Mammalian target of rapamycin: a new molecular target for breast cancer

The potential role of reprogrammed glucose metabolism: an emerging actionable codependent target in thyroid cancer

Although the incidence of thyroid cancer is increasing year by year, most patients, especially those with differentiated thyroid cancer, can usually be cured with surgery, radioactive iodine, and thyroid-stimulating hormone suppression. However, treatment options for patients with poorly differentiated thyroid cancers or radioiodine-refractory thyroid cancer have historically been limited. Altered energy metabolism is one of the hallmarks of cancer and a well-documented feature in thyroid cancer. In a hypoxic environment with extreme nutrient deficiencies resulting from uncontrolled growth, thyroid cancer cells utilize "metabolic reprogramming" to satisfy their energy demand and support malignant behaviors such as metastasis. This review summarizes past and recent advances in our understanding of the reprogramming of glucose metabolism in thyroid cancer cells, which we expect will yield new therapeutic approaches for patients with special pathological types of thyroid cancer by targeting reprogrammed glucose metabolism.

ONC201/TIC10 enhances durability of mTOR inhibitor everolimus in metastatic ER+ breast cancer

The mTOR inhibitor, everolimus, is an important clinical management component of metastatic ER+ breast cancer (BC). However, most patients develop resistance and progress on therapy, highlighting the need to discover strategies that increase mTOR inhibitor effectiveness. We developed ER+ BC cell lines, sensitive or resistant to everolimus, and discovered that combination treatment of ONC201/TIC10 with everolimus inhibited cell growth in 2D/3D in vitro studies. We confirmed increased therapeutic response in primary patient cells progressing on everolimus, supporting clinical relevance. We show that ONC201/TIC10 mechanism in metastatic ER+ BC cells involves oxidative phosphorylation inhibition and stress response activation. Transcriptomic analysis in everolimus resistant breast patient tumors and mitochondrial functional assays in resistant cell lines demonstrated increased mitochondrial respiration dependency, contributing to ONC201/TIC10 sensitivity. We propose that ONC201/TIC10 and modulation of mitochondrial function may provide an effective add-on therapy strategy for patients with metastatic ER+ BCs resistant to mTOR inhibitors.

B-box1 Domain of MID1 Interacts with the Ube2D1 E2 Enzyme Differently Than RING E3 Ligases

The MID1 TRIM protein is important for ventral midline development in vertebrates, and mutations of its B-box1 domain result in several birth defects. The B-box1 domain of the human MID1 protein binds two zinc atoms and adopt a similar ββα-RING structure. This domain is required for the efficient ubiquitination of protein phosphatase 2A, alpha4, and fused kinase. Considering the structural similarity, the MID1 B-box1 domain exhibits mono-autoubiquitination activity, in contrast to poly-autoubiquitination observed for RING E3 ligases. To understand its mechanism of action, the interaction of the B-box1 domain with Ube2D1 (UbcH5a, E2), a preferred E2 ligase, is investigated. Using isothermal titration calorimetry, the MID1 RING and B-box1 domains were observed to have similar binding affinities with the Ube2D1 protein. However, NMR ¹⁵N-¹H Heteronuclear Single Quantum Coherence titration, ¹⁵N relaxation data, and High Ambiguity Driven protein-protein DOCKing (HADDOCK) calculations show the B-box1 domain binding on a surface distinct from where RING domains bind. The novel binding interaction shows the B-box1 domain partially overlapping the noncovalent Ube2D1 and a ubiquitin binding site that is necessary for poly-autoubiquitination activity. The B-box1 domain also displaces the ubiquitin from the Ube2D1 protein. These studies reveal a novel binding interaction between the zinc-binding ββα-fold B-box1 domain and the Ube2D enzyme family and that this difference in binding, compared to RING E3 ligases, provides a rationale for its auto-monoubiquitination E3 ligase activity.

The Effects of Deoxyelephantopin on the Akt/mTOR/P70S6K Signaling Pathway in MCF-7 Breast Carcinoma Cells In Vitro

Objective

To determine the effects of deoxyelephantopin on mTOR and its related target molecules (Akt/mTOR/P70S6K) in the ER-positive breast cancer cell line.

Materials and Methods

Primary in silico simulations were determined, and the effects of deoxyelephantopin on the phosphorylation of the Akt/mTOR/P70S6K molecules were evaluated using AlphaScreen-based assays and western blot analysis, respectively.

Results

Based on the estimated FEB and K i values, deoxyelephantopin appeared to have a stronger affinity toward P70S6K as compared with Akt and mTOR. Both deoxyelephantopin and control inhibitors were observed to form hydrogen bonds with the same key residue, Leu175 of the P70S6K molecule. Deoxyelephantopin downregulated the p-P70S6K protein expression significantly from 18 µM ( P < .05) and onward. Based on the AlphaScreen assay, deoxyelephantopin produced a concentration-dependent inhibition on the phosphorylation of P70S6K with an IC50 value of 7.13 µM.

Conclusion

Deoxyelephantopin induced cell death in MCF-7 cells, possibly via DNA fragmentation, inhibition of the phosphorylation of P70SK6, and downregulation of the relative p-p70S6K protein expression levels.

The Translational Regulation in mTOR Pathway

The mechanistic/mammalian target of rapamycin (mTOR) plays a master role in cell proliferation and growth in response to insulin, amino acids, energy levels, and oxygen. mTOR can coordinate upstream signals with downstream effectors, including transcriptional and translational apparatuses to regulate fundamental cellular processes such as energy utilization, protein synthesis, autophagy, cell growth, and proliferation. Of the above, protein synthesis is highly energy-consuming; thus, mRNA translation is under the tight and immediate control of mTOR signaling. The translational regulation driven by mTOR signaling mainly relies on eukaryotic translation initiation factor 4E (eIF4E)-binding protein (4E-BP), ribosomal protein S6 kinase (S6K), and its downstream players, which are significant in rapid cellular response to environmental change. mTOR signaling not only controls the general mRNA translation, but preferential mRNA translation as well. This means that mTOR signaling shows the stronger selectivity to particular target mRNAs. Some evidence has supported the contribution of 4E-BP and La-related proteins 1 (LARP1) to such translational regulation. In this review, we summarize the mTOR pathway and mainly focus on mTOR-mediated mRNA translational regulation. We introduce the major components of mTOR signaling and their functions in translational control in a general or particular manner, and describe how the specificity of regulation is coordinated. Furthermore, we summarize recent research progress and propose additional ideas for reference. Because the mTOR pathway is on the center of cell growth and metabolism, comprehensively understanding this pathway will contribute to the therapy of related diseases, including cancers, type 2 diabetes, obesity, and neurodegeneration.

