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1.  A Phase Ib Study of Combined VEGFR and mTOR Inhibition With Vatalanib and Everolimus in Patients With Advanced Renal Cell Carcinoma 
Clinical genitourinary cancer  2013;12(4):241-250.
Vatalanib is an oral vascular endothelial growth factor receptor (VEGFR) tyrosine kinase inhibitor and everolimus inhibits mammalian target of rapamycin (mTOR). A phase Ib study of vatalanib and everolimus was performed in patients with advanced solid tumors to determine the maximum tolerated dose (MTD) of the combination. Although treatment at the full therapeutic dose for both agents was not feasible, evidence of efficacy and long-term tolerability was demonstrated in some patients. This suggests that with dose adjustments, combination therapy with certain VEGFR and mTOR inhibitors may be possible and efficacious, particularly in renal cell carcinoma (RCC).
Vatalanib is an oral vascular endothelial growth factor receptor (VEGFR) tyrosine kinase inhibitor (TKI), whereas everolimus inhibits mammalian target of rapamycin (mTOR). Combination therapy with VEGFR and mTOR inhibitors has not been well tolerated to date but may have efficacy in renal cell carcinoma (RCC).
Patients and Methods
A phase Ib study of vatalanib and everolimus was performed in patients with advanced solid tumors to determine the maximum tolerated dose (MTD), safety, and tolerability of the combination. A dose-expansion cohort of 20 patients with metastatic RCC was studied to further define toxicity and preliminary efficacy in patients with RCC.
We evaluated 32 patients over 3 dose levels and a dose-expansion cohort. The most common toxicities of any grade were proteinuria, fatigue, hypertriglyceridemia, nausea, and vomiting. Dose-limiting toxicities (DLTs) included severe hypertension, diarrhea, neutropenia, mucositis, and fatigue. The MTD for the combination was vatalanib 1000 mg daily and everolimus 5 mg daily. In all patients, median overall survival (OS) was 16.3 months. In patients with RCC, median progression-free survival (PFS) was 5.8 months, and OS was 16.5 months. OS was significantly better in treatment-naive patients (25.1 months) compared with patients who had received previous vascular endothelial growth factor (VEGF)-targeted therapy (6.3 months). Seven of 24 (29.2%) evaluable patients demonstrated a partial response, and an additional 15 patients exhibited stable disease. Long-term tolerability (> 1 year) was demonstrated in 19% of patients.
Relevant doses of vatalanib and everolimus were achieved in combination, with expected toxicities. A substantial number of patients with RCC achieved an objective response in the treatment-naive setting, with prolonged tolerability and survival. Further comparative phase II/III studies of specifically targeted VEGF and mTOR inhibitor combinations may be warranted in patients with RCC.
PMCID: PMC4623321  PMID: 24685058
Clinical trial; mTOR inhibitor; Renal cell carcinoma; VEGFR inhibitor
2.  Active-Site Inhibitors of mTOR Target Rapamycin-Resistant Outputs of mTORC1 and mTORC2 
PLoS Biology  2009;7(2):e1000038.
The mammalian target of rapamycin (mTOR) regulates cell growth and survival by integrating nutrient and hormonal signals. These signaling functions are distributed between at least two distinct mTOR protein complexes: mTORC1 and mTORC2. mTORC1 is sensitive to the selective inhibitor rapamycin and activated by growth factor stimulation via the canonical phosphoinositide 3-kinase (PI3K)→Akt→mTOR pathway. Activated mTORC1 kinase up-regulates protein synthesis by phosphorylating key regulators of mRNA translation. By contrast, mTORC2 is resistant to rapamycin. Genetic studies have suggested that mTORC2 may phosphorylate Akt at S473, one of two phosphorylation sites required for Akt activation; this has been controversial, in part because RNA interference and gene knockouts produce distinct Akt phospho-isoforms. The central role of mTOR in controlling key cellular growth and survival pathways has sparked interest in discovering mTOR inhibitors that bind to the ATP site and therefore target both mTORC2 and mTORC1. We investigated mTOR signaling in cells and animals with two novel and specific mTOR kinase domain inhibitors (TORKinibs). Unlike rapamycin, these TORKinibs (PP242 and PP30) inhibit mTORC2, and we use them to show that pharmacological inhibition of mTOR blocks the phosphorylation of Akt at S473 and prevents its full activation. Furthermore, we show that TORKinibs inhibit proliferation of primary cells more completely than rapamycin. Surprisingly, we find that mTORC2 is not the basis for this enhanced activity, and we show that the TORKinib PP242 is a more effective mTORC1 inhibitor than rapamycin. Importantly, at the molecular level, PP242 inhibits cap-dependent translation under conditions in which rapamycin has no effect. Our findings identify new functional features of mTORC1 that are resistant to rapamycin but are effectively targeted by TORKinibs. These potent new pharmacological agents complement rapamycin in the study of mTOR and its role in normal physiology and human disease.
Author Summary
Growth factor pathways are required for normal development but are often inappropriately activated in many cancers. One growth-factor–sensitive pathway of increasing interest to cancer researchers relies on the mammalian target of rapamycin (mTOR), a kinase that (like all kinases) delivers phosphate groups from ATP to amino acid residues of downstream proteins. TOR proteins were first discovered in yeast as the cellular targets of rapamycin, a small, naturally occurring molecule derived from bacteria that is widely used as an immunosuppressant and more recently in some cancer therapies. The study of TOR proteins has relied heavily on the use of rapamycin, but rapamycin does not directly inhibit TOR kinase activity; rather, rapamycin influences TOR's enzymatic activities by binding to a domain far from the kinase's active site. Some mTOR functions are resistant to rapamycin, as a result of the kinase activity of one kind of multiprotein complex, the mTOR complex 2 (mTORC2), whereas rapamycin-sensitive functions of mTOR are due to the mTOR complex 1 (mTORC1). We have developed new inhibitors of mTOR that bind to the ATP-binding site of mTOR and inhibit the catalytic activity of both mTORC1 and mTORC2 without inhibiting other kinases. Unexpectedly, these inhibitors had profound effects on protein synthesis and cell proliferation due to their inhibition of mTORC1 rather than mTORC2. We found that the phosphorylation of a protein that controls protein synthesis, the mTORC1 substrate 4E binding protein (4EBP) is partially resistant to rapamycin but fully inhibited by our new inhibitors. The finding that 4EBP phosphorylation is resistant to rapamycin suggests that active-site inhibitors may be more effective than rapamycin in the treatment of cancer and may explain why rapamycin is so well tolerated when taken for immunosuppression.
Cells rely on the mammalian target of rapamycin kinase (mTOR) to sense growth factors. Inhibition of all forms of mTOR using newly developed inhibitors of its active site reveals new insights into the function of two mTOR-containing protein complexes and their potential as therapeutic targets.
