PGP and brain neoplasm: Furthermore, to investigate the impact of efflux pumps on OMA’s PK profile and accumulation in the brain tumor tissue, we assessed the affinity of this drug for the human P-gp (ABCB1) and BCRP (ABCG2) transporters and the murine variants (Abcb1a and Abcg2) using a Transwell filter transporter assay.