PROX1, a Key Mediator of the Anti-Proliferative Effect of Rapamycin on Hepatocellular Carcinoma Cells

The MTOR signal is known to be activated in various cancer cells including hepatocellular carcinoma (HCC) cells. Rapamycin, a specific inhibitor of MTOR, has been widely used as an immunosuppressant in organ transplant patients, and its clinical application has been recently expanded to cancer therapy. In this study, the anti-proliferative effect of rapamycin was investigated in four different HCC cell lines. Rapamycin effectively inhibited the proliferation of Huh7 or Hep3B, but not that of HepG2 or SNU3160 cells. Interestingly, rapamycin increased Prospero-related homeobox 1 (PROX1) expression at the protein level, but did not affect its transcript in Huh7 as well as Hep3B cells. Moreover, immunoprecipitation assays showed that PROX1 ubiquitination was downregulated by rapamycin. Furthermore, PROX1 over-expression or siRNA knock-down in Huh7 and Hep3B cells reduced or increased proliferation, respectively. The effect of PROX1 over-expression on the sensitivity to rapamycin was not synergistic, but the effect of MTOR inhibition on cell proliferation was diminished by PROX1 siRNA. Finally, Huh7 cells were inoculated into the flanks of nude mice and rapamycin was injected daily for 14 days. The xenograft volume was decreased and PROX1 expression was increased by rapamycin. These results indicate that PROX1 plays a key role in the anti-proliferative effect of rapamycin and suggest that the increased PROX1 by MTOR inhibition can be used as a useful marker for predicting whether HCC cells can be affected by rapamycin.

Novel regulators of airway epithelial barrier function during inflammation: potential targets for drug repurposing

INTRODUCTION

Endogenous inflammatory signaling molecules resulting from deregulated immune responses, can impair airway epithelial barrier function and predispose individuals with airway inflammatory diseases to exacerbations and lung infections. Targeting the specific endogenous factors disrupting the airway barrier therefore has the potential to prevent disease exacerbations without affecting the protective immune responses.

AREAS COVERED

Here, we review the endogenous factors and specific mechanisms disrupting airway epithelial barrier during inflammation and reflect on whether these factors can be specifically targeted by repurposed existing drugs. Literature search was conducted using PubMed, drug database of US FDA and European Medicines Agency until and including September 2021.

EXPERT OPINION

IL-4 and IL-13 signaling are the major pathways disrupting the airway epithelial barrier during airway inflammation. However, blocking IL-4/IL-13 signaling may adversely affect protective immune responses and increase susceptibility of host to infections. An alternate approach to modulate airway epithelial barrier function involves targeting specific downstream component of IL-4/IL-13 signaling or different inflammatory mediators responsible for regulation of airway epithelial barrier. Airway epithelium-targeted therapy using inhibitors of HDAC, HSP90, MIF, mTOR, IL-17A and VEGF may be a potential strategy to prevent airway epithelial barrier dysfunction in airway inflammatory diseases.

The selective serotonin reuptake inhibitors enhance the cytotoxicity of sorafenib in hepatocellular carcinoma cells

Sertraline and fluoxetine are the two most commonly used selective serotonin reuptake inhibitors (SSRIs) in the treatment of depression. Accumulating evidence has revealed that SSRIs can reduce the risk of hepatocellular carcinoma (HCC), but their therapeutic effects in HCC have not yet been elucidated. Previous studies have reported that sertraline and fluoxetine can suppress the growth of gastric carcinoma, melanoma and nonsmall cell lung cancers by inhibiting the mammalian target rapamycin (mTOR) activity. In this study, we found that sertraline and fluoxetine blocked the protein kinase B (AKT)/mTOR pathway and suppressed the growth of HCC cells in vitro, in xenografts and in diethylnitrosamine/carbon tetrachloride (DEN/CCL4)-induced primary liver mouse model. Sertraline and fluoxetine can synergize with sorafenib, the first approved standard therapy for advanced HCC, to inhibit the viability of HCC cells in vitro and in vivo. In addition, the combination of sorafenib and SSRIs synergistically inhibited the effects of the AKT/mTOR pathway. These results reveal novel therapeutic effects of a combination of SSRIs and sorafenib in HCC.

Preclinical autophagy modulatory nanomedicines: big challenges, slow advances

INTRODUCTION

Autophagy is a critical housekeeping pathway to remove toxic protein aggregates, damaged organelles, providing cells with bioenergetic substrates needed to survive under adverse conditions. Since altered autophagy is associated with diverse diseases, its pharmacological modulation is considered of therapeutic interest. Nanomedicines may reduce the toxicity and improve the activity of toxic autophagy modulatory drugs (amd).

AREAS COVERED

The status of the most relevant anti-tumor, anti-inflammatory, and anti-infectious treatments mediated by autophagy modulatory nanomedicines (amN) published in the last 5 years is discussed.

EXPERT OPINION

Antitumor and anti-inflammatory treatments may be improved by administering amN for selective, massive, and targeted delivery of amd to diseased tissues. The use of amN as antimicrobial agent remains almost underexploited. Assessing the effect of amN on the complex autophagy machinery operating under different basal diseases, however, is not a trivial task. Besides structural reproducibility, nanomedicines must grant higher efficiency, and lower adverse effects than conventional medication. Simplicity of design, carefully chosen (scalable) preparation techniques, and rigorous monitoring of preclinical efficacy and nanotoxicity will improve the chances of clinical success. Currently, available data are not sufficient to envisage a fast-succeeding translation. Application of quality by design criteria would help to reach such milestones.

