ABCB1 and brain cancer: While both verapamil and cyclosporin A enhanced brain delivery of several drugs in animal brain cancer and epilepsy models (Tatsuta et al., 1992; Chikhale et al., 1995; Drion et al., 1996; Cox et al., 2001), responses were small due to their low ABCB1 binding affinity and competitive transporter inhibition that was easily overcome (Cisternino et al., 2001; Kemper et al., 2003; Thomas and Coley, 2003).