PMCID: PMC2637922  PMID: 19209957
3.  Chemical Inhibitors and microRNAs (miRNA) Targeting the Mammalian Target of Rapamycin (mTOR) Pathway: Potential for Novel Anticancer Therapeutics 
The mammalian target of rapamycin (mTOR) is a critical regulator of many fundamental features in response to upstream cellular signals, such as growth factors, energy, stress and nutrients, controlling cell growth, proliferation and metabolism through two complexes, mTORC1 and mTORC2. Dysregulation of mTOR signalling often occurs in a variety of human malignant diseases making it a crucial and validated target in the treatment of cancer. Tumour cells have shown high susceptibility to mTOR inhibitors. Rapamycin and its derivatives (rapalogs) have been tested in clinical trials in several tumour types and found to be effective as anticancer agents in patients with advanced cancers. To block mTOR function, they form a complex with FKBP12 and then bind the FRB domain of mTOR. Furthermore, a new generation of mTOR inhibitors targeting ATP-binding in the catalytic site of mTOR showed potent and more selective inhibition. More recently, microRNAs (miRNA) have emerged as modulators of biological pathways that are essential in cancer initiation, development and progression. Evidence collected to date shows that miRNAs may function as tumour suppressors or oncogenes in several human neoplasms. The mTOR pathway is a promising target by miRNAs for anticancer therapy. Extensive studies have indicated that regulation of the mTOR pathway by miRNAs plays a major role in cancer progression, indicating a novel way to investigate the tumorigenesis and therapy of cancer. Here, we summarize current findings of the role of mTOR inhibitors and miRNAs in carcinogenesis through targeting mTOR signalling pathways and determine their potential as novel anti-cancer therapeutics.
PMCID: PMC3588076  PMID: 23434669
mTOR; Akt; S6K; Rapamycin; cancer; therapy; miRNA
4.  A Retro-inhibition Approach Reveals a Tumor Cell-Autonomous Response to Rapamycin in Head and Neck Squamous Carcinoma 
Cancer research  2008;68(4):1144-1153.
Emerging evidence supporting the activation of the Akt-mTOR signaling network in head and neck squamous cell carcinoma (HNSCC) progression has provided the rationale for exploring the therapeutic potential of inhibiting this pathway for HNSCC treatment. Indeed, rapamycin, a clinically relevant mTOR inhibitor, promotes the rapid regression of HNSCC-tumor xenografts in mice. However, rapamycin does not affect the growth of HNSCC cells in vitro, thus raising the possibility that, as for other cancer types, rapamycin may not target cancer cells directly but may instead act on a component of the tumor microenvioronment, such as tumor-associated vasculature. Here, we utilized a retro-inhibition approach to assess the contribution of cancer cell-autonomous actions of rapamycin to its antitumor activity in HNSCC. A rapamycin-resistant form of mTOR (mTOR-RR) was expressed in HNSCC cells, while retaining the wild-type (rapamycin-sensitive) mTOR alleles in host-derived endothelial and stromal cells. Expression of mTOR-RR prevented the decrease in phospho-S6 levels caused by rapamycin through mTOR in HNSCC cells but not in stromal cells, and rendered HNSCC xenografts completely resistant to the antitumoral activity of rapamycin. This reverse-pharmacology strategy also enabled monitoring the direct consequences of inhibiting mTOR in cancer cells within the complex tumor micro-environment, which revealed that mTOR controls the accumulation of HIF-1α and the consequent expression of VEGF and a glucose transporter, Glut-1, in HNSCC cells. These findings indicate that HNSCC cells are the primary target of rapamycin in vivo, and provide evidence that its anti-angiogenic effects may represent a downstream consequence of mTOR inhibition in HNSCC cells.
PMCID: PMC3443567  PMID: 18281490
mTOR; xenograft; signal transduction; human squamous cell carcinoma; drug discovery; rapamycin; lentivirus
5.  Phosphorylation of mTOR and S6RP predicts the efficacy of everolimus in patients with metastatic renal cell carcinoma 
BMC Cancer  2014;14:376.
The incidence of renal cell cancer (RCC) has been increasing for the past decade, and the 5-year survival for patients with metastatic RCC (mRCC) is rather low. Everolimus (RAD001), a new inhibitor for mammalian target of rapamycin (mTOR), is generally well tolerated, and demonstrates clinical benefit to patients with anti-VEGF-refractory mRCC. However, factors for selection of patients who may benefit from everolimus remain largely unknown. Here we aimed to explore potential molecular indicators for mRCC patients who may benefit from everolimus treatment.
Paraffin-embedded tumor tissue specimens derived from 18 mRCC patients before everolimus treatment, who participated the phase 1b trial of everolimus in VEGF receptor (VEGFR)-tyrosine kinase inhibitor (TKI)-refractory Chinese patients with mRCC (, NCT01152801), were examined for the expression levels of phosphorylated AKT, mTOR, eukaryotic initiation factor 4E (eIF4E) binding protein-1 (4EBP1) and 40S ribosomal protein S6 (S6RP) by immunohistochemistry. Clinical benefit rate (complete response [CR], partial response [PR], plus stable disease [SD] ≥ 6 months) and progression-free survival time (PFS) were correlated with expression levels of these mTOR-associated molecules.
In these 18 patients, there were 1 PR, 15 SDs (including 9 SDs ≥ 6 months), and 2 progressive diseases (PD). The clinical benefit rate (CBR) was 55.6% (10/18), and the median PFS time was 8.4 months. Patients with positive expression of phospho-mTOR showed a better CBR (71.4% versus 0%, P = 0.023) and PFS time (11.3 versus 3.7 months, P = 0.001) than those patients with negative expression. The median PFS of patients with positive phospho-S6RP expression was longer (11.3 versus 3.7 months, P = 0.002) than that of patients negative for phospho-S6RP expression. However, expression levels of phospho-4EBP1 and phospho-AKT were unassociated to efficacy of everolimus treatment with respect to CBR and PFS. Co-expression of phosphorylated mTOR, S6RP and/or 4EBP1 may improve the predictive value of the biomarkers for patients treated with everolimus.
The expression levels of phospho-mTOR and phospho-S6RP may be potential predictive biomarkers for efficacy of everolimus in patients with mRCC. Combining examinations of phosphorylated mTOR, S6RP and/or 4EBP1 may be a potential strategy to select mRCC patients sensitive to mTOR inhibitor treatment.
PMCID: PMC4041340  PMID: 24886512
Metastatic renal cell carcinoma; Targeted therapy; Mammalian target of rapamycin; Clinical response; Predictive biomarker
6.  Role of mTOR in anticancer drug resistance 
The mammalian target of rapamycin (mTOR) pathway plays a central role in regulating protein synthesis, ribosomal protein translation, and cap-dependent translation. Deregulations in mTOR signaling are frequently associated with tumorigenesis, angiogenesis, tumor growth and metastasis. This review highlights the role of the mTOR in anticancer drug resistance. We discuss the network of signaling pathways in which the mTOR kinase is involved, including the structure and activation of the mTOR complex and the pathways upstream and downstream of mTOR as well as other molecular interactions of mTOR. Major upstream signaling components in control of mTOR activity are PI3K/PTEN/AKT and Ras/Raf/MEK/ERK pathways. We discuss the central role of mTOR in mediating the translation of mRNAs of proteins related to cell cycle progression, those involved in cell survival such as c-myc, hypoxia inducible factor 1α (HIF-1α) and vascular endothelial growth factor (VEGF), cyclin A, cyclin dependent kinases (cdk1/2), cdk inhibitors (p21Cip1 and p27Kip1), retinoblastoma (Rb) protein, and RNA polymerases I and III. We then discuss the potential therapeutic opportunities for using mTOR inhibitors rapamycin, CCI-779, RAD001, and AP-23573 in cancer therapy as single agents or in combinations to reverse drug resistance.
