PGP and central nervous system cancer: ABCB1/P-gp, ABCG2/BCRP, ABCC1/MRP1, ABCC4/MRP4, and ABCC5/MRP5 [14,16,104] up-regulation has been observed in glioma cells at the mRNA and/or protein level (Table 3); moreover, MRP3 de novo protein expression has also been detected in high grade gliomas (detailed below) [16,337].