sirolimus and Precursor-T-Cell-Lymphoblastic-Leukemia-Lymphoma

Deregulation of v-myc avian myelocytomatosis viral oncogene homolog (MYC) occurs in a broad range of human cancers and often predicts poor prognosis and resistance to therapy. However, directly targeting oncogenic MYC remains unsuccessful, and indirectly inhibiting MYC emerges as a promising approach. Checkpoint kinase 1 (CHK1) is a protein kinase that coordinates the G2/M cell cycle checkpoint and protects cancer cells from excessive replicative stress. Using c-MYC-mediated T-cell acute lymphoblastic leukemia (T-acute lymphoblastic leukemia) and N-MYC-driven neuroblastoma as model systems, we reveal that both c-MYC and N-MYC directly bind to the CHK1 locus and activate its transcription. CHIR-124, a selective CHK1 inhibitor, impairs cell viability and induces remarkable synergistic lethality with mTOR inhibitor rapamycin in MYC-overexpressing cells. Mechanistically, rapamycin inactivates carbamoyl-phosphate synthetase 2, aspartate transcarbamoylase, and dihydroorotase (CAD), the essential enzyme for the first three steps of de novo pyrimidine synthesis, and deteriorates CHIR-124-induced replicative stress. We further demonstrate that dual treatments impede T-acute lymphoblastic leukemia and neuroblastoma progression in vivo. These results suggest simultaneous targeting of CHK1 and mTOR as a novel and powerful co-treatment modality for MYC-mediated tumors.

Topics: Animals; Antineoplastic Combined Chemotherapy Protocols; Cell Line, Tumor; Checkpoint Kinase 1; Datasets as Topic; Disease Progression; Drug Synergism; Gene Expression Profiling; Gene Expression Regulation, Neoplastic; Humans; Male; Mice; N-Myc Proto-Oncogene Protein; Neuroblastoma; Precursor T-Cell Lymphoblastic Leukemia-Lymphoma; Prognosis; Proto-Oncogene Proteins c-myc; Quinolines; Quinuclidines; Sirolimus; TOR Serine-Threonine Kinases; Xenograft Model Antitumor Assays

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive malignancy. Understanding of the molecular pathogenesis may lead to novel therapeutic targets. Rapamycin, the mammalian target of rapamycin (mTOR) inhibitor, showed inhibitory effects on T-ALL cells. In this study, we showed that rapamycin significantly reduced MYCN mRNA and protein in a concentration-dependent manner in T-ALL cells. Selective knockdown of MYCN by small interfering RNA had similar effects to rapamycin to inhibit T-ALL proliferation and colony formation and to induce G1-phase cell-cycle arrest and apoptosis. The inhibitory effects of rapamycin and MYCN depletion were also found in a Molt-4 xenograft model. Rapamycin and MYCN inhibition suppressed both Wnt/β-catenin and mTOR signaling pathways. The results suggest the effects of rapamycin on adult T-ALL is likely mediated by downregulation of MYCN. The findings suggest MYCN a potential target for the treatment of adult T-ALL. Additionally, dual targeting of mTOR and Wnt/β-catenin pathways may represent a novel strategy in the treatment of adult T-ALL.

Topics: Animals; Antibiotics, Antineoplastic; beta Catenin; Cell Proliferation; Humans; Mice; Mice, Inbred NOD; N-Myc Proto-Oncogene Protein; Precursor T-Cell Lymphoblastic Leukemia-Lymphoma; Sirolimus; TOR Serine-Threonine Kinases; Wnt Signaling Pathway; Xenograft Model Antitumor Assays

AMPK acts downstream of the tumor suppressor LKB1, yet its role in cancer has been controversial. AMPK is activated by biguanides, such as metformin and phenformin, and metformin use in diabetics has been associated with reduced cancer risk. However, whether this is mediated by cell-autonomous AMPK activation within tumor progenitor cells has been unclear. We report that T-cell-specific loss of AMPK-α1 caused accelerated growth of T cell acute lymphoblastic leukemia/lymphoma (T-ALL) induced by PTEN loss in thymic T cell progenitors. Oral administration of phenformin, but not metformin, delayed onset and growth of lymphomas, but only when T cells expressed AMPK-α1. This differential effect of biguanides correlated with detection of phenformin, but not metformin, in thymus. Phenformin also enhanced apoptosis in T-ALL cells both in vivo and in vitro. Thus, AMPK-α1 can be a cell-autonomous tumor suppressor in the context of T-ALL, and phenformin may have potential for the prevention of some cancers.

