NSC-23925 is a potent plasma membrane glycoprotein 1(Pgp1) inhibitor. It inhibits Pgp1 and reverses MDR1 (Pgp1) but does not inhibit MRP or BCRP-mediated MDR. NSC23925 directly inhibits the function of Pgp1 in a dose-dependent manner without altering the total expression level of Pgp1. NSC23925 stimulates ATPase activity of Pgp.