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 0.2 nmol/L for pemetrexed and an LLOQ of 0.5 nmol/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 20 nmol/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 5-250 nmol/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.

Additional Metadata
Keywords Lung carcinoma, Mass spectrometry, Metabolites, Pemetrexed, Plasma
Persistent URL dx.doi.org/10.1016/j.jpba.2016.04.036, hdl.handle.net/1765/81328
Journal Journal of Pharmaceutical and Biomedical Analysis
Citation
Stoop, M.P, Visser, S, van Dijk, E, Aerts, J.G.J.V, Stricker, B.H.Ch, & Luider, T.M. (2016). A new quantification method for assessing plasma concentrations of pemetrexed and its polyglutamate metabolites. Journal of Pharmaceutical and Biomedical Analysis, 128, 1–8. doi:10.1016/j.jpba.2016.04.036