Decomposition Profile Data Analysis for Deep Understanding of Multiple Effects of Natural Products

It is difficult to understand the entire effect of a natural product because such products generally have multiple effects. We propose a strategy to understand these effects effectively by decomposing them with a profile data analysis method we developed. A transcriptome profile data set was obtained from a public database and analyzed. Considering their high similarity in structure and transcriptome profile, we focused on rescinnamine and syrosingopine. Decomposed effects predicted clear differences between the compounds. Two of the decomposed effects, SREBF1 activation and HDAC inhibition, were investigated experimentally because the relationship between these effects and the compounds had not yet been reported. Analyses in vitro validated these effects, and their strength was consistent with predicted scores. Moreover, the number of outliers in decomposed effects per compound was higher in natural products than in drugs in the data set, which is consistent with the nature of the effects of natural products.

Distinct Roles of mTOR Targets S6K1 and S6K2 in Breast Cancer

The mechanistic target of rapamycin (mTOR) is a master regulator of protein translation, metabolism, cell growth and proliferation. It forms two complexes, mTOR complex 1 (mTORC1) and 2 (mTORC2). mTORC1 is frequently deregulated in many cancers, including breast cancer, and is an important target for cancer therapy. The immunosuppressant drug rapamycin and its analogs that inhibit mTOR are currently being evaluated for their potential as anti-cancer agents, albeit with limited efficacy. mTORC1 mediates its function via its downstream targets 40S ribosomal S6 kinases (S6K) and eukaryotic translation initiation factor 4E (eIF4E)-binding protein 1 (4E-BP1). There are two homologs of S6K: S6K1 and S6K2. Most of the earlier studies focused on S6K1 rather than S6K2. Because of their high degree of structural homology, it was generally believed that they behave similarly. Recent studies suggest that while they may share some functions, they may also exhibit distinct or even opposite functions. Both homologs have been implicated in breast cancer, although how they contribute to breast cancer may differ. The purpose of this review article is to compare and contrast the expression, structure, regulation and function of these two S6K homologs in breast cancer.

mTOR up-regulation of PFKFB3 is essential for acute myeloid leukemia cell survival

Although mTOR (mammalian target of rapamycin) activation is frequently observed in acute myeloid leukemia (AML) patients, the precise function and the downstream targets of mTOR are poorly understood. Here we revealed that PFKFB3, but not PFKFB1, PFKFB2 nor PFKFB4 was a novel downstream substrate of mTOR signaling pathway as PFKFB3 level was augmented after knocking down TSC2 in THP1 and OCI-AML3 cells. Importantly, PFKFB3 silencing suppressed glycolysis and cell proliferation of TSC2 silencing OCI-AML3 cells and activated apoptosis pathway. These results suggested that mTOR up-regulation of PFKFB3 was essential for AML cells survival. Mechanistically, Rapamycin treatment or Raptor knockdown reduced the expression of PFKFB3 in TSC2 knockdown cells, while Rictor silencing did not have such effect. Furthermore, we also revealed that mTORC1 up-regulated PFKFB3 was dependent on hypoxia-inducible factor 1α (HIF1α), a positive regulator of glycolysis. Moreover, PFKFB3 inhibitor PFK15 and rapamycin synergistically blunted the AML cell proliferation. Taken together, PFKFB3 was a promising drug target in AML patients harboring mTOR hyper-activation.

Rapamycin regulates the proliferation of Huh7, a hepatocellular carcinoma cell line, by up-regulating p53 expression

Rapamycin, a specific inhibitor of mTOR used extensively as an immunosuppressant, has been expanded recently to cancer therapy, because the mTOR signal is known to be up-regulated in various cancer cells including hepatocellular carcinoma (HCC) cells. In spite of extensive efforts to employ mTOR inhibitors as anti-HCC therapy, they have not yet been approved by the FDA. Because of the heterogeneity and complexity of molecular signaling in HCC, suitable biomarkers should be identified or discovered to improve clinical efficacy of mTOR-specific inhibitors to HCC cells. In this study, the effect of rapamycin was investigated on two different HCC cell lines, Huh7 cells and HepG2 cells. Rapamycin was found to inhibit the proliferation of Huh7 cells but not of HepG2 cells. Moreover, it was found that rapamycin can up-regulate p53 at the protein level, but not affect its transcript. To understand the critical role of p53 in the rapamycin effect, knock-down experiments were performed using small-interfering RNAs (siRNAs). The anti-proliferative effect of rapamycin on Huh7 cells clearly disappeared after blocking p53 production with siRNA, which indicates that p53 is a critical factor in the anti-proliferative effect of rapamycin in HCC cells. The over-expression system of p53 was also employed to mimic the effect of rapamycin and found that cell proliferation was clearly down-regulated by p53 over-expression. Finally, we found that the extracellular signal-regulated kinase 1/2 (ERK1/2) signal was regulated by p53 whose expression was induced by rapamycin. Overall, this study demonstrates that rapamycin inhibited the proliferation of Huh7 cells by up-regulating the expression of p53 and down-regulating the ERK1/2 signal, indicating that p53 is a useful biomarker for anti-cancer therapy using the specific inhibitor of mTOR signal, rapamycin, against hepatocellular carcinoma cells.

Rapamycin up-regulates triglycerides in hepatocytes by down-regulating Prox1

Background

Although the prolonged use of rapamycin may cause unwanted side effects such as hyperlipidemia, the underlying mechanism remains unknown. Prox1 is a transcription factor responsible for the development of several tissues including lymphatics and liver. There is growing evidences that Prox1 participates in metabolism in addition to embryogenesis. However, whether Prox1 is directly related to lipid metabolism is currently unknown.

Methods

HepG2 human hepatoma cells were treated with rapamycin and total lipids were analyzed by thin layer chromatography. The effect of rapamycin on the expression of Prox1 was determined by western blotting. To investigate the role of Prox1 in triglycerides regulation, siRNA and overexpression system were employed. Rapamycin was injected into mice for 2 weeks and total lipids and proteins in liver were measured by thin layer chromatography and western blot analysis, respectively.

Results

Rapamycin up-regulated the amount of triglyceride and down-regulated the expression of Prox1 in HepG2 cells by reducing protein half-life but did not affect its transcript. The loss-of-function of Prox1 was coincident with the increase of triglycerides in HepG2 cells treated with rapamycin. The up-regulation of triglycerides by rapamycin in HepG2 cells reverted to normal levels by the compensation of Prox1 using the overexpression system. Rapamycin also down-regulated Prox1 expression but increased triglycerides in mouse liver.

Conclusion

This study suggests that rapamycin can increase the amount of triglycerides by down-regulating Prox1 expression in hepatocytes, which means that the mammalian target of rapamycin (mTOR) signaling is important for the regulation of triglycerides by maintaining Prox1 expression.

