Multidrug resistance (MDR) is a major problem in cancer chemotherapy. The best characterized resistance mechanism is the one mediated by the over-expression of drug efflux transporters, permeability-glycoprotein (P-gp), which pump a variety of anticancer drugs out of the cells, resulting in lowered intracellular drug accumulation. A series of flavonoid dimers are developed in this invention, which are linked together by linker groups of various lengths. These flavonoid dimers are found to be efficient P-gp modulators that increase cytotoxicity of anticancer drugs in vitro and dramatically enhance their intracellular drug accumulation. It is found that the flavonoid dimers of this invention is also useful in reducing drug resistance in treating parasitic diseases.
