mTOR target NDRG1 confers MGMT-dependent resistance to alkylating chemotherapy

Epigenetic inhibitors eliminate senescent melanoma BRAFV600E cells that survive long‑term BRAF inhibition

It is estimated that ~50% of patients with melanoma harbour B‑Raf (BRAF)V600 driver mutations, with the most common of these being BRAFV600E, which leads to the activation of mitogen‑activated protein kinase proliferative and survival pathways. BRAF inhibitors are used extensively to treat BRAF‑mutated metastatic melanoma; however, acquired resistance occurs in the majority of patients. The effects of long‑term treatment with PLX4032 (BRAFV600 inhibitor) were studied in vitro on sensitive V600E BRAF‑mutated melanoma cell lines. After several weeks of treatment with PLX4032, the majority of the melanoma cells died; however, a proportion of cells remained viable and quiescent, presenting senescent cancer stem cell‑like characteristics. This surviving population was termed SUR cells, as discontinuing treatment allowed the population to regrow while retaining equal drug sensitivity to that of parental cells. RNA sequencing analysis revealed that SUR cells exhibit changes in the expression of 1,415 genes (P<0.05) compared with parental cells. Changes in the expression levels of a number of epigenetic regulators were also observed. These changes and the reversible nature of the senescence state were consistent with epigenetic regulation; thus, it was investigated as to whether the senescent state could be reversed by epigenetic inhibitors. It was found that both parental and SUR cells were sensitive to different histone deacetylase (HDAC) inhibitors, such as SAHA and MGCD0103, and to the cyclin‑dependent kinase (CDK)9 inhibitor, CDKI‑73, which induced apoptosis and reduced proliferation both in the parental and SUR populations. The results suggested that the combination of PLX4032 with HDAC and CDK9 inhibitors may achieve complete elimination of SUR cells that persist after BRAF inhibitor treatment, and reduce the development of resistance to BRAF inhibitors.

Identification of putative biomarkers for Infantile Hemangiomas and Propranolol treatment via data integration

Infantile hemangiomas (IHs) are the most common benign tumors in early childhood. They show a distinctive mechanism of tumor growth in which a rapid proliferative phase is followed by a regression phase (involution). Propranolol is an approved treatment for IHs, but its mechanism of action remains unclear. We integrated and harmonized microRNA and mRNA transcriptome data from newly generated microarray data on IHs with publicly available data on toxicological transcriptomics from propranolol exposure, and with microRNA data from IHs and propranolol exposure. We identified subsets of putative biomarkers for proliferation and involution as well as a small set of putative biomarkers for propranolol's mechanism of action for IHs, namely EPAS1, LASP1, SLC25A23, MYO1B, and ALDH1A1. Based on our integrative data approach and confirmatory experiments, we concluded that hypoxia in IHs is regulated by EPAS1 (HIF-2α) instead of HIF-1α, and also that propranolol-induced apoptosis in endothelial cells may occur via mitochondrial stress.

Overexpression miR-486-3p Promoted by Allicin Enhances Temozolomide Sensitivity in Glioblastoma Via Targeting MGMT

Glioblastoma is the most common primary tumor of the central nervous system that develops chemotherapy resistance. Previous studies showed that Allicin could inhibit multiple cancer cells including glioblastoma, but the function of Allicin in glioblastoma is still unclear. Our work aimed to investigate the underlying molecular mechanism. The results showed that miR-486-3p levels were greatly increased in glioblastoma during Allicin treatment. Overexpression of miR-486-3p increased chemosensitivity to temozolomide (TMZ) in vitro and in vivo. O6-methylguanine-DNA methyltransferase (MGMT) was identified as a direct target of miR-486-3p, and miR-486-3p overexpression prevented the protein translation of MGMT. Moreover, overexpression of MGMT restored miR-486-3p-induced chemosensitivity to TMZ. Taken together, our studies revealed that Allicin could upregulate miR-486-3p and enhance TMZ sensitivity in glioblastoma. The results suggested that in the future, Allicin can be used as an adjuvant therapy with TMZ to improve the prognosis of patients, and miR-486-3p may be a potential target for glioblastoma treatment to improve the curative effects.

