Tariquidar is a potent, specific, noncompetitive inhibitor of P-glycoprotein (P-gp) (Kd = 5.1 nM). Tariquidar inhibits the ATPase activity of P-gp, suggesting that the modulating effect is derived from the inhibition of substrate binding, inhibition of ATP hydrolysis or both. At low concentrations, Tariquidar acts selectively as an inhibitor of P-gp and as a substrate of BCRP (breast cancer resistance protein). At much higher concentrations (≥100 nM). Tariquidar acts as an inhibitor of both P-gp and BCRP. MW: 646.73. Purity ≥98% by HPLC