Topics: Administration, Oral; AMP-Activated Protein Kinases; Animals; Cell Proliferation; Disease Models, Animal; Disease-Free Survival; Female; Glycolysis; Hypoglycemic Agents; Male; Mechanistic Target of Rapamycin Complex 1; Metformin; Mice; Mice, Inbred C57BL; Mice, Knockout; Phenformin; Precursor T-Cell Lymphoblastic Leukemia-Lymphoma; PTEN Phosphohydrolase; Signal Transduction; Sirolimus

T-cell acute lymphoblastic leukemia (T-ALL) has a relatively improved remission rate, but the poor outcomes are primarily due to resistance and relapse. Moreover, organs infiltration trends to occur during remission. Rapamycin was applied to treat malignancies for decades. In this investigation, we aimed to explore the molecular mechanisms and pathway changes during the T-ALL therapeutic process. T-ALL cell line Molt-4 cells were treated with rapamycin and performed microarray analysis to identify the deregulated miRNAs and mRNAs (log2 fold change>2 or <-2). To obtain regulatory miRNA/mRNA network, miRNA target prediction softwares and Cytoscape were used to plot and modularize the rapamycin treatment-related network. Surprisingly, the enriched pathways were not involved in mediating either cell death or apoptosis but were responsible for angiogenesis, cell survival, and anti-apoptosis, which is consistent with the Gene Ontology analysis and PPI network based on all deregulated mRNAs, indicating that these elements likely play a role in promoting Molt-4 cell survival or escaping from rapamycin. The expression of 3 miRNAs (miR-149-3p, miR-361-3p, and miR-944) and their putative targets, which play central roles in their module, were validated by qRT-PCR. These results provide novel insight into potentially relevant biological pathways for T-ALL cells escaping from chemotherapy or developing central nervous system infiltration.

Topics: Cell Line, Tumor; Cell Lineage; Gene Expression Profiling; Humans; MicroRNAs; Oligonucleotide Array Sequence Analysis; Precursor T-Cell Lymphoblastic Leukemia-Lymphoma; RNA, Messenger; Signal Transduction; Sirolimus; T-Lymphocytes

miR-150 functions as a tumor suppressor in malignancies of the lymphocyte lineage and its expression is significantly reduced in these cells. However, the mechanism of miR-150 repression is unknown and so are pharmacological interventions that can reverse it. Here, we report that reduced expression of miR-150 in human Jurkat T-cell acute lymphoblastic leukemia (T-ALL) cells is mediated by constitutive mTOR signaling, a common characteristic of T-ALL cell lines and clinical isolates. Activating mTOR signaling in non-malignant T cells also resulted in a significant miR-150 down-regulation. Conversely, treatment with a pharmacological mTOR inhibitor, rapamycin, increased miR-150 expression in a dose-dependent manner in Jurkat cells, as well as in other leukemia cells. Interestingly, ectopic over-expression of miR-150 acted in a feed-forward loop and further sensitized Jurkat cells to a rapamycin-induced cell cycle arrest by targeting a large network of cell cycle genes. These findings suggest that miR-150 is normally expressed in quiescent T lymphocytes to reinforce an anti-proliferative state, and that mTOR signaling promotes cell proliferation in part by inhibiting miR-150 expression. Restoration of the miR-150-dependent anti-proliferative loop constitutes a novel mechanism underlying the efficacy of rapamycin in a T-ALL cell line. Further investigation of this mechanism in clinical isolates of T-ALL and other hematopoietic malignancies could help better guide development of targeted therapies.