Targeting SGK1 enhances the efficacy of radiotherapy in locally advanced rectal cancer

Radiotherapy (RT) is a key component of neoadjuvant chemoradiotherapy to treat locally advanced rectal cancer (LARC). However, the therapeutic effect is limited due to radioresistance. Investigating the biomarkers of radioresistance might assist in the development of more effective therapeutic strategies for LARC.In this study, we investigated the different gene expressions in tumor samples from 110 patients using transcriptome analysis and immunohistochemistry (IHC), and identified serum- and glucocorticoid-regulated kinase 1 (SGK1) as a modulator of LARC radioresistance. We evaluated the impact of genetic and pharmacologic inhibition of the gene associated with radioresistance in vitro and in vivo. We found that the expression of SGK1 was upregulated in non-pathological complete response (non-pCR) patients. A high SGK1 expression was associated with radioresistance, whereas the genetic or pharmacologic inhibition of SGK1 expression reduced the radioresistance. We found that activate transcription factor 3 (ATF3) is a regulator of SGK1 in radioresistance.In conclusion, our findings indicate that SGK1 is a key player in LARC radioresistance, and drives radioresistance in an ATF3 dependent manner, which provides insights for future radio-sensitizer design.

A Small Hypoxia Signature Predicted pCR Response to Bevacizumab in the Neoadjuvant GeparQuinto Breast Cancer Trial

PURPOSE

In breast cancer, bevacizumab increased pCR rate but not long-term survival and no predictive markers are available to identify patients with long-term benefit from the drug.

EXPERIMENTAL DESIGN

We profiled 289 pretherapeutic formalin-fixed, paraffin-embedded (FFPE) biopsies of HER2-negative patients from the GeparQuinto trial of neoadjuvant chemotherapy ± bevacizumab by exome-capture RNA-sequencing (RNA-seq). In a prospectively planned study, we tested molecular signatures for response prediction. IHC validation was performed using tissue microarrays.

RESULTS

We found strong agreement of molecular and pathologic parameters as hormone receptors, grading, and lymphocyte infiltration in 221 high-quality samples. Response rates (49.3% pCR overall) were higher in basal-like (68.9%) and HER2-enriched (45.5%) than in luminal B (35.7%), luminal A (17.9%), and normal-like (20.0%) subtypes. T-cell (OR = 1.60; 95% confidence interval, 1.21-2.12; P = 0.001), proliferation (OR = 2.88; 95% CI, 2.00-4.15; P < 0.001), and hypoxia signatures (OR = 1.92; 95% CI, 1.41-2.60; P < 0.001) significantly predicted pCR in univariate analysis. In a prespecified multivariate logistic regression, a small hypoxia signature predicted pCR (OR = 2.40; 95% CI, 1.28-4.51; P = 0.006) with a significant interaction with bevacizumab treatment (P = 0.020). IHC validation using NDRG1 as marker revealed highly heterogenous expression within tissue leading to profound loss of sensitivity in TMA analysis, still a significant predictive value for pCR was detected (P = 0.025).

CONCLUSIONS

Exome-capture RNA-seq characterizes small FFPE core biopsies by reliably detecting factors as for example ER status, grade, and tumor-infiltrating lymphocytes levels. Beside molecular subtypes and immune signatures, a small hypoxia signature predicted pCR to bevacizumab, which could be validated by IHC. The signature can have important applications for bevacizumab treatment in different cancer types and might also have a role for novel combination therapies of bevacizumab with immune checkpoint inhibition.

Hypoxia Inducible Factor 1α Inhibits the Expression of Immunosuppressive Tryptophan-2,3-Dioxygenase in Glioblastoma

