The Benefits of using Stable Labelled Glutathione for Reactive Metabolite Screening

Adverse drug reactions (ADRs) represent a significant safety concern in the development of drugs. ADRs can be classified as ‘on-target’ reactions that are predictable from the pharmacology of the drug, or ‘off-target’ reactions which are idiosyncratic. Idiosyncratic drug reactions occur rarely and unpredictably in the population. Drug metabolism acts as a detoxification mechanism, facilitating the excretion of drugs from the body. However, drugs may also be bioactivated to a reactive metabolite which, in the absence of adequate detoxification mechanisms, may bind covalently to biological macromolecules (e.g., proteins or DNA) in the body.  There is evidence to suggest reactive metabolites may play a role in the etiology of these idiosyncratic effects resulting in drug-induced toxicity.

As part of an early stage screening programme, the potential for a new chemical entity to form electrophilic reactive metabolites can be assessed in vitro using trapping agents in the presence of a drug metabolising system. The resulting adducts formed can be easily characterised by LC-MS/MS. Glutathione (GSH) is one of the most frequently used trapping agents as it can react with reactive soft electrophiles. A common approach for confirmation of GSH conjugation is detection of GSH neutral losses post-acquisition using high resolution mass spectrometry. Whilst this continues to be a useful diagnostic tool, the interpretation of the results can be somewhat subjective and therefore has the potential to lead to reporting of false positives and false negatives.

At the recent HT-ADME 2021 event, Cyprotex presented data on an alternative GSH trapping method using combined stable labelled GSH (GSH-13C2,15N) with unlabelled GSH. Due to the presence of an easily identifiable splitting pattern, this method provides advantages over the use of neutral loss method alone, and provides a robust and efficient additional diagnostic tool for detecting reactive metabolite formation.

Learn more about validation of this technique by reading our poster.

Read our poster

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