PGP and glioblastoma: After 72 h of co-culture with GBM cells the apical-to-basolateral permeability of DOX (a substrate of Pgp), MXR (a substrate of BCRP) and DEXT (transported when TJs are impaired) was increased compared to hCMEC/D3 monolayer alone (Fig. 1b, Supplementary Figure S2a).