title: Methoxypolyethylene glycol-block-polycaprolactone diblock copolymers reduce P-glycoprotein efflux in the absence of a membrane fluidization effect while stimulating P-glycoprotein ATPase activity.
abstract: We have previously shown that amphiphilic diblock copolymers composed of methoxypolyethylene glycol-b-polycaprolactone (MePEG-b-PCL) increased the cellular accumulation and reduced the basolateral to apical flux of the P-glycoprotein substrate, rhodamine 123 (R-123) in caco-2 cells. The purpose of this study was to investigate membrane perturbation effects of MePEG-b-PCL diblock copolymers with erythrocyte membranes and caco-2 cells and the effect on P-gp ATPase activity. The diblock copolymer MePEG(17)-b-PCL(5) induced increasing erythrocyte hemolysis at concentrations which correlated with increasing accumulation of R-123 into caco-2 cells. However, no increase in cellular accumulation of R-123 by non-P-gp expressing cells was observed, suggesting that diblock did not enhance the transmembrane passive diffusion of R-123, but that the accumulation enhancement effect of the diblock in caco-2 cells was likely mediated primarily via P-gp inhibition. Fluorescence anisotropy measurements of membrane fluidity and P-gp ATPase activity demonstrated that MePEG(17)-b-PCL(5) decreased caco-2 membrane fluidity while stimulating ATPase activity approximately threefold at concentrations that maximally enhanced R-123 caco-2 accumulation. These results suggest that inhibition of P-gp efflux by MePEG(17)-b-PCL(5) does not appear to be related to increases in membrane fluidity or through inhibition in P-gp ATPase activities, which are two commonly reported cellular effects for P-gp inhibition mediated by surfactants.
authors.affiliation: Department of Pharmaceutical Sciences, Leslie Dan Faculty of Pharmacy, University of Toronto, 144 College St. Toronto, Ontario, Canada M5S 3M2.
authors.forename: Jason
authors.initials: J
authors.lastname: Zastre
authors.forename: John K
authors.initials: JK
authors.lastname: Jackson
authors.forename: Wesley
authors.initials: W
authors.lastname: Wong
authors.forename: Helen M
authors.initials: HM
authors.lastname: Burt
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000493:pharmacokinetics*; D000251:Adenosine Triphosphatases / Q000378:metabolism*; D045744:Cell Line, Tumor; D006461:Hemolysis / Q000187:drug effects; D006801:Humans; D008560:Membrane Fluidity / Q000187:drug effects*; D017830:Octoxynol / Q000494:pharmacology; D011091:Polyesters / Q000494:pharmacology*; D011092:Polyethylene Glycols / Q000494:pharmacology*; D020112:Rhodamine 123 / Q000378:metabolism
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D011091:Polyesters; D020112:Rhodamine 123; C016240:polycaprolactone; D011092:Polyethylene Glycols; D017830:Octoxynol; C028210:monomethoxypolyethylene glycol; D000251:Adenosine Triphosphatases