Experiments for a systematic comparison between stable-isotope-(deuterium) labeling and radio-(14C) labeling for the elucidation of the in vitro metabolic pattern of pharmaceutical drugs

• Published in: Journal of pharmaceutical and biomedical analysis Vol. 85; pp. 138 - 144
• Main Authors: Grunwald, Helge, Hargreaves, Patrick, Gebhardt, Klaus, Klauer, Dominique, Serafyn, Arnaud, Schmitt-Hoffmann, Anne, Schleimer, Michael, Schlotterbeck, Goetz, Wind, Mathias
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-11-2013
• Subjects: deuterium; Drug metabolism; drugs; ketoconazole; liver; Mass spectrometry; metabolism; metabolites; Radiolabeling; radionuclides; rats; stable isotopes; Stable-isotope labeling; Structure elucidation; Drug metabolism; Radiolabeling; Mass spectrometry; Structure elucidation; Stable-isotope labeling
• ISSN: 0731-7085; 1873-264X
• DOI: 10.1016/j.jpba.2013.07.004

A systematic comparison between two labeling approaches for the investigation of the in vitro metabolic pattern of pharmaceutical drugs was performed by examining the use of (i) radiolabeled drugs analyzed with LC–MS-offline radiodetection and (ii) stable-isotope labeled drugs, used in a defined mixture with the unlabeled drug and analyzed by LC–MS with recognition of the specific isotopic pattern. 14C was used for the radioisotope-approach and deuterium for the stable-isotope approach. Olanzapine, diclofenac and ketoconazole were chosen as model drugs, as they are commercially available in their non-, radio- and stable-isotope labeled forms. For all three model drugs, liver microsome- and hepatocyte-incubations (both from rat) were performed with various concentrations and incubation times for both, the radio- and the stable-isotope approaches. The metabolic pattern, including structure elucidation of all detected metabolites, was performed independently for all individual compounds and incubations. Subsequently, the metabolic patterns of the radio-, and the stable-isotope approaches were compared. In conclusion, all metabolites found with the radioisotope approach could also be found with the stable-isotope approach. Although the stable-isotope approach does not provide a quantitative result, it can be considered to be a highly suited analytical alternative for early in vitro metabolism investigations, especially when radiolabeled drug analogues are not yet available and quantitative results are not yet necessary.
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•A comparison between the metabolic pattern found with radio (14C)- and stable-isotope (deuterium) labeling was performed.•For the model compounds olanzapine, diclofenac and ketoconazole incubations in microsomes and hepatocytes of rat were investigated.•As conclusion all metabolites found with the radioisotope-approach were also found with the stable-isotope approach.