Abnormal circulation in solid tumors results in hypoxia, which modulates both tumor intrinsic malignant properties as well as anti-tumor immune responses. Given the importance of hypoxia in glioblastoma (GBM) biology and particularly in shaping anti-tumor immunity, we analyzed which immunomodulatory genes are differentially regulated in response to hypoxia in GBM cells. Gene expression analyses identified the immunosuppressive enzyme tryptophan-2,3-dioxygenase (TDO2) as the second most downregulated gene in GBM cells cultured under hypoxic conditions. TDO2 catalyses the oxidation of tryptophan to N-formyl kynurenine, which is the first and rate-limiting step of Trp degradation along the kynurenine pathway (KP). In multiple GBM cell lines hypoxia reduced TDO2 expression both at mRNA and protein levels. The downregulation of TDO2 through hypoxia was reversible as re-oxygenation rescued TDO2 expression. Computational modeling of tryptophan metabolism predicted reduced flux through the KP and lower intracellular concentrations of kynurenine and its downstream metabolite 3-hydroxyanthranilic acid under hypoxia. Metabolic measurements confirmed the predicted changes, thus demonstrating the ability of the mathematical model to infer intracellular tryptophan metabolite concentrations. Moreover, we identified hypoxia inducible factor 1α (HIF1α) to regulate TDO2 expression under hypoxic conditions, as the HIF1α-stabilizing agents dimethyloxalylglycine (DMOG) and cobalt chloride reduced TDO2 expression. Knockdown of HIF1α restored the expression of TDO2 upon cobalt chloride treatment, confirming that HIF1α controls TDO2 expression. To investigate the immunoregulatory effects of this novel mechanism of TDO2 regulation, we co-cultured isolated T cells with TDO2-expressing GBM cells under normoxic and hypoxic conditions. Under normoxia TDO2-expressing GBM cells suppressed T cell proliferation, while hypoxia restored the proliferation of the T cells, likely due to the reduction in kynurenine levels produced by the GBM cells. Taken together, our data suggest that the regulation of TDO2 expression by HIF1α may be involved in modulating anti-tumor immunity in GBM.

Bidirectional Regulation between NDRG1 and GSK3β Controls Tumor Growth and Is Targeted by Differentiation Inducing Factor-1 in Glioblastoma

The development of potent and selective therapeutic approaches to glioblastoma (GBM), one of the most aggressive primary brain tumors, requires identification of molecular pathways that critically regulate the survival and proliferation of GBM. Previous studies have reported that deregulated expression of N-myc downstream regulated gene 1 (NDRG1) affects tumor growth and clinical outcomes of patients with various types of cancer including glioma. Here, we show that high level expression of NDRG1 in tumors significantly correlated with better prognosis of patients with GBM. Loss of NDRG1 in GBM cells upregulated GSK3β levels and promoted cell proliferation, which was reversed by selective inhibitors of GSK3β. In contrast, NDRG1 overexpression suppressed growth of GBM cells by decreasing GSK3β levels via proteasomal degradation and by suppressing AKT and S6 cell growth signaling, as well as cell-cycle signaling pathways. Conversely, GSK3β phosphorylated serine and threonine sites in the C-terminal domain of NDRG1 and limited the protein stability of NDRG1. Furthermore, treatment with differentiation inducing factor-1, a small molecule derived from Dictyostelium discoideum, enhanced NDRG1 expression, decreased GSK3β expression, and exerted marked NDRG1-dependent antitumor effects in vitro and in vivo. Taken together, this study revealed a novel molecular mechanism by which NDRG1 inhibits GBM proliferation and progression. Our study thus identifies the NDRG1/GSK3β signaling pathway as a key growth regulatory program in GBM, and suggests enhancing NDRG1 expression in GBM as a potent strategy toward the development of anti-GBM therapeutics. SIGNIFICANCE: This study identifies NDRG1 as a potent and endogenous suppressor of glioblastoma cell growth, suggesting the clinical benefits of NDRG1-targeted therapeutics against glioblastoma.

SNAP reverses temozolomide resistance in human glioblastoma multiforme cells through down-regulation of MGMT

Glioblastoma multiforme (GBM) is the most frequently occurring and gravest primary tumor of the CNS in adults. The development of chemoresistance to temozolomide (TMZ), the first-line chemotherapy for GBM, is an important factor contributing to poor treatment outcomes. Down-regulation of O-6-methylguanine-DNA methyltransferase (MGMT) expression in GBM cells is an attractive strategy for overcoming TMZ resistance and improving outcomes. This study revealed that the nitric oxide (NO) donor S-nitroso-N-acetylpenicillamine (SNAP) exerts antitumorigenic effects on TMZ-sensitive and TMZ-resistant (TMZ-R) glioma cells. Pretreatment with SNAP not only induced apoptosis, mitochondrial dysfunction, and hypoxia-inducing factor 1, but also resensitized TMZ-R GBM cells to TMZ through down-regulation of MGMT expression. SNAP acted principally through post-translational modification of p53, phosphorylated N-myc downstream regulated gene 1, and MGMT protein stability in TMZ-R GBM cells. Additionally, when applied together, SNAP and TMZ enhanced the inhibition of tumor growth in vitro and in vivo. This study sheds new light on a potential strategy to overcome TMZ resistance in GBM and thus possesses the potential for prolonging survival of patients with GBM.-Tsai, C.-K., Huang, L.-C., Wu, Y.-P., Kan, I.-Y., Hueng, D.-Y. SNAP reverses temozolomide resistance in human glioblastoma multiforme cells through down-regulation of MGMT.

