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Structural identification of imatinib cyanide adducts by mass spectrometry and elucidation of bioactivation pathway
Austin C Li1, Erya Yu, Steven C Ring
1Drug Metabolism and Pharmacokinetics, Teva Branded Pharmaceutical Products R&D, Inc., 145 Brandywine Parkway, West Chester, PA, 19380, USA.
Rationale:
Recent publications have reported that imatinib forms cyanide and methoxylamine adducts in vitro but without detail structural identification. The current work reports the identification of seven cyanide adducts that elucidate the bioactivation pathways and may provide hints for observed clinical adverse effects of the drug.
Methods:
Imatinib was incubated with human liver microsomal proteins in the presence of a NADPH-regeneration system and the trapping agents reduced GSH, potassium cyanide and methoxylamine. Samples were analyzed by high-performance liquid chromatography (HPLC) coupled with a LTQ-Orbitrap data collection system. Chemical structures were determined and/or postulated based on data-dependent high-resolution tandem mass spectrometric (MS(n)) exact mass measurements in both positive and negative scan modes, as well as in combination with hydrogen-deuterium exchange (HDX).
Results:
GSH and methoxylamine conjugates were either not detected or were in insufficient quantities for characterization. However, seven cyanide conjugates were identified, indicating that the piperazine and p-toluidine partial structures in imatinib can become bioactivated and subsequently trapped by the nucleophile cyanide ion. The reactive intermediates were postulated as imine and imine-carbonyl conjugate (α,β-unsaturated) structures on the piperazine ring, and imine-methide on the p-toluidine partial structure.
Conclusions:
Chemical structures of seven cyanide adducts of imatinib have been identified or proposed based on high-resolution MS/MS data. Mechanisms for the formation of the conjugates were also proposed. The findings may help to understand the mechanism of hepatotoxicity of imatinib in humans.
Insights
Researchers identified seven cyanide adducts of imatinib, revealing potential bioactivation pathways. These findings may explain imatinib
Area of Science:
- Pharmacology
- Medicinal Chemistry
- Biochemistry
Background:
- Imatinib is a crucial drug for treating certain cancers, but its clinical adverse effects, particularly hepatotoxicity, are a concern.
- Previous studies suggested imatinib forms adducts with cyanide and methoxylamine in vitro, but detailed structural information was lacking.
Purpose of the Study:
- To identify and structurally characterize imatinib adducts formed in vitro.
- To elucidate the bioactivation pathways of imatinib.
- To provide insights into the mechanisms underlying imatinib-induced hepatotoxicity.
Main Methods:
- Incubation of imatinib with human liver microsomes and NADPH-regeneration system.
- Use of trapping agents: reduced glutathione (GSH), potassium cyanide, and methoxylamine.
- Analysis via high-performance liquid chromatography (HPLC) coupled with LTQ-Orbitrap mass spectrometry (MS).
- Structural determination using high-resolution MS/MS and hydrogen-deuterium exchange (HDX).
Main Results:
- Seven cyanide adducts of imatinib were identified and structurally characterized.
- GSH and methoxylamine conjugates were not detected or were present in insufficient quantities.
- Bioactivation occurred at the piperazine and p-toluidine moieties of imatinib, forming reactive intermediates.
- Postulated intermediates include imine, imine-carbonyl (α,β-unsaturated), and imine-methide structures.
Conclusions:
- The study successfully identified and proposed structures for seven cyanide adducts of imatinib.
- Proposed mechanisms for the formation of these adducts shed light on imatinib bioactivation.
- These findings contribute to understanding the molecular basis of imatinib-related hepatotoxicity.
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