Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P42345 (mTOR)
 26,049 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The mammalian target of rapamycin mTOR is a central element in an evolutionary conserved signalling pathway that regulates cell growth, survival and proliferation, orchestrating signals originating from growth factors, nutrients or particular stress stimuli. Two important modulators of mTOR activity are the AKT and ERK/MAPK signalling pathways. Many studies have shown that mTOR plays an important role in the biology of malignant cells, including deregulation of the cell cycle, inactivation of apoptotic machinery and resistance to chemotherapeutic agents. The development of several mTOR inhibitors, in addition to rapamycin, has facilitated studies of the role of mTOR in cancer, and verified the antitumour effect of mTOR inhibition in many types of neoplasms, including lymphomas. Clinical trials of rapamycin derivatives in lymphoma patients are already in development and there are encouraging preliminary results, such as the substantial response of a subset of mantle cell lymphoma patients to the rapamycin analogue temsirolimus. Based on results obtained from in vitro and in vivo studies of the mTOR pathway in lymphomas, it seems that better understanding of mTOR regulation will reveal aspects of lymphomagenesis and contribute to the development of more powerful, targeted therapies for lymphoma patients.
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PMID:Mammalian target of rapamycin (mTOR) pathway signalling in lymphomas. 1824 20

Functional characterization of signaling pathways that critically control mantle cell lymphoma (MCL) cell growth and survival is relevant to designing new therapies for this lymphoma. We herein demonstrate that the constitutive activation of Akt correlates with the expression of the phosphorylated, inactive form of PTEN. Phosphatidyl-inositol-3 kinase (PI3-K)/Akt or mammalian target of rapamycin (mTOR) inhibition decreased the growth of both primary MCL cultures and established cell lines and antagonizes the growth-promoting activity of CD40 triggering and IL-4. These effects are mediated by nuclear accumulation of the p27(Kip1) inhibitor induced by down-regulation of the p45(Skp2) and Cks1 proteins, which target p27(Kip1) for degradation. Moreover, Akt inhibition down-regulated cyclin D1 by promoting its proteasome-dependent degradation driven by GSK-3. Intriguingly, mTOR inhibition affected cyclin D1 proteolysis only in MCL cells in which GSK-3 is under the direct control of mTOR, suggesting that different MCL subsets could be differently responsive to mTOR inhibition. Finally, PI3-K/Akt inhibitors, but not rapamycin, induced variable levels of caspase-dependent apoptosis and reduced telomerase activity. These results indicate that Akt and mTOR activation have distinct functional relevance in MCL and suggest that targeting Akt may result in more effective therapeutic effects compared with mTOR inhibition.
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PMID:Distinct functional significance of Akt and mTOR constitutive activation in mantle cell lymphoma. 1833 99

Mantle cell lymphoma (MCL) represents 6% of non-Hodgkin lymphomas, but is one of the most active fields of clinical investigation. Unfortunately, there is still no standard or curative therapy in MCL. Front-line therapy appears to benefit from intensification either through high-dose therapy with stem cell transplant consolidation or dose-intense chemotherapy with hyperfractionated cyclophosphamide, vincristine, adriamycin/doxorubicin and dexamethasone/rituximab. Most patients still relapse and a multitude of novel agents are currently being tested in this setting, including proteasome inhibitors with bortezomib (the first of its class and the first US FDA-approved drug for MCL), mTOR inhibitors, Bcl-2 inhibitors, antiangiogenesis agents and histone deacetylase inhibitors among others. An obvious effort is needed to enroll patients on clinical trials, the design of which might benefit from pharmacogenomics and a better understanding of MCL biology and its diversity.
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PMID:Bortezomib in mantle cell lymphoma. 1840 30