Topics: Cell Cycle Checkpoints; Dose-Response Relationship, Drug; Gene Expression Regulation, Leukemic; Genes, Tumor Suppressor; Humans; Jurkat Cells; MicroRNAs; Neoplasm Proteins; Precursor T-Cell Lymphoblastic Leukemia-Lymphoma; Signal Transduction; Sirolimus; TOR Serine-Threonine Kinases

Although the treatment of adult T-cell acute lymphoblastic leukemia (T-ALL) has been significantly improved, the heterogeneous genetic landscape of the disease often causes relapse. Aberrant activation of mammalian target of rapamycin (mTOR) pathway in T-ALL is responsible for treatment failure and relapse, suggesting that mTOR inhibition may represents a new therapeutic strategy. In this study, we investigated whether the mTOR complex 1 (mTORC1) inhibitor everolimus could be used as a therapeutic agent against human T-ALL. We showed that rapamycin and its analog RAD001 (everolimus) exerted only mild inhibition on the viability of Jurkat, CEM and Molt-4 cell lines (for everolimus the maximum inhibition was <40% at 100 nM), but greatly enhanced the phosphorylation of eIF4E, a downstream substrate of MAPK-interacting kinase (MNK) that was involved in promoting cell survival. Furthermore, we demonstrated in Jurkat cells that mTOR inhibitor-induced eIF4E phosphorylation was independent of insulin-like growth factor-1/insulin-like growth factor-1 receptor axis, but was secondary to mTOR inhibition. Then we examined the antileukemia effects of CGP57380, a MNK1 inhibitor, and we found that CGP57380 (4-16 μM) dose-dependently suppressed the expression of both phosphor-MNK1 and phosphor-eIF4E, thereby inhibiting downstream targets such as c-Myc and survivin in T-ALL cells. Importantly, CGP57380 produced a synergistic growth inhibitory effect with everolimus in T-ALL cells, and treatment with this targeted therapy overcame everolimus-induced eIF4E phosphorylation. In conclusion, our results suggest that dual-targeting of mTOR and MNK1/eIF4E signaling pathways may represent a novel therapeutic strategy for the treatment of human T-ALL.

Topics: Aniline Compounds; Antineoplastic Agents; Cell Line, Tumor; Drug Synergism; Eukaryotic Initiation Factor-4E; Everolimus; Humans; Intracellular Signaling Peptides and Proteins; Mechanistic Target of Rapamycin Complex 1; Phosphorylation; Precursor T-Cell Lymphoblastic Leukemia-Lymphoma; Protein Serine-Threonine Kinases; Purines; Sirolimus

T-cell acute lymphoblastic leukemias (T-ALLs) are clonal lymphoid malignancies with a poor prognosis, and still a lack of effective treatment. Here we examined the interactions between the mammalian target of rapamycin (mTOR) inhibitor rapamycin and idarubicin (IDA) in a series of human T-ALL cell lines Molt-4, Jurkat, CCRF-CEM and CEM/C1. Co-exposure of cells to rapamycin and IDA synergistically induced T-ALL cell growth inhibition and apoptosis mediated by caspase activation via the intrinsic mitochondrial pathway and extrinsic pathway. Combined treatment with rapamycin and IDA down-regulated Bcl-2 and Mcl-1, and inhibited the activation of phosphoinositide 3-kinase (PI3K)/mTOR and extracellular signal-related kinase (ERK). They also played synergistic pro-apoptotic roles in the drug-resistant microenvironment simulated by mesenchymal stem cells (MSCs) as a feeder layer. In addition, MSCs protected T-ALL cells from IDA cytotoxicity by up-regulating ERK phosphorylation, while rapamycin efficiently reversed this protective effect. Taken together, we confirm the synergistic antitumor effects of rapamycin and IDA, and provide an insight into the potential future clinical applications of combined rapamycin-IDA regimens for treating T-cell malignancies.

