Rapamycin, the mTOR kinase inhibitor, sensitizes acute myeloid leukemia cells, HL-60 cells, to the cytotoxic effect of arabinozide cytarabine

MNK, mTOR or eIF4E-selecting the best anti-tumor target for blocking translation initiation

Overexpression of eIF4E is common in patients with various solid tumors and hematologic cancers. As a potential anti-cancer target, eIF4E has attracted extensive attention from researchers. At the same time, mTOR kinases inhibitors and MNK kinases inhibitors, which are directly related to regulation of eIF4E, have been rapidly developed. To explore the optimal anti-cancer targets among MNK, mTOR, and eIF4E, this review provides a detailed classification and description of the anti-cancer activities of promising compounds. In addition, the structures and activities of some dual-target inhibitors are briefly described. By analyzing the different characteristics of the inhibitors, it can be concluded that MNK1/2 and eIF4E/eIF4G interaction inhibitors are superior to mTOR inhibitors. Simultaneous inhibition of MNK and eIF4E/eIF4G interaction may be the most promising anti-cancer method for targeting translation initiation.

Higher mTOR Expression: A Marker of Poor Outcome in Patients with de Novo AML

Acute myeloid leukemia (AML) displays significant clinical diversity mainly due to the variation in the underlying molecular defects, which is now recognized as the main driver for leukemogenesis. mTOR deregulation is thought to promote the proliferation and survival of leukemic blasts. This work aimed to study mTOR gene expression as a prognostic marker and a potential therapeutic target in AML. Quantitative real-time PCR evaluated mTOR expression in 45 new AML cases in relation to disease characteristics and outcome. mTOR was overexpressed in AML patients and higher levels were seen in the group that was not in complete remission (CR), at the end of induction, compared to those who achieved remission (17.03 ± 16.44 vs 3.91 ± 2.55 respectively, p < 0.001). In addition, mTOR expression inversely correlated with survival (p < 0.001). Patients with mTOR expression > 5.2 had a median overall survival of 10 months as opposed to 23 months in those with an expression of ≤ 5.2, p < 0.001. mTOR was an independent risk factor for failure of response in our patient group (p 0.007 and OR 1.54). mTOR has prognostic implications as it predicted the response and survival in our patients.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12288-022-01569-3.

Reinduction therapy with everolimus in combination with dexamethasone, high-dose cytarabin and cisplatinum in patients with relapsed or refractory classical Hodgkin lymphoma: an experimental phase I/II multicentre trial of the German Hodgkin Study Group (GHSG HD-R3i)

Reinduction chemotherapy followed by high-dose chemotherapy and autologous stem cell transplant (HDCT + ASCT) is second-line standard of care for transplant-eligible patients with relapsed/refractory classical Hodgkin lymphoma (r/r cHL) but has a high failure rate. Because response to reinduction is predictive of the outcome after HDCT + ASCT, we aimed to improve the standard dexamethasone, high-dose cytarabine and cisplatinum (DHAP) reinduction regimen by addition of the oral mammalian target of rapamycin inhibitor everolimus (everDHAP). Transplant-eligible patients aged 18-60 years with histologically confirmed r/r cHL were included in this experimental phase I/II trial. Everolimus (10 mg/day, determined in phase-I-part) was administered on day 0-13 of each DHAP cycle. From July 2014 to March 2018, 50 patients were recruited to the phase II everDHAP group; two were not evaluable, three discontinued due to toxicity. Randomization to a placebo group stopped in October 2015 due to poor recruitment after nine patients. The primary end-point of computed tomography (CT)-based complete remission (CR) after two cycles of everDHAP was expected to be ≥40%. With a CT-based CR rate of 27% (n = 12/45) after two cycles of everDHAP the trial did not meet the primary end-point. Adding everolimus to DHAP is thus feasible; however, the everDHAP regimen failed to show an improved efficacy.

Mitochondrial metabolism as a target for acute myeloid leukemia treatment

Acute myeloid leukemias (AML) are a group of aggressive hematologic malignancies resulting from acquired genetic mutations in hematopoietic stem cells that affect patients of all ages. Despite decades of research, standard chemotherapy still remains ineffective for some AML subtypes and is often inappropriate for older patients or those with comorbidities. Recently, a number of studies have identified unique mitochondrial alterations that lead to metabolic vulnerabilities in AML cells that may present viable treatment targets. These include mtDNA, dependency on oxidative phosphorylation, mitochondrial metabolism, and pro-survival signaling, as well as reactive oxygen species generation and mitochondrial dynamics. Moreover, some mitochondria-targeting chemotherapeutics and their combinations with other compounds have been FDA-approved for AML treatment. Here, we review recent studies that illuminate the effects of drugs and synergistic drug combinations that target diverse biomolecules and metabolic pathways related to mitochondria and their promise in experimental studies, clinical trials, and existing chemotherapeutic regimens.

