ABCB1 and cancer: Tariquidar is a non-marketed, third-generation ABCB1 inhibitor, which was originally developed to overcome multidrug resistance in cancer patients (Fox and Bates, 2007) and which has been re-purposed to inhibit ABCB1 at the BBB in an experimental setting (Bauer et al., 2012; Bauer et al., 2015; Bauer et al., 2017).