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ACS Chem Neurosci. 2011 Feb 16;2(2):82-9. doi: 10.1021/cn100078a. Epub 2010 Oct 21.

The "specific" P-glycoprotein inhibitor Tariquidar is also a substrate and an inhibitor for breast cancer resistance protein (BCRP/ABCG2).

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Molecular Imaging Branch, National Institute of Mental Health, Bethesda, Maryland, 20892, USA; Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden.


Tariquidar was developed as a specific inhibitor of the efflux transporter ABCB1. Recent positron emission tomographic brain imaging studies using [(11)C]tariquidar to measure ABCB1 (P-gp, P-glycoprotein) density in mice indicate that the inhibitor may not be as specific as previously thought. We examined its selectivity as an inhibitor and a substrate for the human transporters P-gp, breast cancer resistance protein (BCRP, ABCG2), and multidrug resistance protein 1 (MRP1, ABCC1). Our results show that at low concentrations, tariquidar acts selectively as an inhibitor of P-gp and also as a substrate of BCRP. At much higher concentrations (≥100 nM), tariquidar acts as an inhibitor of both P-gp and BCRP. Thus, the in vivo specificity of tariquidar depends on concentration and the relative density and capacity of P-gp vs BCRP.


P-glycoprotein; Positron emission tomography; blood−brain barrier; breast cancer resistance protein; drug transporters; tariquidar; transport inhibitors

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