ABCB1 single-nucleotide variants and survival in patients with glioblastoma treated with radiotherapy concomitant with temozolomide

Standard treatment for glioblastoma (GBM) patients is surgery and radiochemotherapy (RCT) with temozolomide (TMZ). TMZ is a substrate for ABCB1, a transmembrane drug transporter. It has been suggested that survival for GBM patients receiving TMZ is influenced by different single-nucleotide variants (SNV) of ABCB1. We therefore examined SNV:s of ABCB1, namely 1199G>A, 1236C>T, 2677G>T/A, and 3435C>T and correlated to survival for GBM patients receiving RCT. In a pilot cohort (97 patients) a significant correlation to survival was found for SNV 1199G>A, with median OS for variant G/G patients being 18.2 months versus 11.5 months for A/G (p = 0.012). We found no correlation to survival for the other SNV:s. We then expanded the cohort to 179 patients (expanded cohort) and also included a confirmatory cohort (49 patients) focusing on SNV 1199G>A. Median OS for G/G versus A/G plus A/A was 15.7 and 11.5 months, respectively (p = 0.085) for the expanded cohort and 13.8 versus 16.8 months (p = 0.19) for the confirmatory. In conclusion, in patients with GBM receiving RCT with TMZ, no correlation with survival was found for the SNV:s 1236C>T, 2677G>T/A, and 3435C>T of ABCB1. Although the SNV 1199G>A might have some impact, a clinically significant role could not be confirmed.

Nervous NDRGs: the N-myc downstream-regulated gene family in the central and peripheral nervous system

The N-Myc downstream-regulated gene (NDRG) family consists of four members (NDRG1, NDRG2, NDRG3, NDRG4) that are differentially expressed in various organs and function in important processes, like cell proliferation and differentiation. In the last couple of decades, interest in this family has risen due to its connection with several disorders of the nervous system including Charcot-Marie-Tooth disease and dementia, as well as nervous system cancers. By combining a literature review with in silico data analysis of publicly available datasets, such as the Mouse Brain Atlas, BrainSpan, the Genotype-Tissue Expression (GTEx) project, and Gene Expression Omnibus (GEO) datasets, this review summarizes the expression and functions of the NDRG family in the healthy and diseased nervous system. We here show that the NDRGs have a differential, relatively cell type-specific, expression pattern in the nervous system. Even though NDRGs share functionalities, like a role in vesicle trafficking, stress response, and neurite outgrowth, other functionalities seem to be unique to a specific member, e.g., the role of NDRG1 in myelination. Furthermore, mutations, phosphorylation, or changes in expression of NDRGs are related to nervous system diseases, including peripheral neuropathy and different forms of dementia. Moreover, NDRG1, NDRG2, and NDRG4 are all involved in cancers of the nervous system, such as glioma, neuroblastoma, or meningioma. All in all, our review elucidates that although the NDRGs belong to the same gene family and share some functional features, they should be considered unique in their expression patterns and functional importance for nervous system development and neuronal diseases.

Second Generation mTOR Inhibitors as a Double-Edged Sword in Malignant Glioma Treatment

Glioblastomas (GBs) frequently display activation of the epidermal growth factor receptor (EGFR) and mammalian target of rapamycin (mTOR). mTOR exists as part of two multiprotein complexes, mTOR complex 1 (mTORC1) and 2 (mTORC2). In GBs, mTORC1 inhibitors such as rapamycin have performed poorly in clinical trials, and in vitro protect GB cells from nutrient and oxygen deprivation. Next generation ATP-competitive mTOR inhibitors with affinity for both mTOR complexes have been developed, but data exploring their effects on GB metabolism are scarce. In this study, we compared the ATP-competitive mTORC1/2 inhibitors torin2, INK-128 and NVP-Bez235 to the allosteric mTORC1 inhibitor rapamycin under conditions that mimic the glioma microenvironment. In addition to inhibiting mTORC2 signaling, INK-128 and NVP-Bez235 more effectively blocked mTORC1 signaling and prompted a stronger cell growth inhibition, partly by inducing cell cycle arrest. However, under hypoxic and nutrient-poor conditions mTORC1/2 inhibitors displayed even stronger cytoprotective effects than rapamycin by reducing oxygen and glucose consumption. Thus, therapies that arrest proliferation and inhibit anabolic metabolism must be expected to improve energy homeostasis of tumor cells. These results mandate caution when treating physiologically or therapeutically induced hypoxic GBs with mTOR inhibitors.

