Vitamin E TPGS P-Glycoprotein Inhibition Mechanism: Influence on Conformational Flexibility, Intracellular ATP Levels, and Role of Time and Site of Access

Abstract

Previous work conducted in our laboratories established the notion that TPGS 1000 (d-alpha-tocopheryl polyethylene glycol 1000 succinate), a nonionic surfactant, modulates P-glycoprotein (P-gp) efflux transport via P-gp ATPase inhibition. The current in vitro research using Caco-2 cells was conducted to further explore the P-gp ATPase inhibition mechanism. Using a monoclonal CD243 P-gp antibody shift assay (UIC2), we probed P-gp conformational changes induced via TPGS 1000. In the presence of TPGS 1000, UIC2 binding was slightly decreased. TPGS 1000 does not appear to be a P-gp substrate, nor does it function as a competitive inhibitor in P-gp substrate efflux transport. The reduction in UIC2 binding with TPGS 1000 was markedly weaker than with orthovanadate, data ruling out trapping P-gp in a transition state by direct interaction with one or both of the P-gp ATP nucleotide binding domains. An intracellular ATP depletion mechanism could be ruled out in the UIC2 assay, and by monitoring intracellular ATP levels in the presence of TPGS 1000. Indicating slow distribution of TPGS 1000 into the membrane, and in agreement with an intramembranal or intracellular side of action, Caco-2 cell monolayer experiments preincubated with TPGS 1000 produce stronger substrate inhibitory activity than those conducted by direct substrate and surfactant coapplication.

The combined use of paclitaxel-loaded nanoparticles with a low-molecular-weight copolymer inhibitor of P-glycoprotein to overcome drug resistance

“…It has been proposed that nonionic surfactants inhibit/modulate P-gp by various mechanisms, including changing membrane fluidity, inhibiting P-gp ATPase activity, and depleting ATP stores. [36][37][38][39][40] Interestingly, as we have previously demonstrated, if PCL5 is not maintained above an inhibitory concentration, PTX rapidly effluxes from the MDCKII-MDR1 cells, resulting in reduced inhibition of cell proliferation. 20 An additional experiment was conducted to determine the IC 50 of PTX-loaded nanospheres or micelles in the presence of PCL5 at its most effective concentration (0.05%).…”

Fabrication of genistein-loaded biodegradable TPGS-b-PCL nanoparticles for improved therapeutic effects in cervical cancer cells

“…[18][19][20][21] Other than being an excellent emulsifier, TPGS itself has been reported to have anticancer efficacy because of its function as an inhibitor of P-glycoprotein to surmount multidrug resistance in tumor cells. [22][23][24] In this work, the TPGS-b-PCL copolymer was synthesized and characterized. The genistein-loaded NPs were prepared with a modified nanoprecipitation method instead of solvent extraction/evaporation method and characterized.…”

Fmoc-Conjugated PEG-Vitamin E2 Micelles for Tumor-Targeted Delivery of Paclitaxel: Enhanced Drug-Carrier Interaction and Loading Capacity

“…TPGS has intrinsic P-gp inhibitory effect which helps to overcome multidrug resistance (10,11). TPGS is self-assembled into micelles in aqueous solution; however, the high critical micelle concentration (CMC) decreases the stability of micelles in physiological environment (12).…”