PMCID: PMC2519122  PMID: 18440854
mTOR; drug resistance; p70S6K1; PI3K; AKT; MAP kinase; VEGF; CCI-779; RAD001 (everolimus); AP-23573; neurofibromatosis 1
7.  A critical role for mTORC1 in erythropoiesis and anemia 
eLife  2014;3:e01913.
Red blood cells (RBC) must coordinate their rate of growth and proliferation with the availability of nutrients, such as iron, but the signaling mechanisms that link the nutritional state to RBC growth are incompletely understood. We performed a screen for cell types that have high levels of signaling through mTORC1, a protein kinase that couples nutrient availability to cell growth. This screen revealed that reticulocytes show high levels of phosphorylated ribosomal protein S6, a downstream target of mTORC1. We found that mTORC1 activity in RBCs is regulated by dietary iron and that genetic activation or inhibition of mTORC1 results in macrocytic or microcytic anemia, respectively. Finally, ATP competitive mTOR inhibitors reduced RBC proliferation and were lethal after treatment with phenylhydrazine, an inducer of hemolysis. These results identify the mTORC1 pathway as a critical regulator of RBC growth and proliferation and establish that perturbations in this pathway result in anemia.
eLife digest
To multiply and grow, cells need to create more of the molecules—such as proteins—that make up their structure. This only happens if the cell has a good supply of the nutrients used to build the proteins.
Red blood cells are particularly sensitive to the supply of nutrients, especially iron, which is a key component of the hemoglobin molecules that enable the cells to transport oxygen around the body. A lack of iron can lead to a shortage of red blood cells and a condition called anemia. People with mild forms of anemia may feel tired or weak, but more severe forms of anemia can cause heart problems and even death.
A protein called mTOR forms part of a protein complex that helps alert the cells of many different organisms to the presence of nutrients. mTOR can add phosphate groups to ribosomes—the molecular machines that translate molecules of mRNA to build proteins. In 2012, researchers developed a technique called Phospho-Trap that can isolate these phosphorylated ribosomes from cells. Cells with an activated mTOR complex express more mTOR protein and in turn have more ribosomes that are modified. Examining the mRNA molecules associated with these ribosomes can reveal which proteins are produced in greater amounts in these cells.
Previous experiments using Phospho-Trap found the proteins that make up hemoglobin in unexpectedly high amounts in the mouse brain. Now, Knight et al.—and other researchers involved in the 2012 work—have established that the hemoglobin was not coming from the brain cells but from immature red blood cells circulating within the brain. These immature blood cells were found to have a highly active mTOR complex that promotes the production of hemoglobin and new blood cells.
Using genetic techniques in mice, Knight et al. found that the mTOR complex can cause anemia if it is underactive or overactive. Underactive mTOR complexes cause a type of anemia that produces small red blood cells and is usually triggered by a lack of iron. This made sense because mTOR is known to regulate both protein production and cell size. Boosting the activity of the mTOR complex leads to a type of anemia in which the cells are much larger than normal, and which is normally associated with inadequate amounts of folate and B12 vitamins.
When Knight et al. gave mice a drug that inhibits the mTOR protein, the mice developed anemia that resolved when the treatment stopped. However, mice that were given the mTOR inhibitor at the same time as a drug that destroys red blood cells, all died within days. Clinical trials are currently testing mTOR inhibitors as a possible cancer treatment; however, a common side effect of chemotherapy is that it stops new red blood cells being produced. Knight et al. suggest that the red blood cells of patients in these clinical trials must be closely monitored before deciding whether to continue the treatment further.
PMCID: PMC4179304  PMID: 25201874
mTOR; mTORC1; anemia; erythropoiesis; RBC; mouse
8.  The mTOR Signalling Pathway in Human Cancer 
The conserved serine/threonine kinase mTOR (the mammalian target of rapamycin), a downstream effector of the PI3K/AKT pathway, forms two distinct multiprotein complexes: mTORC1 and mTORC2. mTORC1 is sensitive to rapamycin, activates S6K1 and 4EBP1, which are involved in mRNA translation. It is activated by diverse stimuli, such as growth factors, nutrients, energy and stress signals, and essential signalling pathways, such as PI3K, MAPK and AMPK, in order to control cell growth, proliferation and survival. mTORC2 is considered resistant to rapamycin and is generally insensitive to nutrients and energy signals. It activates PKC-α and AKT and regulates the actin cytoskeleton. Deregulation of multiple elements of the mTOR pathway (PI3K amplification/mutation, PTEN loss of function, AKT overexpression, and S6K1, 4EBP1 and eIF4E overexpression) has been reported in many types of cancers, particularly in melanoma, where alterations in major components of the mTOR pathway were reported to have significant effects on tumour progression. Therefore, mTOR is an appealing therapeutic target and mTOR inhibitors, including the rapamycin analogues deforolimus, everolimus and temsirolimus, are submitted to clinical trials for treating multiple cancers, alone or in combination with inhibitors of other pathways. Importantly, temsirolimus and everolimus were recently approved by the FDA for the treatment of renal cell carcinoma, PNET and giant cell astrocytoma. Small molecules that inhibit mTOR kinase activity and dual PI3K-mTOR inhibitors are also being developed. In this review, we aim to survey relevant research, the molecular mechanisms of signalling, including upstream activation and downstream effectors, and the role of mTOR in cancer, mainly in melanoma.
PMCID: PMC3291999  PMID: 22408430
mTOR; cancer; melanoma; therapy; rapamycin
9.  Predictive value of phosphorylated mammalian target of rapamycin for disease-free survival in breast cancer patients receiving neoadjuvant chemotherapy 
Oncology Letters  2014;8(6):2642-2648.
The mammalian target of rapamycin (mTOR)/eukaryotic translation initiation factor 4E-binding protein 1 (4E-BP1) pathway plays a critical role in cell growth, survival and angiogenesis, and has been demonstrated to correlate with human epidermal growth factor receptor 2 (HER2) status. Neoadjuvant chemotherapy (NAC), also known as preoperative therapy, is now well established in the treatment of inoperable locally advanced and inflammatory breast cancer. In vitro study has shown that mTOR inhibitors, together with cytotoxic agents, exhibit tumor cell killing activity. A number of non-randomized studies in HER2-positive trastuzumab-resistant metastatic breast cancer have revealed the antitumor activity of mTOR inhibitors when used together with standard chemotherapy plus trastuzumab. In the present study, the expression levels of phosphorylated (p)-mTOR and p-4E-BP1 were analyzed in breast cancer patients prior to and following NAC, to determine whether p-mTOR and p-4E-BP1 affect the response to NAC and the subsequent survival. Formalin-fixed, paraffin-embedded tissues representing matched pairs of core biopsy (pre-NAC) and surgical specimen (post-NAC) from 83 patients with invasive ductal carcinomas were collected. Immunohistochemistry was performed to evaluate the expression of p-mTOR and p-4E-BP1 using a semi-quantitative scoring system by two pathologists. It was found that the expression of p-mTOR and p-4E-BP1 was downregulated following NAC. The decrease in mTOR expression following NAC was found to positively correlate with HER2 expression and the reduction of tumor sizes. The high expression of p-mTOR and p-4E-BP1 in pre-NAC specimens was associated with poor disease-free survival (DFS). Furthermore, the high expression of p-mTOR in post-NAC specimens was associated with poor DFS, regardless of whether the expression was high or low in the pre-NAC specimens. In conclusion, NAC was found to decrease the expression levels of p-mTOR and p-4E-BP1. The p-mTOR expression post-NAC may potentially serve as a predictor for DFS. However, further study is required to clarify the mechanism and to evaluate the predictive value of the phosphatidylinositol 3-kinase/Akt/mTOR/4E-BP1 pathway in NAC.