Co-loaded paclitaxel/rapamycin liposomes: Development, characterization and in vitro and in vivo evaluation for breast cancer therapy

Paclitaxel and rapamycin have been reported to act synergistically to treat breast cancer. Albeit paclitaxel is available for breast cancer treatment, the most commonly used formulation in the clinic presents side effects, limiting its use. Furthermore, both drugs present pharmacokinetics drawbacks limiting their in vivo efficacy and clinic combination. As an alternative, drug delivery systems, particularly liposomes, emerge as an option for drug combination, able to simultaneously deliver co-loaded drugs with improved therapeutic index. Therefore, the purpose of this study is to develop and characterize a co-loaded paclitaxel and rapamycin liposome and evaluate it for breast cancer efficacy both in vitro and in vivo. Results showed that a SPC/Chol/DSPE-PEG (2000) liposome was able to co-encapsulate paclitaxel and rapamycin with suitable encapsulation efficiency values, nanometric particle size, low polydispersity and neutral zeta potential. Taken together, FTIR and thermal analysis evidenced drug conversion to the more bioavailable molecular and amorphous forms, respectively, for paclitaxel and rapamycin. The pegylated liposome exhibited excellent colloidal stability and was able to retain drugs encapsulated, which were released in a slow and sustained fashion. Liposomes were more cytotoxic to 4T1 breast cancer cell line than the free drugs and drugs acted synergistically, particularly when co-loaded. Finally, in vivo therapeutic evaluation carried out in 4T1-tumor-bearing mice confirmed the in vitro results. The co-loaded paclitaxel/rapamycin pegylated liposome better controlled tumor growth compared to the solution. Therefore, we expect that the formulation developed herein might be a contribution for future studies focusing on the clinical combination of paclitaxel and rapamycin.

Exenatide inhibits the growth of endometrial cancer Ishikawa xenografts in nude mice

Studies have showed that diabetes is one of the high risk factors of endometrial cancer; however, no reports describe the anti- or pro-cancer effect of a new kind of anti-diabetes drug, glucagon-like peptide-1 receptor agonist exenatide (exendin-4), on endometrial cancer. To investigate whether exenatide promotes or inhibits the growth of endometrial cancer, we used the subcutaneous human endometrial cancer cell Ishikawa xenografts in nude mouse model, and divided them into control group and exenatide-treated group. The tumor growth rate in exenatide group was slower than that in control group, and the apoptosis rate of exenatide group was higher than that in control group. In vitro, exendin-4 also attenuated Ishikawa cell viability and clone formation rate, but promoted cell apoptosis. There was an increase of phosphorylated-AMPK protein, a decrease of phosphorylated-mTOR protein both in vivo and in vitro after exenatide or exendin-4 treatment. Moreover, when treated with exendin-4 plus AICAR, an AMPK activator, cell apoptosis increased with higher ratio of phosphorylayed-AMPK/AMPK, lower ratio of phosphorylated-mTOR/mTOR and higher expression of cleaved caspase-3 than those in exendin-4 alone group, and the results were the opposite when treated with exendin-4 plus compound C, an AMPK inhibitor. Our results suggest that exenatide could attenuate the growth of endometrial cancer Ishikawa xenografts in nude mice, and AMPK may be the target of the mechanism.

MicroRNA-147 suppresses proliferation, invasion and migration through the AKT/mTOR signaling pathway in breast cancer

The Akt/mTOR pathway is considered to be the most frequently aberrantly activated pathway in human tumors. It is activated in a variety of types of tumor, and is therefore an attractive target for study, including it's potential regulation by microRNAs. A number of microRNAs (miRs) have been demonstrated to target the Akt/mTOR pathway. A previous study reported that miR-147 targets the EGFR-driven cell-cycle protein network in breast cancer. EGFR serves a crucial role upstream to Akt/mTOR. To define the function and mechanism of miR-147 in breast cancer, the present study assessed miR-147 expression in a normal mammary epithelial cell line and three breast cancer cell lines, and observed that miR-147 expression was markedly low in the highly invasive cell line, MDA-MB-231. Ectopic expression of miR-147 in MDA-MB-231 resulted in a reduction of the phosphorylation of crucial molecules in the Akt/mTOR pathway and the proliferation, invasion and migration of the cell line was also reduced. The effects of miR-147 expression are similar to that of shRNA which is specifically designed to silence the expression of Akt. The findings of the present study indicate that miR-147 suppressed the proliferation, invasion and migration of breast cancer cells through targeting the Akt/mTOR signaling pathway. As a new microRNA targeting Akt/mTOR pathway. Using miR-147 may therefore provide an effective therapeutic approach to suppress tumorigenicity in breast cancer.

Effects of mTOR inhibitors and cytoskeletal-directed agents alone and in combination against normal and neoplastic hematopoietic cells in vitro

The mechanistic target of rapamycin (mTOR) controls cell growth and enlargement and has been found to be aberrant in a wide variety of malignancies. Although mTOR is already an attractive antineoplastic target, overexpression or aberrant expression of mTOR may also provide an opportunity to further increase the size differential between malignant and normal cells, providing an opportunity to amplify and exploit cell size differences between neoplastic cells and their normal counterparts using physiochemical treatment modalities. Therefore, this study sought to quantify the concentration response and time course effects of rapamycin on cell cycle entry, cell enlargement, and cell proliferation in U937 human monocytic leukemia and human hematopoietic stem cells (hHSCs). In addition, the effects of combination treatment with mTOR inhibitors (rapamycin, everolimus, and temsirolimus) and cytoskeletal-directed agents (cytochalasin B and vincristine) in leukemic cells (U937, THP1, K562, Molt-4, and L1210) were assessed for potential drug synergy. While both U937 cells and hHSCs exhibited a marked reduction in cell volume, U937 cells were able to proliferate in the presence of rapamycin ranging from 0.5 nM to 10 μM (10,000 nM), whereas hHSCs were able to proliferate only at lower concentrations, and were completely inhibited from proliferation by 8 nM rapamycin. These effects were observed with as little as 0.5 nM rapamycin, demonstrating the profound affinity the compound has for FK-binding protein 12 (FKBP12), which subsequently forms the FKBP12/rapamycin complex to inhibit mTOR. Rapamycin continued to exert effects on cell size and proliferation even at 10 μM, without producing marked cytotoxicity. Although cytochalasin B and vincristine were unable to substantially enlarge rapamycin-treated leukemia cells, it appears that rapamycin and its associated analogs everolimus and temsirolimus have notable synergistic potential with microfilament-disrupting cytochalasin B and microtubule-disrupting vincristine as assessed by comparative effects on cell growth, annexin V staining, IC30 isobolograms, and Chou-Talalay statistics. These observations indicate a potentially novel therapeutic rationale for hematological malignancies and for other cancers to elicit the preferential destruction of neoplastic cells that aberrantly express mTOR.