Topics: Apoptosis; Cell Line, Tumor; Cell Proliferation; Drug Resistance, Neoplasm; Drug Synergism; Extracellular Signal-Regulated MAP Kinases; Humans; Idarubicin; Leukemia, T-Cell; Mesenchymal Stem Cells; Precursor T-Cell Lymphoblastic Leukemia-Lymphoma; Proto-Oncogene Proteins c-akt; Proto-Oncogene Proteins c-bcl-2; Signal Transduction; Sirolimus; TOR Serine-Threonine Kinases; Tumor Microenvironment

mTOR is an evolutionarily conserved kinase that plays a critical role in sensing and responding to environmental determinants. Recent studies have shown that fine-tuning of the activity of mTOR complexes contributes to organogenesis and tumorigenesis. Although rapamycin, an allosteric mTOR inhibitor, is an effective immunosuppressant, the precise roles of mTOR complexes in early T-cell development remain unclear. Here we show that mTORC1 plays a critical role in the development of both early T-cell progenitors and leukemia. Deletion of Raptor, an essential component of mTORC1, produced defects in the earliest development of T-cell progenitors in vivo and in vitro. Deficiency of Raptor resulted in cell cycle abnormalities in early T-cell progenitors that were associated with instability of the Cyclin D2/D3-CDK6 complexes; deficiency of Rictor, an mTORC2 component, did not have the same effect, indicating that mTORC1 and -2 control T-cell development in different ways. In a model of myeloproliferative neoplasm and T-cell acute lymphoblastic leukemia (T-ALL) evoked by Kras activation, Raptor deficiency dramatically inhibited the cell cycle in oncogenic Kras-expressing T-cell progenitors, but not myeloid progenitors, and specifically prevented the development of T-ALL. Although rapamycin treatment significantly prolonged the survival of recipient mice bearing T-ALL cells, rapamycin-insensitive leukemia cells continued to propagate in vivo. In contrast, Raptor deficiency in the T-ALL model resulted in cell cycle arrest and efficient eradication of leukemia. Thus, understanding the cell-context-dependent role of mTORC1 illustrates the potential importance of mTOR signals as therapeutic targets.

Topics: Adaptor Proteins, Signal Transducing; Animals; Carrier Proteins; Cell Cycle; DNA Primers; Flow Cytometry; Gene Expression Profiling; Immunoblotting; Immunohistochemistry; Lymphopoiesis; Mechanistic Target of Rapamycin Complex 1; Mechanistic Target of Rapamycin Complex 2; Mice; Models, Immunological; Multiprotein Complexes; Precursor Cells, T-Lymphoid; Precursor T-Cell Lymphoblastic Leukemia-Lymphoma; Rapamycin-Insensitive Companion of mTOR Protein; Regulatory-Associated Protein of mTOR; Signal Transduction; Sirolimus; TOR Serine-Threonine Kinases

Posttransplant lymphoproliferative disease (PTLD) is a life-threatening complication after allogeneic hematopoietic stem cell transplantation. We describe here the case of a boy with history of induction failure of a T-cell acute lymphoblastic leukemia, who presented a life-threatening situation of nonengraftment and rituximab-refractory PTLD after the first hematopoietic stem cell transplantation. We decided to use an unusual strategy of combining a nonmyeloablative conditioning (fludarabine and cyclophosphamide) with a calcineurin inhibitor-free GvHD prophylaxis (sirolimus and mycophenolate mofetil). This strategy had permitted the control of an Epstein-Barr virus PLTD in umbilical cord blood transplantation without further reactivation.

Topics: Antibodies, Monoclonal, Murine-Derived; Antineoplastic Agents; Calcineurin; Child; Combined Modality Therapy; Drug Resistance, Neoplasm; Graft vs Host Disease; Hematopoietic Stem Cell Transplantation; Humans; Immunosuppressive Agents; Lymphoproliferative Disorders; Male; Mycophenolic Acid; Precursor T-Cell Lymphoblastic Leukemia-Lymphoma; Prognosis; Rituximab; Sirolimus; Transplantation Conditioning; Transplantation, Homologous; Vidarabine

