Mechanism of inhibition of P-glycoprotein mediated efflux by vitamin E TPGS: influence on ATPase activity and membrane fluidity.
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.
Collnot
Eva-Maria
EM
Biopharmaceutics and Pharmaceutical Technology, Saarland University, 66123 Saarbrücken, Germany, Eastman Chemical Company.
Baldes
Christiane
C
Wempe
Michael F
MF
Kappl
Reinhard
R
Hüttermann
Jürgen
J
Hyatt
John A
JA
Edgar
Kevin J
KJ
Schaefer
Ulrich F
UF
Lehr
Claus-Michael
CM
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
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