title: Functional analysis of P-glycoprotein and multidrug resistance associated protein related multidrug resistance in AML-blasts.
abstract: Despite the high effectiveness of various P-glycoprotein (P-gp) modulating substances in vitro their clinical value e.g. for combination treatment of acute myelogenous leukemias (AML) remains still unclear. This might be explainable by recent findings that other factors than P-gp (e.g. the multidrug resistance associated protein (MRP)) may also be involved in clinical occurring drug resistance. To study P-gp and MRP mediated MDR in AML blasts from patients with relapses at the functional level we measured rhodamine 123 (RHO) efflux in combination with a P-gp specific (SDZ PSC 833) or a MRP specific (MK571) modulator, respectively. Furthermore, direct antineoplastic drug action was monitored by determination of damaged cell fraction of a blast population using flow cytometry. We generally found strongly modulated RHO efflux by SDZ PSC 833 but slight RHO-efflux modulation by MK571 in blasts from relapsed states of AML expressing MDR1 or MRP mRNA at various levels. We could not demonstrate, though, significant PSC 833 or MK571 mediated modulation of the cytotoxic effects of etoposide. The results point to the possibility that combination of etoposide and a modulator might not improve responses to chemotherapy by targeting P-gp or MRP exclusively.
authors.affiliation: Universitäts-Kinderklinik, Abteilung I: Allegemeine Pädiatrie, Hämatologie, Onkologie, Tübingen, Germany.
authors.forename: D
authors.initials: D
authors.lastname: Brügger
authors.forename: H
authors.initials: H
authors.lastname: Herbart
authors.forename: V
authors.initials: V
authors.lastname: Gekeler
authors.forename: G
authors.initials: G
authors.lastname: Seitz
authors.forename: C
authors.initials: C
authors.lastname: Liu
authors.forename: T
authors.initials: T
authors.lastname: Klingebiel
authors.forename: T
authors.initials: T
authors.lastname: Orlikowsky
authors.forename: H
authors.initials: H
authors.lastname: Einsele
authors.forename: C
authors.initials: C
authors.lastname: Denzlinger
authors.forename: P
authors.initials: P
authors.lastname: Bader
authors.forename: D
authors.initials: D
authors.lastname: Niethammer
authors.forename: J F
authors.initials: JF
authors.lastname: Beck
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000032:analysis*; D000208:Acute Disease; D000972:Antineoplastic Agents, Phytogenic; D002469:Cell Separation; D048429:Cell Size; D018076:DNA, Complementary / Q000235:genetics; D005047:Etoposide / Q000627:therapeutic use; D005434:Flow Cytometry; D006801:Humans; D007951:Leukemia, Myeloid / Q000097:blood* / Q000188:drug therapy; D016133:Polymerase Chain Reaction; D020112:Rhodamine 123; D014407:Tumor Cells, Cultured; D014410:Tumor Stem Cell Assay
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000972:Antineoplastic Agents, Phytogenic; D018076:DNA, Complementary; D020112:Rhodamine 123; D005047:Etoposide