Inhibition of β-glucuronidase by natural glucuronides of Kampo, medicines using glucuronide of SN-38 (7-ethyl-10-hydroxycamptothecin) as a substrate

Abstract

1. 7-Ethyl-10-[4-(piperidino)-1-piperidino] carbonyloxycamptothecin (CPT-11), a potent anticancer agent currently under development for clinical use, is metabolized in vivo, to 7-ethyl-10-hydroxycamptothecin (SN-38), which is subsequently conjugated to 7-ethyl-10-hydroxycamptothecin glucuronide (SN-38-glucuronide). The SN-38-glucuronide was hydrolysed by β-glucuronidase from E. coli to aglycones and glucuronic acid.

2. Four purified natural glucuronides including baicalin, wogonoside, luteolin-3′-glucuronide, and glycyrrhizin, inhibited β-glucuronidase using SN-38-glucuronide as substrate. The inhibition potencies of these natural glucuronides toward β-glucuronidase were similar to that of saccharic acid 1,4-lactone.

3. These results indicate that plant materials of Kampo (Japanese herbal) medicines containing these glucuronides could be used in vivo to decrease the enterohepatic circulation of SN-38 and possibly that of other drugs.