Predicted mechanisms of resistance to mTOR inhibitors

Contractile and Genetic Characterization of Cardiac Constructs Engineered from Human Induced Pluripotent Stem Cells: Modeling of Tuberous Sclerosis Complex and the Effects of Rapamycin

The implementation of three-dimensional tissue engineering concurrently with stem cell technology holds great promise for in vitro research in pharmacology and toxicology and modeling cardiac diseases, particularly for rare genetic and pediatric diseases for which animal models, immortal cell lines, and biopsy samples are unavailable. It also allows for a rapid assessment of phenotype-genotype relationships and tissue response to pharmacological manipulation. Mutations in the TSC1 and TSC2 genes lead to dysfunctional mTOR signaling and cause tuberous sclerosis complex (TSC), a genetic disorder that affects multiple organ systems, principally the brain, heart, skin, and kidneys. Here we differentiated healthy (CC3) and tuberous sclerosis (TSP8-15) human induced pluripotent stem cells (hiPSCs) into cardiomyocytes to create engineered cardiac tissue constructs (ECTCs). We investigated and compared their mechano-elastic properties and gene expression and assessed the effects of rapamycin, a potent inhibitor of the mechanistic target of rapamycin (mTOR). The TSP8-15 ECTCs had increased chronotropy compared to healthy ECTCs. Rapamycin induced positive inotropic and chronotropic effects (i.e., increased contractility and beating frequency, respectively) in the CC3 ECTCs but did not cause significant changes in the TSP8-15 ECTCs. A differential gene expression analysis revealed 926 up- and 439 down-regulated genes in the TSP8-15 ECTCs compared to their healthy counterparts. The application of rapamycin initiated the differential expression of 101 and 31 genes in the CC3 and TSP8-15 ECTCs, respectively. A gene ontology analysis showed that in the CC3 ECTCs, the positive inotropic and chronotropic effects of rapamycin correlated with positively regulated biological processes, which were primarily related to the metabolism of lipids and fatty and amino acids, and with negatively regulated processes, which were predominantly associated with cell proliferation and muscle and tissue development. In conclusion, this study describes for the first time an in vitro TSC cardiac tissue model, illustrates the response of normal and TSC ECTCs to rapamycin, and provides new insights into the mechanisms of TSC.

Drug-Eluting Stent Restenosis: Modern Approach to a Classic Challenge

In-stent restenosis (ISR) is a recognized complication following percutaneous coronary intervention in which the luminal diameter is narrowed through neointimal hyperplasia and vessel remodeling. Although rates of ISR have decreased in most recent years owing to newer generation drug-eluting stents, thinner struts, and better intravascular imaging modalities, ISR remains a prevalent dilemma that proves to be challenging to manage. Several factors have been proposed to contribute to ISR formation, including mechanical stent characteristics, technical factors during the coronary intervention, and biological aspects of drug-eluting stents. Presentation of ISR can range from asymptomatic to late myocardial infarction and could be difficult to differentiate from acute thrombus formation. No definite guidelines are present on the management of ISR. In this review, we will discuss the mechanisms underlying ISR and provide insight into patient-related and procedural risk factors contributing to ISR, in addition to highlighting common treatment approaches utilized in the management of ISR.

Targeting mTOR in the Context of Diet and Whole-body Metabolism

The mechanistic target of the rapamycin (mTOR) signaling pathway is the central regulator of cell growth and proliferation by integrating growth factor and nutrient availability. Under healthy physiological conditions, this process is tightly coordinated and essential to maintain whole-body homeostasis. Not surprisingly, dysregulated mTOR signaling underpins several diseases with increasing incidence worldwide, including obesity, diabetes, and cancer. Consequently, there is significant clinical interest in developing therapeutic strategies that effectively target this pathway. The transition of mTOR inhibitors from the bench to bedside, however, has largely been marked with challenges and shortcomings, such as the development of therapy resistance and adverse side effects in patients. In this review, we discuss the current status of first-, second-, and third-generation mTOR inhibitors as a cancer therapy in both preclinical and clinical settings, with a particular emphasis on the mechanisms of drug resistance. We focus especially on the emerging role of diet as an important environmental determinant of therapy response, and posit a conceptual framework that links nutrient availability and whole-body metabolic states such as obesity with many of the previously defined processes that drive resistance to mTOR-targeted therapies. Given the role of mTOR as a central integrator of cell metabolism and function, we propose that modulating nutrient inputs through dietary interventions may influence the signaling dynamics of this pathway and compensatory nodes. In doing so, new opportunities for exploiting diet/drug synergies are highlighted that may unlock the therapeutic potential of mTOR inhibitors as a cancer treatment.

Direct phosphorylation and stabilization of HIF-1α by PIM1 kinase drives angiogenesis in solid tumors

Angiogenesis is essential for the sustained growth of solid tumors. Hypoxia-inducible factor 1 (HIF-1) is a master regulator of angiogenesis and constitutive activation of HIF-1 is frequently observed in human cancers. Therefore, understanding the mechanisms governing the activation of HIF-1 is critical for successful therapeutic targeting of tumor angiogenesis. Herein, we establish a new regulatory mechanism responsible for the constitutive activation of HIF-1α in cancer, irrespective of oxygen tension. PIM1 kinase directly phosphorylates HIF-1α at threonine 455, a previously uncharacterized site within its oxygen-dependent degradation domain. This phosphorylation event disrupts the ability of prolyl hydroxylases to bind and hydroxylate HIF-1α, interrupting its canonical degradation pathway and promoting constitutive transcription of HIF-1 target genes. Moreover, phosphorylation of the analogous site in HIF-2α (S435) stabilizes the protein through the same mechanism, indicating post-translational modification within the oxygen-dependent degradation domain as a mechanism of regulating the HIF-α subunits. In vitro and in vivo models demonstrate that expression of PIM1 is sufficient to stabilize HIF-1α and HIF-2α in normoxia and stimulate angiogenesis in a HIF-1-dependent manner. CRISPR mutants of HIF-1α (Thr455D) promoted increased tumor growth, proliferation, and angiogenesis. Moreover, HIF-1α-T455D xenograft tumors were refractory to the anti-angiogenic and cytotoxic effects of PIM inhibitors. These data identify a new signaling axis responsible for hypoxia-independent activation of HIF-1 and expand our understanding of the tumorigenic role of PIM1 in solid tumors.

High-dose rapamycin exerts a temporary impact on T. reesei RUT-C30 through gene trFKBP12

BACKGROUND

Knowledge with respect to regulatory systems for cellulase production is prerequisite for exploitation of such regulatory networks to increase cellulase production, improve fermentation efficiency and reduce the relevant production cost. The target of rapamycin (TOR) signaling pathway is considered as a central signaling hub coordinating eukaryotic cell growth and metabolism with environmental inputs. However, how and to what extent the TOR signaling pathway and rapamycin are involved in cellulase production remain elusive.

RESULT

At the early fermentation stage, high-dose rapamycin (100 μM) caused a temporary inhibition effect on cellulase production, cell growth and sporulation of Trichoderma reesei RUT-C30 independently of the carbon sources, and specifically caused a tentative morphology defect in RUT-C30 grown on cellulose. On the contrary, the lipid content of T. reesei RUT-C30 was not affected by rapamycin. Accordingly, the transcriptional levels of genes involved in the cellulase production were downregulated notably with the addition of rapamycin. Although the mRNA levels of the putative rapamycin receptor trFKBP12 was upregulated significantly by rapamycin, gene trTOR (the downstream effector of the rapamycin-FKBP12 complex) and genes associated with the TOR signaling pathways were not changed markedly. With the deletion of gene trFKBP12, there is no impact of rapamycin on cellulase production, indicating that trFKBP12 mediates the observed temporary inhibition effect of rapamycin.

CONCLUSION

Our study shows for the first time that only high-concentration rapamycin induced a transient impact on T. reesei RUT-C30 at its early cultivation stage, demonstrating T. reesei RUT-C30 is highly resistant to rapamycin, probably due to that trTOR and its related signaling pathways were not that sensitive to rapamycin. This temporary influence of rapamycin was facilitated by gene trFKBP12. These findings add to our knowledge on the roles of rapamycin and the TOR signaling pathways play in T. reesei.