Autophagy and apoptosis induction by sesamin in MOLT-4 and NB4 leukemia cells

Sesamin, the major furofuran lignan found in the seeds of Sesamum indicum L., has been investigated for its various medicinal properties. In the present study, the anti-leukemic effects of sesamin and its underlying mechanisms were investigated in MOLT-4 and NB4 acute leukemic cells. Leukemic cells were treated with various concentrations of sesamin. Cell viability was determined using an MTT assay. Flow cytometry using Annexin V-FITC/PI staining and anti-LC3/FITC antibodies was applied to detect the level of apoptosis and autophagy, respectively. Reverse transcription-quantitative PCR was performed to examine the alterations in the mRNA expression of apoptotic and autophagic genes. In addition, bioinformatics tools were used to predict the possible interactions between sesamin and its targets. The results revealed that sesamin inhibited MOLT-4 and NB4 cell proliferation in a dose-dependent manner. In addition, sesamin induced both apoptosis and autophagy. In sesamin-treated cells, the gene expression levels of caspase 3 and unc-51 like autophagy activating kinase 1 (ULK1) were upregulated, while those of mTOR were downregulated compared with in the control. Notably, the protein-chemical interaction network indicated that caspase 3, mTOR and ULK1 were the essential factors involved in the effects of sesamin treatment, as with anticancer agents, such as rapamycin, AZD8055, Torin1 and 2. Overall, the findings of the present study suggested that sesamin inhibited MOLT-4 and NB4 cell proliferation, and induced apoptosis and autophagy through the regulation of caspase 3 and mTOR/ULK1 signaling, respectively.

Rapamycin downregulates NKG2D ligands in acute myeloid leukemia cells via an activation of the STAT3 pathway: a potential mechanism for rapamycin-induced immune escape in leukemia

Background

The constitutive activation of the mammalian target of rapamycin (mTOR) is involved in the pathogenesis of many cancers. Rapamycin (RAPA), a specific inhibitor of mTOR, has been applied to the clinical treatment of tumors, and its anti-leukemia effect has also been confirmed.

Methods

We detected apoptosis and the NKG2D ligands expression in acute myeloid leukemia (AML) cells using flow cytometry and investigated the cytotoxicity of AML cells that had been co-cultured with natural killer (NK) cells using CFSE staining. We evaluated the signal pathways with a western blot assay.

Results

In this study, we found that RAPA can significantly inhibit the proliferation of AML cells. Further studies showed that the use of RAPA alone reduced the expression of NKG2D ligands on the membranes of HL-60 and THP-1 AML cells. Also, RAPA blocked the upregulation of the NKG2D ligand when AML cells were cultured with the demethylation drug decitabine (DAC). We found that RAPA decreased the expression of the NKG2D ligands by inducing the STAT3 phosphorylation of AML cells.

Conclusions

The discovery of this mechanism might further optimize the clinical use of RAPA for the treatment of AML.

Dueling for dual inhibition: Means to enhance effectiveness of PI3K/Akt/mTOR inhibitors in AML

The phosphatidylinositol 3-kinase/protein kinase B (Akt)/mechanistic target of rapamycin (PI3K/Akt/mTOR) pathway is amplified in 60-80% of patients with acute myelogenous leukemia (AML). Since this complex pathway is crucial to cell functions such as growth, proliferation, and survival, inhibition of this pathway would be postulated to inhibit leukemia initiation and propagation. Inhibition of the mTORC1 pathway has met with limited success in AML due to multiple resistance mechanisms including direct insensitivity of the mTORC1 complex, feedback activation of the PI3k/Akt signaling network, insulin growth factor-1 (IGF-1) activation of PI3K, and others. This review explores the role of mTOR inhibition in AML, mechanisms of resistance, and means to improve outcomes through use of dual mTORC1/2 inhibitors or dual TORC/PI3K inhibitors. How these inhibitors interface with currently available therapies in AML will require additional preclinical experiments and conduct of well-designed clinical trials.

