Complete inhibition of p-glycoprotein by simultaneous treatment with a distinct class of modulators and the UIC2 monoclonal antibody

Katalin Goda, Ferenc Fenyvesi, Zsolt Bacsó, Henrietta Nagy, Teréz Márián, Attila Megyeri, Zoltán Krasznai, István Juhász, Miklós Vecsernyés, Szabó Gábor

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36 Citations (Scopus)


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 ∼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.

Original languageEnglish
Pages (from-to)81-88
Number of pages8
JournalJournal of Pharmacology and Experimental Therapeutics
Issue number1
Publication statusPublished - 2007

ASJC Scopus subject areas

  • Molecular Medicine
  • Pharmacology

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