Targeting Regorafenib-Induced Toxicity through Inhibition of Gut Microbial β-Glucuronidases

Area of Science:

• Pharmacology
• Microbiology
• Biochemistry

Background:

• Regorafenib (Stivarga) is a kinase inhibitor for metastatic colorectal cancer, hepatocellular carcinomas, and gastrointestinal stromal tumors.
• Diarrhea is a common adverse effect of regorafenib, potentially caused by gut microbial reactivation of regorafenib-glucuronide.
• Understanding this reactivation is crucial for mitigating regorafenib toxicity.

Purpose of the Study:

• To elucidate the molecular mechanisms of regorafenib-glucuronide processing by human intestinal beta-glucuronidase (GUS) enzymes.
• To identify specific gut microbial GUS enzymes involved in regorafenib reactivation.
• To explore potential inhibition strategies for these enzymes.

Main Methods:

• Screening of 31 unique gut microbial GUS enzymes for regorafenib-glucuronide processing activity.
• Utilizing crystal structures to identify key molecular features of active GUS enzymes.
• Conducting a pilot screen for inhibitors, including FDA-approved drugs and novel analogs.

Main Results:

• Only four out of 31 screened microbial GUS enzymes processed regorafenib-glucuronide.
• Specific molecular features responsible for regorafenib-glucuronide processing activity were identified.
• Raloxifene was identified as an inhibitor, with novel analogs showing enhanced potency in vitro and ex vivo.

Conclusions:

• Regorafenib reactivation in the GI tract is exclusively catalyzed by specific gut microbial GUS enzymes.
• These identified GUS enzymes are potential targets for therapeutic inhibition.
• Targeted inhibition offers a promising strategy to improve clinical outcomes and reduce regorafenib-induced toxicity.