Deciphering Differential Gut Bacterial Drug Metabolism with Activity-Based Protein Profiling

Gut bacterial β-glucuronidases (GUS) promote the toxic side effects of therapeutics by reactivating drugs from their inactive glucuronide conjugates. It is increasingly clear that the interindividual variability of bacterial GUS-producing species in the gut microbiota contributes to differential drug responses. Indeed, the anticancer drug irinotecan exhibits variable clinical toxicity outcomes that have been linked to interindividual differences in the composition of the gut microbiota. However, identification of the specific GUS enzymes responsible for drug metabolism in the context of the complexity of the human fecal microbiota has not been achieved. Here we pinpoint the specific bacterial GUS enzymes that reactivate SN-38, the active metabolite of irinotecan, from complex human fecal microbiota samples with activity-based protein profiling (ABPP). We identify and quantify gut bacterial GUS enzymes from human feces with ABPP-enabled proteomics and then integrate this information with ex vivo kinetics to reveal the specific GUS enzymes responsible for the reactivation of SN-38. The same ABPP approach also reveals the molecular basis for differential gut bacterial GUS inhibition between human fecal samples. Taken together, this work provides an unprecedented pipeline to identify the specific bacterial GUS enzymes responsible for drug-induced GI toxicity from the complexity of human feces, which may serve as highly precise biomarkers of clinical outcomes for irinotecan and other therapeutics.