The Inhibition Kinetics and Potential Anti-Migration Activity of NQO1 Inhibitory Coumarins on Cholangiocarcinoma Cells

Altered expression of a cytosolic flavoenzyme NAD(P)H:quinone oxidoreductase-1 (NQO1) has been seen in many human tumors. Its remarkable overexpression in cholangiocarcinoma (CCA; an aggressive malignancy of the biliary duct system) was associated with poor prognosis and short survival of the patients. Inhibition of NQO1 has been proposed as a potential strategy to improve the efficacy of anticancer drugs in various cancers including CCA. This study investigated novel NQO1 inhibitors and verified the mechanisms of their enzyme inhibition. Among the different chemical classes of natural NQO1 inhibitors are coumarins, flavonoids, and triterpenoids. Coumarins are a group of particularly potent NQO1 inhibitors. The mechanisms and kinetics of enzyme inhibition of coumarin, aesculetin, umbelliferone, and scopoletin using the cell lysates as a source of NQO1 enzyme best fit with an uncompetitive inhibition model. Among the NOQ1 inhibitors tested in KKU-100 CCA cells, scopoletin and umbelliferone had the strongest inhibitory effect on this enzyme, while aesculetin and coumarin barely affected intracellular NQO1. All coumarins were further tested for cytotoxicity and anti-migration activity. At modest cytotoxic doses, scopoletin and umbelliferone greatly inhibited the migration of KKU-100 cells, whereas coumarin and aesculetin barely reduced cell migration. The anti-migration effect of scopoletin was associated with decreased ratio of matrix metalloproteinase 9/tissue inhibitors of metalloproteinases 1 (MMP9/TIMP1) mRNA. These findings suggest that natural compounds with potent inhibitory effect on intracellular NQO1 have useful anti-migration effects on CCA cells. In order to prove that the potent NQO1 inhibitor, scopoletin, is clinically useful in the enhancement of CCA treatment, additional in vivo studies to elucidate the mechanism of these effects are needed.