Quantitative Chemical Proteomic Profiling of the <i>in Vivo</i> Targets of Reactive Drug Metabolites

Idiosyncratic
liver toxicity represents an important problem in
drug research and pharmacotherapy. Reactive drug metabolites that
modify proteins are thought to be a principal factor in drug-induced
liver injury. Here, we describe a quantitative chemical proteomic
method to identify the targets of reactive drug metabolites in vivo. Treating mice with clickable analogues of four
representative hepatotoxic drugs, we demonstrate extensive covalent
binding that is confined primarily to the liver. Each drug exhibited
a distinct target profile that, in certain cases, showed strong enrichment
for specific metabolic pathways (e.g., lipid/sterol
pathways for troglitazone). Site-specific proteomics revealed that
acetaminophen reacts with high stoichiometry with several conserved,
functional (seleno)­cysteine residues throughout the liver proteome.
Our findings thus provide an advanced experimental framework to characterize
the proteomic reactivity of drug metabolites in vivo, revealing target profiles that may help to explain mechanisms and
identify risk factors for drug-induced liver injury.