/methotrexate ratios ranged between 0.1 and 32.4, respectively.
The new method showed comparable analytical performances as the fluorescence polarization immunoassay, but analyte specificity and sensitivity of the newly developed method were significantly better.
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ABSTRACT: A new ultrafast quantitative and high-throughput mass spectrometric method using matrix-assisted laser desorption/ionization triple quadrupole tandem mass spectrometry has been developed and validated for determination of intracellular erythrocyte concentrations of the antifolate drug methotrexate (MTX) and its polyglutamate metabolites. The method consists of a solid-phase extraction of MTX and MTX-polyglutamate metabolites from deproteinized erythrocyte lysates spiked with aminopterin as internal standard. The newly developed method was validated according to the most recent FDA guidelines on linearity, recovery, within-run and between-run accuracy and precision and stability of the analytes. The low limit of quantification (LLOQ) was 10 nmol/L for all analytes while the limit of detection (LOD) determined at a signal-to-noise (S/N) ratio = 3:1 in drug- free erythrocyte lysate was on average 0.3 nmol/L. After validation, the new method was used in the measurement of intracellular erythrocyte concentrations of MTX and MTX-polyglutamate metabolites (MTXPG2 to MTXPG7) in packed human erythrocyte samples collected from patients with rheumatoid arthritis receiving low-dose oral methotrexate therapy. Mean (SD) intracellular erythrocyte concentrations observed in patient samples were 12.8 (12.6), 12.4 (9.4), 44.4 (30.0), 33.6 (35.9) and 9.4 (8.2) nmol/L for MTX to MTXPG5, respectively, in 10(6) erythrocytes. The highest observed glutamylation degree of MTX was MTXPG5, the very long chain MTX-polyglutamate metabolites MTXPG6 and MTXPG7 were not detected in the packed erythrocyte pellets collected from rheumatoid arthritis patients.Rapid Communications in Mass Spectrometry 10/2011; 25(20):3063-70. · 2.51 Impact Factor
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ABSTRACT: High-dose methotrexate (MTX) is used in the treatment of proliferative diseases such as acute lymphoblastic leukemia. Therapeutic drug monitoring of plasma MTX is important to monitor efficacy and adverse events. The authors aimed to develop a liquid chromatography, electrospray ionization, tandem mass spectrometry (LC-ESI-MS/MS)-based method to determine MTX in plasma for therapeutic drug monitoring and pharmacokinetic studies. Samples were analyzed using a Waters Acquity UPLC and Quattro Premier XE. A Waters Acquity UPLC BEH C18 column (2.1 mm × 100 mm, 1.7 μm) was used running an isocratic mobile phase of 21% methanol and 10 mM ammonium bicarbonate. The electrospray was operated in the positive ionization mode monitoring the following mass transitions: m/z 455.2 > 308.2 for MTX and m/z 458.2 > 311.2 for MTXd3. The analysis combined straightforward sample preparation, consisting of dilution and protein precipitation, with a 3-minute run time. The method was linear up to 50 μM (r > 0.99), and the coefficient of variation was <6% for intraday and <10% for interday precision. Average recovery was 99%. There were no significant matrix effects. The lower limit of quantitation, defined as the lowest concentration at which the coefficient of variation <20% and S/N > 1:10, was 5 nM. Method comparison with the Abbott TDx fluorescent polarization immunoassay (FPIA) showed excellent agreement, and a small but significant negative constant bias was detected (LC-MS/MS = 0.98 × FPIA - 7.3). CONLUSIONS: The authors developed a specific and sensitive stable isotope dilution LC-ESI-MS/MS method to monitor MTX concentrations in plasma within the clinically relevant range. The method can be easily applied in clinical laboratories because it combines straightforward sample pretreatment with LC-MS/MS.Therapeutic drug monitoring 06/2012; 34(4):432-9. · 2.43 Impact Factor