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

Abstract

<div>Abstract<p><b>Purpose:</b> Irinotecan (CPT-11) induced diarrhea occurs frequently in patients with cancer and limits its usage. Bacteria β-glucuronidase (GUS) enzymes in intestines convert the nontoxic 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 a potent GUS inhibitor <i>in vitro</i>. 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 <i>in vivo</i> efficacy on mice in combination with CPT-11.</p><p><b>Experimental Design:</b> The binding of amoxapine, its metabolites, 7-hydroxyamoxapine and 8-hydroxyamoxapine, and a control drug loxapine with GUS was explored by computational protocols. The <i>in vitro</i> potencies of metabolites were measured by <i>Escherichia coli</i> GUS enzyme and cell-based assay. Low-dosage daily oral administration was designed to use along with CPT-11 to treat tumor-bearing mice.</p><p><b>Results:</b> 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 <i>in vitro</i>. Administration of low dosages of amoxapine with CPT-11 in mice achieved significant suppression of diarrhea and reduced tumor growth.</p><p><b>Conclusions:</b> Amoxapine has great clinical potential to be rapidly translated to human subjects for irinotecan-induced diarrhea. <i>Clin Cancer Res; 20(13); 3521–30. ©2014 AACR</i>.</p></div>