PMCID: PMC4214504  PMID: 25364442
phosphorylated-mammalian target of rapamycin; phosphorylated-eukaryotic translation initiation factor 4E-binding protein; neoadjuvant chemotherapy; predictive value
10.  Antitumor Activity of Rapamycin in a Phase I Trial for Patients with Recurrent PTEN-Deficient Glioblastoma 
PLoS Medicine  2008;5(1):e8.
There is much discussion in the cancer drug development community about how to incorporate molecular tools into early-stage clinical trials to assess target modulation, measure anti-tumor activity, and enrich the clinical trial population for patients who are more likely to benefit. Small, molecularly focused clinical studies offer the promise of the early definition of optimal biologic dose and patient population.
Methods and Findings
Based on preclinical evidence that phosphatase and tensin homolog deleted on Chromosome 10 (PTEN) loss sensitizes tumors to the inhibition of mammalian target of rapamycin (mTOR), we conducted a proof-of-concept Phase I neoadjuvant trial of rapamycin in patients with recurrent glioblastoma, whose tumors lacked expression of the tumor suppressor PTEN. We aimed to assess the safety profile of daily rapamycin in patients with glioma, define the dose of rapamycin required for mTOR inhibition in tumor tissue, and evaluate the antiproliferative activity of rapamycin in PTEN-deficient glioblastoma. Although intratumoral rapamycin concentrations that were sufficient to inhibit mTOR in vitro were achieved in all patients, the magnitude of mTOR inhibition in tumor cells (measured by reduced ribosomal S6 protein phosphorylation) varied substantially. Tumor cell proliferation (measured by Ki-67 staining) was dramatically reduced in seven of 14 patients after 1 wk of rapamycin treatment and was associated with the magnitude of mTOR inhibition (p = 0.0047, Fisher exact test) but not the intratumoral rapamycin concentration. Tumor cells harvested from the Ki-67 nonresponders retained sensitivity to rapamycin ex vivo, indicating that clinical resistance to biochemical mTOR inhibition was not cell-intrinsic. Rapamycin treatment led to Akt activation in seven patients, presumably due to loss of negative feedback, and this activation was associated with shorter time-to-progression during post-surgical maintenance rapamycin therapy (p < 0.05, Logrank test).
Rapamycin has anticancer activity in PTEN-deficient glioblastoma and warrants further clinical study alone or in combination with PI3K pathway inhibitors. The short-term treatment endpoints used in this neoadjuvant trial design identified the importance of monitoring target inhibition and negative feedback to guide future clinical development.
Trial registration: (#NCT00047073).
In a Phase I clinical trial Charles Sawyers and colleagues investigated the role of rapamycin in patients with PTEN-deficient glioblastoma.
Editors' Summary
Glioblastoma is a highly malignant tumor of the brain. As with other tumors, it can result from a number of different molecular changes. Traditional chemotherapy does little more than contain these tumors, and cannot cure it. An alternative approach to the treatment of such tumors is to target specific molecular changes in the tumor. Obviously such targeted treatment will work only in patients who have the specific molecular defect being targeted. Hence, traditional clinical trials, which include a large variety of different patients and tumors with different genetic changes, may be an inappropriate way to test how effective targeted treatments are.
One specific change that has been identified in around 40% of patients with glioblastoma is inactivation of a gene known as PTEN, which acts as a tumor suppressor gene. When PTEN is inactivated it has previously been shown to make cells more sensitive to a class of drugs known as mTOR inhibitors—one of which is rapamycin (trade name Sirolimus). mTOR is a protein that is involved in the regulation of a number of cellular processes including growth and proliferation. Drugs active against mTOR are currently being tested for effectiveness against other cancers and as immunosuppressive agents.
Why Was This Study Done?
This was a Phase I study—that is, the earliest type of a drug study that is done in humans—which aimed to look at the safety of rapamycin in a selected group of patients who were undergoing surgery after recurrence of glioblastoma, and whose tumors did not express PTEN. In addition, the authors also wanted to assess the feasibility of incorporating detailed molecular studies of the action of this drug into such a Phase I study and whether these molecular studies could predict whether patients were more or less likely to respond to rapamycin.
What Did the Researchers Do and Find?
A total of 15 patients were treated with rapamycin at differing doses for one week before surgery and then again after surgery until there was evidence that the tumors were progressing. There was no evidence of very severe toxicity in any of the patients, though there were some adverse effects that required treatment. When samples from the patients were tested after surgery, seven of them showed a reduction in how rapidly the tumor cells divided, and this reduction was associated with how much inhibition there was of mTOR. Two of these patients showed evidence on scans of a reduction in tumor mass. Cells from tumors that appeared resistant to rapamycin in patients were sensitive to rapamycin in tissue culture, suggesting that the lack of response was due to the drug not being able to penetrate the tumor. A second, unfortunate effect of rapamycin was to cause activation of another intracellular protein, Akt, in some patients; when this activation occurred, patients had a shorter time between surgery and a return of their disease.
What Do These Findings Mean?
The detailed molecular studies within this Phase I trial allow a better understanding of how this targeted drug works. These findings suggest that the rapamycin can reduce the proliferation rate of glioblastoma cells, and that this reduction appears to be related to how well the drug is able to penetrate the tumor and inhibit mTOR. However, in some patients the activation of a second pathway can speed up the course of the disease, so further trials should incorporate inhibitors of this second pathway.
Additional Information.
Please access these Web sites via the online version of this summary at
The US National Cancer Institute provides information on all aspects of cancer (in English and Spanish)
The UK charity Cancerbackup provides information on brain tumors
Wikipedia has a page on mTOR (note that Wikipedia is a free online encyclopedia that anyone can edit; available in several languages)
PMCID: PMC2211560  PMID: 18215105
11.  Use of mTOR inhibitors in the treatment of breast cancer: an evaluation of factors that influence patient outcomes 
Many systemic treatment options are available for advanced breast cancer, including endocrine therapy, chemotherapy, anti-human epidermal growth factor receptor 2 (HER2) therapy, and other targeted agents. Recently, everolimus, a mammalian target of rapamycin (mTOR) inhibitor, combined with exemestane, an aromatase inhibitor, has been approved in Europe and the USA for patients suffering from estrogen receptor-positive, HER2-negative advanced breast cancer previously treated by a nonsteroidal aromatase inhibitor, based on the results of BOLERO-2 (Breast cancer trials of OraL EveROlimus). This study showed a statistically significant and clinically meaningful improvement in median progression-free survival. Results concerning the impact on overall survival are expected in the near future. This clinically oriented review focuses on the use of mTOR inhibitors in breast cancer. Results reported with first-generation mTOR inhibitors (ridaforolimus, temsirolimus, everolimus) are discussed. The current and potential role of mTOR inhibitors is reported according to breast cancer subtype (estrogen receptor-positive HER2-negative, triple-negative, and HER2-positive ER-positive/negative disease). Everolimus is currently being evaluated in the adjuvant setting in high-risk estrogen receptor-positive, HER2-negative early breast cancer. Continuing mTOR inhibition or alternatively administering other drugs targeting the phosphatidylinositol-3-kinase/protein kinase B-mTOR pathway after progression on treatments including an mTOR inhibitor is under evaluation. Potential biomarkers to select patients showing a more pronounced benefit are reviewed, but we are not currently using these biomarkers in routine practice. Subgroup analysis of BOLERO 2 has shown that the benefit is consistent in all subgroups and that it is impossible to select patients not benefiting from addition of everolimus to exemestane. Side effects and impact on quality of life are other important issues discussed in this review. Second-generation mTOR inhibitors and dual mTOR-phosphatidylinositol-3-kinase inhibitors are currently being evaluated in clinical trials.
