ABCB1 and liver cancer: The synergistic effect has been clearly shown in an in vivo mouse model of chemoresistant liver cancer in which the presence of GTPs markedly enhanced the anticancer activity of doxorubicin (DOX) by inhibiting P-glycoprotein (P-gp) efflux pump activity and enabling intracellular DOX to accumulate and effectively kill the liver cancer cells (11).