sirolimus and Blast-Crisis

Chronic myelogenous leukemia (CML) is a stem cell disorder, and leukemia stem cells (LSCs) can contribute to the relapse of the disease. Quiescent LSCs are BCR-ABL independent and resistant to imatinib; therefore, there is an unmet need to identify new therapeutic targets in LSCs. Inhibition of the mammalian target of rapamycin (mTOR) in imatinib-resistant BCR-ABL1-positive cells was effective in vitro, but in a pilot clinical trial, only a few patients responded to the treatment. In this study, we demonstrate that mTOR activation in CML CD34(+) progenitor cells is ERK dependent in chronic phase of the disease and ERK independent in blast crisis. Rapamycin effectively inhibits mTOR in all phases of CML, but does not reduce number of LSC-enriched CD34(+) blast crisis (BC) cells, neither alone nor in combination with imatinib in CML-BC cells. These results show that potential therapeutic benefits of mTOR inhibition may be the result of effects on differentiated leukemic cells and may be potentially achieved only in the chronic phase of the disease.

Topics: Animals; Antineoplastic Agents; Benzamides; Blast Crisis; Blotting, Western; Cell Line; Drug Resistance, Neoplasm; Enzyme Activation; Extracellular Signal-Regulated MAP Kinases; Flow Cytometry; Fusion Proteins, bcr-abl; Humans; Imatinib Mesylate; K562 Cells; Leukemia, Myeloid, Chronic-Phase; Neoplastic Stem Cells; Piperazines; Protein Kinase Inhibitors; Pyrimidines; Signal Transduction; Sirolimus; TOR Serine-Threonine Kinases; Tumor Cells, Cultured

Topics: Adult; Antibiotics, Antineoplastic; Benzamides; Blast Crisis; Drug Resistance, Neoplasm; Humans; Imatinib Mesylate; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Male; Piperazines; Pyrimidines; Sirolimus

The phosphorylation state of the S6 ribosomal protein was measured in the peripheral blasts of 19 newly diagnosed patients with acute leukemia.. We employed a flow cytometry protocol that enabled correlated measurement of pS6, phosphorylation of extracellular signal-regulated kinase (pERK), and cluster differentiation surface markers. Baseline levels of pS6 in leukemic blasts were compared with those found when the samples were activated using stem cell factor, or exposed to rapamycin, LY294002, or the mitogen-activated protein kinase inhibitor U0126.. Results showed a considerable degree of intra- and intertumoral heterogeneity in the constitutive levels of pS6. Rapamycin and LY294002 suppressed pS6 in 10 of 11 cases that showed increased basal levels, consistent with phosphatidylinositol 3 (PI3)-kinase/Akt/mTOR signaling being the predominant upstream signaling pathway. However, in 6 of 11 cases pS6 was also suppressed by U0126, indicating that the ERK pathway can significantly input to pS6.. The constitutive activation of pS6 in acute leukemia patients likely reflects alterations in growth factor signaling that can be mediated by the ERK as well as the mTOR pathway, and could potentially have prognostic significance. As well as identifying aberrant signal transduction in leukemia patients, the flow cytometry methodology has potential for the pharmacodynamic monitoring of novel agents that inhibit ERK or PI3-kinase/Akt/mTOR signaling.

Topics: Acute Disease; Antibiotics, Antineoplastic; Blast Crisis; Butadienes; Chromones; Drug Evaluation, Preclinical; Enzyme Inhibitors; Extracellular Signal-Regulated MAP Kinases; Female; Flow Cytometry; Humans; Leukemia; Male; MAP Kinase Signaling System; Morpholines; Nitriles; Phosphorylation; Prognosis; Protein Kinases; Protein Processing, Post-Translational; Ribosomal Protein S6; Sirolimus; Stem Cell Factor; TOR Serine-Threonine Kinases

The phosphatidyl-inositol 3 kinase (PI3k)/Akt pathway has been implicated in childhood acute lymphoblastic leukemia (ALL). Because rapamycin suppresses the oncogenic processes sustained by PI3k/Akt, we investigated whether rapamycin affects blast survival. We found that rapamycin induces apoptosis of blasts in 56% of the bone marrow samples analyzed. Using the PI3k inhibitor wortmannin, we show that the PI3k/Akt pathway is involved in blast survival. Moreover, rapamycin increased doxorubicin-induced apoptosis even in nonresponder samples. Anthracyclines activate nuclear factor kappaB (NF-kappaB), and disruption of this signaling pathway increases the efficacy of apoptogenic stimuli. Rapamycin inhibited doxorubicin-induced NF-kappaB in ALL samples. Using a short interfering (si) RNA approach, we demonstrate that FKBP51, a large immunophilin inhibited by rapamycin, is essential for drug-induced NF-kappaB activation in human leukemia. Furthermore, rapamycin did not increase doxorubicin-induced apoptosis when NF-kappaB was overexpressed. In conclusion, rapamycin targets 2 pathways that are crucial for cell survival and chemoresistance of malignant lymphoblasts--PI3k/Akt through the mammalian target of rapamycin and NF-kappaB through FKBP51--suggesting that the drug could be beneficial in the treatment of childhood ALL.

Topics: Adolescent; Apoptosis; Blast Crisis; Bone Marrow Cells; Child; Child, Preschool; Doxorubicin; Drug Synergism; Female; Humans; Infant; Male; NF-kappa B; Phosphatidylinositol 3-Kinases; Precursor Cell Lymphoblastic Leukemia-Lymphoma; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-akt; Signal Transduction; Sirolimus; Tacrolimus Binding Proteins; Tumor Cells, Cultured