PMCID: PMC4000187  PMID: 24833916
breast cancer; treatment; everolimus; mTOR inhibitors; biomarkers; phosphatidylinositol-3-kinase/protein kinase B-mTOR pathway
12.  Safety and clinical efficacy of everolimus in the treatment of advanced renal cell carcinoma (RCC) 
Renal cell carcinoma (RCC) is one of the most lethal genitourinary malignancies. Recently, there has been a paradigm shift in the management of advanced RCC. New targeted therapies including vascular endothelial growth factor (VEGF) and mammalian target of rapamycin (mTOR) inhibitors have been developed which have shown promising results in a patient population who otherwise had very few options for treatment. The first mTOR inhibitor, temsirolimus, an intravenous prodrug, has shown improved overall survival in poor prognosis patients. More recently, an oral mTOR inhibitor, everolimus (RAD 001), has been developed which has been shown to delay disease progression in patients with metastatic RCC who have progressed on other targeted therapies. Although a survival advantage in phase III trials is seen with everolimus, associated systemic toxicities, while generally well tolerated, are not insignificant. These include mucositis, hyperglycemia, hyperlipidemia, and pneumonitis. Despite the side effects, emerging evidence points to everolimus as the optimal second-line treatment for patients with advanced renal cell carcinoma.
PMCID: PMC3108692  PMID: 21701620
metastatic renal cell carcinoma; everolimus; mTOR inhibitors; VEGF inhibitors
13.  Phase I-II study of everolimus and low-dose oral cyclophosphamide in patients with metastatic renal cell cancer 
BMC Cancer  2011;11:505.
For patients with metastatic renal cell cancer (mRCC) who progressed on vascular endothelial growth factor (VEGF) receptor tyrosine kinase inhibitor therapy, the orally administered mammalian target of rapamycin (mTOR) inhibitor everolimus has been shown to prolong progression free survival. Intriguingly, inhibition of mTOR also promotes expansion of immunosuppressive regulatory T cells (Tregs) that can inhibit anti-tumor immune responses in a clinically relevant way in various tumor types including RCC. This study intends to investigate whether the antitumor efficacy of everolimus can be increased by preventing the detrimental everolimus induced expansion of Tregs using a metronomic schedule of cyclophosphamide.
This phase I-II trial is a national multi-center study of different doses and schedules of low-dose oral cyclophosphamide in combination with a fixed dose of everolimus in patients with mRCC not amenable to or progressive after a VEGF-receptor tyrosine kinase inhibitor containing treatment regimen. In the phase I part of the study the optimal Treg-depleting dose and schedule of metronomic oral cyclophosphamide when given in combination with everolimus will be determined. In the phase II part of the study we will evaluate whether the percentage of patients progression free at 4 months of everolimus treatment can be increased from 50% to 70% by adding metronomic cyclophosphamide (in the dose and schedule determined in the phase I part). In addition to efficacy, we will perform extensive immune monitoring with a focus on the number, phenotype and function of Tregs, evaluate the safety and feasibility of the combination of everolimus and cyclophosphamide, perform monitoring of selected angiogenesis parameters and analyze everolimus and cyclophosphamide drug levels.
This phase I-II study is designed to determine whether metronomic cyclophosphamide can be used to counter the mTOR inhibitor everolimus induced Treg expansion in patients with metastatic renal cell carcinoma and increase the antitumor efficacy of everolimus.
Trial Registration Identifier NCT01462214, EudraCT number 2010-024515-13, Netherlands Trial Register number NTR3085.
PMCID: PMC3305518  PMID: 22129044
14.  First-Line Mammalian Target of Rapamycin Inhibition in Metastatic Renal Cell Carcinoma: An Analysis of Practice Patterns From the International Metastatic Renal Cell Carcinoma Database Consortium 
Clinical genitourinary cancer  2014;12(5):335-340.
Using an established international renal cell carcinoma (RCC) database, we retrospectively characterized the use and efficacy of mammalian target of rapamycin (mTOR) inhibitors in treatment-naive metastatic RCC (mRCC) patients. Front-line mTOR inhibitors are used in clinical practice mostly in select patients, who have non-clear cell histology, poor prognostic features, or as part of clinical trials.
Approval of the mTOR inhibitors for the treatment of mRCC was based on efficacy in poor-risk patients in the first-line setting for temsirolimus and in vascular endothelial growth factor inhibitor-refractory patients for everolimus. We strove to characterize temsirolimus and everolimus use and effectiveness in the first-line setting.
Patients and Methods
We performed a retrospective database analysis of mRCC patients who received mTOR inhibitors as first-line targeted therapy. The Kaplan-Meier product-limit method was used to estimate the distribution of progression-free survival (PFS) and overall survival (OS).
We identified 127 mRCC patients who had received a first-line mTOR inhibitor. Temsirolimus was administered in 93 patients (73%) and everolimus in 34 patients (27%). The main reasons for choice of temsirolimus were poor-risk disease (38%), non-clear cell histology (27%), and clinical trial availability (15%), whereas clinical trial (82%) and non-clear cell histology (6%) drove everolimus selection. Of the temsirolimus and everolimus patients, 58% and 32% were poor-risk according to the International mRCC Database Consortium criteria, respectively. The median PFS and OS were 3.4 and 12.5 months and 4.8 and 15.9 months with temsirolimus and everolimus, respectively. Although limited by small numbers, this study characterizes a real-world, international experience with the use of mTOR inhibition in treatment-naive mRCC patients.
Poor-risk RCC, non-clear cell histology, and clinical trials were the predominant reasons for mTOR inhibitor selection in the front-line setting. Because of the different patient populations in which they were administered, direct comparisons of the front-line efficacy of temsirolimus and everolimus cannot be made.
PMCID: PMC4164603  PMID: 24787966
Everolimus; mTOR inhibitor; Targeted therapy; Temsirolimus; Treatment-naive
15.  Akt-dependent and independent mechanisms of mTOR regulation in cancer 
Cellular signalling  2009;21(5):656-664.
The protein kinase mTOR (mammalian target of rapamycin) is a critical regulator of cellular metabolism, growth, and proliferation. These processes contribute to tumor formation, and many cancers are characterized by aberrant activation of mTOR. Although activating mutations in mTOR itself have not been identified, deregulation of upstream components that regulate mTOR are prevalent in cancer. The prototypic mechanism of mTOR regulation in cells is through activation of the PI3K/Akt pathway, but mTOR receives input from multiple signaling pathways. This review will discuss Akt-dependent and independent mechanisms of mTOR regulation in response to mitogenic signals, as well as its regulation in response to energy and nutrient-sensing pathways. Preclinical and clinical studies have demonstrated that tumors bearing genetic alterations that activate mTOR are sensitive to pharmacologic inhibition of mTOR. Elucidation of novel pathways that regulate mTOR may help identify predictive factors for sensitivity to mTOR inhibitors and could provide new therapeutic targets for inhibiting the mTOR pathway in cancer. This review will also highlight pharmacologic approaches that inhibit mTOR via activation of the AMP-activated protein kinase (AMPK), an important inhibitor of the mTOR pathway and an emerging target in cancer.