Discovery of a novel rhein-SAHA hybrid as a multi-targeted anti-glioblastoma drug

Glioblastoma multiforme (GBM) is the most common malignant tumor of the central nervous system (CNS). Effective treatments remain limited. Therefore, novel chemotherapy drugs with high efficiency and few adverse effects are urgently needed. Histone deacetylase (HDAC) and serum and glucocorticoid-regulated protein kinase 1 (SGK1) are targets for the prevention and treatment of GBM. Rhein has antitumor and SGK1 suppression effects, although its biological activity is limited by poor bioavailability. To improve the drug-like properties of rhein, we constructed a novel rhein-hydroxyethyl hydroxamic acid derivative (SYSUP007), which combined rhein with the HDAC inhibitor, suberoylanilide hydroxamic acid (SAHA). In the present study, the human GBM cell lines, T98G, U87 and U251, were used to investigate the anticancer effects of SYSUP007 in vitro. We found that SYSUP007 was more effective in inhibiting glioma cell proliferation, invasion and migration in vitro compared with the effects of rhein and SAHA. We also confirmed that SYSUP007 increased the expression of Ac-K100 and NDRG1 (targets of HDAC and SGK1). The present study indicates the potential that SYSUP007, as a novel rhein and SAHA derivative, for development as an anti-cancer therapy.

A combined ANXA2-NDRG1-STAT1 gene signature predicts response to chemoradiotherapy in cervical cancer

BACKGROUND

A better understanding of locally advanced cervical cancer (LACC) is mandatory for further improving the rates of disease control, since a significant proportion of patients still fail to respond or undergo relapse after concurrent chemoradiation treatment (CRT), and survival for these patients has generally remained poor.

METHODS

To identify specific markers of CRT response, we compared pretreatment biopsies from LACC patients with pathological complete response (sensitive) with those from patients showing macroscopic residual tumor (resistant) after neoadjuvant CRT, using a proteomic approach integrated with gene expression profiling. The study of the underpinning mechanisms of chemoradiation response was carried out through in vitro models of cervical cancer.

RESULTS

We identified annexin A2 (ANXA2), N-myc downstream regulated gene 1 (NDRG1) and signal transducer and activator of transcription 1 (STAT1) as biomarkers of LACC patients' responsiveness to CRT. The dataset collected through qPCR on these genes was used as training dataset to implement a Random Forest algorithm able to predict the response of new patients to this treatment. Mechanistic investigations demonstrated the key role of the identified genes in the balance between death and survival of tumor cells.

CONCLUSIONS

Our results define a predictive gene signature that can help in cervical cancer patient stratification, thus providing a useful tool towards more personalized treatment modalities.

The kinase inhibitor SI113 induces autophagy and synergizes with quinacrine in hindering the growth of human glioblastoma multiforme cells

Background

Glioblastoma multiforme (GBM), due to its location, aggressiveness, heterogeneity and infiltrative growth, is characterized by an exceptionally dismal clinical outcome. The small molecule SI113, recently identified as a SGK1 inhibitor, has proven to be effective in restraining GBM growth in vitro and in vivo, showing also encouraging results when employed in combination with other antineoplastic drugs or radiotherapy. Our aim was to explore the pharmacological features of SI113 in GBM cells in order to elucidate the pivotal molecular pathways affected by the drug. Such knowledge would be of invaluable help in conceiving a rational offensive toward GBM.

Methods

We employed GBM cell lines, either established or primary (neurospheres), and used a Reverse-Phase Protein Arrays (RPPA) platform to assess the effect of SI113 upon 114 protein factors whose post-translational modifications are associated with activation or repression of specific signal transduction cascades.

Results

SI113 strongly affected the PI3K/mTOR pathway, evoking a pro-survival autophagic response in neurospheres. These results suggested the use of SI113 coupled, for maximum efficiency, with autophagy inhibitors. Indeed, the association of SI113 with an autophagy inhibitor, the antimalarial drug quinacrine, induced a strong synergistic effect in inhibiting GBM growth properties in all the cells tested, including neurospheres.