Current perspectives on targeting PIM kinases to overcome mechanisms of drug resistance and immune evasion in cancer

PIM kinases are a class of serine/threonine kinases that play a role in several of the hallmarks of cancer including cell cycle progression, metabolism, inflammation and immune evasion. Their constitutively active nature and unique catalytic structure has led them to be an attractive anticancer target through the use of small molecule inhibitors. This review highlights the enhanced activity of PIM kinases in cancer that can be driven by hypoxia in the tumour microenvironment and the important role that aberrant PIM kinase activity plays in resistance mechanisms to chemotherapy, radiotherapy, anti-angiogenic therapies and targeted therapies. We highlight an interaction of PIM kinases with numerous major oncogenic players, including but not limited to, stabilisation of p53, synergism with c-Myc, and notable parallel signalling with PI3K/Akt. We provide a comprehensive overview of PIM kinase's role as an escape mechanism to targeted therapies including PI3K/mTOR inhibitors, MET inhibitors, anti-HER2/EGFR treatments and the immunosuppressant rapamycin, providing a rationale for co-targeting treatment strategies for a more durable patient response. The current status of PIM kinase inhibitors and their use as a combination therapy with other targeted agents, in addition to the development of novel multi-molecularly targeted single therapeutic agents containing a PIM kinase targeting moiety are discussed.

The role of mTOR pathway as target for treatment in adrenocortical cancer

Adrenocortical carcinomas (ACCs) are rare tumors with scant treatment options for which new treatments are required. The mTOR pathway mediates the intracellular signals of several growth factors, including the insulin-like growth factors (IGFs), and therefore represents a potential attractive pathway for the treatment of several malignancies including ACCs. Several mTOR inhibitors, including sirolimus, temsirolimus and everolimus, have been clinically developed. This review summarizes the results of the studies evaluating the expression of the mTOR pathway components in ACCs, the effects of the mTOR inhibitors alone or in combination with other drugs in preclinical models of ACCs and the early experience with the use of these compounds in the clinical setting. The mTOR pathway seems a potential target for treatment of patients with ACC, but further investigation is still required to define the potential role of mTOR inhibitors alone or in combination with other drugs in the treatment of ACC patients.

HPV-16 E7 expression up-regulates phospholipase D activity and promotes rapamycin resistance in a pRB-dependent manner

Background

Human Papillomavirus (HPV) infection is the main risk factor for the development and progression of cervical cancer. HPV-16 E6 and E7 expression is essential for induction and maintenance of the transformed phenotype. These oncoproteins interfere with the function of several intracellular proteins, including those controlling the PI3K/AKT/mTOR pathway in which Phospolipase D (PLD) and Phosphatidic acid (PA) play a critical role.

Methods

PLD activity was measured in primary human keratinocytes transduced with retroviruses expressing HPV-16 E6, E7 or E7 mutants. The cytostatic effect of rapamycin, a well-known mTOR inhibitor with potential clinical applications, was evaluated in monolayer and organotypic cultures.

Results

HPV-16 E7 expression in primary human keratinocytes leads to an increase in PLD expression and activity. Moreover, this activation is dependent on the ability of HPV-16 E7 to induce retinoblastoma protein (pRb) degradation. We also show that cells expressing HPV-16 E7 or silenced for pRb acquire resistance to the antiproliferative effect of rapamycin.

Conclusion

This is the first indication that HPV oncoproteins can affect PLD activity. Since PA can interfere with the ability of rapamycin to bind mTOR, the use of combined strategies to target mTOR and PLD activity might be considered to treat HPV-related malignancies.

Electronic supplementary material

The online version of this article (10.1186/s12885-018-4392-8) contains supplementary material, which is available to authorized users.

An oral quinoline derivative, MPT0B392, causes leukemic cells mitotic arrest and overcomes drug resistant cancer cells

Despite great advances in the treatment of acute leukemia, a renaissance of current chemotherapy needs to be improved. The present study elucidates the underlying mechanism of a new synthetic quinoline derivative, MPT0B392 (B392) against acute leukemia and its potential anticancer effect in drug resistant cells. B392 caused mitotic arrest and ultimately led to apoptosis. It was further demonstrated to be a novel microtubule-depolymerizing agent. The effects of oral administration of B392 showed relative potent anti-leukemia activity in an in vivo xenograft model. Further investigation revealed that B392 triggered induction of the mitotic arrest, followed by mitochondrial membrane potential loss and caspases cleavage by activation of c-Jun N-terminal kinase (JNK). In addition, B392 enhanced the cytotoxicity of sirolimus in sirolimus-resistant acute leukemic cells through inhibition of Akt/mTOR pathway and Mcl-1 protein expression, and also was active in the p-glycoprotein (p-gp)-overexpressing National Cancer Institute/Adriamycin-Resistant cells with little susceptibility to p-gp. Taken together, B392 has potential as an oral mitotic drug and adjunct treatment for drug resistant cancer cells.

Targeting mTOR pathway inhibits tumor growth in different molecular subtypes of triple-negative breast cancers

Triple-negative breast cancers (TNBC) are characterized by frequent alterations in the PI3K/AKT/mTOR signaling pathway. In this study, we analyzed PI3K pathway activation in 67 patient-derived xenografts (PDX) of breast cancer and investigated the anti-tumor activity of the mTOR inhibitor everolimus in 15 TNBC PDX with different expression and mutational status of PI3K pathway markers.

Expression of the tumor suppressors PTEN and INPP4B was lost in 55% and 76% of TNBC PDX, respectively, while mutations in PIK3CA and AKT1 genes were rare. In 7 PDX treatment with everolimus resulted in a tumor growth inhibition higher than 50%, while 8 models were classified as low responder or resistant. Basal-like, LAR (Luminal AR), mesenchymal and HER2-enriched tumors were present in both responder and resistant groups, suggesting that tumor response to everolimus is not restricted to a specific TNBC subtype. Analysis of treated tumors showed a correlation between tumor response and post-treatment phosphorylation of AKT, increased in responder PDX, while PI3K pathway markers at baseline were not sufficient to predict everolimus response.

In conclusion, targeting mTOR decreased tumor growth in 7 out of 15 TNBC PDX tested. Response to everolimus occurred in different TNBC subtypes and was associated with post-treatment increase of P-AKT.

MLN0128, a novel mTOR kinase inhibitor, disrupts survival signaling and triggers apoptosis in AML and AML stem/ progenitor cells

mTOR activation leads to enhanced survival signaling in acute myeloid leukemia (AML) cells. The active-site mTOR inhibitors (asTORi) represent a promising new approach to targeting mTOR in AKT/mTOR signaling. MLN0128 is an orally-administered, second-generation asTORi, currently in clinical development. We examined the anti-leukemic effects and the mechanisms of action of MLN0128 in AML cell lines and primary samples, with a particular focus on its effect in AML stem/progenitor cells. MLN0128 inhibited cell proliferation and induced apoptosis in AML by attenuating the activity of mTOR complex 1 and 2. Using time-of-flight mass cytometry, we demonstrated that MLN0128 selectively targeted and functionally inhibited AML stem/progenitor cells with high AKT/mTOR signaling activity. Using the reverse-phase protein array technique, we measured expression and phosphorylation changes in response to MLN0128 in 151 proteins from 24 primary AML samples and identified several pro-survival pathways that antagonize MLN0128-induced cellular stress. A combined blockade of AKT/mTOR signaling and these pro-survival pathways facilitated AML cell killing. Our findings provide a rationale for the clinical use of MLN0128 to target AML and AML stem/progenitor cells, and support the use of combinatorial multi-targeted approaches in AML therapy.

Lung function response and side effects to rapamycin for lymphangioleiomyomatosis: a prospective national cohort study

Rationale

Mechanistic target of rapamycin inhibitors reduce loss of lung function in lymphangioleiomyomatosis (LAM), although their benefit varies between individuals. We examined lung function response and side effects to rapamycin in a national cohort.

Methods

Subjects were receiving rapamycin for progressive lung disease. Clinical evaluation, detailed phenotyping, serial lung function, rapamycin and safety monitoring were performed according to a clinical protocol. Lung function change, measured as FEV1 slope (ΔFEV1), was reported for those treated for 1 year or longer.

Results

Rapamycin was associated with improved ΔFEV1 in 21 individuals where pretreatment data were available (p<0.0001). In 47 treated for a mean duration of 35.8 months, mean ΔFEV1 was +11 (SD 75) mL/year, although it varied from +254 to −148 mL/year. The quartile with the highest positive ΔFEV1 had greater pretreatment FEV1 (p=0.02) and shorter disease durations (p=0.02) than the lowest quartile. Serum rapamycin level was positively associated with side effects (p=0.02) but not ΔFEV1 over 1 year. Within the first month of therapy, apthous ulcers, nausea and diarrhoea were associated with higher rapamycin levels. Acne, oedema and menstrual irregularities tended to increase over the first year of therapy. At the end of observation, the prevalence of side effects was 5% or less.

