title: P-glycoprotein (ABCB1) interacts directly with lipid-based anti-cancer drugs and platelet-activating factors.
abstract: The P-glycoprotein multidrug transporter (Pgp; ABCB1) is an ATP-binding cassette (ABC) protein that has been implicated in the multidrug resistance of human cancers. Pgp couples ATP hydrolysis to active extrusion from the cell of a broad array of amphipathic compounds via an ill-defined mechanism. Substrates are believed to interact with Pgp within the membrane. Reconstituted Pgp functions as an ATP-dependent flippase for a variety of fluorescently labelled membrane lipids. The protein may also function as a drug 'flippase', moving its substrates from the inner to the outer leaflet of the bilayer. We show that lipid-based anti-cancer drugs, such as miltefosine, and signaling molecules, such as platelet-activating factors, bind saturably to Pgp with Kd values in the low micromolar range, and modulate its ATPase activity. These compounds also inhibit Pgp-mediated flipping of fluorescent lipids and transport of Hoechst 33342 and tetramethylrosamine, which occupy different subsites in the drug-binding pocket. Bacterial lipid A modulates Pgp ATPase activity, and glycolipid flipping is inhibited by unlabelled glucosylceramide, suggesting that these lipids also interact with the transporter. These results indicate that Pgp treats a variety of lipid-based molecules as substrates, and likely interacts with lipids and drugs in the same manner.
authors.affiliation: Department of Molecular and Cellular Biology, University of Guelph, Guelph ON N1G 2W1, Canada.
authors.forename: Paul D W
authors.initials: PD
authors.lastname: Eckford
authors.forename: Frances J
authors.initials: FJ
authors.lastname: Sharom
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000302:isolation & purification / Q000378:metabolism*; D000251:Adenosine Triphosphatases / Q000032:analysis; D000970:Antineoplastic Agents / Q000737:chemistry* / Q000378:metabolism*; D005453:Fluorescence; D006801:Humans; D015394:Molecular Structure; D010972:Platelet Activating Factor / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000970:Antineoplastic Agents; D010972:Platelet Activating Factor; D000251:Adenosine Triphosphatases