title: Compensatory PI3-kinase/Akt/mTor activation regulates imatinib resistance development.
abstract: BCR/ABL-kinase mutations frequently mediate clinical resistance to the selective tyrosine kinase inhibitor Imatinib mesylate (IM, Gleevec). However, mechanisms that promote survival of BCR/ABL-positive cells before clinically overt IM resistance occurs have poorly been defined so far. Here, we demonstrate that IM-treatment activated the phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTor)-pathway in BCR/ABL-positive LAMA-cells and primary leukemia cells in vitro, as well as in a chronic phase CML patient in vivo. In fact, PI3K/Akt-activation critically mediated survival during the early phase of IM resistance development before manifestation of BCR/ABL-dependent strong IM resistance such as through a kinase mutation. Accordingly, inhibition of IM-induced Akt activation using mTor inhibitors and Akt-specific siRNA effectively antagonized development of incipient IM-resistance in vitro. In contrast, IM-resistant chronic myeloid leukemia (CML) patients with BCR/ABL kinase mutations (n=15), and IM-refractory BCR/ABL-positive acute lymphatic leukemia patients (n=2) displayed inconsistent and kinase mutation-independent autonomous patterns of Akt-pathway activation, and mTor-inhibition overcame IM resistance only if Akt was strongly activated. Together, an IM-induced compensatory Akt/mTor activation may represent a novel mechanism for the persistence of BCR/ABL-positive cells in IM-treated patients. Treatment with mTor inhibitors may thus be particularly effective in IM-sensitive patients, whereas Akt-pathway activation variably contributes to clinically overt IM resistance.
authors.affiliation: Klinikum der Philipps Universität Marburg, Klinik für Hämatologie, Onkologie und Immunologie, Marburg, Germany. burchert@mailer.uni-marburg.de
authors.forename: A
authors.initials: A
authors.lastname: Burchert
authors.forename: Y
authors.initials: Y
authors.lastname: Wang
authors.forename: D
authors.initials: D
authors.lastname: Cai
authors.forename: N
authors.initials: N
authors.lastname: von Bubnoff
authors.forename: P
authors.initials: P
authors.lastname: Paschka
authors.forename: S
authors.initials: S
authors.lastname: Müller-Brüsselbach
authors.forename: O G
authors.initials: OG
authors.lastname: Ottmann
authors.forename: J
authors.initials: J
authors.lastname: Duyster
authors.forename: A
authors.initials: A
authors.lastname: Hochhaus
authors.forename: A
authors.initials: A
authors.lastname: Neubauer
mesh_terms: D000970:Antineoplastic Agents / Q000627:therapeutic use*; D017209:Apoptosis / Q000187:drug effects*; D001549:Benzamides; D015153:Blotting, Western; D002453:Cell Cycle / Q000187:drug effects; D019008:Drug Resistance, Neoplasm; D004789:Enzyme Activation / Q000187:drug effects; D000068338:Everolimus; D016044:Fusion Proteins, bcr-abl / Q000235:genetics / Q000378:metabolism; D006801:Humans; D000068877:Imatinib Mesylate; D007166:Immunosuppressive Agents / Q000494:pharmacology; D015464:Leukemia, Myelogenous, Chronic, BCR-ABL Positive / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D016296:Mutagenesis; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D010879:Piperazines / Q000627:therapeutic use*; D011494:Protein Kinases / Q000737:chemistry / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D011743:Pyrimidines / Q000627:therapeutic use*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000494:pharmacology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism; D020123:Sirolimus / Q000031:analogs & derivatives / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases; D014407:Tumor Cells, Cultured
chemical_list: D000970:Antineoplastic Agents; D001549:Benzamides; D000068338:Everolimus; D016044:Fusion Proteins, bcr-abl; D000068877:Imatinib Mesylate; D007166:Immunosuppressive Agents; D019869:Phosphatidylinositol 3-Kinases; D010879:Piperazines; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D011743:Pyrimidines; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D020123:Sirolimus; D058570:TOR Serine-Threonine Kinases; C546842:MTOR protein, human; C494918:AKT1 protein, human