Conclusions

RPPA clearly identified the molecular pathways influenced by SI113 in GBM cells, highlighting their vulnerability when the drug was administered in association with autophagy inhibitors, providing a strong molecular rationale for testing SI113 in clinical trials in associative GBM therapy.

Electronic supplementary material

The online version of this article (10.1186/s13046-019-1212-1) contains supplementary material, which is available to authorized users.

How Cancer Cells Resist Chemotherapy: Design and Development of Drugs Targeting Protein-Protein Interactions

Background:

Resistance toward chemotherapeutics is one of the main obstacles on the way to effective cancer treatment. Personalization of chemotherapy could improve clinical outcome. However, despite preclinical significance, most of the potential markers have failed to reach clinical practice partially due to the inability of numerous studies to estimate the marker’s impact on resistance properly.

Objective:

The analysis of drug resistance mechanisms to chemotherapy in cancer cells, and the proposal of study design to identify bona fide markers.

Methods:

A review of relevant papers in the field. A PubMed search with relevant keywords was used to gather the data. An example of a search request: drug resistance AND cancer AND paclitaxel.

Results:

We have described a number of drug resistance mechanisms to various chemotherapeutics, as well as markers to underlie the phenomenon. We also proposed a model of a rational-designed study, which could be useful in determining the most promising potential biomarkers.

Conclusion:

Taking into account the most reasonable biomarkers should dramatically improve clinical outcome by choosing the suitable treatment regimens. However, determining the leading biomarkers, as well as validating of the model, is a work for further investigations.

Chronic TGF-β exposure drives stabilized EMT, tumor stemness, and cancer drug resistance with vulnerability to bitopic mTOR inhibition

Tumors comprise cancer stem cells (CSCs) and their heterogeneous progeny within a stromal microenvironment. In response to transforming growth factor-β (TGF-β), epithelial and carcinoma cells undergo a partial or complete epithelial-mesenchymal transition (EMT), which contributes to cancer progression. This process is seen as reversible because cells revert to an epithelial phenotype upon TGF-β removal. However, we found that prolonged TGF-β exposure, mimicking the state of in vivo carcinomas, promotes stable EMT in mammary epithelial and carcinoma cells, in contrast to the reversible EMT induced by a shorter exposure. The stabilized EMT was accompanied by stably enhanced stem cell generation and anticancer drug resistance. Furthermore, prolonged TGF-β exposure enhanced mammalian target of rapamycin (mTOR) signaling. A bitopic mTOR inhibitor repressed CSC generation, anchorage independence, cell survival, and chemoresistance and efficiently inhibited tumorigenesis in mice. These results reveal a role for mTOR in the stabilization of stemness and drug resistance of breast cancer cells and position mTOR inhibition as a treatment strategy to target CSCs.

The physiological mTOR complex 1 inhibitor DDIT4 mediates therapy resistance in glioblastoma

Background

Despite significant advances in the understanding of glioblastoma genetics and biology, survival is still poor. Hypoxia and nutrient depletion in the tumour microenvironment induce adaptive signalling and metabolic responses, which can influence sensitivity to therapeutic regimens. DNA damage-inducible transcript 4 (DDIT4) is a protein induced by hypoxia and in response to DNA stress. Mechanistically, DDIT4 inhibits mammalian target of rapamycin complex 1 (mTORC1) signalling by activation of the tuberous sclerosis 1/2 (TSC1/2) complex.

Methods

Using short hairpin RNA-mediated gene suppression as well as doxycycline-regulated gene induction, we developed a glioblastoma cell model to study effects of DDIT4 under conditions of the glioblastoma microenvironment and therapy.

Results

We found an intact DDIT4-mTORC1 signalling axis in human glioblastoma cells that was inducible by hypoxia. Temozolomide and radiotherapy also induced DDIT4 and repressed mTORC1 activity in some glioblastoma cell lines. DDIT4 gene suppression sensitised glioma cells towards hypoxia-induced cell death, while DDIT4 overexpression protected them. Additionally, in clonogenic survival analyses, DDIT4 induction conferred protection from radiotherapy and temozolomide, while DDIT4 gene suppression sensitised cells.