Conclusions

Rapamycin reduces lung function loss in LAM, although in some, ΔFEV1 continues to fall at an accelerated rate. Poor response to rapamycin was associated with lower pretreatment lung function and longer disease duration but not serum level. Early intervention with low-dose rapamycin may preserve lung function and reduce side effects.

mTOR Kinase Inhibition Effectively Decreases Progression of a Subset of Neuroendocrine Tumors that Progress on Rapalog Therapy and Delays Cardiac Impairment

Inhibition of mTOR signaling using the rapalog everolimus is an FDA-approved targeted therapy for patients with lung and gastroenteropancreatic neuroendocrine tumors (NET). However, patients eventually progress on treatment, highlighting the need for additional therapies. We focused on pancreatic NETs (pNET) and reasoned that treatment of these tumors upon progression on rapalog therapy, with an mTOR kinase inhibitor (mTORKi), such as CC-223, could overcome a number of resistance mechanisms in tumors and delay cardiac carcinoid disease. We performed preclinical studies using human pNET cells in vitro and injected them subcutaneously or orthotopically to determine tumor progression and cardiac function in mice treated with either rapamycin alone or switched to CC-223 upon progression. Detailed signaling and RNA sequencing analyses were performed on tumors that were sensitive or progressed on mTOR treatment. Approximately 57% of mice bearing pNET tumors that progressed on rapalog therapy showed a significant decrease in tumor volume upon a switch to CC-223. Moreover, mice treated with an mTORKi exhibited decreased cardiac dilation and thickening of heart valves than those treated with placebo or rapamycin alone. In conclusion, in the majority of pNETs that progress on rapalogs, it is possible to reduce disease progression using an mTORKi, such as CC-223. Moreover, CC-223 had an additional transient cardiac benefit on valvular fibrosis compared with placebo- or rapalog-treated mice. These results provide the preclinical rationale to further develop mTORKi clinically upon progression on rapalog therapy and to further test their long-term cardioprotective benefit in those NET patients prone to carcinoid syndrome. Mol Cancer Ther; 16(11); 2432-41. ©2017 AACR.

Autophagy as a potential therapeutic target during epithelial to mesenchymal transition in renal cell carcinoma: An in vitro study

Cancer progression toward invasive and metastatic disease is aided by reactivation of epithelial-mesenchymal transition (EMT), involving transdifferentiation of epithelial cells into mesenchymal phenotype. This leads to increased migratory and stem cell-like features in the cells. These EMT cells are more resistant to chemotherapy and it is hypothesized that the phenomenon of autophagy induces resistance, providing a survival strategy for cells. In the present study, we induced EMT-like phenotype in renal carcinoma cells and identified corresponding higher autophagy flux in these cells. The EMT transformed cells may be a representative of the resistant cancer stem cell(CSC)-like phenotype. Autophagy was identified as a potential mechanism of cell survival in these cells thus implying that autophagy inhibition can lead to enhanced cell death. We also observed that tumor cells especially EMT transformed cells, have been 'primed' to undergo autophagy by mTOR inhibition. We observed that combined use of autophagy inhibitor and temsirolimus (TEM) improved antitumor activity against RCC in EMT transformed metastatic cells. One of the approaches for inhibiting autophagy was the use of lysosomotropic anti-malarial drug, chloroquine (CQ) and we explored the therapeutic potential of combination of CQ and the mTOR inhibitor, TEM. EMT transformed cells showed increased cell cytotoxicity when autophagy was impaired by addition CQ with TEM. This led us to conclude that inhibition of autophagy with the current therapeutic regimen could be useful in targeting the EMT transformed cells along with the bulk tumor cells in RCC.

PIM2 regulates stemness through phosphorylation of 4E-BP1

Embryonic stem cells (ESCs) can undergo unlimited self-renewal and maintain pluripotency to differentiate into any cell type of the three germ layers. Extensive studies have shown ESC identity is regulated by transcription factors, epigenetic regulators and multiple signal transduction pathways. However, the kinase regulation of pluripotency is not well understood. Here we show that the serine/threonine kinase PIM2, which is highly expressed in ESCs but not in somatic cells, functions as a crucial stemness regulator in ESCs. Knockout of Pim2 inhibits the self-renewal and differentiation capability of ESCs. Mechanistic studies identified that PIM2 can directly phosphorylate 4E-BP1, leading to release of eIF4E which facilitates the translation of pluripotent genes in ESCs. Our study highlights a novel kinase cascade pathway for ESC identity maintenance.

In silico evaluation of DNA Damage Inducible Transcript 4 gene (DDIT4) as prognostic biomarker in several malignancies

DDIT4 gene encodes a protein whose main action is to inhibit mTOR under stress conditions whilst several in vitro studies indicate that its expression favors cancer progression. We have previously described that DDIT4 expression is an independent prognostic factor for tripe negative breast cancer resistant to neoadjuvant chemotherapy. We herein report that high DDIT4 expression is related to the outcome (recurrence-free survival, time to progression and overall survival) in several cancer types. We performed in silico analysis in online platforms, in pooled datasets from KM Plotter and meta-analysis of individual datasets from SurvExpress. High levels of DDIT4 were significantly associated with a worse prognosis in acute myeloid leukemia, breast cancer, glioblastoma multiforme, colon, skin and lung cancer. Conversely, a high DDIT4 expression was associated with an improved prognostic in gastric cancer. DDIT4 was not associated with the outcome of ovarian cancers. Analysis with data from the Cell Miner Tool in 60 cancer cell lines indicated that although rapamycin activity was correlated with levels of MTOR, it is not influenced by DDIT4 expression. In summary, DDIT4 might serve as a novel prognostic biomarker in several malignancies. DDIT4 activity could be responsible for resistance to mTOR inhibitors and is a potential candidate for the development of targeted therapy.

Metformin induces degradation of mTOR protein in breast cancer cells

Activation of mTOR is implicated in the development and progression of breast cancer. mTOR inhibition exhibited promising antitumor effects in breast cancer; however, its effect is compromised by several feedback mechanisms. One of such mechanisms is the upregulation of mTOR pathway in breast cancer cells. Despite the established role of mTOR activation in breast cancer, the status of total mTOR protein and its impact on the tumor behavior and response to treatment are poorly understood. Besides, the mechanisms underlying mTOR protein degradation in normal and cancer breast cells are still largely unknown. We and others found that total mTOR protein level is elevated in breast cancer cells compared to their nonmalignant counterparts. We have detected defective proteolysis of mTOR protein in breast cancer cells, which could, at least in part, explain the high level of mTOR protein in these cells. We show that metformin treatment in MCF‐7 breast cancer cells induced degradation of mTOR and sequestration of this protein in a perinuclear region. The decrease in mTOR protein level in these cells correlated positively with a concomitant inhibition of proliferation and migration potentials of these cells. These findings provided a novel mechanism for the metformin action in breast cancer treatment. Understanding the proteolytic mechanism responsible for mTOR level in breast cancer may pave the way for improving the efficacy of breast cancer treatment regimens and mitigating drug resistance as well as providing a basis for potential novel therapeutic modalities for breast cancer.

Differential effects of rapalogues, dual kinase inhibitors on human ovarian carcinoma cells in vitro

Ovarian cancer is the second most common gynaecological malignancy and was diagnosed in over 7,000 women in 2011 in the UK. There are currently no reliable biomarkers available for use in a regular screening assay for ovarian cancer and due to characteristic late presentation (78% in stages III and IV) ovarian cancer has a low survival rate (35% after 10 years). The mTOR pathway is a central regulator of growth, proliferation, apoptosis and angiogenesis; providing balance between available resources such as amino acids and growth factors, and stresses such as hypoxia, to control cellular behaviour accordingly. Emerging data links mTOR with the aetiopathogenesis of ovarian cancer. We hypothesised that mTOR inhibitors could play a therapeutic role in ovarian cancer treatment. In this study we began by validating the expression of four main mTOR pathway components, mTOR, DEPTOR, rictor and raptor, at gene and protein level in in vitro models of endometrioid (MDAH-2774) and clear cell (SKOV3) ovarian cancer using qPCR and ImageStream technology. Using a wound healing assay we show that inhibition of the mTOR pathway using rapamycin, rapalogues, resveratrol and NVP BEZ-235 induces a cytostatic and not cytotoxic response up to 18 h in these cell lines. We extended these findings up to 72 h with a proliferation assay and show that the effects of inhibition of the mTOR pathway are primarily mediated by the dephosphorylation of p70S6 kinase. We show that mTOR inhibition does not involve alteration of mTOR pathway components or induce caspase 9 cleavage. Preclinical studies including ovarian tissue of ovarian cancer patients, unaffected controls and patients with unrelated gynaecological conditions show that DEPTOR is reliably upregulated in ovarian cancer.

