title: Distinct biological impact of dephosphorylation vs. downregulation of p210Bcr-Abl: implications for imatinib mesylate response and resistance.
abstract: Imatinib mesylate suppresses phosphorylation of its kinase target, Bcr-Abl. We hypothesized that loss of p210Bcr-Abl (the kinase target) may lead to imatinib mesylate resistance. We studied K562 cells [chronic myelogenous leukemia (CML) blast crisis line] and MO7E/MBA-1 cells (with MBA-1 cells representing MO7E cells stably transfected with BCR-ABL). Imatinib mesylate resistance developed when p210Bcr-Abl expression was abolished. Furthermore, K562 cells were significantly more growth suppressed after imatinib mesylate exposure than after downregulation of Bcr-Abl expression. Signaling pathways which were functional in the absence of Bcr-Abl expression (NF-kappaB and mitogen-activated protein kinase activation or the growth factor pathway) were disrupted when p210Bcr-Abl was present but dephosphorylated, suggesting that an intact, but enzymatically inactive Bcr-Abl, may interfere with critical growth/signaling pathways. Downregulation of p210Bcr-Abl may be a mechanism by which imatinib mesylate resistance emerges. Samples from three of 15 patients with imatinib mesylate-resistant CML blast crisis had undetectable levels of p210Bcr-Abl. We conclude that retention of a dephosphorylated p210Bcr-Abl has a biologic impact distinct from that of downregulation/loss of p210Bcr-Abl and, in a subset of patients, loss of the target of the kinase inhibitor may lead to imatinib mesylate resistance.
authors.affiliation: Division of Cancer Medicine, The University of Texas, M.D. Anderson Cancver Center, Houston, Texas 77230-1402, USA. rkurzroc@mdanderson.org
authors.forename: Razelle
authors.initials: R
authors.lastname: Kurzrock
authors.forename: Moshe
authors.initials: M
authors.lastname: Talpaz
authors.forename: Lan
authors.initials: L
authors.lastname: Li
authors.forename: Zeev
authors.initials: Z
authors.lastname: Estrov
mesh_terms: D001549:Benzamides; D001752:Blast Crisis / Q000378:metabolism; D002460:Cell Line; D049109:Cell Proliferation / Q000187:drug effects; D015536:Down-Regulation; D019008:Drug Resistance, Neoplasm; D016044:Fusion Proteins, bcr-abl / Q000032:analysis / Q000235:genetics*; D006801:Humans; D000068877:Imatinib Mesylate; D020014:K562 Cells; D015464:Leukemia, Myelogenous, Chronic, BCR-ABL Positive / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D010879:Piperazines / Q000494:pharmacology*; D011743:Pyrimidines / Q000494:pharmacology*; D015398:Signal Transduction; D014162:Transfection
chemical_list: D001549:Benzamides; D010879:Piperazines; D011743:Pyrimidines; D000068877:Imatinib Mesylate; D016044:Fusion Proteins, bcr-abl