N-Methyl-N-nitrosourea as a mammary carcinogenic agent

The administration of chemical carcinogens is one of the most commonly used methods to induce tumors in several organs in laboratory animals in order to study oncologic diseases of humans. The carcinogen agent N-methyl-N-nitrosourea (MNU) is the oldest member of the nitroso compounds that has the ability to alkylate DNA. MNU is classified as a complete, potent, and direct alkylating compound. Depending on the animals' species and strain, dose, route, and age at the administration, MNU may induce tumors' development in several organs. The aim of this manuscript was to review MNU as a carcinogenic agent, taking into account that this carcinogen agent has been frequently used in experimental protocols to study the carcinogenesis in several tissues, namely breast, ovary, uterus, prostate, liver, spleen, kidney, stomach, small intestine, colon, hematopoietic system, lung, skin, retina, and urinary bladder. In this paper, we also reviewed the experimental conditions to the chemical induction of tumors in different organs with this carcinogen agent, with a special emphasis in the mammary carcinogenesis.

Effect of Polypurine Reverse Hoogsteen Hairpins on Relevant Cancer Target Genes in Different Human Cell Lines

We studied the ability of polypurine reverse Hoogsteen hairpins (PPRHs) to silence a variety of relevant cancer-related genes in several human cell lines. PPRHs are hairpins formed by two antiparallel polypurine strands bound by intramolecular Hoogsteen bonds linked by a pentathymidine loop. These hairpins are able to bind to their target DNA sequence through Watson-Crick bonds producing specific silencing of gene expression. We designed PPRHs against the following genes: BCL2, TOP1, mTOR, MDM2, and MYC and tested them for mRNA levels, cytotoxicity, and apoptosis in prostate, pancreas, colon, and breast cancer cell lines. Even though all PPRHs were effective, the most remarkable results were obtained with those against BCL2 and mammalian target of rapamycin (mTOR) in decreasing cell survival and mRNA levels and increasing apoptosis in prostate, colon, and pancreatic cancer cells. In the case of TOP1, MDM2, and MYC, their corresponding PPRHs produced a strong effect in decreasing cell viability and mRNA levels and increasing apoptosis in breast cancer cells. Thus, we confirm that the PPRH technology is broadly useful to silence the expression of cancer-related genes as demonstrated using target genes involved in metabolism (DHFR), proliferation (mTOR), DNA topology (TOP1), lifespan and senescence (telomerase), apoptosis (survivin, BCL2), transcription factors (MYC), and proto-oncogenes (MDM2).

Induction of apoptosis by 4-(3-(tert-butylamino)imidazo[1,2-α]pyridine-2-yl) benzoic acid in breast cancer cells via upregulation of PTEN

We have previously reported that 4-(3-(tert-butylamino)imidazo[1,2-α]pyridine-2-yl)benzoic acid, a bicyclic N-fused aminoimidazoles derivative (BNFA-D), possesses anticancer potentiality against breast and kidney cancer cells with minimal toxicities to corresponding normal cells. Here, we explored the mechanism of action of BNFA-D in breast cancer cells using multiple cell-based assays such as MTT, DAPI, FACS, Western blot, and immunoprecipitation. BNFA-D caused apoptosis by upregulating PTEN leading to inhibition of Wnt/TCF signaling cascade and arresting S phase in breast cancer cells. Expression levels of β-catenin, cyclin D1, C-MYC, and phospho-AKT (Ser(473)) decreased with simultaneous increase in the levels of GSK3β, CK1, and PTEN in BNFA-D-treated MCF-7 cells. Interestingly, silencing of PTEN in breast cancer cells reversed the phenomenon of Wnt/TCF signaling cascade inhibition after BNFA-D treatment.

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.

Combination of cetuximab and rapamycin enhances the therapeutic efficacy in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most deadly cancers worldwide. It is well known that the activation of PI3K/AKT/mTOR and the Ras/MAPK signaling pathway plays a critical role in cellular metabolism, growth and proliferation, and its inhibitors have been used as therapeutic drugs for hepatocellular carcinoma. Cetuximab, a chimerical monoclonal EGFR IgG1 antibody, can block the binding of EGF or other ligands to EGFR and thus inhibit ligands-induced receptor phosphorylation. In the present study, we found that rapamycin could enhance the antiproliferation effect of cetuximab in both HepG2 cells and Huh-7 cells and arrest the cell cycle. Cetuximab in combination with rapamycin had synergistic effects on inhibiting the phosphrylation of proteins in PI3K/AKT/mTOR and Ras/MAPK signaling pathway. Combination of cetuximab with rapamycin treatment significantly suppressed the HCC development in HepG2 cells-xenografted mice and improved the survival. Cetuximab and rapamycin inhibited the growth of HCC both in vitro and in vivo. These results suggest that the combination therapy using the inhibitors for both EGFR and PI3K/AKT/mTOR signaling pathways may be a novel therapeutic approach for HCC.

Insulin induces neurite outgrowth via SIRT1 in SH-SY5Y cells

Insulin plays diverse roles, including learning and memory, in the central nervous system. SIRT1 has been reported to be involved in the processes of normal learning, memory, and synaptic plasticity. However, whether insulin is directly involved in regulating SIRT1 expression in neurons or whether it affects synapses remains largely unknown. Here, we show that insulin promotes neurite outgrowth and increases SIRT1 expression in SH-SY5Y cells. LY294002, a phosphatidylinositol 3-kinase inhibitor, inhibited the expression of insulin-induced increases in SIRT1. Conversely, the downregulation of SIRT1 using a SIRT1 inhibitor and SIRT1-siRNA resulted in a significant reduction in the length of neurite outgrowth. Taken together, these results suggest that the regulation of SIRT1 by insulin is important for the neurite outgrowth of neuroblastoma cells.