4EBP1/c-MYC/PUMA and NF-κB/EGR1/BIM pathways underlie cytotoxicity of mTOR dual inhibitors in malignant lymphoid cells

The mammalian target of rapamycin (mTOR), a kinase that regulates proliferation and apoptosis, has been extensively evaluated as a therapeutic target in multiple malignancies. Rapamycin analogs, which partially inhibit mTOR complex 1 (mTORC1), exhibit immunosuppressive and limited antitumor activity, but sometimes activate survival pathways through feedback mechanisms involving mTORC2. Thus, attention has turned to agents targeting both mTOR complexes by binding the mTOR active site. Here we show that disruption of either mTOR-containing complex is toxic to acute lymphocytic leukemia (ALL) cells and identify 2 previously unrecognized pathways leading to this cell death. Inhibition of mTORC1-mediated 4EBP1 phosphorylation leads to decreased expression of c-MYC and subsequent upregulation of the proapoptotic BCL2 family member PUMA, whereas inhibition of mTORC2 results in nuclear factor-κB-mediated expression of the Early Growth Response 1 (EGR1) gene, which encodes a transcription factor that binds and transactivates the proapoptotic BCL2L11 locus encoding BIM. Importantly, 1 or both pathways contribute to death of malignant lymphoid cells after treatment with dual mTORC1/mTORC2 inhibitors. Collectively, these observations not only provide new insight into the survival roles of mTOR in lymphoid malignancies, but also identify alterations that potentially modulate the action of mTOR dual inhibitors in ALL.

The Enigma of Rapamycin Dosage

The mTOR pathway is a critical regulator of cell growth, proliferation, metabolism, and survival. Dysregulation of mTOR signaling has been observed in most cancers and, thus, the mTOR pathway has been extensively studied for therapeutic intervention. Rapamycin is a natural product that inhibits mTOR with high specificity. However, its efficacy varies by dose in several contexts. First, different doses of rapamycin are needed to suppress mTOR in different cell lines; second, different doses of rapamycin are needed to suppress the phosphorylation of different mTOR substrates; and third, there is a differential sensitivity of the two mTOR complexes mTORC1 and mTORC2 to rapamycin. Intriguingly, the enigmatic properties of rapamycin dosage can be explained in large part by the competition between rapamycin and phosphatidic acid (PA) for mTOR. Rapamycin and PA have opposite effects on mTOR whereby rapamycin destabilizes and PA stabilizes both mTOR complexes. In this review, we discuss the properties of rapamycin dosage in the context of anticancer therapeutics.

The PI3K/AKT Pathway as a Target for Cancer Treatment

Anticancer targeted therapies are designed to exploit a particular vulnerability in the tumor, which in most cases results from its dependence on an oncogene and/or loss of a tumor suppressor. Genes in the phosphoinositide 3-kinase (PI3K)/AKT pathway are the most frequently altered in human cancers. Aberrant activation of this pathway, as a result of these somatic alterations, is associated with cellular transformation, tumorigenesis, cancer progression, and drug resistance. Several drugs targeting PI3K/ATK are currently in clinical trials, alone or in combination, in both solid tumors and hematologic malignancies. These drugs are the focus of this review.

Targeting mTOR/p70S6K/glycolysis signaling pathway restores glucocorticoid sensitivity to 4E-BP1 null Burkitt Lymphoma

Background

Increasing evidence indicates that rapamycin could be used as a potential glucocorticoid (GC) sensitizer in lymphoblastic malignancies via genetic prevention of 4E-BP1 phosphorylation. Interestingly, we found that combined rapamycin with dexamethasone can effectively reverse GC resistance in 4E-BP1 null lymphoma cells. In this study, we investigated the potential link between mTOR/p70S6K signaling pathway, glycolysis, autophagy and GC resistance.

Methods

Antitumor effects of the combination of rapamycin and dexamethasone were evaluated on cell viability by MTT assay and in vivo studies, on cell cycle and apoptosis by flow cytometry, on autophagy by western blot, MDC staining and transmission electron microscopy and on cell signaling by western blot. Moreover, to test whether inhibiting glycolysis is the core mechanism in rapamycin restoring GC sensitivity, we took glycolysis inhibitor 2-deoxyglucose to replace rapamycin and then evaluated the antitumor effects in vitro.

Results

Raji cells are resistant to rapamycin (IC₅₀ > 1000 nM) or dexamethasone (IC₅₀ > 100 μM) treatment alone. The combination of rapamycin and dexamethasone synergistically inhibited the viability of Raji cells in vitro and in vivo by inducing caspase-dependent and -independent cell death and G₀/G₁ cell cycle arrest. These effects were achieved by the inhibition of mTOR/p70S6K signaling pathway, which led to the inhibition of glycolysis and the induction of autophagy. Pretreatment with pan-caspase inhibitor z-VAD-fmk or autophagy inhibitor 3-MA failed to protect the cells from combined treatment-induced death. Glycolysis inhibitor combined with dexamethasone produced a similar antitumor effects in vitro.

Conclusions

Inhibition of mTOR/p70S6K/glycolysis signaling pathway is the key point of therapy in reversing GC resistant in Burkitt lymphoma patients.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1535-z) contains supplementary material, which is available to authorized users.

Hydroxychloroquine Destabilizes Phospho-S6 in Human Renal Carcinoma Cells

mTOR inhibitors are used to treat metastatic renal cell cancer (RCC), but most patients eventually become resistant. One possible mechanism for resistance is upregulation of autophagy, a pathway that helps recycle intracellular proteins and promotes cell survival. Hydroxychloroquine (HCQ), a potent autophagy inhibitor used to treat malaria and autoimmune disorders, is currently being studied in the context of cancer treatment. Here, we have investigated the effects of HCQ on three different renal carcinoma derived cell lines. We found that HCQ treatment inhibits RCC cell growth, promotes apoptosis, inhibits mitochondrial oxygen consumption, and increases rates of glycolysis. To understand the molecular mechanism behind these effects, we examined various nodes in the mTOR pathway and compared the effects of HCQ with the effects of the mTOR inhibitor RAD001. A key downstream readout of the pathway, phospho-S6 protein, was inhibited by both HCQ and RAD001. However, the upstream kinase, P70S6K was only inhibited by RAD001 and not HCQ, suggesting that the block by HCQ was downstream of P70S6K. Treatment with the proteasome inhibitor bortezomib restored phospho-S6 levels, suggesting that the reduction of phospho-S6 is caused by increased degradation of phospho-S6, but not total S6. Surprisingly, treatment with other autophagy inhibitors did not exhibit the same effects. Our findings suggest that HCQ causes the down-regulation of phospho-S6 in RCC cell lines via a novel mechanism that is not shared with other autophagy inhibitors.

Suppression of MAPK Signaling and Reversal of mTOR-Dependent MDR1-Associated Multidrug Resistance by 21α-Methylmelianodiol in Lung Cancer Cells

Lung cancer is the leading cause of cancer-related deaths worldwide and remains the most prevalent. Interplay between PI3K/AMPK/AKT and MAPK pathways is a crucial effector in lung cancer growth and progression. These signals transduction protein kinases serve as good therapeutic targets for non-small cell lung cancer (NSCLC) which comprises up to 90% of lung cancers. Here, we described whether 21α-Methylmelianodiol (21α-MMD), an active triterpenoid derivative of Poncirus trifoliate, can display anticancer properties by regulating these signals and modulate the occurrence of multidrug resistance in NSCLC cells. We found that 21α-MMD inhibited the growth and colony formation of lung cancer cells without affecting the normal lung cell phenotype. 21α-MMD also abrogated the metastatic activity of lung cancer cells through the inhibition of cell migration and invasion, and induced G0/G1 cell cycle arrest with increased intracellular ROS generation and loss of mitochondrial membrane integrity. 21α-MMD regulated the expressions of PI3K/AKT/AMPK and MAPK signaling which drove us to further evaluate its activity on multidrug resistance (MDR) in lung cancer cells by specifying on P-glycoprotein (P-gp)/MDR1-association. Employing the established paclitaxel-resistant A549 cells (A549-PacR), we further found that 21α-MMD induced a MDR reversal activity through the inhibition of P-gp/MDR1 expressions, function, and transcription with regained paclitaxel sensitivity which might dependently correlate to the regulation of PI3K/mTOR signaling pathway. Taken together, these findings demonstrate, for the first time, the mechanistic evaluation in vitro of 21α-MMD displaying growth-inhibiting potential with influence on MDR reversal in human lung cancer cells.