Targeting mTOR signaling pathways and related negative feedback loops for the treatment of acute myeloid leukemia

An accumulating understanding of the complex pathogenesis of acute myeloid leukemia (AML) continues to lead to promising therapeutic approaches. Among the key aberrant intracellular signaling pathways involved in AML, the phosphatidylinositol 3-kinase/AKT/mammalian target of rapamycin (PI3K/AKT/mTOR) axis is of major interest. This axis modulates a wide array of critical cellular functions, including proliferation, metabolism, and survival. Pharmacologic inhibitors of components of this pathway have been developed over the past decade, but none has an established role in the treatment of AML. This review will discuss the preclinical data and clinical results driving ongoing attempts to exploit the PI3K/AKT/mTOR pathway in patients with AML and address issues related to negative feedback loops that account for leukemic cell survival. Targeting the PI3K/AKT/mTOR pathway is of high interest for the treatment of AML, but combination therapies with other targeted agents may be needed to block negative feedback loops in leukemia cells.

Mammalian target of rapamycin inhibitor rapamycin enhances anti-leukemia effect of imatinib on Ph+ acute lymphoblastic leukemia cells

BCR-ABL fusion gene typically causes a type of acute lymphoblastic leukemia (ALL), known as Ph+ ALL. Although imatinib (IM) treatment induced high rates of complete response (CR), serious acute and late complications are frequent, whereas more vexatiously resistance to chemotherapy and clinical relapse develops. Therefore, the efficacy of treatment in Ph+ ALL is still to be determined. In this study, we focused our attention on the potential benefit of rapamycin (RAPA), an mammalian target of rapamycin (mTOR) inhibitor, in combination with IM on a Ph+ ALL cell line SUP-B15 and a primary Ph+ ALL sample in vitro. Analysis of cell proliferation showed that RAPA (50 nm) plus IM exerted good synergistic effect on Ph+ ALL cells. Notably, we found that IM treatment induced the abnormal activation of the components of mTOR signaling pathway and p-BCR-ABL, whereas RAPA potently eliminated this deleterious side effect induced by IM and might overcome the resistance to IM. The synergistic effect was also associated with the increase in autophagy, which seemed to have an opposite role with apoptosis in Ph+ ALL cells, and cell cycle arrest in G1 phase. Altogether, our results suggested that IM in combination with RAPA was more effective for Ph+ ALL cells than IM alone.

Acute myeloid leukemia: potential for new therapeutic approaches targeting mRNA translation pathways

Despite advances in molecular research related to acute myeloid leukemia (AML) and a better understanding of the mechanisms of leukemogenesis and pathophysiology of the disease, the pharmacological agents used in the treatment of AML have remained essentially unchanged for the last three decades. Advances in the clinical management of AML patients have been achieved by defining better molecular prognostic markers, but there remains a need for new targeted drugs that disrupt non-overlapping pathways in leukemia cells. The mTOR cellular cascade is critical for cell metabolism, growth, proliferation and survival. Extensive preclinical work suggests that targeting mTOR may provide a powerful approach to block AML precursor cells, while other findings suggest enhanced antileukemic effects by combining mTOR inhibitors with traditional chemotherapy. Such combinations may increase antileukemic responses further, offering unique ways to overcome leukemic cell resistance and to eliminate primitive leukemic precursors.

Targeting the PI3K/AKT/mTOR signaling axis in children with hematologic malignancies

The phosphatidylinositiol 3-kinase (PI3K), AKT, mammalian target of rapamycin (mTOR) signaling pathway (PI3K/AKT/mTOR) is frequently dysregulated in disorders of cell growth and survival, including a number of pediatric hematologic malignancies. The pathway can be abnormally activated in childhood acute lymphoblastic leukemia (ALL), acute myelogenous leukemia (AML), and chronic myelogenous leukemia (CML), as well as in some pediatric lymphomas and lymphoproliferative disorders. Most commonly, this abnormal activation occurs as a consequence of constitutive activation of AKT, providing a compelling rationale to target this pathway in many of these conditions. A variety of agents, beginning with the rapamycin analogue (rapalog) sirolimus, have been used successfully to target this pathway in a number of pediatric hematologic malignancies. Rapalogs demonstrate significant preclinical activity against ALL, which has led to a number of clinical trials. Moreover, rapalogs can synergize with a number of conventional cytotoxic agents and overcome pathways of chemotherapeutic resistance for drugs commonly used in ALL treatment, including methotrexate and corticosteroids. Based on preclinical data, rapalogs are also being studied in AML, CML, and non-Hodgkin's lymphoma. Recently, significant progress has been made using rapalogs to treat pre-malignant lymphoproliferative disorders, including the autoimmune lymphoproliferative syndrome (ALPS); complete remissions in children with otherwise therapy-resistant disease have been seen. Rapalogs only block one component of the pathway (mTORC1), and newer agents are under preclinical and clinical development that can target different and often multiple protein kinases in the PI3K/AKT/mTOR pathway. Most of these agents have been tolerated in early-phase clinical trials. A number of PI3K inhibitors are under investigation. Of note, most of these also target other protein kinases. Newer agents are under development that target both mTORC1 and mTORC2, mTORC1 and PI3K, and the triad of PI3K, mTORC1, and mTORC2. Preclinical data suggest these dual- and multi-kinase inhibitors are more potent than rapalogs against many of the aforementioned hematologic malignancies. Two classes of AKT inhibitors are under development, the alkyl-lysophospholipids (APLs) and small molecule AKT inhibitors. Both classes have agents currently in clinical trials. A number of drugs are in development that target other components of the pathway, including eukaryotic translation initiation factor (eIF) 4E (eIF4E) and phosphoinositide-dependent protein kinase 1 (PDK1). Finally, a number of other key signaling pathways interact with PI3K/AKT/mTOR, including Notch, MNK, Syk, MAPK, and aurora kinase. These alternative pathways are being targeted alone and in combination with PI3K/AKT/mTOR inhibitors with promising preclinical results in pediatric hematologic malignancies. This review provides a comprehensive overview of the abnormalities in the PI3K/AKT/mTOR signaling pathway in pediatric hematologic malignancies, the agents that are used to target this pathway, and the results of preclinical and clinical trials, using those agents in childhood hematologic cancers.