The Notch1 signaling pathway plays an essential role in cell growth and differentiation. Over-expression of the intracellular Notch1 domain (ICN1) in murine hematopoietic cells is able to induce robust T-cell acute lymphoblastic leukemia (T-ALL) in mice. Here we explored the drug sensitivity of T-ALL cells in two subpopulations of CD8(+)CD4(+) and CD8(+)CD4(-) cells in Notch1-induced T-ALL mice. We found that Notch1 induced T-ALL cells could be decreased by chemotherapeutic drug cyclophosphamide (CTX). CD8(+)CD4(-) T-ALL cells were more sensitive to CTX treatment than CD8(+)CD4(+) T-ALL cells. The percentage of apoptotic cells induced by CTX treatment was higher in CD8(+)CD4(-) T-ALL cells. T-ALL cells were also inhibited by inhibitor of mTORC1 rapamycin. CD8(+)CD4(+) T-ALL cells were more susceptible to rapamycin treatment than CD8(+)CD4(-) T-ALL cells. Rapamycin treatment selectively arrested more CD8(+)CD4(+) T-ALL cells at G0 phase of cell cycle. A combination of the two drugs significantly improved overall survival of T-ALL bearing mice when compared with CTX or rapamycin alone. These results indicated that CD8(+)CD4(+) and CD8(+)CD4(-) leukemia cell populations had distinct drug sensitivity.

Topics: Animals; Antineoplastic Combined Chemotherapy Protocols; Apoptosis; Blotting, Western; CD8-Positive T-Lymphocytes; Cell Proliferation; Cyclophosphamide; Disease Models, Animal; Drug Resistance, Neoplasm; Humans; Mice; Mice, Inbred C57BL; Precursor T-Cell Lymphoblastic Leukemia-Lymphoma; Real-Time Polymerase Chain Reaction; Receptor, Notch1; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Sirolimus; Tumor Cells, Cultured

Multiple genetic or molecular alterations are known to be associated with cancer stem cell formation and cancer development. Targeting such alterations, therefore, may lead to cancer prevention. By crossing our previously established phosphatase and tensin homolog (Pten)-null acute T-lymphoblastic leukemia (T-ALL) model onto the recombination-activating gene 1(-/-) background, we show that the lack of variable, diversity and joining [V(D)J] recombination completely abolishes the Tcrα/δ-c-myc translocation and T-ALL development, regardless of β-catenin activation. We identify mammalian target of rapamycin (mTOR) as a regulator of β-selection. Rapamycin, an mTOR-specific inhibitor, alters nutrient sensing and blocks T-cell differentiation from CD4(-)CD8(-) to CD4(+)CD8(+), the stage where the Tcrα/δ-c-myc translocation occurs. Long-term rapamycin treatment of preleukemic Pten-null mice prevents Tcrα/δ-c-myc translocation and leukemia stem cell (LSC) formation, and it halts T-ALL development. However, rapamycin alone fails to inhibit mTOR signaling in the c-Kit(mid)CD3(+)Lin(-) population enriched for LSCs and eliminate these cells. Our results support the idea that preventing LSC formation and selectively targeting LSCs are promising approaches for antileukemia therapies.

Topics: Animals; Antibiotics, Antineoplastic; CD4-Positive T-Lymphocytes; CD8-Positive T-Lymphocytes; Cell Differentiation; Female; Flow Cytometry; Homeodomain Proteins; Immunoglobulin Variable Region; In Situ Hybridization, Fluorescence; Male; Mice; Mice, 129 Strain; Mice, Inbred C57BL; Mice, Knockout; Neoplastic Stem Cells; Precursor T-Cell Lymphoblastic Leukemia-Lymphoma; Proto-Oncogene Proteins c-myc; PTEN Phosphohydrolase; Receptors, Antigen, T-Cell, alpha-beta; Receptors, Antigen, T-Cell, gamma-delta; Recombination, Genetic; Sirolimus; T-Lymphocytes; Thymus Gland