Combination treatment with hypoxia-activated prodrug evofosfamide (TH-302) and mTOR inhibitors results in enhanced antitumor efficacy in preclinical renal cell carcinoma models

Tumors often consist of hypoxic regions which are resistant to chemo- and radiotherapy. Evofosfamide (also known as TH-302), a 2-nitroimidazole triggered hypoxia-activated prodrug, preferentially releases the DNA cross-linker bromo-isophosphoramide mustard in hypoxic cells. The intracellular kinase mTOR plays a key role in multiple pathways which are important in cancer progression. Here we investigated the enhanced efficacy profile and possible mechanisms of evofosfamide in combination with mTOR inhibitor (mTORi) everolimus or temsirolimus in renal cell carcinoma (RCC) xenograft models. The antitumor activities of the mTORi everolimus or temsirolimus alone, evofosfamide alone, or the combination were investigated in the 786-O and Caki-1 RCC cells in vitro and in vivo xenograft models. Two schedules were tested in which evofosfamide was started on the same day as the mTORi or 1 week after. Combination mechanisms were investigated by measuring a panel of pharmacodynamic biomarkers by immunohistochemistry. Antitumor efficacy in both RCC xenograft models was enhanced by the combination of evofosfamide and mTORi. Evofosfamide reduced the increased hypoxia induced by mTORi. Combination treatment induced increased DNA damage, decreased cell proliferation, and decreased survivin. Addition of mTORi did not change evofosfamide-mediated cytotoxicity in 786-O or Caki-1 cells in vitro which might suggest cell non-autonomous effects, specifically increased tumor hypoxia, are important for the in vivo combination activity. Taken together, evofosfamide potentiates the antitumor efficacy of mTOR inhibitors and inhibits the increased tumor hypoxia caused by mTOR inhibition. These studies provide a translational rationale for combining evofosfamide with mTOR inhibitors in clinical studies.

Profiling of the fetal and adult rat liver transcriptome and translatome reveals discordant regulation by the mechanistic target of rapamycin (mTOR)

The mechanistic target of rapamycin (mTOR) integrates growth factor signaling, nutrient abundance, cell growth, and proliferation. On the basis of our interest in somatic growth in the late gestation fetus, we characterized the role of mTOR in the regulation of hepatic gene expression and translation initiation in fetal and adult rats. Our strategy was to manipulate mTOR signaling in vivo and then characterize the transcriptome and translating mRNA in liver tissue. In adult rats, we used the nonproliferative growth model of refeeding after a period of fasting and the proliferative model of liver regeneration following partial hepatectomy. We also studied livers from preterm fetal rats (embryonic day 19) in which fetal hepatocytes are asynchronously proliferating. All three models employed rapamycin to inhibit mTOR signaling. Analysis of the transcriptome in fasted-refed animals showed rapamycin-mediated induction of genes associated with oxidative phosphorylation. Genes associated with RNA processing were downregulated. In liver regeneration, rapamycin induced genes associated with lysosomal metabolism, steroid metabolism, and the acute phase response. In fetal animals, rapamycin inhibited expression of genes in several functional categories that were unrelated to effects in the adult animals. Translation control showed marked fetal-adult differences. In both adult models, rapamycin inhibited the translation of genes with complex 5' untranslated regions, including those encoding ribosomal proteins. Fetal translation was resistant to the effects of rapamycin. We conclude that the mTOR pathway in liver serves distinct physiological roles in the adult and fetus, with the latter representing a condition of rapamycin resistance.

The 4E-BP1/eIF4E ratio is a determinant for rapamycin response in esophageal cancer cells

OBJECTIVES

Rapamycin inhibits products of molecular pathways in esophageal squamous cell carcinoma and limits tumor cell growth by targeting 4E-BP1- and eIF4E-dependent gene translation. In this study, we investigate the influence of 4E-BP1-to-eIF4E ratio on rapamycin response in esophageal squamous cell carcinoma cells, and the underlying mechanism is discussed.

METHODS

The response to rapamycin treatment was examined in 6 esophageal cancer cell lines. Adjustment of the 4E-BP1/eIF4E ratio was carried out by knockdown or overexpression of 4E-BP1 and eIF4E. The relationship between Egr-1 and 4E-BP1 expression in esophageal cancer cells was also studied.

RESULTS

The 4E-BP1/eIF4E ratio was adjusted to evaluate the response to rapamycin treatment in TE1 and TE2 esophageal cancer cells. TE2 cells are sensitized to rapamycin treatment after overexpression of 4E-BP1 or knockdown of eIF4E; TE1 cells become resistant to rapamycin after knockdown of 4E-BP1 or overexpression of eIF4E. These data suggest that the 4E-BP1/eIF4E ratio is a determinant for the response of TE1 and TE2 cells to rapamycin treatment. Egr-1 expression was higher in TE2 cells compared with other esophageal cancer cell lines, and its knockdown increased 4E-BP1 expression in TE2 cells, which became sensitive to rapamycin treatment.

CONCLUSIONS

The 4E-BP1/eIF4E ratio is a determinant of the response of rapamycin treatment in esophageal cancer cells. Egr-1 can reduce 4E-BP1 gene expression and render esophageal squamous cell carcinoma cells resistant to rapamycin with a relatively low 4E-BP1/eIF4E ratio. Thus, the 4E-BP1/eIF4E ratio may represent a therapeutic index for the prediction of clinical outcome of rapamycin treatment in patients with esophageal squamous cell carcinoma.

What is the potential of using PI3K inhibitors in the management of breast cancer in the clinic?

SUMMARY 

Even with hormone- and HER2-targeted anticancer agents, intrinsic and acquired resistance is a common occurrence in estrogen receptor-positive and HER2-positive breast cancers, respectively. As for triple-negative breast cancer, its relative uncommonness, aggressiveness and impressive heterogeneity have been only a few of the challenges researchers and clinicians face in making strides against this disease. This article reviews the involvement of the PI3K pathway in these resistance mechanisms. It also summarizes preclinical and clinical data suggesting the potential of combination therapy with PI3K inhibitors in preventing resistance and restoring sensitivity to hormone-targeted, HER2-targeted agents and chemotherapy.

Targeted therapy for sarcomas

Sarcomas are tumors of mesenchymal origin that make up approximately 1% of human cancers. They may arise as primary tumors in either bone or soft tissue, with approximately 11,280 soft tissue tumors and 2,650 bone tumors diagnosed each year in the United States. There are at least 50 different subtypes of soft tissue sarcoma, with new ones described with ever-increasing frequency. One way to look at sarcomas is to divide them into categories on the basis of their genetic make-up. One group of sarcomas has an identifiable, relatively simple genetic signature, such as the X:18 translocation seen in synovial sarcoma or the 11:22 translocation seen in Ewing's sarcoma. These specific abnormalities often lead to the presence of fusion proteins, such as EWS-FLI1 in Ewing's sarcoma, which are helpful as diagnostic tools and may become therapeutic targets in the future. Another group of sarcomas is characterized by complex genetic abnormalities as seen in leiomyosarcoma, osteosarcoma, and undifferentiated sarcoma. It is important to keep these distinctions in mind when contemplating the development of targeted agents for sarcomas. Different abnormalities in sarcoma could be divided by tumor subtype or by the molecular or pathway abnormality. However, some existing drugs or drugs in development may interfere with or alter more than one of the presented pathways.

Impact of dual mTORC1/2 mTOR kinase inhibitor AZD8055 on acquired endocrine resistance in breast cancer in vitro

Introduction

Upregulation of PI3K/Akt/mTOR signalling in endocrine-resistant breast cancer (BC) has identified mTOR as an attractive target alongside anti-hormones to control resistance. RAD001 (everolimus/Afinitor®), an allosteric mTOR inhibitor, is proving valuable in this setting; however, some patients are inherently refractory or relapse during treatment requiring alternative strategies. Here we evaluate the potential for novel dual mTORC1/2 mTOR kinase inhibitors, exemplified by AZD8055, by comparison with RAD001 in ER + endocrine resistant BC cells.

Methods

In vitro models of tamoxifen (TamR) or oestrogen deprivation resistance (MCF7-X) were treated with RAD001 or AZD8055 alone or combined with anti-hormone fulvestrant. Endpoints included growth, cell proliferation (Ki67), viability and migration, with PI3K/AKT/mTOR signalling impact monitored by Western blotting. Potential ER cross-talk was investigated by immunocytochemistry and RT-PCR.