Intravenous (i.v.) temsirolimus, a novel inhibitor of mammalian target of rapamycin, is approved for the treatment of advanced renal cell carcinoma and is being studied in patients with mantle cell lymphoma. Because temsirolimus and its primary metabolite, sirolimus, are metabolised by the cytochrome P450 3A4 pathway (CYP3A4), the potential exists for pharmacokinetic (PK) drug interactions with the numerous agents that modulate CYP3A4 isozyme activity. We investigated the effects of ketoconazole, a potent CYP3A4 inhibitor, on the PK profile of i.v. temsirolimus in healthy adults. Coadministration of 400 mg oral ketoconazole with 5 mg i.v. temsirolimus had no significant effect on temsirolimus maximum concentration (C(max)) or area under the concentration curve (AUC). However, mean AUC increased 3.1-fold and AUC(sum) (sum of temsirolimus plus sirolimus AUCs) increased 2.3-fold compared with temsirolimus alone. A single 5-mg dose of temsirolimus with ketoconazole was well tolerated, and there were no unexpected safety results. Therefore, in cancer patients receiving 25 mg i.v. temsirolimus, concomitant treatment with agents that have strong CYP3A4 inhibition potential should be avoided. If a concomitant strong CYP3A4 inhibitor is necessary, a temsirolimus dose reduction to 12.5 mg weekly should be considered.
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PMID:Differential effects of ketoconazole on exposure to temsirolimus following intravenous infusion of temsirolimus. 1845 75

Therapeutic inhibition of the mammalian target of rapamycin (mTOR) has recently demonstrated a 30% to 40% response rate in patients with relapsed mantle cell lymphoma (MCL).(1,2) However, the exact mechanisms underlying this clinically significant response rate remain poorly understood. Here, we discuss the potential molecular mechanisms underlying this activity, and how to improve the therapeutic value of mTOR inhibitors by combining them with other agents that may target different molecular pathways.
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PMID:Therapeutic activity of mTOR inhibitors in mantle cell lymphoma: clues but no clear answers. 1846 12

Strategies able to downregulate the aberrant expression of cyclin D1 may prove of therapeutic relevance in cancer patients. This is particularly true for mantle cell lymphoma (MCL) in which cyclin D1 is overexpressed as a consequence of the t(11;14)(q13;q32) translocation. We have recently demonstrated that an increased cyclin D1 stability also contributes to the high levels of this protein observed in MCL cells. This effect is mediated by a constitutive activation of PI3-K/Akt, which keeps GSK-3beta inhibited. Here we show that inhibition of PI3-K/Akt induces a 40% decrease of cyclin D1 half-life as a result of accumulation of the dephosphorylated/active form of GSK-3beta within the nucleus, where this kinase can phosphorylate cyclin D1 on Thr286 thereby promoting its nuclear export. Translocation of cyclin D1 into the cytoplasm is mediated by the nuclear exportin CRM1, whose association with cyclin D1 increases following PI3-K/Akt inhibition. Notably, rapamycin downregulated GSK-3beta Ser9 phosphorylation with concurrent nuclear export of cyclin D1 only in MCL cells in which GSK-3beta is under the control of mTOR. These findings suggest that the ability to downregulate cyclin D1 through GSK-3beta may identify subsets of MCL patients who may benefit from the treatment with mTOR inhibitors and stimulate further studies to assess whether the inability to affect GSK-3beta activity may constitute a clinically relevant resistance factor to mTOR inhibitors.
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PMID:GSK-3beta inhibition: at the crossroad between Akt and mTOR constitutive activation to enhance cyclin D1 protein stability in mantle cell lymphoma. 1876 47

Mantle cell lymphoma (MCL) is an incurable hematologic malignancy whose pathogenesis is only partly understood. The aim of the present study was to define a "core phosphoproteome" in MCL cell lines that is representative of primary MCL in order to improve knowledge of the signal transduction pathways involved in its tumorigenesis. We have analyzed phosphorylated proteins in several MCL cell lines by immobilized metal affinity chromatography and separation by 2-D PAGE, followed by RP-HPLC coupled with MS/MS identification. These data were correlated with information on copy number gains obtained by SNP-chip analysis. Several of the proteins identified could be linked to a specific signal transduction pathway, and have been recently recognized as important players in MCL pathogenesis, such as nuclear factor-kappaB (NF-kappaB) and phosphoinositide-3 kinase-mammalian target of rapamycin (PI3K-mTOR). However, our data also implicate a number of novel proteins and pathways in the pathobiology of MCL, one of which is mitochondrial signaling. A second-level analysis identified MAPK1, CK2, CK1, PKCzeta, and PKCepsilon as candidate upstream molecules. Our study provides new insights in MCL pathogenesis and helps to form the basis for testing new target-specific therapeutics.
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PMID:Signal transduction pathways of mantle cell lymphoma: a phosphoproteome-based study. 1882 25

