title: Inhibition of PI3K/mTOR overcomes nilotinib resistance in BCR-ABL1 positive leukemia cells through translational down-regulation of MDM2.
abstract: Chronic myeloid leukemia (CML) is a cytogenetic disorder resulting from formation of the Philadelphia chromosome (Ph), that is, the t(9;22) chromosomal translocation and the formation of the BCR-ABL1 fusion protein. Tyrosine kinase inhibitors (TKI), such as imatinib and nilotinib, have emerged as leading compounds with which to treat CML. t(9;22) is not restricted to CML, 20-30% of acute lymphoblastic leukemia (ALL) cases also carry the Ph. However, TKIs are not as effective in the treatment of Ph+ ALL as in CML. In this study, the Ph+ cell lines JURL-MK2 and SUP-B15 were used to investigate TKI resistance mechanisms and the sensitization of Ph+ tumor cells to TKI treatment. The annexin V/PI (propidium iodide) assay revealed that nilotinib induced apoptosis in JURL-MK2 cells, but not in SUP-B15 cells. Since there was no mutation in the tyrosine kinase domain of BCR-ABL1 in cell line SUP-B15, the cells were not generally unresponsive to TKI, as evidenced by dephosphorylation of the BCR-ABL1 downstream targets, Crk-like protein (CrkL) and Grb-associated binder-2 (GAB2). Resistance to apoptosis after nilotinib treatment was accompanied by the constitutive and nilotinib unresponsive activation of the phosphoinositide 3-kinase (PI3K) pathway. Treatment of SUP-B15 cells with the dual PI3K/mammalian target of rapamycin (mTOR) inhibitor BEZ235 alone induced apoptosis in a low percentage of cells, while combining nilotinib and BEZ235 led to a synergistic effect. The main role of PI3K/mTOR inhibitor BEZ235 and the reason for apoptosis in the nilotinib-resistant cells was the block of the translational machinery, leading to the rapid downregulation of the anti-apoptotic protein MDM2 (human homolog of the murine double minute-2). These findings highlight MDM2 as a potential therapeutic target to increase TKI-mediated apoptosis and imply that the combination of PI3K/mTOR inhibitor and TKI might form a novel strategy to combat TKI-resistant BCR-ABL1 positive leukemia.
authors.affiliation: Leibniz-Institute DSMZ-German Collection of Microorganisms and Cell Cultures, Department of Human and Animal Cell Lines, Braunschweig, Germany.
authors.forename: Jie
authors.initials: J
authors.lastname: Ding
authors.affiliation: Leibniz-Institute DSMZ-German Collection of Microorganisms and Cell Cultures, Department of Human and Animal Cell Lines, Braunschweig, Germany.
authors.forename: Julia
authors.initials: J
authors.lastname: Romani
authors.affiliation: Leibniz-Institute DSMZ-German Collection of Microorganisms and Cell Cultures, Department of Human and Animal Cell Lines, Braunschweig, Germany.
authors.forename: Margarete
authors.initials: M
authors.lastname: Zaborski
authors.affiliation: Leibniz-Institute DSMZ-German Collection of Microorganisms and Cell Cultures, Department of Human and Animal Cell Lines, Braunschweig, Germany.
authors.forename: Roderick A F
authors.initials: RA
authors.lastname: MacLeod
authors.affiliation: Leibniz-Institute DSMZ-German Collection of Microorganisms and Cell Cultures, Department of Human and Animal Cell Lines, Braunschweig, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Nagel
authors.affiliation: Leibniz-Institute DSMZ-German Collection of Microorganisms and Cell Cultures, Department of Human and Animal Cell Lines, Braunschweig, Germany.
authors.forename: Hans G
authors.initials: HG
authors.lastname: Drexler
authors.affiliation: Leibniz-Institute DSMZ-German Collection of Microorganisms and Cell Cultures, Department of Human and Animal Cell Lines, Braunschweig, Germany.
authors.forename: Hilmar
authors.initials: H
authors.lastname: Quentmeier
mesh_terms: D045744:Cell Line, Tumor; D015536:Down-Regulation / Q000187:drug effects; D019008:Drug Resistance, Neoplasm / Q000187:drug effects*; D016044:Fusion Proteins, bcr-abl; D015973:Gene Expression Regulation, Leukemic / Q000187:drug effects*; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology*; D007938:Leukemia / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D051736:Proto-Oncogene Proteins c-mdm2 / Q000096:biosynthesis* / Q000235:genetics; D011743:Pyrimidines / Q000494:pharmacology*; D011804:Quinolines / Q000494:pharmacology*; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*
chemical_list: D016044:Fusion Proteins, bcr-abl; D007093:Imidazoles; D019869:Phosphatidylinositol 3-Kinases; D047428:Protein Kinase Inhibitors; D051736:Proto-Oncogene Proteins c-mdm2; D011743:Pyrimidines; D011804:Quinolines; D058570:TOR Serine-Threonine Kinases; C581634:BCR-ABL1 fusion protein, human; C497206:MDM2 protein, human; C546842:MTOR protein, human; C498826:nilotinib; C531198:dactolisib