Results

RAD001 was a poor growth inhibitor of MCF7-derived TamR and MCF7-X cells (IC₅₀ ≥1 μM), rapidly inhibiting mTORC1 but not mTORC2/AKT signalling. In contrast AZD8055, which rapidly inhibited both mTORC1 and mTORC2/AKT activity, was a highly effective (P <0.001) growth inhibitor of TamR (IC₅₀ 18 nM) and MCF7-X (IC₅₀ 24 nM), and of a further T47D-derived tamoxifen resistant model T47D-tamR (IC₅₀ 19 nM). AZD8055 significantly (P <0.05) inhibited resistant cell proliferation, increased cell death and reduced migration. Furthermore, dual treatment of TamR or MCF7-X cells with AZD8055 plus fulvestrant provided superior control of resistant growth versus either agent alone (P <0.05). Co-treating with AZD8055 alongside tamoxifen (P <0.01) or oestrogen deprivation (P <0.05) also effectively inhibited endocrine responsive MCF-7 cells. Although AZD8055 inhibited oestrogen receptor (ER) ser167 phosphorylation in TamR and MCF7-X, it had no effect on ER ser118 activity or expression of several ER-regulated genes, suggesting the mTOR kinase inhibitor impact was largely ER-independent. The capacity of AZD8055 for ER-independent activity was further evidenced by growth inhibition (IC₅₀18 and 20 nM) of two acquired fulvestrant resistant models lacking ER.

Conclusions

This is the first report demonstrating dual mTORC1/2 mTOR kinase inhibitors have potential to control acquired endocrine resistant BC, even under conditions where everolimus fails. Such inhibitors may prove of particular benefit when used alongside anti-hormonal treatment as second-line therapy in endocrine resistant disease, and also potentially alongside anti-hormones during the earlier endocrine responsive phase to hinder development of resistance.

GNAQ and BRAF mutations show differential activation of the mTOR pathway in human transformed cells

Somatic mutations in GNAQ gene were described as being the main oncogenic activation in uveal melanomas, whereas mutations in BRAF gene have been described as a key genetic alteration that contributes to skin melanoma development. We have previously reported differential activation of the MAPK and AKT/mTOR signalling pathways in uveal and skin melanomas harbouring, respectively, GNAQ and BRAF mutations. The aim of this work was to compare the functional effect of GNAQ and BRAF mutations in mTOR and MAPK pathway activation, cell proliferation and apoptosis. In this work, we performed transient transfection of HEK293 cells with BRAF^WT, BRAF^{V 600E}, GNAQ^WT, GNAQ^Q209P and GNAQ^Q209L vectors. We treated melanoma cell lines displaying different BRAF and GNAQ mutational status with the mTOR inhibitor RAD001 and with the MEK1/2 inhibitor U0126 and evaluated the effects in the growth of the cell lines and in mTOR and MAPK pathway effectors expression. At variance with the significant increase in the level of pmTOR Ser2448 and pS6 Ser235/236 proteins observed in cells transfected with BRAF vectors, no significant alteration in mTOR pathway effectors was observed in cells transfected with the three GNAQ expressing vectors. Also, GNAQ overexpression enhances Stat3 activation, which might mediate GNAQ oncogenic effects. None of the vectors led to significant differences in proliferation or apoptosis in the transfected cell lines. Cell lines harbouring a BRAF mutation were more sensitive to RAD001 treatment. U0126 leads to the reduction of MAPK and mTOR pathways activation in all cell lines tested. Our results indicate that GNAQ and BRAF activation drive distinct intracellular signalling pathways that may be useful for therapeutic decisions in human melanomas.

Implantation of a drug-eluting stent with a different drug (switch strategy) in patients with drug-eluting stent restenosis. Results from a prospective multicenter study (RIBS III [Restenosis Intra-Stent: Balloon Angioplasty Versus Drug-Eluting Stent])

OBJECTIVES

This study sought to assess the effectiveness of a strategy of using drug-eluting stents (DES) with a different drug (switch) in patients with DES in-stent restenosis (ISR).

BACKGROUND

Treatment of patients with DES ISR remains a challenge.

METHODS

The RIBS-III (Restenosis Intra-Stent: Balloon Angioplasty Versus Drug-Eluting Stent) study was a prospective, multicenter study that aimed to assess results of coronary interventions in patients with DES ISR. The use of a different DES was the recommended strategy. The main angiographic endpoint was minimal lumen diameter at 9-month follow-up. The main clinical outcome measure was a composite of cardiac death, myocardial infarction, and target lesion revascularization.

RESULTS

This study included 363 consecutive patients with DES ISR from 12 Spanish sites. The different-DES strategy was used in 274 patients (75%) and alternative therapeutic modalities (no switch) in 89 patients (25%). Baseline characteristics were similar in the 2 groups, although lesion length was longer in the switch group. At late angiographic follow-up (77% of eligible patients, median: 278 days) minimal lumen diameter was larger (1.86 ± 0.7 mm vs. 1.40 ± 0.8 mm, p = 0.003) and recurrent restenosis rate lower (22% vs. 40%, p = 0.008) in the different-DES group. At the last clinical follow-up (99% of patients, median: 771 days), the combined clinical endpoint occurred less frequently (23% vs. 35%, p = 0.039) in the different-DES group. After adjustment using propensity score analyses, restenosis rate (relative risk: 0.41, 95% confidence interval [CI]: 0.21 to 0.80, p = 0.01), minimal lumen diameter (difference: 0.41 mm, 95% CI: 0.19 to 0.62, p = 0.001), and the event-free survival (hazard ratio: 0.56, 95% CI: 0.33 to 0.96, p = 0.038) remained significantly improved in the switch group.

CONCLUSIONS

In patients with DES ISR, the implantation of a different DES provides superior late clinical and angiographic results than do alternative interventional modalities.

Nuclear PIM1 confers resistance to rapamycin-impaired endothelial proliferation

The PIM serine/threonine kinases and the mTOR/AKT pathway integrate growth factor signaling and promote cell proliferation and survival. They both share phosphorylation targets and have overlapping functions, which can partially substitute for each other. In cancer cells PIM kinases have been reported to produce resistance to mTOR inhibition by rapamycin. Tumor growth depends highly on blood vessel infiltration into the malignant tissue and therefore on endothelial cell proliferation. We therefore investigated how the PIM1 kinase modulates growth inhibitory effects of rapamycin in mouse aortic endothelial cells (MAEC). We found that proliferation of MAEC lacking Pim1 was significantly more sensitive to rapamycin inhibition, compared to wildtype cells. Inhibition of mTOR and AKT in normal MAEC resulted in significantly elevated PIM1 protein levels in the cytosol and in the nucleus. We observed that truncation of the C-terminal part of Pim1 beyond Ser 276 resulted in almost exclusive nuclear localization of the protein. Re-expression of this Pim1 deletion mutant significantly increased the proliferation of Pim1(-/-) cells when compared to expression of the wildtype Pim1 cDNA. Finally, overexpression of the nuclear localization mutant and the wildtype Pim1 resulted in complete resistance to growth inhibition by rapamycin. Thus, mTOR inhibition-induced nuclear accumulation of PIM1 or expression of a nuclear C-terminal PIM1 truncation mutant is sufficient to increase endothelial cell proliferation, suggesting that nuclear localization of PIM1 is important for resistance of MAEC to rapamycin-mediated inhibition of proliferation.

Cap-dependent mRNA translation and the ubiquitin-proteasome system cooperate to promote ERBB2-dependent esophageal cancer phenotype

Pathological post-transcriptional control of the proteome composition is a central feature of malignancy. Two steps in this pathway, eIF4F-driven cap-dependent mRNA translation and the ubiquitin-proteasome system (UPS), are deregulated in most if not all cancers. We tested a hypothesis that eIF4F is aberrantly activated in human esophageal adenocarcinoma (EAC) and requires elevated rates of protein turnover and proteolysis and thereby activated UPS for its pro-neoplastic function. Here, we show that 80% of tumors and cell lines featuring amplified ERBB2 display an aberrantly activated eIF4F. Direct genetic targeting of the eIF4F in ERBB2-amplified EAC cells with a constitutively active form of the eIF4F repressor 4E-BP1 decreased colony formation and proliferation and triggered apoptosis. In contrast, suppression of m-TOR-kinase activity towards 4E-BP1with rapamycin only modestly inhibited eIF4F-driven cap-dependent translation and EAC malignant phenotype; and promoted feedback activation of other cancer pathways. Our data show that co-treatment with 2 FDA-approved agents, the m-TOR inhibitor rapamycin and the proteasome inhibitor bortezomib, leads to strong synergistic growth-inhibitory effects. Moreover, direct targeting of eIF4F with constitutively active 4E-BP1 is significantly more potent in collaboration with bortezomib than rapamycin. These data support the hypothesis that a finely tuned balance between eIF4F-driven protein synthesis and proteasome-mediated protein degradation is required for the maintenance of ERBB2-mediated EAC malignant phenotype. Altogether, our study supports the development of pharmaceuticals to directly target eIF4F as most efficient strategy; and provides a clear rationale for the clinical evaluation of combination therapy with m-TOR inhibitors and bortezomib for EAC treatment.

