SELECTIVE MODULATION OF THE MICROBIOME: EFFORTS TOWARD A NEW PARADIGM IN HUMAN THERAPEUTICS

Drug-induced toxicity, side effects of certain therapeutics, is often more toxic than the original disease and limits the potential for dose intensification. The dose-limiting side effect of the mainstay anticancer therapeutic CPT-11, which is a prodrug for its active metabolite SN-38, is delayed onset diarrhea. Detoxified in the liver through conjugation with glucuronic acid, SN-38-glucuronide acts as a substrate for an enzyme, β-glucuronidase, expressed by the symbiotic microbiota naturally populating the mammalian gastrointestinal tract. Thus, bacterial β-glucuronidase inhibitors should alleviate the delayed onset diarrhea as a side effect of CPT-11. Initial high-throughput screen hits were established as potent inhibitors in biochemical assays against a range of β-glucuronidase enzymes from GI-associated bacterial species and as non-toxic to mammalian or bacterial cells. Importantly, they proved to be selective for the bacterial enzyme relative to the mammalian orthologue and proved effective in preclinical models of toxicity. X-ray crystallographic analysis of several inhibitors in complex with the bacterial enzymes highlighted structural features critical for inhibition. Exploiting these features, we were able to synthesize analogues from original screening hits that have since displayed improved in vitro and in vivo properties. These inhibitors are effective in models of drug-induced toxicity beyond CPT-11, including NSAIDinduced enteropathy in the small intestine. This work is designed to ultimately create a clinical co-therapy for drugs that are limited by their toxic GI side effects caused by bacterial β-glucuronidase. This appears to be a new paradigm of drug therapy – inhibition of a bacterial enzyme for therapeutic gain without harming the microbial symbiotes essential for human health.Doctor of Philosoph