mTOR kinase inhibitors as a treatment strategy in hematological malignancies

The mammalian target of rapamycin (mTOR) kinase is a key element of intracellular signal transduction, responsible for the regulation of cell growth and proliferation. Since abnormal activation of the mTOR pathway was found in several tumors, including human malignancies, it may be an attractive target for antineoplastic treatment. The first identified mTOR inhibitor was rapamycin (sirolimus). Subsequently, the most potent rapamycin analogues (rapalogues), such as everolimus, temsirolimus and deforolimus, have been developed. After encouraging preclinical experiments, several clinical trials testing the rapalogues in monotherapy or in combinations with other cytotoxic agents have been conducted in patients with hematological malignancies. Results of these studies, described in this review, indicate that inhibition of the mTOR pathway may be a very promising strategy of anti-tumor treatment in several types of lymphomas and leukemias. Recently, a second generation of more effective mTOR inhibitors has been developed. These are currently being assessed in preclinical, Phase I or I/II clinical studies.

Acute myeloid leukaemia: optimal management and recent developments

The current treatment of patients with acute myeloid leukaemia yields poor results, with expected cure rates in the order of 30-40% depending on the biological characteristics of the leukaemic clone. Therefore, new agents and schemas are intensively studied in order to improve patients' outcomes. This review summarizes some of these new paradigms, including new questions such as which anthracycline is most effective and at what dose. High doses of daunorubicin have shown better responses in young patients and are well tolerated in elderly patients. Monoclonal antibodies are promising agents in good risk patients. Drugs blocking signalling pathways could be used in combination with chemotherapy or in maintenance with promising results. Epigenetic therapies, particularly after stem cell transplantation, are also discussed. New drugs such as clofarabine and flavopiridol are reviewed and the results of their use discussed. It is clear that many new approaches are under study and hopefully will be able to improve on the outcomes of the commonly used '7+3' regimen of an anthracycline plus cytarabine with daunorubicin, which is clearly an ineffective therapy in the majority of patients.

Antileukaemia effect of rapamycin alone or in combination with daunorubicin on Ph+ acute lymphoblastic leukaemia cell line

The translocation (9;22) (q34;q11), known as the Philadelphia (Ph) chromosome and bcr-abl fusion gene, is the common cytogenetic abnormality and an unfavourable prognosis in adult acute lymphoblastic leukaemia (ALL). Although chemotherapeutic treatment produced high rates of complete response in approximately 70%-80% of newly diagnosed Ph+ ALL, the onset of resistance and clinical relapse is rapid. Therefore, the efficacy of treatment in Ph+ ALL is still to be determined. In this study, we aimed to assess the antileukemic activity of rapamycin (RAPA) (Sigma-Aldrich Corporation, MO, USA), a mammalian target of rapamycin inhibitor, alone and in combination with daunorubicin (DNR) (Pharmacia & Upjohn Company, Germany) in a Ph+ acute lymphoblastic cell line SUP-B15 and a primary Ph+ ALL sample in vitro. Here, we demonstrated that 50 nmol/L of RAPA significantly intensified the inhibition induced by DNR on both Ph+ ALL cell line and a primary Ph+ ALL sample. Notably, we reported that the consequence of DNR treatment induced the over expression of the components of mammalian target of rapamycin signalling pathway, whereas RAPA effectively eliminated this deleterious side effect of DNR, which might enhance DNR's ability to kill drug-resistant cancer. The synergistic effect was also associated with the increase in autophagy, blockage of cell cycle progression in the G1 phase. Altogether, our results suggest that DNR in combination with RAPA is more effective in the treatment of Ph+ ALL compared with DNR alone.