The role of mTOR inhibitors in the inhibition of growth and cortisol secretion in human adrenocortical carcinoma cells

Patients with adrenocortical carcinoma (ACC) need new treatment options. The aim of this study was to evaluate the effects of the mTOR inhibitors sirolimus and temsirolimus on human ACC cell growth and cortisol production. In H295, HAC15, and SW13 cells, we have evaluated mTOR, IGF2, and IGF1 receptor expressions; the effects of sirolimus and temsirolimus on cell growth; and the effects of sirolimus on apoptosis, cell cycle, and cortisol production. Moreover, the effects of sirolimus on basal and IGF2-stimulated H295 cell colony growth and on basal and IGF1-stimulated phospho-AKT, phospho-S6K1, and phospho-ERK in H295 and SW13 were studied. Finally, we have evaluated the effects of combination treatment of sirolimus with an IGF2-neutralizing antibody. We have found that H295 and HAC15 expressed IGF2 at a >1800-fold higher level than SW13. mTOR inhibitors suppressed cell growth in a dose-/time-dependent manner in all cell lines. SW13 were the most sensitive to these effects. Sirolimus inhibited H295 colony surviving fraction and size. These effects were not antagonized by IGF2, suggesting the involvement of other autocrine regulators of mTOR pathways. In H295, sirolimus activated escape pathways. The blocking of endogenously produced IGF2 increased the antiproliferative effects of sirolimus on H295. Cortisol production by H295 and HAC15 was inhibited by sirolimus. The current study demonstrates that mTOR inhibitors inhibit the proliferation and cortisol production in ACC cells. Different ACC cells have different sensitivity to the mTOR inhibitors. mTOR could be a target for the treatment of human ACCs, but variable responses might be expected. In selected cases of ACC, the combined targeting of mTOR and IGF2 could have greater effects than mTOR inhibitors alone.

PI3K and mTOR signaling pathways in cancer: new data on targeted therapies

The mammalian target of rapamycin (mTOR) and the phosphoinositide 3-kinase (PI3K) signaling pathways are commonly deregulated in cancers and promote cellular growth, proliferation, and survival. mTOR is part of two complexes, mTORC1 and mTORC2, with different biochemical structures and substrates specificity. PI3K/AKT activation may result from genetic hits affecting different components of the pathway, whereas the mechanisms leading to constitutive mTORC1 activation remain globally unknown. The connections between the PI3K and mTOR kinases are multiple and complex, including common substrates, negative feedback loops, or direct activation mechanisms. First-generation allosteric mTOR inhibitors (eg, rapamycin) are mainly active on mTORC1 and mostly display cytostatic anti-tumor activity. Recently, second-generation catalytic mTOR inhibitors targeting both mTOR complexes 1 and 2 have been developed. Some of them also inhibit class IA PI3K. Here, we highlight recent data generated with these new inhibitors against cancer cells and their potential as anti-cancer drugs.

Activation of PI3K/AKT and MAPK pathway through a PDGFRβ-dependent feedback loop is involved in rapamycin resistance in hepatocellular carcinoma

BACKGROUND

Rapamycin is an attractive approach for the treatment and prevention of HCC recurrence after liver transplantation. However, the objective response rates of rapamycin achieved with single-agent therapy were modest, supporting that rapamycin resistance is a frequently observed characteristic of many cancers. Some studies have been devoted to understanding the mechanisms of rapamycin resistance, however, the mechanisms are cell-type-dependent and studies on rapamycin resistance in HCC are extremely limited.

METHODOLOGY/PRINCIPAL FINDINGS

The anti-tumor sensitivity of rapamycin was modest in vitro and in vivo. In both human and rat HCC cells, rapamycin up-regulated the expression and phosphorylation of PDGFRβ in a time and dose-dependent manner as assessed by RT-PCR and western blot analysis. Using siRNA mediated knockdown of PDGFRβ, we confirmed that subsequent activation of AKT and ERK was PDGFRβ-dependent and compromised the anti-tumor activity of rapamycin. Then, blockade of this PDGFRβ-dependent feedback loop by sorafenib enhanced the anti-tumor sensitivity of rapamycin in vitro and in an immunocompetent orthotopic rat model of HCC.

CONCLUSIONS

Activation of PI3K/AKT and MAPK pathway through a PDGFRβ-dependent feedback loop compromises the anti-tumor activity of rapamycin in HCC, and blockade of this feedback loop by sorafenib is an attractive approach to improve the anti-tumor effect of rapamycin, particularly in preventing or treating HCC recurrence after liver transplantation.

Clinical Outcomes and Treatment After Drug-Eluting Stent Failure

Background—

The optimal percutaneous treatment of drug-eluting stent (DES) in-stent restenosis (ISR) and the correlates for recurrent DES ISR remain unclear.

Methods and Results—

From 2003 to 2008, 563 patients presenting with recurrent symptoms of ischemia and angiographic ISR after DES implantation were included. Of these, 327 were treated with re-DES (58.1%), 132 underwent vascular brachytherapy (23.4%), and 104 were treated with conventional balloon angioplasty (18.5%). Variables associated with target lesion revascularization at 1 year were explored by individual proportional hazard models. This population presents a high prevalence of comorbidities, including diabetes (43.7%), previous myocardial infarction (MI) (45.8%), coronary bypass graft surgery (39.2%), chronic renal failure (18.8%), and heart failure (17.3%). Baseline clinical characteristics were balanced among the 3 groups; however, patients undergoing vascular brachytherapy presented with more complex lesions and a higher prevalence of prior stent/vascular brachytherapy failure than did the rest of the population. The overall incidence of recurrent DES failure at 1-year follow-up was 12.2%, which was similar among the 3 groups ( P =0.41). The rate of the composite end point (death, Q-wave-MI and target lesion revascularization) at 1-year follow-up was 14.1% for re-DES, 17.5% for vascular brachytherapy, and 18.0% for conventional balloon angioplasty ( P =0.57). After univariable analysis tested the traditional known covariates related to ISR, none of them were associated with repeat target lesion revascularization.

Conclusions—

Recurrence of ISR after DES treatment failure is neither infrequent nor benign, and optimal therapy remains unclear and challenging. Given the absence of traditional risk factors for ISR in this population, further research is required to elucidate both the correlates involved in DES ISR and the optimal treatment for this condition.

Therapeutic resistance resulting from mutations in Raf/MEK/ERK and PI3K/PTEN/Akt/mTOR signaling pathways

Chemotherapy remains a commonly used therapeutic approach for many cancers. Indeed chemotherapy is relatively effective for treatment of certain cancers and it may be the only therapy (besides radiotherapy) that is appropriate for certain cancers. However, a common problem with chemotherapy is the development of drug resistance. Many studies on the mechanisms of drug resistance concentrated on the expression of membrane transporters and how they could be aberrantly regulated in drug resistant cells. Attempts were made to isolate specific inhibitors which could be used to treat drug resistant patients. Unfortunately most of these drug transporter inhibitors have not proven effective for therapy. Recently the possibilities of more specific, targeted therapies have sparked the interest of clinical and basic researchers as approaches to kill cancer cells. However, there are also problems associated with these targeted therapies. Two key signaling pathways involved in the regulation of cell growth are the Ras/Raf/MEK/ERK and PI3K/PTEN/Akt/mTOR pathways. Dysregulated signaling through these pathways is often the result of genetic alterations in critical components in these pathways as well as mutations in upstream growth factor receptors. Furthermore, these pathways may be activated by chemotherapeutic drugs and ionizing radiation. This review documents how their abnormal expression can contribute to drug resistance as well as resistance to targeted therapy. This review will discuss in detail PTEN regulation as this is a critical tumor suppressor gene frequently dysregulated in human cancer which contributes to therapy resistance. Controlling the expression of these pathways could improve cancer therapy and ameliorate human health.

[m-TOR inhibitors: biology and use in the treatment of haematological diseases]

Mammalian target of rapamycyin (mTOR) is a downstream serine/threonine kinase of the PI3K/AKT pathway that integrates signals from the microenvironment such as cytokines, growth factors, and nutriments to regulate multiple cellular processes, including mRNA translation, autophagy, metabolism, growth and survival. mTOR operates in two distinct multi-protein complexes: mTORC1 and mTORC2; sharing mTOR kinase as a common catalytic subunit, mTORC1 controls cell growth and mTORC2 modulates cell survival and drug resistance. mTOR signalling pathway has been found to be deregulated in many haematological malignancies, and has been designed as an attractive anti-tumor target. Thereby, mTOR inhibition with rapamycin (sirolimus) or its derivates (rapalogs) represents promising treatments, either alone or in combination with strategies to target other pathways that may overcome resistance. At present time, numerous clinical trials with mTOR inhibitors are ongoing for treatment of haematological diseases with modest or promising results. The aim of this review is to present the rationale for using mTOR inhibitors in haematology, first via biological explanations and secondly, by focusing on each haematological malignancies with new perspective of treatment.

