title: Selective modulation of P-glycoprotein-mediated drug resistance.
abstract: Multidrug resistance associated with the overexpression of the multidrug transporter P-glycoprotein is a serious impediment to successful cancer treatment. We found that verapamil reversed resistance of CEM/VLB(100) cells to vinblastine and fluorescein-colchicine, but not to colchicine. Chlorpromazine reversed resistance to vinblastine but not to fluorescein-colchicine, and it increased resistance to colchicine. Initial influx rates of fluorescein-colchicine were similar in resistant and parental cells, whereas vinblastine uptake was about 10-fold lower in the resistant cells. These results provide indirect evidence that fluorescein-colchicine is transported from the inner leaflet of the membrane and vinblastine from the outer membrane leaflet. Verapamil inhibited fluorescein-colchicine transport in inside-out vesicles made from resistant cells, whilst chlorpromazine was found to activate the transport of fluorescein-colchicine. The chlorpromazine-induced activation of fluorescein-colchicine transport was temperature-dependent and may reflect its interaction with phospholipids localised in the same bilayer leaflet. Conversely, chlorpromazine localisation in this leaflet may be responsible for its allosteric inhibition of vinblastine transport from the opposing membrane leaflet. The proposed relationship between the selectivity of modulation of P-glycoprotein and the membrane localisation of the cytotoxic drug substrates and modulators may have important implications in the rational design of regimes for the circumvention of multidrug resistance clinically.
authors.affiliation: Faculty of Pharmacy, The University of Sydney, N.S.W 2006, Australia.
authors.forename: M
authors.initials: M
authors.lastname: Bebawy
authors.forename: M B
authors.initials: MB
authors.lastname: Morris
authors.forename: B D
authors.initials: BD
authors.lastname: Roufogalis
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000037:antagonists & inhibitors* / Q000502:physiology; D000494:Allosteric Regulation; D000972:Antineoplastic Agents, Phytogenic / Q000378:metabolism / Q000494:pharmacology*; D001693:Biological Transport, Active / Q000187:drug effects; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D002455:Cell Division / Q000187:drug effects; D002462:Cell Membrane / Q000187:drug effects; D002746:Chlorpromazine / Q000494:pharmacology*; D003078:Colchicine / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D018432:Drug Resistance, Multiple; D019008:Drug Resistance, Neoplasm; D005452:Fluoresceins / Q000378:metabolism / Q000494:pharmacology; D006801:Humans; D008563:Membrane Lipids / Q000378:metabolism; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors* / Q000502:physiology; D010743:Phospholipids / Q000378:metabolism; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000473:pathology; D013696:Temperature; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000378:metabolism; D014700:Verapamil / Q000494:pharmacology*; D014747:Vinblastine / Q000378:metabolism / Q000494:pharmacology*
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000972:Antineoplastic Agents, Phytogenic; D002121:Calcium Channel Blockers; D005452:Fluoresceins; D008563:Membrane Lipids; D009363:Neoplasm Proteins; D010743:Phospholipids; D014747:Vinblastine; C016457:fluorescein colchicine; D014700:Verapamil; D003078:Colchicine; D002746:Chlorpromazine