A Conformationally Gated Model of Methadone and Loperamide Transport by P-Glycoprotein

作者：Gibbs Morgan E; Wilt Laura A; Ledwitch Kaitlyn V; Roberts Arthur G^*

来源：Journal of Pharmaceutical Sciences, 2018, 107(7): 1937-1947.

DOI：10.1016/j.xphs.2018.02.019

• ATP-binding cassette transporters
• P-glycoprotein
• fluorescence
• nuclear magnetic resonance (NMR)
• opioids

P-glycoprotein (Pgp) is a multidrug resistance transporter that limits the penetration of a wide range of neurotherapeutics into the brain including opioids. The diphenylpropylamine opioids methadone and loperamide are structurally similar, but loperamide has about a 4-fold higher Pgp-mediated transport rate. In addition to these differences, they showed significant differences in their effects on Pgp-mediated adenosine triphosphate (ATP) hydrolysis. The activation of Pgp-mediated ATP hydrolysis by methadone was monophasic, whereas loperamide activation of ATP hydrolysis was biphasic implying methadone has a single binding site and loperamide has 2 binding sites on Pgp. Quenching of tryptophan fluorescence with these drugs and digoxin showed competition between the opioids and that loperamide does not compete for the digoxin-binding site. Acrylamide quenching of tryptophan fluorescence to probe Pgp conformational changes revealed that methadone- and loperamide-induced conformational changes were distinct. These results were used to develop a model for Pgp-mediated transport of methadone and loperamide where opioid binding and conformational changes are used to explain the differences in the opioid transport rates between methadone and loperamide.

• 出版日期2018-7