ABCB1 and cancer: As previously reported, the anticancer drug paclitaxel, a substrate for the ABCB1 transporter (43), inhibited the in vitro growth of the non-drug resistant, parental KB-3-1 cancer cells, whereas paclitaxel was much less potent (920-fold less) in the ABCB1 overexpressing KB-C2 cancer cells that are resistant to paclitaxel.