PGP and glioblastoma: Finally, as a proof-of-concept, we designed a BBB-brain chip to contain a BBB-in-a-CUBE and a Glioblastoma-in-a-CUBE model to demonstrate, as reported by Tivnan et al.29, that the BBB blocking of the PGP substrate drug Vincristine into the brain can be overcome with the addition of PGP inhibitor Reversan.