Rationally designed therapies aim at the specific disruption of critical signaling pathways activated by malignant transformation or signals from the tumor microenvironment. Because mammalian target of rapamycin (mTOR) is an important signal integrator and a key translational regulator, we evaluated its potential involvement in T-cell acute lymphoblastic leukemia (T-ALL) and whether mTOR blockade synergizes with chemotherapeutic agents or other signaling antagonists to inhibit primary leukemia T cells.. mTOR signaling status was assessed using biochemical, immunostaining, and molecular regulation studies and functional assays performed to assess the impact of mTOR blockade on T-ALL proliferation, survival, and cell cycle.. We observed that mTOR signaling is highly activated in all T-ALL patients tested, with phosphorylation of its downstream substrates eIF4G and S6 ribosomal protein. mTOR activation was detected in vivo and was further increased in vitro by stimulation with interleukin-7, a potentially leukemogenic cytokine normally produced by the bone marrow microenvironment. In T-ALL cells, mTOR blockade was associated with accumulation of the cyclin-dependent kinase inhibitor p27(kip1), which preferentially adopted a nuclear localization. Functional studies using rapamycin or CCI-779 showed a dominant inhibitory effect of mTOR blockade on interleukin-7-induced proliferation, survival, and cell-cycle progression of T-ALL cells. Furthermore, mTOR blockade markedly potentiated the antileukemia effects of dexamethasone and doxorubicin, and showed highly synergistic interactions in combination with specific inhibitors of phosphatidylinositol 3-kinase/Akt and Janus kinase 3 signaling.. This study shows activation of mTOR signaling in primary T-ALL cells evolving in the leukemic bone marrow, and supports the inclusion of mTOR antagonists in current therapeutic regimens for this cancer.

Topics: Antibiotics, Antineoplastic; Cell Cycle; Cell Line, Tumor; Cell Proliferation; Cell Survival; Chromones; Dexamethasone; Doxorubicin; Drug Synergism; Enzyme Inhibitors; Eukaryotic Initiation Factor-4G; Humans; Immunoblotting; Immunohistochemistry; Janus Kinase 3; Microscopy, Fluorescence; Morpholines; Phosphatidylinositol 3-Kinase; Phosphoinositide-3 Kinase Inhibitors; Phosphorylation; Precursor T-Cell Lymphoblastic Leukemia-Lymphoma; Proto-Oncogene Proteins c-akt; Quinazolines; Signal Transduction; Sirolimus; TOR Serine-Threonine Kinases

The mammalian Target Of Rapamycin (mTOR) serine/threonine kinase belongs to two multi-protein complexes, referred to as mTORC1 and mTORC2. mTOR-generated signals have critical roles in leukemic cell biology by controlling mRNA translation of genes that promote proliferation and survival. However, allosteric inhibition of mTORC1 by rapamycin has only modest effects in T-cell acute lymphoblastic leukemia (T-ALL). Recently, ATP-competitive inhibitors specific for the mTOR kinase active site have been developed. In this study, we have explored the therapeutic potential of active-site mTOR inhibitors against both T-ALL cell lines and primary samples from T-ALL patients displaying activation of mTORC1 and mTORC2. The inhibitors affected T-ALL cell viability by inducing cell-cycle arrest in G(0)/G(1) phase, apoptosis and autophagy. Western blot analysis demonstrated a Ser 473 Akt dephosphorylation (indicative of mTORC2 inhibition) and a dephosphorylation of mTORC1 downstream targets. Unlike rapamycin, we found a marked inhibition of mRNA translation in T-ALL cell lines treated with active-site mTOR inhibitors. The inhibitors strongly synergized with both vincristine and the Bcl-2 inhibitor, ABT-263. Remarkably, the drugs targeted a putative leukemia-initiating cell sub-population (CD34(+)/CD7(-)/CD4(-)) in patient samples. In conclusion, the inhibitors displayed remarkable anti-leukemic activity, which emphasizes their future development as clinical candidates for therapy in T-ALL.

