title: MDR1 gene overexpression confers resistance to imatinib mesylate in leukemia cell line models.
abstract: Inappropriate expression of the multidrug resistance (MDR1) gene encoding the P-glycoprotein (Pgp) has been frequently implicated in resistance to different chemotherapeutic drugs. We have previously generated chronic myeloid leukemia (CML) cell lines resistant to the tyrosine kinase inhibitor imatinib mesylate (STI571), and one line (LAMA84-r) showed overexpression not only of the Bcr-Abl protein but also of Pgp. In the present study, we investigated this phenomenon in other cell lines overexpressing exclusively Pgp. Thus, cells from the K562/DOX line, described as resistant to doxorubicin due to MDR1 gene overexpression, grew continuously in the presence of 1 microM imatinib, but died in 4 to 5 days if the Pgp pump modulators verapamil or PSC833 were added to the imatinib-treated culture. Analysis of cell proliferation by the MTS (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium) assay confirmed the differential sensitivity of K562/DOX to imatinib, which was also reversed by verapamil or PSC833. Flow cytometric analysis of the total phosphotyrosine content by intracytoplasmic staining after a 2-hour incubation with escalating doses of imatinib showed that the inhibitory concentrations of 50% (IC(50)) for inhibition of cellular protein tyrosine phosphorylation were 15, 10, and 5 microM for K562/DOX, K562/DOX plus verapamil, and K562, respectively. Retroviral-mediated transfection of the BCR-ABL(+) AR230 cell line with the MDR1 gene decreased its sensitivity to imatinib, an effect that was also reversed by verapamil. The possible role of MDR overexpression in clinical resistance to imatinib remains to be defined. We therefore confirm that imatinib should be added to the extensive list of drugs that can be affected by the MDR phenomenon.
authors.affiliation: Laboratoire Greffe de Moelle, Université Victor Segalen, Bordeaux, France. francois-xavier.mahon@umr5540.u-bordeaux2.fr
authors.forename: François-Xavier
authors.initials: FX
authors.lastname: Mahon
authors.forename: Francis
authors.initials: F
authors.lastname: Belloc
authors.forename: Valérie
authors.initials: V
authors.lastname: Lagarde
authors.forename: Claudine
authors.initials: C
authors.lastname: Chollet
authors.forename: François
authors.initials: F
authors.lastname: Moreau-Gaudry
authors.forename: Josy
authors.initials: J
authors.lastname: Reiffers
authors.forename: John M
authors.initials: JM
authors.lastname: Goldman
authors.forename: Junia V
authors.initials: JV
authors.lastname: Melo
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics; D017209:Apoptosis / Q000187:drug effects; D001549:Benzamides; D016923:Cell Death / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D003114:Colony-Forming Units Assay; D003524:Cyclosporins / Q000494:pharmacology; D004317:Doxorubicin / Q000494:pharmacology / Q000627:therapeutic use; D019008:Drug Resistance, Neoplasm / Q000235:genetics*; D005434:Flow Cytometry; D015870:Gene Expression; D019450:Genes, MDR / Q000235:genetics*; D006801:Humans; D000068877:Imatinib Mesylate; D007938:Leukemia / Q000188:drug therapy* / Q000473:pathology; D015464:Leukemia, Myelogenous, Chronic, BCR-ABL Positive / Q000188:drug therapy / Q000235:genetics / Q000473:pathology; D019000:Phosphotyrosine / Q000032:analysis; D010879:Piperazines / Q000494:pharmacology / Q000627:therapeutic use*; D011743:Pyrimidines / Q000494:pharmacology / Q000627:therapeutic use*; D014162:Transfection; D014407:Tumor Cells, Cultured; D014700:Verapamil / Q000494:pharmacology
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D001549:Benzamides; D003524:Cyclosporins; D010879:Piperazines; D011743:Pyrimidines; D019000:Phosphotyrosine; D004317:Doxorubicin; D000068877:Imatinib Mesylate; D014700:Verapamil; C070272:valspodar