PGP and neoplasm: As a result, many efforts have been made to improve tumor drug delivery by using competitive or non-competitive inhibitors, and many P-gp and BCRP inhibitors, such as valspodar [39], dexverapamil [40], tariquidar [41], biricodar [40], and elacridar, have been clinically evaluated for use as adjuvants on chemotherapy to treat non-brain tumors, as well as indirect inhibition by anti-P-gp monoclonal antibodies.