Medroxyprogestogen enhances apoptosis of SKOV-3 cells via inhibition of the PI3K/Akt signaling pathway

We sought to assess the effect of progestin on the apoptosis of epithelial ovarian cancer cell line SKOV-3 and via regulation of phosphorylation signaling in. Epithelial ovarian cancer cell line SKOV-3 was treated with medroxyprogestogen, phosphatidylinositol 3-kinase inhibitor LY294002 and vehicle control. Akt, phospho-Akt, Bcl-2 and phospho-Bad proteins were examined by immunoblotting assays. Medroxyprogestogen-induced apoptosis was assessed by MTT assays and Annexin V apoptosis assay. We found no significant difference in Akt and Bad expression in both the medroxyprogestogen groups and the control group. The levels of phospho-Akt, Bcl-2 and phospho-Bad were decreased in all the medroxyprogestogen groups and significantly decreased in the high dose mitogen-activated protein (MAP) group (10 µmol/L). Viability of SKOV-3 was reduced and apparent apoptosis of SKOV-3 cells was observed with increased doses of MAP. The findings suggest that medroxyprogestogen can induce SKOV-3 cell apoptosis by inhibiting Akt phosphorylation.

NMR studies of the C-terminus of alpha4 reveal possible mechanism of its interaction with MID1 and protein phosphatase 2A

Alpha4 is a regulatory subunit of the protein phosphatase family of enzymes and plays an essential role in regulating the catalytic subunit of PP2A (PP2Ac) within the rapamycin-sensitive signaling pathway. Alpha4 also interacts with MID1, a microtubule-associated ubiquitin E3 ligase that appears to regulate the function of PP2A. The C-terminal region of alpha4 plays a key role in the binding interaction of PP2Ac and MID1. Here we report on the solution structure of a 45-amino acid region derived from the C-terminus of alpha4 (alpha45) that binds tightly to MID1. In aqueous solution, alpha45 has properties of an intrinsically unstructured peptide although chemical shift index and dihedral angle estimation based on chemical shifts of backbone atoms indicate the presence of a transient α-helix. Alpha45 adopts a helix-turn-helix HEAT-like structure in 1% SDS micelles, which may mimic a negatively charged surface for which alpha45 could bind. Alpha45 binds tightly to the Bbox1 domain of MID1 in aqueous solution and adopts a structure consistent with the helix-turn-helix structure observed in 1% SDS. The structure of alpha45 reveals two distinct surfaces, one that can interact with a negatively charged surface, which is present on PP2A, and one that interacts with the Bbox1 domain of MID1.

Metformin promotes progesterone receptor expression via inhibition of mammalian target of rapamycin (mTOR) in endometrial cancer cells

Progesterone has been used in the hormonal treatment of endometrial cancer (EC) for many years, but the response rates are unsatisfying. The down-regulated progesterone receptor (PR) is the main reason for treatment failure. The insulin-like growth factor (IGF) system is related to EC risk, and IGF-I can inhibit PR transcription in breast cancer. Recent evidence suggests that metformin-combined oral contraceptives may reverse progesterone-resistant atypical endometrial hyperplasia, but the mechanism is unclear. We attempt to investigate the interaction of metformin, PR and IGF-II expression, and identify whether metformin can enhance the antitumor effect of medroxyprogesterone acetate (MPA) using Ishikawa and HEC-1B EC cell lines. We found that both IGF-I and IGF-II inhibit PR A/B mRNA and protein expression, whereas metformin markedly promotes PR expression. In parallel, IGF-II increases phosphorylation of AKT and p70S6K, while metformin increases AMPK phosphorylation and decreases p70S6K phosphorylation. The effects of metformin on PR A/B and p70S6K are partially reversed by an AMPK inhibitor. Furthermore, metformin synergistically antiproliferates MPA in two cell lines, with the peak synergy occurring with 10μM metformin combined with 1μM MPA (CI=0.20448 for Ishikawa, CI=0.12801 for HEC-1B). Our results demonstrate that metformin promotes PR expression, which can be inhibited by overexpressed IGF-II in EC. This effect is partially mediated through activating AMPK followed by inhibiting the overactivated mTOR pathway.

Targeting mTOR in HIV-Negative Classic Kaposi's Sarcoma

A 66-year old female with HIV-negative classic Kaposi's sarcoma responded to mTOR targeting by rapamycin. The response was well documented by PET-CT. This case provides supporting evidence that the mTOR pathway may be important in the tumorigenesis of KS and that rapamycin may have activity in this disease.

The mTOR protein as a target in thyroid cancer

INTRODUCTION

The mammalian target of rapamycin (mTOR) protein is a downstream effector of the phosphatidilinositol-3 kinase (PI3K)/Akt pathway, which regulates not only cell proliferation and viability, but also iodide uptake in thyroid cells. Genetic alterations in the PI3K/Akt/mTOR pathway are common during thyroid cancer progression, and thus, these proteins are attractive targets for cancer therapy. So far, specific mTOR inhibitors, such as rapamycin analogs, have been developed and studied as anti-cancer agents.

AREAS COVERED

This review discusses evidence that justifies the potential use of mTOR signaling pathway inhibitors as therapeutic agents for thyroid cancer.

EXPERT OPINION

In the near future, mTOR-targeted drugs might represent a new approach for the therapy of thyroid cancer patients; rapamycin analogs have already been developed and are currently being clinically tested. Besides the antiproliferative action of mTOR inhibition, the stimulatory effect on thyroid iodide uptake can also be useful in the treatment of recurrent thyroid cancer. Therefore, if rapamycin analogs are able to increase iodide uptake in thyroid cancer, either alone or in combination with other agents, this will represent a new approach for the treatment of thyroid cancer, which may possibly improve the treatment of patients in which radioiodine therapy is not effective.

Aging and TOR: interwoven in the fabric of life

Longstanding results with calorie and growth factor restriction plus recent results with the first interventional drug suggest that retarding the pace of aging to improve the quality of life of older people is at hand. The biological system targeted by these approaches is the target of rapamycin (TOR), which is central for cellular responses to a variety of stimuli including stressors, growth factors, and nutrients and energy states. That the life-extending response to reducing its activity is highly conserved from yeast to mammals is consistent with the evolution of aging as a strategy to preserve reproductive potential of young cells and animals.