PMCID: PMC2650010  PMID: 19166931
mTOR; cancer; Akt; AMPK
16.  Pivotal Role of mTOR Signaling in Hepatocellular Carcinoma 
Gastroenterology  2008;135(6):1972-198411.
The advent of targeted therapies in hepatocellular carcinoma (HCC) has underscored the importance of pathway characterization to identify novel molecular targets for treatment. Based on its role in cell growth and differentiation, we evaluated mTOR signaling activation in human HCC, as well as the anti-tumoral effect of a dual-level blockade of the mTOR pathway.
The mTOR pathway was assessed using integrated data from mutation analysis (direct sequencing), DNA copy number changes (SNP-array), mRNA levels (qRT-PCR and gene expression microarray), and protein activation (immunostaining) in 351 human samples, including HCC (n=314), and non-tumoral tissue (n=37). Effects of dual blockade of mTOR signaling using a rapamycin analog (everolimus) and an EGFR/VEGFR inhibitor (AEE788) were evaluated in liver cancer cell lines, and in a tumor xenograft model.
Aberrant mTOR signaling (phosphorylated-RPS6) was present in half of the cases, associated with IGF pathway activation, EGF upregulation, and PTEN dysregulation. PTEN and PI3KCA-B mutations were rare events. Chromosomal gains in RICTOR (25% of patients) and positive pRPS6 staining correlated with recurrence. RICTOR-specific siRNA downregulation reduced tumor cell viability in vitro. Blockage of mTOR signaling with everolimus in vitro and in a xenograft model decelerated tumor growth and increased survival. This effect was enhanced in vivo after EGFR blockade.
MTOR signaling has a critical role in the pathogenesis of HCC, with evidence for the role of RICTOR in tumor oncogenesis. MTOR blockade with everolimus is effective in vivo. These findings establish a rationale for targeting mTOR pathway in clinical trials in HCC.
PMCID: PMC2678688  PMID: 18929564
17.  mTOR inhibition as a Therapeutic Strategy in the Management of Urologic Malignancies 
Molecular cancer therapeutics  2008;7(6):1347-1354.
The mammalian target of rapamycin (mTOR) is a protein kinase that regulates protein translation, cell growth and apoptosis. Recently, there has been an enormous increase in our understanding on molecular mechanisms underlying the therapeutics of rapamycin in cancer. Alterations in the pathway regulating mTOR occur in many solid malignancies including prostate, bladder and kidney cancer; and in-vitro and in-vivo models of prostate and bladder cancer have established the importance of the mTOR pathway in control of cancer progression and metastasis. Temsirolimus (Torisel™) and everolimus (RAD-001), two ester analogues of rapamycin, as well as rapamycin itself have clear antitumor activity in in-vitro and in-vivo models, and are under clinical trial investigations for prostate and bladder cancer. Phase II and III trials have already established the clinical efficacy of temsirolimus in renal cancer, and current renal trials are evaluating the combined effects of VEGF and mTOR inhibition. Ongoing studies in prostate and bladder cancer will soon define the activity and safety profiles of everolimus and temsirolimus. Recent molecular advances have uncovered a startling complexity in the macromolecular function of mTOR complexes, with the identification of new mTOR partners (raptor, rictor, FKBP38, PRAS40 and mSIN1), putative cancer therapeutic/prognostic targets for future clinical trials.
PMCID: PMC2587303  PMID: 18566209
prostate; rapamycin; everolimus; RAD-001; temsirolimus; CCI-779; Kidney; neoadjuvant; TGF-β; Akt; IGF-I; mTOR; Smad
18.  Inhibition of Mammalian Target of Rapamycin Induces Phosphatidylinositol 3-Kinase-Dependent and Mnk-Mediated Eukaryotic Translation Initiation Factor 4E Phosphorylation▿ †  
Molecular and Cellular Biology  2007;27(21):7405-7413.
The initiation factor eukaryotic translation initiation factor 4E (eIF4E) plays a critical role in initiating translation of mRNAs, including those encoding oncogenic proteins. Therefore, eIF4E is considered a survival protein involved in cell cycle progression, cell transformation, and apoptotic resistance. Phosphorylation of eIF4E (usually at Ser209) increases its binding affinity for the cap of mRNA and may also favor its entry into initiation complexes. Mammalian target of rapamycin (mTOR) inhibitors suppress cap-dependent translation through inhibition of the phosphorylation of eIF4E-binding protein 1. Paradoxically, we have shown that inhibition of mTOR signaling increases eIF4E phosphorylation in human cancer cells. In this study, we focused on revealing the mechanism by which mTOR inhibition increases eIF4E phosphorylation. Silencing of either mTOR or raptor could mimic mTOR inhibitors’ effects to increase eIF4E phosphorylation. Moreover, knockdown of mTOR, but not rictor or p70S6K, abrogated rapamycin's ability to increase eIF4E phosphorylation. These results indicate that mTOR inhibitor-induced eIF4E phosphorylation is secondary to mTOR/raptor inhibition and independent of p70S6K. Importantly, mTOR inhibitors lost their ability to increase eIF4E phosphorylation only in cells where both Mnk1 and Mnk2 were knocked out, indicating that mTOR inhibitors increase eIF4E phosphorylation through a Mnk-dependent mechanism. Given that mTOR inhibitors failed to increase Mnk and eIF4E phosphorylation in phosphatidylinositol 3-kinase (PI3K)-deficient cells, we conclude that mTOR inhibition increases eIF4E phosphorylation through a PI3K-dependent and Mnk-mediated mechanism. In addition, we also suggest an effective therapeutic strategy for enhancing mTOR-targeted cancer therapy by cotargeting mTOR signaling and Mnk/eIF4E phosphorylation.
