Old Drug New Use—Amoxapine and Its Metabolites as Potent Bacterial β-Glucuronidase Inhibitors for Alleviating Cancer Drug Toxicity

Abstract

Purpose Irinotecan (CPT-11) induced diarrhea occurs frequently in cancer patients and limits its usage. Bacteria β-glucuronidase (GUS) enzymes in intestines convert the non-toxic metabolite of CPT-11, SN-38G, to toxic SN-38, and finally lead to damage of intestinal epithelial cells and diarrhea. We previously reported amoxapine as potent GUS inhibitor in vitro. To further understand the molecular mechanism of amoxapine and its potential for treatment of CPT-11 induced diarrhea, we studied the binding modes of amoxapine and its metabolites by docking and molecular dynamics simulation, and tested the in vivo efficacy on mice in combination with CPT-11. Experimental Design The binding of amoxapine, its metabolites, 7-hydroxyamoxapine and 8-hydroxyamoxapine, and a control drug loxapine with GUS was explored by computational protocols. The in vitro potencies of metabolites were measured by E. Coli GUS enzyme and cell-based assay. Low dosage daily oral administration was designed to use along with CPT-11 to treat tumor-bearing mice. Results Computational modeling results indicated that amoxapine and its metabolites bound in the active site of GUS and satisfied critical pharmacophore features: aromatic features near bacterial loop residue F365’ and hydrogen bond toward E413. Amoxapine and its metabolites were demonstrated as potent in vitro. Administration of low dosages of amoxapine with CPT-11 in mice achieved significant suppression of diarrhea and reduced tumor growth. Conclusions Amoxapine has great clinical potential to be rapidly translated to human subjects for irinotecan induced diarrhea.

Structure and Inhibition of Microbiome β-Glucuronidases Essential to the Alleviation of Cancer Drug Toxicity

“…The data presented here support the conclusion that reabsorption of reactivated SN-38 from the GI tract does not play a role in plasma levels of this compound, CPT-11, or SN-38-G. We therefore hypothesize that inhibition of GI bacterial β-glucuronidases would not negatively affect tumor response to CPT-11. Recent data from another group validates this hypothesis and demonstrates that Inhibitor 1 and other β-glucuronidase inhibitors improve tumor regression in mice receiving CPT-11 (Kong et al, 2014). Thus, by reducing the GI side effects of CPT-11, bacterial β-glucuronidase inhibitors might also improve outcomes in human patients receiving CPT-11 as part of the FOLFIRI or FOLFIRINOX regimen for colon and pancreas cancers, respectively.…”

New Role for FDA-Approved Drugs in Combating Antibiotic-Resistant Bacteria

“…The current therapeutic dosage of AXPN is recommended not to exceed 600 mg daily, with the average dosage being around 300 mg daily, placing the dosage of 3 mg/kg used in this study well below that of the therapeutic window (61). In addition to its use as an antidepressant, AXPN and its metabolites have shown efficacy for alleviating cancer drug toxicity and resistance through potent bacterial ␤-glucuronidase and P-glycoprotein transporter inhibitor activities (62)(63)(64). In regard to host responses to infection, AXPN has been shown to have membrane-stabilizing activity, which causes inhibition of a fast inward passive Na ϩ current, resulting in membrane hyperpolarization and upregulation of immune cell activity (65)(66)(67).…”

Gut microbiota modulation of chemotherapy efficacy and toxicity

“…Furthermore, the bacterial enzyme contains a 'bacterial loop' not found in the human form of the enzyme, enabling highly selective inhibitors of the bacterial enzyme to be developed, two of which blocked the active site of the E. coli β-glucuronidase, but had no effect on bovine liver glucuronidase. The quinolone antibiotic ciprofloxacin has also been shown to inhibit this enzyme, and low doses of amoxapine, a known inhibitor of bacterial β-glucuronidases, suppressed diarrhoea associated with irinotecan in a rat model 46,47 . An analysis of crystal structures of representative β-…”

“…Secondly, it also suggests that there is a role for selective antibiotic use, and that retired compounds can be repurposed for engineering the microbiota. The precedent has been set with amoxapine, a tetracyclic antidepressant, which was repurposed as a selective β-glucuronidase inhibitor for alleviating chemotoxicity 47 .…”