Conclusions

We identified DDIT4 as a cell-intrinsic regulator for adaptive responses and therapy resistance in glioblastoma cells which may interfere with cell death induction by temozolomide, radiotherapy or hypoxia by inhibiting mTORC1 activity.

mTOR Signaling in Cancer and mTOR Inhibitors in Solid Tumor Targeting Therapy

The mammalian or mechanistic target of rapamycin (mTOR) pathway plays a crucial role in regulation of cell survival, metabolism, growth and protein synthesis in response to upstream signals in both normal physiological and pathological conditions, especially in cancer. Aberrant mTOR signaling resulting from genetic alterations from different levels of the signal cascade is commonly observed in various types of cancers. Upon hyperactivation, mTOR signaling promotes cell proliferation and metabolism that contribute to tumor initiation and progression. In addition, mTOR also negatively regulates autophagy via different ways. We discuss mTOR signaling and its key upstream and downstream factors, the specific genetic changes in the mTOR pathway and the inhibitors of mTOR applied as therapeutic strategies in eight solid tumors. Although monotherapy and combination therapy with mTOR inhibitors have been extensively applied in preclinical and clinical trials in various cancer types, innovative therapies with better efficacy and less drug resistance are still in great need, and new biomarkers and deep sequencing technologies will facilitate these mTOR targeting drugs benefit the cancer patients in personalized therapy.

Characterization of the epithelial membrane protein 3 interaction network reveals a potential functional link to mitogenic signal transduction regulation

Epithelial Membrane Protein 3 (EMP3), a 4-transmembrane glycoprotein, first gained attention as a putative tumor suppressor. Accumulating evidence, however, points to a more tumor promotive function of EMP3. The biological function of EMP3 remains largely unclear. To elucidate more of EMP3's interaction network, we performed a Yeast-Two-Hybrid (Y2H) screening, followed by validation of candidate interactors by Biomolecular Fluorescence Complementation (BiFC) and Proximity Ligation Assay (PLA). Furthermore, we generated stable EMP3 knockdown cell lines and measured cell proliferation, migration and sensitivity to apoptosis induction as well as the expression and activation levels of important signal pathway components. The Y2H screening yielded 10 novel interactions of EMP3, eight of which could also be detected by BiFC and PLA interaction assays. All newly discovered interaction partners are involved in signaling or trafficking regulation. Most notably, FLOT1 and HTATIP2 have well described roles in the regulation of EGFR signaling. In addition, knockdown of EMP3 resulted in reduced levels of p-AKT, p-ERK and p-EGFR, attenuated cell proliferation and migration and sensitized cells to apoptosis induction by TRAIL and Staurosporine. Based on these observations we hypothesize that EMP3 might be involved in the regulation of receptor-tyrosine-kinase mediated mitogenic signaling.

The proneural gene ASCL1 governs the transcriptional subgroup affiliation in glioblastoma stem cells by directly repressing the mesenchymal gene NDRG1

Achaete-scute homolog 1 gene (ASCL1) is a gene classifier for the proneural (PN) transcriptional subgroup of glioblastoma (GBM) that has a relevant role in the neuronal-like differentiation of GBM cancer stem cells (CSCs) through the activation of a PN gene signature. Besides prototypical ASCL1 PN target genes, the molecular effectors mediating ASCL1 function in regulating GBM differentiation and, most relevantly, subgroup specification are currently unknown. Here we report that ASCL1 not only promotes the acquisition of a PN phenotype in CSCs by inducing a glial-to-neuronal lineage switch but also concomitantly represses mesenchymal (MES) features by directly downregulating the expression of N-Myc downstream-regulated gene 1 (NDRG1), which we propose as a novel gene classifier of MES GBMs. Increasing the expression of ASCL1 in PN CSCs results in suppression of self-renewal, promotion of differentiation and, most significantly, decrease in tumorigenesis, which is also reproduced by NDRG1 silencing. Conversely, both abrogation of ASCL1 expression in PN CSCs and enforcement of NDRG1 expression in either PN or MES CSCs induce proneural-to-mesenchymal transition (PMT) and enhanced mesenchymal features. Surprisingly, ASCL1 overexpression in MES CSCs increases malignant features and gives rise to a neuroendocrine-like secretory phenotype. Altogether, our results propose that the fine interplay between ASCL1 and its target NDRG1 might serve as potential subgroup-specific targetable vulnerability in GBM; enhancing ASCL1 expression in PN GBMs might reduce tumorigenesis, whereas repressing NDRG1 expression might be actionable to hamper the malignancy of GBM belonging to the MES subgroup.

