u03bcm nobiletin respectively meanwhile nobiletin at tested concentrations had no effect on the ic 50 of ptx and dox in parental non resistant a2780 cells as shown in fig3 a and 3f moreover at concentration of 4 5 u03bcm nobiletin also reduced ic 50 values of docetaxel and daunorubicin with reversal fold of 15 8 and 13 6 respectively whereas it also slightly decreased the ic 50 values of 5 fluorouracil non substrate of abcb1 with reversal fold of 6 3 as shown in table 1 in another abcb1 overexpressing non small cell human lung cancer cell line a549 t which is also ptx resistant and its parental cells a549 it was observed that similar reversal effects of nobiletin to ptx the intrinsic cytotoxicity of nobiletin in a549 and a549 t was also measured by the srb assay nobiletin have similar ic 50 for both a549 and a549 t without adding 0 94 u03bcm ptx to culture medium as shown in fig2 f notably the results showed that nobiletin at 9 u03bcm demonstrated no obvious cytotoxic effect to both cell lines and more than 90 cells were viable based on this result nobiletin was tested in the reversal assays at a maximum concentration of 9 u03bcm in fig3 e the treatment of nobiletin on a549 cell line at 0 5 1 5.