Curcuminoids purified from turmeric powder modulate the function of human multidrug resistance protein 1 (ABCC1)

Multidrug resistance is a major cause of chemotherapy failure in cancer patients. One of the resistance mechanisms is the overexpression of drug efflux pumps such as P-glycoprotein and multidrug resistance protein 1 (MRP1, (ABCC1)). In this study, curcumin mixture and three major curcuminoids purified from turmeric ( curcumin I, II, and III) were tested for their ability to modulate the function of MRP1 using HEK293 cells stably transfected with MRP1-pcDNA3.1 and pcDNA3.1 vector alone. The IC50 of curcuminoids in these cell lines ranged from 14.5-39.3 mu M. Upon treating the cells with etoposide in the presence of 10 mu M curcuminoids, the sensitivity of etoposide was increased by several folds only in MRP1 expressing and not in pcDNA3.1-HEK 293 cells. Western blot analysis showed that the total cellular level of MRP1 protein level was not affected by treatment with 10 mu M curcuminoids for three days. The modulatory effect of curcuminoids on MRP1 function was confirmed by the inhibition of efflux of two fluorescent substrates, calcein-AM and fluo4-AM. Although all the three curcuminoids increased the accumulation of fluorescent substrates in a concentration-dependent manner, curcumin I was the most effective inhibitor. In addition, curcuminoids did not affect 8-azido[alpha-P-32] ATP binding, however they did stimulate the basal ATPase activity and inhibited the quercetin-stimulated ATP hydrolysis of MRP1 indicating that these bioflavonoids interact most likely at the substrate-binding site(s). In summary, these results demonstrate that curcuminoids effectively inhibit MRP1-mediated transport and among curcuminoids, curcumin I, a major constituent of curcumin mixture, is the best modulator.