PMCID: PMC2169067  PMID: 17724079
19.  Morphoproteomic Evidence of Constitutively Activated and Overexpressed mTOR Pathway in Cervical Squamous Carcinoma and High Grade Squamous Intraepithelial Lesions 
Human papilloma virus (HPV) infection of the uterine cervix is linked to the pathogenesis of cervical cancer. Preclinical in vitro and in vivo studies using HPV-containing human cervical carcinoma cell lines have shown that the mammalian target of rapamycin (mTOR) inhibitor, rapamycin, and epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitor, erlotinib, can induce growth delay of xenografts. Activation of Akt and mTOR are also observed in cervical squamous cell carcinoma and, the expression of phosphorylated mTOR was reported to serve as a marker to predict response to chemotherapy and survival of cervical cancer patients. Therefore, we investigated: a) the expression level of EGFR in cervical squamous cell carcinoma (SCC) and high-grade squamous intraepithelial lesions (HSIL) versus non-neoplastic cervical squamous epithelium; b) the state of activation of the mTOR pathway in these same tissues; and c) any impact of these signal transduction molecules on cell cycle. Formalin-fixed paraffin-embedded tissue microarray blocks containing 20 samples each of normal cervix, HSIL and invasive SCC, derived from a total of 60 cases of cervical biopsies and cervical conizations were examined. Immunohistochemistry was utilized to detect the following antigens: EGFR; mTOR pathway markers, phosphorylated (p)-mTOR (Ser2448) and p-p70S6K (Thr389); and cell cycle associated proteins, Ki-67 and S phase kinase-associated protein (Skp)2. Protein compartmentalization and expression were quantified in regard to proportion (0-100%) and intensity (0-3+). Mitotic index (MI) was also assessed. An expression index (EI) for pmTOR, p-p70S6K and EGFR, respectively was calculated by taking the product of intensity score and proportion of positively staining cells. We found that plasmalemmal EGFR expression was limited to the basal/parabasal cells (2-3+, EI = 67) in normal cervical epithelium (NL), but was diffusely positive in all HSIL (EI = 237) and SCC (EI 226). The pattern of cytoplasmic p-mTOR and nuclear p-p70S6K expression was similar to that of EGFR; all showed a significantly increased EI in HSIL/SCC versus NL (p<0.02). Nuclear translocation of p-mTOR was observed in all SCC lesions (EI = 202) and was significantly increased versus both HSIL (EI = 89) and NL (EI = 54) with p<0.015 and p<0.0001, respectively. Concomitant increases in MI and proportion of nuclear Ki-67 and Skp2 expression were noted in HSIL and SCC. In conclusion, morphoproteomic analysis reveals constitutive activation and overexpression of the mTOR pathway in HSIL and SCC as evidenced by: increased nuclear translocation of pmTOR and p-p70S6K, phosphorylated at putative sites of activation, Ser2448 and Thr389, respectively; correlative overexpression of the upstream signal transducer, EGFR, and increases in cell cycle correlates, Skp2 and mitotic indices. These results suggest that the mTOR pathway plays a key role in cervical carcinogenesis and targeted therapies may be developed for SCC as well as its precursor lesion, HSIL.
PMCID: PMC2600462  PMID: 19079619
mTOR pathway; cervical squamous carcinoma; high grade SIL; morphoproteomics
20.  CXCR4 and CXCR7 transduce through mTOR in human renal cancer cells 
Cell Death & Disease  2014;5(7):e1310-.
Treatment of metastatic renal cell carcinoma (mRCC) has improved significantly with the advent of agents targeting the mTOR pathway, such as temsirolimus and everolimus. However, their efficacy is thought to be limited by feedback loops and crosstalk with other pathways leading to the development of drug resistance. As CXCR4–CXCL12–CXCR7 axis has been described to have a crucial role in renal cancer; the crosstalk between the mTOR pathway and the CXCR4–CXCL12–CXCR7 chemokine receptor axis has been investigated in human renal cancer cells. In SN12C and A498, the common CXCR4–CXCR7 ligand, CXCL12, and the exclusive CXCR7 ligand, CXCL11, activated mTOR through P70S6K and 4EBP1 targets. The mTOR activation was specifically inhibited by CXCR4 antagonists (AMD3100, anti-CXCR4-12G5 and Peptide R, a newly developed CXCR4 antagonist) and CXCR7 antagonists (anti-CXCR7-12G8 and CCX771, CXCR7 inhibitor). To investigate the functional role of CXCR4, CXCR7 and mTOR in human renal cancer cells, both migration and wound healing were evaluated. SN12C and A498 cells migrated toward CXCL12 and CXCL11; CXCR4 and CXCR7 inhibitors impaired migration and treatment with mTOR inhibitor, RAD001, further inhibited it. Moreover, CXCL12 and CXCL11 induced wound healing while was impaired by AMD3100, the anti CXCR7 and RAD001. In SN12C and A498 cells, CXCL12 and CXCL11 promoted actin reorganization characterized by thin spikes at the cell periphery, whereas AMD3100 and anti-CXCR7 impaired CXCL12/CXCL11-induced actin polymerization, and RAD001 treatment further reduced it. In addition, when cell growth was evaluated in the presence of CXCL12, CXCL11 and mTOR inhibitors, an additive effect was demonstrated with the CXCR4, CXCR7 antagonists and RAD001. RAD001-resistant SN12C and A498 cells recovered RAD001 sensitivity in the presence of CXCR4 and CXCR7 antagonists. In conclusion, the entire axis CXCR4–CXCL12–CXCR7 regulates mTOR signaling in renal cancer cells offering new therapeutic opportunities and targets to overcome resistance to mTOR inhibitors.
PMCID: PMC4123065  PMID: 24991762
21.  mTOR: dissecting regulation and mechanism of action to understand human disease 
Biochemical Society transactions  2009;37(Pt 1):213-216.
This timely meeting brought together groups with shared interests in the regulation and effects of the mammalian Target Of Rapamycin (mTOR, see Figure 1), a highly conserved serine/threonine protein kinase with roles in cell metabolism, cell growth and cell survival. Although for some years it has been known that mTOR acts as a hub for inputs from growth factors (in particular insulin and insulin-like growth factors), nutrients and cellular stresses, some of the mechanisms involved are still poorly understood. Recent work implicating mTOR in a variety of important human pathologies, including cancer, Type 2 diabetes and neurodegenerative disorders has heightened interest and accelerated progress in dissecting out the control and functions of mTOR. An important goal of this meeting was to bring together individuals approaching the key problems from very different perspectives. In particular discussion of work addressing the role of nutrient sensors and transporters in mTOR regulation, brought a novel flavour to this TOR-centric meeting, which was welcomed by many delegates. The meeting was divided into three sessions, all intimately linked: ‘Insulin/TOR signalling and translational control’, ‘Nutrient regulation of mTOR’ and ‘The mTOR signalling pathway: physiology, pathology and treatments’. The scientific programme resulted in a lively and interactive meeting with extensive discussion following talks and also around posters. It was especially useful in raising some of the remaining questions that have yet to be fully addressed and in highlighting recent work that may ultimately help to provide several of the answers. Since the discovery of TOR proteins in yeast by Mike Hall and colleagues in the early nineteen-nineties working in Basel, more than 3000 papers on mTOR have been published; moreover, as Michael Hall indicated in his excellent introductory lecture, the literature is still expanding exponentially. It is only the newer areas covered at this meeting that are very briefly reviewed here.
PMCID: PMC2639772  PMID: 19143634
22.  Clinical features, epidemiology, and therapy of lymphangioleiomyomatosis 
Clinical Epidemiology  2015;7:249-257.