Methoxychalcone induces cell-cycle arrest and apoptosis in human hormone-resistant prostate cancer cells through PI 3-kinase-independent inhibition of mTOR pathways

BACKGROUND

Chalcones are contained in fruits and vegetables, and have been suggested to display anticancer activities. In this study, the anticancer mechanism of WJ9708011 (a methoxychalcone derivative) was delineated in human prostate cancer cells.

METHOD

Cell proliferation was examined by sulforhodamine B and clonogenic assays. Cell-cycle progression and mitochondrial membrane potential (DeltaPsi(m)) were detected by flow cytometric analysis. Expressions of protein and mRNA were detected by Western blot and RT-PCR technique, respectively. The protein synthesis was examined by [(3)H]leucine incorporation assay. The overexpression or knockdown techniques for specific target protein were also used in this study.

RESULTS

WJ9708011 induced time- and concentration-dependent G1 arrest of the cell cycle and subsequent apoptosis in human prostate cancer cells. The G1-arrest effect was confirmed by down-regulated expressions of several G1-phase regulators, including cyclin D1, cyclin E, cyclin-dependent kinase (Cdk)-4, Cdk2, phospho-RB, E2F-1, and Cdc25A. The mRNA expressions of cyclin D1 and cyclin E were also inhibited through the suppression of NF-kappaB. WJ9708011 blocked the protein synthesis and inhibited mammalian target of rapamycin (mTOR) signaling pathways. The suppression of mTOR pathways were irrespective of Akt- and AMPK-activated protein kinase (AMPK), but were attributed to mitochondrial stress, in which the down-regulation of survivin protein level may play a crucial role.

CONCLUSIONS

The data suggest that WJ9708011 induces transcriptional and translational suppression of cell-cycle regulators that might be through Akt- and AMPK-independent loss of DeltaPsi(m) and inhibition of mTOR signaling pathway, leading to G1 arrest of the cell cycle and subsequent apoptotic cell death.

Temsirolimus in the treatment of relapsed and/or refractory mantle cell lymphoma

Patients with mantle cell lymphoma (MCL) have a poor prognosis; consequently, new therapeutic approaches, such as rapamycin and its derivates, mammalian target of rapamycin (mTOR) inhibitors, are warranted. Temsirolimus (also known as CCI-779), a dihydroester of rapamycin, in MCL cell lines inhibited mTOR, downregulated p21 and v-Raf, and induced autophagy. The first clinical trial in MCL patients was performed using 250 mg of temsirolimus weekly for 6-12 cycles. The overall response rate was 38%; the median time to progression was 6.5 months, median overall survival was 12 months, and the median duration of response was 6.9 months. At lower dose (25 mg/week), the overall response rate was 41%, median overall survival was 14 months, and time to progression was 6 months. In another trial, 162 patients were randomly assigned to receive temsirolimus at 2 different doses (175 mg/week for 3 weeks, then 75 mg or 25 mg/week) or a treatment chosen by the investigator among the most frequently adopted single agents for treatment of relapsed MCL. Patients treated with 175/75 mg of temsirolimus had significantly higher response rates and longer progression-free survival than those treated with investigator's choice therapy. These data support the use of mTOR inhibitors for the treatment of MCL, probably in combination with other agents, such as antiangiogenic drugs or histone acetylase inhibitors.

Rapamycin sensitizes Akt inhibition in malignant human breast epithelial cells

Akt and mTOR are therapeutic targets for the treatment of cancer. The effects of inhibiting mTOR, with rapamycin, and Akt, with A-443654, concurrently, on cell morphology, cell proliferation, the cell cycle, and apoptosis were examined using the benign MCF10A and malignant MCF10CA1a human breast epithelial cells. Rapamycin and A-443654 in combination produced the greatest morphological changes and inhibited cell proliferation by G2/M arrest. Rapamycin and A-443654 in combination induced apoptosis at earlier times and at lower A-443654 concentrations in MCF10CA1a tumor cells than in the benign MCF10A cells. Rapamycin and A-443654 increased p53 and p15(INK4B) protein levels, decreased anti-apoptotic Bcl-2 levels, and increased Bad levels in the MCF10CA1a tumor cells by approximately 5-fold. These results suggest that the combined inhibition of Akt and mTOR may have beneficial therapeutic and safety margin effects.

The antidepressant sertraline inhibits translation initiation by curtailing mammalian target of rapamycin signaling

Sertraline, a selective serotonin reuptake inhibitor, is a widely used antidepressant agent. Here, we show that sertraline also exhibits antiproliferative activity. Exposure to sertraline leads to a concentration-dependent decrease in protein synthesis. Moreover, polysome profile analysis of sertraline-treated cells shows a reduction in polysome content and a concomitant increase in 80S ribosomes. The inhibition in translation caused by sertraline is associated with decreased levels of the eukaryotic initiation factor (eIF) 4F complex, altered localization of eIF4E, and increased eIF2alpha phosphorylation. The latter event leads to increased REDD1 expression, which in turn impinges on the mammalian target of rapamycin (mTOR) pathway by affecting TSC1/2 signaling. Sertraline also independently targets the mTOR signaling pathway downstream of Rheb. In the Emu-myc murine lymphoma model where carcinogenesis is driven by phosphatase and tensin homologue (PTEN) inactivation, sertraline is able to enhance chemosensitivity to doxorubicin. Our results indicate that sertraline exerts antiproliferative activity by targeting the mTOR signaling pathway in a REDD1-dependent manner.

Biochanin A Modulates Cell Viability, Invasion, and Growth Promoting Signaling Pathways in HER-2-Positive Breast Cancer Cells

Overexpression of HER-2 receptor is associated with poor prognosis and aggressive forms of breast cancer. Scientific literature indicates a preventive role of isoflavones in cancer. Since activation of HER-2 receptor initiates growth-promoting events in cancer cells, we studied the effect of biochanin A (an isoflavone) on associated signaling events like receptor activation, downstream signaling, and invasive pathways. HER-2-positive SK-BR-3 breast cancer cells, MCF-10A normal breast epithelial cells, and NIH-3T3 normal fibroblast cells were treated with biochanin A (2–100 μM) for 72 hours. Subsequently cell viability assay, western blotting and zymography were carried out. The data indicate that biochanin A inhibits cell viability, signaling pathways, and invasive enzyme expression and activity in SK-BR-3 cancer cells. Biochanin A did not inhibit MCF-10A and NIH-3T3 cell viability. Therefore, biochanin A could be a unique natural anticancer agent which can selectively target cancer cells and inhibit multiple signaling pathways in HER-2-positive breast cancer cells.

