title: A new quantification method for assessing plasma concentrations of pemetrexed and its polyglutamate metabolites.
abstract: Currently no quantification method exists for potentially therapeutically relevant polyglutamate metabolites of the drug pemetrexed which is used for the treatment of lung carcinoma patients. We developed and tested an LC-MS/MS-based analytical assay that uses isotope-labeled internal standards to quantify pemetrexed and its (poly)glutamate metabolites in clinical human plasma samples of lung carcinoma patients. UHPLC chromatography and triple quadrupole mass spectrometry showed an LLOQ of 0.2nmol/L for pemetrexed and an LLOQ of 0.5nmol/L for the two metabolites (one glutamate and two glutamate moieties covalently bound to the pemetrexed molecule, for which no other quantification methods have previously been published). The recoveries for PMTX and its metabolites ranged between 30% and 67%. Precision and accuracy at a concentration of 20nmol/L for all four analytes was well below 15% CV. The precision (RSD) in the biological replicates of the separate days (within-run precision) as well as the reproducibility over several days (between-run precision), tested in the range of 5-250nmol/L, were all below 15%. Autosampler, benchtop and freeze-thaw cycle stability of the analytes was also demonstrated. To illustrate the new assay in a relevant biological context, concentrations of pemetrexed and the two metabolites were quantified in plasma samples of lung carcinoma patients treated with pemetrexed. The assay is straightforward, relatively easy to perform, and has potential for use in therapeutic drug monitoring in non-small cell lung carcinoma patients.
authors.affiliation: Department of Neurology, ErasmusMC, Rotterdam, The Netherlands.
authors.forename: Marcel P
authors.initials: MP
authors.lastname: Stoop
authors.affiliation: Department of Pulmonary Diseases, ErasmusMC, Rotterdam, The Netherlands.
authors.forename: Sabine
authors.initials: S
authors.lastname: Visser
authors.affiliation: Pepscan B.V., Lelystad, The Netherlands.
authors.forename: Evert
authors.initials: E
authors.lastname: van Dijk
authors.affiliation: Department of Pulmonary Diseases, ErasmusMC, Rotterdam, The Netherlands.
authors.forename: Joachim G J V
authors.initials: JGJV
authors.lastname: Aerts
authors.affiliation: Department of Epidemiology, ErasmusMC, Rotterdam, The Netherlands.
authors.forename: Bruno H
authors.initials: BH
authors.lastname: Stricker
authors.affiliation: Department of Neurology, ErasmusMC, Rotterdam, The Netherlands. Electronic address: t.luider@erasmusmc.nl.
authors.forename: Theo M
authors.initials: TM
authors.lastname: Luider
mesh_terms: D000368:Aged; D002289:Carcinoma, Non-Small-Cell Lung / Q000097:blood; D002853:Chromatography, Liquid / Q000379:methods; D016903:Drug Monitoring / Q000379:methods; D005971:Glutamates / Q000097:blood / Q000737:chemistry; D006801:Humans; D008175:Lung Neoplasms / Q000097:blood; D008297:Male; D008875:Middle Aged; D000068437:Pemetrexed / Q000097:blood* / Q000737:chemistry*; D010949:Plasma / Q000737:chemistry*; D011099:Polyglutamic Acid / Q000097:blood* / Q000737:chemistry*; D015203:Reproducibility of Results; D053719:Tandem Mass Spectrometry / Q000379:methods
chemical_list: D005971:Glutamates; D000068437:Pemetrexed; D011099:Polyglutamic Acid
keywords: Lung carcinoma; Mass spectrometry; Metabolites; Pemetrexed; Plasma