Topics: Animals; Apoptosis; Autophagy; Blotting, Western; Catalytic Domain; Cell Cycle; Cell Line, Tumor; Cell Proliferation; Flow Cytometry; Humans; Immunosuppressive Agents; Mechanistic Target of Rapamycin Complex 1; Mice; Multiprotein Complexes; Phosphorylation; Precursor T-Cell Lymphoblastic Leukemia-Lymphoma; Protein Kinase Inhibitors; Proteins; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Sirolimus; TOR Serine-Threonine Kinases; Transcription Factors

To investigate the cytotoxic effects of mTOR inhibitor rapamycin (Rapa) and idarubicin (IDA) on human T-cell acute lymphoblastic leukemia Jurkat cell line.. The proliferation of Jurkat cells was observed by CCK-8 assay. The combined index was analyzed by Isobologram method. Apoptosis was detected by electron microscopy and flow cytometry with Annexin V/PI staining. Protein expressions of Caspase 3, PARP, Caspase 8, Caspase 9, Akt, p-Akt, P85S6K, p-P85S6K, P70S6K, p-P70S6K, ERK1/2 and p-ERK1/2 were determined by Western blotting.. The IC(50) of IDA for Jurkat cells was significantly reduced when combined with 10 nmol/L rapamycin. The combined index was <1. Both electron microscopy and Annexin V/PI staining flow cytometry revealed that rapamycin significantly increased apoptotic sensitivity to IDA. The combination of IDA with rapamycin enhanced the expressions of Caspase 3, PARP, Caspase 8 and Caspase 9. Rapamycin significantly inhibited mTOR signaling upstream Akt and downstream S6K activation triggered by IDA, and the combination of the two agents led to synergistic inhibition of ERK phosphorylation.. Combination of IDA with rapamycin exerted a synergistic anti-proliferative effect and promoted apoptosis by both extrinsic and intrinsic apoptotic pathways in Jurkat cells. Inhibition of ERK phosphorylation and mTOR signaling by rapamycin may play a certain role in this synergistic effect.

Topics: Apoptosis; Caspase 3; Cell Proliferation; Drug Synergism; Humans; Idarubicin; Jurkat Cells; Precursor T-Cell Lymphoblastic Leukemia-Lymphoma; Proto-Oncogene Proteins c-akt; Sirolimus

Glucocorticoid (GC) resistance is frequently seen in acute lymphoblastic leukemia of T-cell lineage (T-ALL). In this study we investigate the potential and mechanism of using rapamycin to restore the sensitivity of GC-resistant T-ALL cells to dexamethasone (Dex) treatment.. Cell proliferation was detected by 3-(4,5-dimethylthiazol-2-yl)- 2,5-diphenyltetrazolium bromide (MTT) assay. Fluorescence-activated cell sorting (FACS) analysis was used to analyze apoptosis and cell cycles. Western blot analysis was performed to test the expression of the downstream effector proteins of mammalian target of rapamycin (mTOR), the cell cycle regulatory proteins, and apoptosis associated proteins.. 10 nM rapamycin markedly increased GC sensitivity in GC-resistant T-ALL cells and this effect was mediated, at least in part, by inhibition of mTOR signaling pathway. Cell cycle arrest was associated with modulation of G1-S phase regulators. Both rapamycin and Dex can induce up-regulation of cyclin-dependent kinase (CDK) inhibitors of p21 and p27 and co-treatment of rapamycin with Dex resulted in a synergistic induction of their expressions. Rapamycin did not obviously affect the expression of cyclin A, whereas Dex induced cyclin A expression. Rapamycin prevented Dex-induced expression of cyclin A. Rapamycin had a stronger inhibition of cyclin D1 expression than Dex. Rapamycin enhanced GC-induced apoptosis and this was not achieved by modulation of glucocorticoid receptor (GR) expression, but synergistically up-regulation of pro-apoptotic proteins like caspase-3, Bax, and Bim, and down-regulation of anti-apoptotic protein of Mcl-1.. Our data suggests that rapamycin can effectively reverse GC resistance in T-ALL and this effect is achieved by inducing cell cycles arrested at G0/G1 phase and activating the intrinsic apoptotic program. Therefore, combination of mTOR inhibitor rapamycin with GC containing protocol might be an attracting new therapeutic approach for GC resistant T-ALL patients.

Topics: Antineoplastic Agents; Apoptosis; Blotting, Western; Cell Cycle; Cell Line, Tumor; Cell Proliferation; Cell Separation; Dexamethasone; Drug Resistance, Neoplasm; Drug Synergism; Flow Cytometry; Humans; Precursor T-Cell Lymphoblastic Leukemia-Lymphoma; Sirolimus