ABCB1 and glioblastoma: Although DOX’s effectiveness in treating GBM is limited by its inability to penetrate the BBB, it has been demonstrated in vitro that DOX can effectively induce GBM cell death and that DOX-coated nanoparticles can penetrate a model of BBB made up of a monolayer of Madin–Darby canine kidney transfected with multidrug resistant protein 1 [69].