ABT-263 is a potent, orally bioavailable inhibitor of the antiapoptotic Bcl-2 family members Bcl-2, Bcl-x(L), and Bcl-w, which is currently in phase I clinical trials. Previous work has shown that this compound has low nanomolar cell-killing activity in a variety of lymphoma and leukemia cell lines, many of which overexpress Bcl-2 through a variety of mechanisms. Rapamycin is a macrolide antibiotic that inhibits the mammalian target of rapamycin complex, leading to cell cycle arrest and inhibition of protein translation. Rapamycin (and its analogues) has shown activity in a variety of tumor cell lines primarily through induction of cell cycle arrest. Activity has also been shown clinically in mantle cell lymphoma and advanced renal cell carcinoma. Here, we show that treatment of the follicular lymphoma lines DoHH-2 and SuDHL-4 with 100 nmol/L rapamycin induces substantial G(0)-G(1) arrest. Addition of as little as 39 nmol/L ABT-263 to the rapamycin regimen induced a 3-fold increase in sub-G(0) cells. Combination of these agents also led to a significant increase in Annexin V staining over ABT-263 alone. In xenograft models of these tumors, rapamycin induced a largely cytostatic response in the DoHH-2 and SuDHL-4 models. Coadministration with ABT-263 induced significant tumor regression, with DoHH-2 and SuDHL-4 tumors showing 100% overall response rates. Apoptosis in these tumors was significantly enhanced by combination therapy as measured by staining with an antibody specific for cleaved caspase-3. These data suggest that combination of ABT-263 and rapamycin or its analogues represents a promising therapeutic strategy for the treatment of lymphoma.
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PMID:ABT-263 and rapamycin act cooperatively to kill lymphoma cells in vitro and in vivo. 1885 30

Mantle cell lymphoma (MCL) is a clinically aggressive B-cell non-Hodgkin lymphoma characterized by the t(11;14)(q13;q32) and overexpression of cyclin D1. A high proportion of MCL tumors harbor wild-type (wt) and potentially functional p53 gene. We show here that stabilization and activation of wt-p53 using a recently developed potent MDM2 inhibitor, nutlin 3A, results in significant p53-dependent G1-S cell cycle arrest and apoptosis in MCL cells through regulation of p53 target genes. As mTOR signaling is activated in MCL and may control cyclin D1 levels, we show that p53 activation may downregulate the AKT/mTOR pathway through a mechanism involving AMP kinase (AMPK). Despite the non-genotoxic mode of nutlin 3A treatment, we show evidence that stabilization of p53 is associated with its phosphorylation at serine 15 residue and activation of AMPK. Stimulation of AMPK kinase activity using AICAR inhibits phosphorylation of critical downstream effectors of mTOR signaling, such as 4E-BP1 and rpS6. Pharmacologic inhibition of AMPK using compound C in nutlin-3A-treated MCL cells harboring wt-p53 did not affect the level of (ser15)p-p53, suggesting that the (ser15)p-p53 --> AMPK is the direction involved in the p53/AMPK/mTOR cross talk. These data establish a p53 --> AMPK --> mTOR mechanism in MCL and uncover a novel biologic effect of potent MDM2 inhibitors in preclinical models of MCL.
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PMID:Stabilization and activation of p53 downregulates mTOR signaling through AMPK in mantle cell lymphoma. 1922 36

The mammalian target of rapamycin (mTOR) is a serine/threonine kinase that functions as a key regulator of cell growth, protein synthesis, and cell-cycle progression through interactions with a number of signalling pathways, including PI3K/AKT, ras, TCL1, and BCR/ABL. Many haematological malignancies have aberrant activation of the mTOR and related signalling pathways. Accordingly, mTOR inhibitors, a class of signal transduction inhibitors that were originally developed as immunosuppressive agents, are being investigated in preclinical models and clinical trials for a number of haematological malignancies. Sirolimus and second-generation mTOR inhibitors, such as temsirolimus and everolimus, are safe and relatively well-tolerated, making them potentially attractive as single agents or in combination with conventional cytotoxics and other targeted therapies. Promising early clinical data suggests activity of mTOR inhibitors in a number of haematological diseases, including acute lymphoblastic leukaemia, chronic myeloid leukaemia, mantle cell lymphoma, anaplastic large cell lymphoma, and lymphoproliferative disorders. This review describes the rationale for using mTOR inhibitors in a variety of haematological diseases with a focus on their use in leukaemia.
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PMID:Mammalian target of rapamycin inhibitors and their potential role in therapy in leukaemia and other haematological malignancies. 1934 92


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