Lymphangioleiomyomatosis (LAM) is a multisystem disease of women, characterized by proliferation of abnormal smooth muscle-like LAM cells, leading to the formation of lung cysts, fluid-filled cystic structures in the axial lymphatics (eg, lymphangioleiomyomas), and renal angiomyolipomas. LAM is caused by mutations of the TSC1 or TSC2 genes, which encode, respectively, hamartin and tuberin, two proteins with a major role in control of the mammalian target of rapamycin (mTOR) signaling pathway. LAM occurs sporadically or in association with tuberous sclerosis complex, an autosomal-dominant syndrome characterized by widespread hamartomatous lesions. LAM may present with progressive dyspnea, recurrent pneumothorax, or chylothorax. Pulmonary function tests show reduced flow rates (forced expiratory volume in the first second) and diffusion capacity. Exercise testing may reveal gas exchange abnormalities, ventilatory limitation, and hypoxemia. The severity and progression of disease may be assessed by lung histology scores, quantification of computed tomography, pulmonary function testing, 6-minute walk tests, cardiopulmonary exercise testing, and measurement of serum vascular endothelial growth factor D levels. Sirolimus and everolimus, two mTOR inhibitors, are effective in stabilizing lung function and reducing the size of chylous effusions, lymphangioleiomyo-mas, and angiomyolipomas. However, inhibition of mTOR complex 1 increases autophagy, possibly enhancing LAM cell survival. Inhibition of autophagy with hydroxychloroquine, in combination with sirolimus, has been proposed as a possible treatment for LAM. Deficiency of tuberin results in increased RhoA GTPase activity and cell survival, an effect that is mediated through mTOR complex 2 signaling. Because sirolimus and everolimus only affect the activity of mTOR complex 1, therapies targeting RhoA GTPases with simvastatin, which inhibits Rho GTPases and promotes apoptosis, are being investigated. As in the case of cancer, LAM may be best treated with multiple drugs targeting signaling pathways considered important in the pathogenesis of disease.
PMCID: PMC4396456  PMID: 25897262
lymphangioleiomyomatosis; tuberous sclerosis; TSC1 and TSC2 mutations; mammalian target of rapamycin signaling pathway
23.  Mammalian Target of Rapamycin Inhibitors Resistance Mechanisms in Clear Cell Renal Cell Carcinoma 
Mammalian target of rapamycin (mTOR) is a kinase protein involved in PI3K/AKT signaling with a central role in the processes of cell growth, survival and angiogenesis. Frequent mutations of this pathway make upstream and downstream components novel targets for tailored therapy design. Two mTOR inhibitors – everolimus and temsirolimus - enable an increase in overall survival (OS) or progression-free survival (PFS) time in a treatment of renal cancer. Despite recent advances in renal cancer treatment, resistance to targeted therapy is common. Understanding of molecular mechanisms is the basis of drug resistance which can facilitate prediction of success or failure in combinational or sequential targeted therapy. The article provides current knowledge on the mTOR signaling network and gives insight into the mechanisms of resistance to mTOR inhibitors from the complex perspective of RCC biology. The mechanisms of resistance developed not only by cancer cells, but also by interactions with tumor microenvironment are analyzed to emphasize the role of angiogenesis in ccRCC pathogenesis. As recent studies have shown the role of PI3K/AKT-mTOR pathway in proliferation and differentiation of cancer stem cells, we discuss cancer stem cell hypothesis and its possible contribution to ccRCC resistance. In the context of drug resistance, we also elaborate on a new approach considering ccRCC as a metabolic disease. In conclusion we speculate on future developments in agents targeting the mTOR pathway taking into consideration the singular biology of ccRCC.
PMCID: PMC4141323  PMID: 25152703
Anti-angiogenic therapy; cancer stem cells; clear cell renal cell carcinoma; drug resistance; dual mTOR inhibitors; everolimus; temsirolimus; tumor microenvironment.
24.  Calcineurin Inhibitor-Induced and Ras-Mediated Overexpression of VEGF in Renal Cancer Cells Involves mTOR through the Regulation of PRAS40 
PLoS ONE  2011;6(8):e23919.
Malignancy is a major problem in patients treated with immunosuppressive agents. We have demonstrated that treatment with calcineurin inhibitors (CNIs) can induce the activation of proto-oncogenic Ras, and may promote a rapid progression of human renal cancer through the overexpression of vascular endothelial growth factor (VEGF). Interestingly, we found that CNI-induced VEGF overexpression and cancer cell proliferation was inhibited by rapamycin treatment, indicating potential involvement of the mammalian target of rapamycin (mTOR) pathway in this tumorigenic process. Here, we examined the role of mTOR pathway in mediating CNI- and Ras-induced overexpression of VEGF in human renal cancer cells (786-0 and Caki-1). We found that the knockdown of raptor (using siRNA) significantly decreased CNI-induced VEGF promoter activity as observed by promoter-luciferase assay, suggesting the role of mTOR complex1 (mTORC1) in CNI-induced VEGF transcription. It is known that mTOR becomes activated following phosphorylation of its negative regulator PRAS40, which is a part of mTORC1. We observed that CNI treatment and activation of H-Ras (through transfection of an active H-Ras plasmid) markedly increased the phosphorylation of PRAS40, and the transfection of cells using a dominant-negative plasmid of Ras, significantly decreased PRAS40 phosphorylation. Protein kinase C (PKC)-ζ and PKC-δ, which are critical intermediary signaling molecules for CNI-induced tumorigenic pathway, formed complex with PRAS40; and we found that the CNI treatment increased the complex formation between PRAS40 and PKC, particularly (PKC)-ζ. Inhibition of PKC activity using pharmacological inhibitor markedly decreased H-Ras-induced phosphorylation of PRAS40. The overexpression of PRAS40 in renal cancer cells significantly down-regulated CNI- and H-Ras-induced VEGF transcriptional activation. Finally, it was observed that CNI treatment increased the expression of phosho-PRAS40 in renal tumor tissues in vivo. Together, the phosphorylation of PRAS40 is critical for the activation of mTOR in CNI-induced VEGF overexpression and renal cancer progression.
PMCID: PMC3160347  PMID: 21886838
25.  mTOR activates hypoxia-inducible factor-1α and inhibits neuronal apoptosis in the developing rat brain during the early phase after hypoxia-ischemia 
Neuroscience letters  2011;507(2):118-123.
The mammalian target of rapamycin (mTOR) exerts neuroprotective effects under hypoxic or ischemic conditions. To explore whether mTOR participates in neuroprotective signaling through regulation of hypoxia-inducible factor-1α (HIF-1α), vascular endothelial growth factor (VEGF) and neuronal apoptosis in developing rat brain with hypoxia-ischemia (HI), we operated on postnatal day 10 rats by ligating the common carotid artery followed by exposure to systemic hypoxia. Brains were collected at various intervals to detect the expression of mTOR, phosphorylated mTOR (p-mTOR), HIF-1α, VEGF and cleaved caspase 3 (CC3), using immunohistochemistry and Western blot analysis. We also used terminal deoxynucleotidyl transferase-mediated dUTP-nick end labeling (TUNEL) to detect neuronal apoptosis. The p-mTOR protein expression increased at 2 h after HI, peaked at 8 h, lasted 24 h, and then dropped to the basal level. Also, the expression of HIF-1α and VEGF was significantly enhanced and peaked at 8 h after HI. Up-regulated expression of CC3 was observed at 2 h, peaked at 24 h, and lasted 72 h after HI. Increased neuronal apoptosis is associated with reduced HIF-1α and VEGF expression. Furthermore, pretreatment with rapamycin, a mTOR specific inhibitor, significantly inhibited HIF-1α and VEGF protein after HI. The expression of CC3 and the number of TUNEL-positive cells were up-regulated at 8 h and down-regulated at 24 h after HI in the rapamycin-treated group. Our findings suggest that mTOR may participate in the regulation of HIF-1α, VEGF and neuronal apoptosis, serving neuroprotective functions after HI in developing rat brain.
PMCID: PMC3525671  PMID: 22178140
hypoxia-ischemia; mammalian target of rapamycin; hypoxia-inducible factor-1α; vascular endothelial growth factor; apoptosis

Results 1-25 (1647043)