Isotopic Labeling of Metabolites in Drug Discovery Applications

Abstract

Understanding the metabolic and pharmacokinetic fate of a drug in humans is a key factor in its development and registration, as well as in the elaboration of new therapeutic agents. To carry out these studies, stable isotope labeling techniques have been effectively used by drug metabolism scientists and toxicologists in order to gain better understanding of the drugs' disposition, bioavailability and toxicity in in vivo studies. Among the different analytical techniques used, mass spectrometry (MS) coupled to separation techniques has become the detection method of choice due to its high sensitivity and selectivity. In vitro quantification of metabolite levels in biofluids by MS is often difficult if a proper internal standard is not available due to the inherent problems associated with the technique (e.g. chromatographic coelutions, ion suppression, low reproducibility etc.). Stable isotope coding approaches alleviate these drawbacks and allow comparative drug metabolomics studies similarly to the differential proteomic techniques developed in the last decade. This review describes a selection of methodological improvements in the use of stable isotopes labeling in combination with MS to detect drug metabolites. In the first part of the paper, the application of labeled compounds to study the absorption, distribution, metabolism, excretion and toxicology of drugs (ADMET) in addition to the elucidation of metabolic pathways is presented. In the second part, recent developments of stable isotope coded tags for the in vitro relative metabolite quantification in biofluids are presented.

Metabolomics in infectious diseases and drug discovery

“…For example, glutathione (GSH) has been used for trapping reactive metabolites due to its natural scavenging properties, and 13 C-labelled GSH has been used in combination with MS to detect glutathionylated drug conjugates. [126][127][128] Based on the abovementioned literature, stable isotope labelling and MFA techniques are widely used to study both pathogens and hosts, as well as their interactions with drugs or drug combinations. Because advances in MS techniques provide higher resolution and wide coverages for the detecting of isotopologues of metabolites, the methodology acts as an invaluable tool with increasing importance in metabolomic studies.…”

Less Cytotoxic Protoflavones as Antiviral Agents: Protoapigenone 1′-O-isopropyl ether Shows Improved Selectivity Against the Epstein–Barr Virus Lytic Cycle

“…It is employed as a tracer in studies that aim to follow the reaction routes or as a reference for determining the influence of isotope effects on the development of a reaction during kinetic studies. Isotope labeling is a versatile technique that can be used many ways, including e.g., metabolomic studies, and the importance of deuterium in isotope labeling is increasing as new applications emerge [15,16].…”

Synthesis of [13C6]3,4-diaminobenzoic acid as a precursor for stable isotope labeled benzimidazoles

“…The synthesis of stable isotope labeled active pharmaceutical ingredients is a vital area of research for drug development. 1 Stable isotopomers are generally employed as LC-MS/MS internal standards to quantify parent API and metabolites in biological matrices. 2 Additionally, isotope-labeling experiments are often employed to determine metabolic reaction rates via measurement of kinetic isotope effects.…”