title: Mechanism of inhibition of P-glycoprotein mediated efflux by vitamin E TPGS: influence on ATPase activity and membrane fluidity.
abstract: Efflux pump (e.g., P-gp, MRP1, and BCRP) inhibition has been recognized as a strategy to overcome multi-drug resistance and improve drug bioavailability. Besides small-molecule inhibitors, surfactants such as Tween 80, Cremophor EL, several Pluronics, and Vitamin E TPGS (TPGS 1000) are known to modulate efflux pump activity. Competitive inhibition of substrate binding, alteration of membrane fluidity, and inhibition of efflux pump ATPase have been proposed as possible mechanisms. Focusing on TPGS 1000, the aim of our study was to unravel the inhibitory mechanism by comparing the results of inhibition experiments in a Caco-2 transport assay with data from electron spin resonance (ESR) and from ATPase activity studies. ESR results, on Caco-2 cells using 5-doxyl stearic acid (5-SA) as a spin probe, ruled out cell membrane fluidization as a major contributor; change of membrane fluidity was only observed at surfactant concentrations 100 times higher than those needed to achieve full efflux inhibition. Concurrently, TPGS 1000 inhibited substrate induced ATPase activity without inducing significant ATPase activity on its own. By investigating TPGS analogues that varied by their PEG chain length, and/or possessed a modified hydrophobic core, transport studies revealed that modulation of ATPase activity correlated with inhibitory potential for P-gp mediated efflux. Hence, these results indicate that ATPase inhibition is an essential factor in the inhibitory mechanism of TPGS 1000 on cellular efflux pumps.
authors: Biopharmaceutics and Pharmaceutical Technology, Saarland University, 66123 Saarbrücken, Germany, Eastman Chemical Company.
authors: Eva-Maria
authors: EM
authors: Collnot
authors: Christiane
authors: C
authors: Baldes
authors: Michael F
authors: MF
authors: Wempe
authors: Reinhard
authors: R
authors: Kappl
authors: Jürgen
authors: J
authors: Hüttermann
authors: John A
authors: JA
authors: Hyatt
authors: Kevin J
authors: KJ
authors: Edgar
authors: Ulrich F
authors: UF
authors: Schaefer
authors: Claus-Michael
authors: CM
authors: Lehr
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism*; D000251:Adenosine Triphosphatases / Q000378:metabolism*; D001693:Biological Transport, Active / Q000187:drug effects; D018938:Caco-2 Cells; D002626:Chemistry, Pharmaceutical; D004337:Drug Carriers / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy; D006801:Humans; D008560:Membrane Fluidity / Q000187:drug effects; D015394:Molecular Structure; D011092:Polyethylene Glycols / Q000737:chemistry / Q000494:pharmacology; D013501:Surface-Active Agents / Q000737:chemistry; D014810:Vitamin E / Q000031:analogs & derivatives* / Q000737:chemistry / Q000494:pharmacology
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D004337:Drug Carriers; D013501:Surface-Active Agents; D014810:Vitamin E; D011092:Polyethylene Glycols; D000251:Adenosine Triphosphatases; C014225:tocophersolan