Rapamycin by itself and additively in combination with carboplatin inhibits the growth of ovarian cancer cells

OBJECTIVE

The current standard treatment for ovarian carcinoma, consisting of surgery followed by chemotherapy with carboplatin and paclitaxel, is fraught with a high rate of recurrences. We hypothesized that targeted inhibition of specific signaling pathways in combination with conventional drugs may increase chemotherapeutic efficacy.

METHODS

We analyzed the expression and activation profiles of various signaling pathways in nine established ovarian cancer cell lines (CAOV-3, ES2, PA-1, SKOV-3, NIHOVCAR3, OV90, TOV112D, A1847, A2780) and 24 freshly procured human ovarian tumors. The PI3 kinase pathway component Akt was frequently overexpressed and/or activated in tumor cells. The effect of several PI3K pathway inhibitors (rapamycin, LY294002, SH-6) and rapamycin in combination with carboplatin on various tumor cell growth characteristics was tested in cell lines and fresh tumor-derived transient monolayer and organ cultures.

RESULTS

Rapamycin by itself and additively with carboplatin inhibited the growth and invasion, and increased the sensitivity to anoikis of most of the ovarian cancer cell lines and fresh tumors. The additive inhibitory effect may be due to enhanced apoptosis as demonstrated by Poly-ADP-Ribose Polymerase (PARP) cleavage and Annexin V staining in cells treated with both rapamycin and carboplatin.

CONCLUSIONS

Rapamycin in combination with standard chemotherapeutic agents may improve the efficiency of ovarian cancer treatment.

Dauricine inhibits insulin-like growth factor-I-induced hypoxia inducible factor 1alpha protein accumulation and vascular endothelial growth factor expression in human breast cancer cells

AIM

To investigate the effects of dauricine (Dau) on insulin-like growth factor-I (IGF-I)-induced hypoxia inducible factor 1alpha (HIF-1alpha) and vascular endothelial growth factor (VEGF) expression in human breast cancer cells (MCF-7).

METHODS

Serum-starved MCF-7 cells were pretreated for 1 h with different concentrations of Dau, followed by incubation with IGF-I for 6 h. HIF-1alpha and VEGF protein expression levels were analyzed by Western blotting and ELISA, respectively. HIF-1alpha and VEGF mRNA levels were determined by real-time PCR. In vitro angiogenesis was observed via the human umbilical vein endothelial cell (HUVEC) tube formation assay. An in vitro invasion assay on HUVECs was performed.

RESULTS

Dau significantly inhibited IGF-I-induced HIF-1alpha protein expression but had no effect on HIF-1alpha mRNA expression. However, Dau remarkably suppressed VEGF expression at both protein and mRNA levels in response to IGF-I. Mechanistically, Dau suppressed IGF-I-induced HIF-1alpha and VEGF protein expression mainly by blocking the activation of PI-3K/AKT/mTOR signaling pathway. In addition, Dau reduced IGF-I-induced HIF-1alpha protein accumulation by inhibiting its synthesis as well as by promoting its degradation. Functionally, Dau inhibited angiogenesis in vitro. Moreover, Dau had a direct effect on IGF-I-induced invasion of HUVECs.

CONCLUSION

Dau inhibits human breast cancer angiogenesis by suppressing HIF-1alpha protein accumulation and VEGF expression, which may provide a novel potential mechanism for the anticancer activities of Dau in human breast cancer.

Targeting the mammalian target of rapamycin in myxoid chondrosarcoma

Myxoid chondrosarcoma is a slow-growing sarcoma poorly responsive to chemotherapy and radiation therapy. Translational research has validated several proteins as optional therapeutic targets. Significant responses are, however, rare. In this paper we report an extraordinary response of myxoid chondrosarcoma to targeted therapy by rapamycin in combination with cyclophosphamide. Our case points to a possible novel therapeutic approach towards myxoid chondrosarcoma, by targeting the mammalian target of rapamycin protein, and probably protein kinase C-alpha, mitogen-activated protein kinase, and Jun N-terminal kinase too, by rapamycin.

Ornithine decarboxylase inhibition by alpha-difluoromethylornithine activates opposing signaling pathways via phosphorylation of both Akt/protein kinase B and p27Kip1 in neuroblastoma

Ornithine decarboxylase (ODC) is a key enzyme in mammalian polyamine biosynthesis that is up-regulated in various types of cancer. We previously showed that treating human neuroblastoma (NB) cells with the ODC inhibitor alpha-difluoromethylornithine (DFMO) depleted polyamine pools and induced G1 cell cycle arrest without causing apoptosis. However, the precise mechanism by which DFMO provokes these changes in NB cells remained unknown. Therefore, we further examined the effects of DFMO, alone and in combination with phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 or Akt/protein kinase B (PKB) inhibitor IV, on the regulation of cell survival and cell cycle-associated pathways in LAN-1 NB cells. In the present study, we found that the inhibition of ODC by DFMO promotes cell survival by inducing the phosphorylation of Akt/PKB at residue Ser473 and glycogen synthase kinase-3beta at Ser9. Intriguingly, DFMO also induced the phosphorylation of p27Kip1 at residues Ser10 (nuclear export) and Thr198 (protein stabilization) but not Thr187 (proteasomal degradation). The combined results from this study provide evidence for a direct cross-talk between ODC-dependent metabolic processes and well-established cell signaling pathways that are activated during NB tumorigenesis. The data suggest that inhibition of ODC by DFMO induces two opposing pathways in NB: one promoting cell survival by activating Akt/PKB via the PI3K/Akt pathway and one inducing p27Kip1/retinoblastoma-coupled G1 cell cycle arrest via a mechanism that regulates the phosphorylation and stabilization of p27Kip1. This study presents new information that may explain the moderate efficacy of DFMO monotherapy in clinical trials and reveals potential new targets for DFMO-based combination therapies for NB treatment.