Utility of mTOR inhibition in hematologic malignancies

The mammalian target of rapamycin (mTOR) is an intracellular serine/threonine kinase that exists as a downstream component of numerous signaling pathways. The activation of mTOR results in the production of proteins involved in cell metabolism, growth, proliferation, and angiogenesis. Aberrant activation of mTOR signaling has been identified in a number of cancers, and targeted inhibition of mTOR has been successful in achieving tumor responses, prolonging progression-free survival, and increasing overall survival in various oncologic patient populations. In particular, persistent activation of mTOR signaling has been identified in cell lines and patient samples with leukemias, Hodgkin's lymphoma (HL), non-Hodgkin's lymphoma (NHL), multiple myeloma (MM), and Waldenström's macroglobulinemia (WM). In vitro and preclinical studies using agents that inhibit mTOR signaling have demonstrated cytostatic and cytotoxic effects in these hematologic malignancies, suggesting that mTOR is a rational target for therapy in these disease states. In addition, the combination of mTOR inhibitors with traditional therapies may help to overcome the development of resistance and may improve response rates over those seen with established regimens through synergistic or additive effects. Inhibitors of mTOR signaling currently are being investigated in clinical trials of hematologic malignancies as single agents and as components of combination regimens. Thus far, promising results have been seen with the application of mTOR inhibitors as single agents in patients with relapsed or refractory leukemia, HL, NHL, MM, and WM.

TNFα-mediated apoptosis in human osteoarthritic chondrocytes sensitized by PI3K-NF-κB inhibitor, not mTOR inhibitor

To investigate apoptosis of osteoarthritic (OA) chondrocytes stimulated with different inhibitors targeting tumor necrosis factor-alpha (TNFα) pathway, we isolated first passage chondrocytes from OA patients and then treated them with the inhibitors in combination with TNFα, and then collected the stimulated chondrocytes for Western blotting. Chondrocytes from OA patients expressed cleaved caspase-3 and PARP, suggesting apoptotic background. We here, validated that 10 ng/ml of TNFα couldn't induce more chondrocytes apoptosis. PI3K inhibitor LY294002 or NF-κB inhibitor CAPE, but not mTOR inhibitor rapamycin and MEK1/2 inhibitor U0126 in combination with TNFα could facilitate apoptosis. CAPE-induced more apoptosis could be explained by c-FLIP downregulation more than cIAP1 upregulation. And, we showed the first time that PI3K-NF-κB pathway, but not mTOR pathway could prevent chondrocytes apoptosis induced by a pro-apoptotic factor TNFα and call for attention while trying to inhibit NF-κB as a therapeutic target.

GCN2 protein kinase is required to activate amino acid deprivation responses in mice treated with the anti-cancer agent L-asparaginase

Asparaginase depletes circulating asparagine and glutamine, activating amino acid deprivation responses (AADR) such as phosphorylation of eukaryotic initiation factor 2 (p-eIF2) leading to increased mRNA levels of asparagine synthetase and CCAAT/enhancer-binding protein beta homologous protein (CHOP) and decreased mammalian target of rapamycin complex 1 (mTORC1) signaling. The objectives of this study were to assess the role of the eIF2 kinases and protein kinase R-like endoplasmic reticulum resident kinase (PERK) in controlling AADR to asparaginase and to compare the effects of asparaginase on mTORC1 to that of rapamycin. In experiment 1, asparaginase increased hepatic p-eIF2 in wild-type mice and mice with a liver-specific PERK deletion but not in GCN2 null mice nor in GCN2-PERK double null livers. In experiment 2, wild-type and GCN2 null mice were treated with asparaginase (3 IU per g of body weight), rapamycin (2 mg per kg of body weight), or both. In wild-type mice, asparaginase but not rapamycin increased p-eIF2, p-ERK1/2, p-Akt, and mRNA levels of asparagine synthetase and CHOP in liver. Asparaginase and rapamycin each inhibited mTORC1 signaling in liver and pancreas but maximally together. In GCN2 null livers, all responses to asparaginase were precluded except CHOP mRNA expression, which remained partially elevated. Interestingly, rapamycin blocked CHOP induction by asparaginase in both wild-type and GCN2 null livers. These results indicate that GCN2 is required for activation of AADR to asparaginase in liver. Rapamycin modifies the hepatic AADR to asparaginase by preventing CHOP induction while maximizing inhibition of mTORC1.