Quercetin inhibits proliferation and drug resistance in KB/VCR oral cancer cells and enhances its sensitivity to vincristine.

Quercetin has been confirmed to possess antihistamine, anti-inflammatory, antiviral, immunomodulatory, and antioxidant properties. Herein, we evaluated their antitumor activity in vitro by using KB/VCR oral cancer cells. We found that quercetin at 25 to 100 μmol/L effectively inhibited the migration and invasion of KB/VCR cells. Quercetin at dose ranging from 25 to 100 μmol/L significantly inhibited the growth of the KB/VCR cells and at 50 μmol/L arrested cells at the G1 phase and decreased the amount of cells in the S and G2 phase. Apoptosis analysis showed that quercetin at 50 or 100 μmol/L induced apoptosis of KB/VCR cells by suppressing expression of Bax and inducing the expression of Caspase-3 and Bcl-2. Furthermore, we also confirmed that quercetin from 25 to 100 μmol/L reversed gene-encoded Pglycoprotein (P-gp)-mediated MDR in KB/VCR cells by inhibiting the expression of P-gp. For combination treatment with vincristin (0.375 μmol/L) and quercetin (50 μmol/L), the proliferation rate significantly decreased and apoptosis rate significantly increased. This study provided evidence that quercetin induced apoptosis and reversed drug resistance in oral tumor cells and may be a potential candidate for other tumors treatment.