Inhibition of SAPK2/p38 enhances sensitivity to mTORC1 inhibition by blocking IRES-mediated translation initiation in glioblastoma

A variety of mechanisms confer hypersensitivity of tumor cells to the macrolide rapamycin, the prototypic mTORC1 inhibitor. Several studies have shown that the status of the AKT kinase plays a critical role in determining hypersensitivity. Cancer cells in which AKT activity is elevated are exquisitely sensitive to mTORC1 inhibitors while cells in which the kinase is quiescent are relatively resistant. Our previous work has shown that a transcript-specific protein synthesis salvage pathway is operative in cells with quiescent AKT levels, maintaining the translation of crucial mRNAs involved in cell-cycle progression in the face of global eIF-4E-mediated translation inhibition. The activation of this salvage pathway is dependent on SAPK2/p38-mediated activation of IRES-dependent initiation of the cyclin D1 and c-MYC mRNAs, resulting in the maintenance of their protein expression levels. Here, we show that both genetic and pharmacologic inhibition of SAPK2/p38 in glioblastoma multiforme cells significantly reduces rapamycin-induced IRES-mediated translation initiation of cyclin D1 and c-MYC, resulting in increased G(1) arrest in vitro and inhibition of tumor growth in xenografts. Moreover, we observed that the AKT-dependent signaling alterations seen in vitro are also displayed in engrafted tumors cells and were able to show that combined inhibitor treatments markedly reduced the mRNA translational state of cyclin D1 and c-MYC transcripts in tumors isolated from mice. These data support the combined use of SAPK2/p38 and mTORC1 inhibitors to achieve a synergistic antitumor therapeutic response, particularly in rapamycin-resistant quiescent AKT-containing cells.

Dual targeting of the insulin-like growth factor and collateral pathways in cancer: combating drug resistance

The insulin-like growth factor pathway, regulated by a complex interplay of growth factors, cognate receptors, and binding proteins, is critically important for many of the hallmarks of cancer such as oncogenesis, cell division, growth, and antineoplastic resistance. Naturally, a number of clinical trials have sought to directly abrogate insulin-like growth factor receptor 1 (IGF-1R) function and/or indirectly mitigate its downstream mediators such as mTOR, PI3K, MAPK, and others under the assumption that such therapeutic interventions would provide clinical benefit, demonstrable by impaired tumor growth as well as prolonged progression-free and overall survival for patients. Though a small subset of patients enrolled within phase I or II clinical trials revealed dramatic clinical response to IGF-1R targeted therapies (most using monoclonal antibodies to IGF-1R), in toto, the anticancer effect has been underwhelming and unsustained, as even those with marked clinical responses seem to rapidly acquire resistance to IGF-1R targeted agents when used alone through yet to be identified mechanisms. As the IGF-1R receptor is just one of many that converge upon common intracellular signaling cascades, it is likely that effective IGF-1R targeting must occur in parallel with blockade of redundant signaling paths. Herein, we present the rationale for dual targeting of IGF-1R and other signaling molecules as an effective strategy to combat acquired drug resistance by carcinomas and sarcomas.

Targeting the translational apparatus to improve leukemia therapy: roles of the PI3K/PTEN/Akt/mTOR pathway

It has become apparent that regulation of protein translation is an important determinant in controlling cell growth and leukemic transformation. The phosphoinositide 3-kinase (PI3K)/phosphatase and tensin homologue deleted on chromosome ten (PTEN)/Akt/mammalian target of rapamycin (mTOR) pathway is often implicated in sensitivity and resistance to therapy. Dysregulated signaling through the PI3K/PTEN/Akt/mTOR pathway is often the result of genetic alterations in critical components in this pathway as well as mutations at upstream growth factor receptors. Furthermore, this pathway is activated by autocrine transformation mechanisms. PTEN is a critical tumor suppressor gene and its dysregulation results in the activation of Akt. PTEN is often mutated, silenced and is often haploinsufficient. The mTOR complex1 (mTORC1) regulates the assembly of the eukaryotic initiation factor4F complex, which is critical for the translation of mRNAs that are important for cell growth, prevention of apoptosis and transformation. These mRNAs have long 5'-untranslated regions that are G+C rich, rendering them difficult to translate. Elevated mTORC1 activity promotes the translation of these mRNAs via the phosphorylation of 4E-BP1. mTORC1 is a target of rapamycin and novel active-site inhibitors that directly target the TOR kinase activity. Although rapamycin and novel rapalogs are usually cytostatic and not cytotoxic for leukemic cells, novel inhibitors that target the kinase activities of PI3K and mTOR may prove more effective for leukemia therapy.

Efficacy of ganitumab (AMG 479), alone and in combination with rapamycin, in Ewing's and osteogenic sarcoma models

Ewing's and osteogenic sarcoma are two of the leading causes of cancer deaths in children and adolescents. Recent data suggest that sarcomas may depend on the insulin-like growth factor type 1 (IGF-1) receptor (IGF1R) and/or the insulin receptor (INSR) to drive tumor growth, survival, and resistance to mammalian target of rapamycin complex 1 (mTORC1) inhibitors. We evaluated the therapeutic value of ganitumab (AMG 479; C(6472)H(10028)N(1728)O(2020)S(42)), an anti-IGF1R, fully human monoclonal antibody, alone and in combination with rapamycin (mTORC1 inhibitor) in Ewing's (SK-ES-1 and A673) and osteogenic (SJSA-1) sarcoma models. IGF1R was activated by IGF-1 but not by insulin in each sarcoma model. INSR was also activated by IGF-1 in the SJSA-1 and SK-ES-1 models, but not in the A673 model where insulin was the preferred INSR ligand. Ganitumab significantly inhibited the growth of SJSA-1 and SK-ES-1 xenografts; inhibition was associated with decreased IGF1R and Akt phosphorylation, reduced total IGF1R and bromodeoxyuridine detection, and increased caspase-3 expression. Ganitumab inhibited rapamycin-induced IGF1R, Akt, and glycogen synthase kinase-3β hyperphosphorylation in each sarcoma model. However, ganitumab in combination with rapamycin also resulted in a marked increase in INSR expression and activity in the SJSA-1 and A673 models. The in vivo efficacy of ganitumab in the two ganitumab-sensitive models (SJSA-1 and SK-ES-1) was significantly enhanced in combination with rapamycin. Our results support studying ganitumab in combination with mTORC1 inhibitors for the treatment of sarcomas and suggest that INSR signaling is an important mechanism of resistance to IGF1R blockade.

Rictor regulates MMP-9 activity and invasion through Raf-1-MEK-ERK signaling pathway in glioma cells

Glioblastoma multiforme (GBM) is the most common and highly aggressive type of primary brain tumor. Tumor-associated macrophages (TAMs) secrete TNF-α that activates important survival pathways including Akt (PKB)/mTOR network. The mammalian target of rapamycin (mTOR) network functions downstream of PI3K/Akt pathway to regulate cell growth, proliferation and survival. mTOR exists in two distinct complexes-mTORC1 and mTORC2 that differ in their components and sensitivity to rapamycin. The rapamycin-insensitive complex (mTORC2) consists of mTOR, mLST8, Rictor, mSin1 and Protor and regulates the actin cytoskeleton in addition to activating Akt (protein kinase B). The present study aimed to investigate the role of Rictor-a core component of mTORC2 in regulating proliferation, survival, and invasion in gliomas. siRNA-mediated loss of Rictor function in human glioma cell lines, LN18 and LN229 and in primary GBM cells resulted in elevated expression and activity of MMP-9 and significant increase in the invasive potential of these cells. Mechanistic studies revealed that the activation of Raf-1-MEK-ERK pathway was essential for induction of MMP-9 activity and enhanced invasion. Interestingly, ablation of Rictor did not affect TNF-α-induced MMP-9 activity and invasiveness suggesting that TNF-α in the microenvironment of tumor might overrule the function of Rictor as a negative regulator of MMP-9 and invasion. Silencing Rictor had no effect on the survival or proliferation in the cell lines in the presence or absence of TNF-α. Our findings identify a role for Rictor in bridging two major pathways-Akt (PKB)/mTOR and Raf-1-MEK-ERK in regulating MMP-9 activity and invasion of glioma tumor cells.