title: Complete inhibition of P-glycoprotein by simultaneous treatment with a distinct class of modulators and the UIC2 monoclonal antibody.
abstract: P-glycoprotein (Pgp) is one of the active efflux pumps that are able to extrude a large variety of chemotherapeutic drugs from the cells, causing multidrug resistance. The conformation-sensitive UIC2 monoclonal antibody potentially inhibits Pgp-mediated substrate transport. However, this inhibition is usually partial, and its extent is variable because UIC2 binds only to 10 to 40% Pgp present in the cell membrane. The rest of the Pgp molecules become recognized by this antibody only in the presence of certain substrates or modulators, including vinblastine, cyclosporine A (CsA), and SDZ PSC 833 (valspodar). Simultaneous application of any of these modulators and UIC2, followed by the removal of the modulator, results in a completely restored steady-state accumulation of various Pgp substrates (calcein-AM, daunorubicin, and 99mTc-hexakis-2-methoxybutylisonitrile), indicating near 100% inhibition of pump activity. Remarkably, the inhibitory binding of the antibody is brought about by coincubation with concentrations of CsA or SDZ PSC 833 approximately 20 times lower than what is necessary for Pgp inhibition when the modulators are applied alone. The feasibility of such a combinative treatment for in vivo multidrug resistance reversal was substantiated by the dramatic increase of daunorubicin accumulation in xenotransplanted Pgp+ tumors in response to a combined treatment with UIC2 and CsA, both administered at doses ineffective when applied alone. These observations establish the combined application of a class of modulators used at low concentrations and of the UIC2 antibody as a novel, specific, and effective way of blocking Pgp function in vivo.
authors.affiliation: Department of Biophysics and Cell Biology, University of Debrecen, Debrecen, Hungary.
authors.forename: Katalin
authors.initials: K
authors.lastname: Goda
authors.forename: Ferenc
authors.initials: F
authors.lastname: Fenyvesi
authors.forename: Zsolt
authors.initials: Z
authors.lastname: Bacsó
authors.forename: Henrietta
authors.initials: H
authors.lastname: Nagy
authors.forename: Teréz
authors.initials: T
authors.lastname: Márián
authors.forename: Attila
authors.initials: A
authors.lastname: Megyeri
authors.forename: Zoltán
authors.initials: Z
authors.lastname: Krasznai
authors.forename: István
authors.initials: I
authors.lastname: Juhász
authors.forename: Miklós
authors.initials: M
authors.lastname: Vecsernyés
authors.forename: Gábor
authors.initials: G
authors.lastname: Szabó
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000037:antagonists & inhibitors* / Q000276:immunology; D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology*; D016572:Cyclosporine / Q000494:pharmacology; D003524:Cyclosporins / Q000494:pharmacology; D003630:Daunorubicin / Q000378:metabolism; D005452:Fluoresceins / Q000378:metabolism; D006801:Humans; D051379:Mice; D041681:NIH 3T3 Cells; D014747:Vinblastine / Q000494:pharmacology
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000911:Antibodies, Monoclonal; D003524:Cyclosporins; D005452:Fluoresceins; D014747:Vinblastine; D016572:Cyclosporine; C070272:valspodar; C007740:fluorexon; D003630:Daunorubicin