Whole transcriptome sequencing analyses of DHA treated glioblastoma cells

Glioblastoma (GBM) is a typical malignant tumor, and there are no effective drugs capable of improving patient survival. Docosahexaenoic acid (DHA), a nutrient essential to animal health and neurodevelopment, exerts an anticancer effect in several types of cancer. However, the function of DHA in GBM is still unclear. Here, we showed that DHA could repress the migration and invasion of GBM U251 cells and promote their apoptosis in a dose- and time-dependent manner, indicating that DHA has an anticancer effect on GBM cells. Whole-transcriptome analysis indicated that DHA treatment mainly regulates the genes associated with receptor binding, oxidoreductase activity, organic acid transmembrane transporter activity, and carboxylic acid transmembrane transporter activity. Long non-coding RNAs (LncRNAs) involved in the regulation network of DHA were also identified, and their targets were assigned to the Gene Ontology (GO) categories. In silico analysis was conducted to predict the pathways related to the differentially expressed genes by DHA treatment. Our findings suggest that DHA acts as an antitumor agent in GBM, which may provide a suitable means of improving the efficacy of GBM treatment in the future.

Hypoxia-mediated mitochondria apoptosis inhibition induces temozolomide treatment resistance through miR-26a/Bad/Bax axis

Glioblastoma multiforme (GBM) is one of the most hypoxic tumors of the central nervous system. Although temozolomide (TMZ) is an effective clinical agent in the GBM therapy, the hypoxic microenvironment remains a major barrier in glioma chemotherapy resistance, and the underlying mechanisms are poorly understood. Here, we find hypoxia can induce the protective response to mitochondrion via HIF-1α-mediated miR-26a upregulation which is associated with TMZ resistance in vitro and in vivo. Further, we demonstrated that HIF-1α/miR-26a axis strengthened the acquisition of TMZ resistance through prevention of Bax and Bad in mitochondria dysfunction in GBM. In addition, miR-26a expression levels negatively correlate with Bax, Bad levels, and GBM progression; but highly correlate with HIF-1α levels in clinical cancer tissues. These findings provide a new link in the mechanistic understanding of TMZ resistance under glioma hypoxia microenvironment, and consequently HIF-1α/miR-26a/Bax/Bad signaling pathway as a promising adjuvant therapy for GBM with TMZ.

Glioblastoma Chemoresistance: The Double Play by Microenvironment and Blood-Brain Barrier

For glioblastoma, the tumor microenvironment (TME) is pivotal to support tumor progression and therapeutic resistance. TME consists of several types of stromal, endothelial and immune cells, which are recruited by cancer stem cells (CSCs) to influence CSC phenotype and behavior. TME also promotes the establishment of specific conditions such as hypoxia and acidosis, which play a critical role in glioblastoma chemoresistance, interfering with angiogenesis, apoptosis, DNA repair, oxidative stress, immune escape, expression and activity of multi-drug resistance (MDR)-related genes. Finally, the blood brain barrier (BBB), which insulates the brain microenvironment from the blood, is strongly linked to the drug-resistant phenotype of glioblastoma, being a major physical and physiological hurdle for the delivery of chemotherapy agents into the brain. Here, we review the features of the glioblastoma microenvironment, focusing on their involvement in the phenomenon of chemoresistance; we also summarize recent advances in generating systems to modulate or bypass the BBB for drug delivery into the brain. Genetic aspects associated with glioblastoma chemoresistance and current immune-based strategies, such as checkpoint inhibitor therapy, are described too.

NDRG2 suppression as a molecular hallmark of photoreceptor-specific cell death in the mouse retina

Photoreceptor cell death is recognized as the key pathogenesis of retinal degeneration, but the molecular basis underlying photoreceptor-specific cell loss in retinal damaging conditions is virtually unknown. The N-myc downstream regulated gene (NDRG) family has recently been reported to regulate cell viability, in particular NDRG1 has been uncovered expression in photoreceptor cells. Accordingly, we herein examined the potential roles of NDRGs in mediating photoreceptor-specific cell loss in retinal damages. By using mouse models of retinal degeneration and the 661 W photoreceptor cell line, we showed that photoreceptor cells are indeed highly sensitive to light exposure and the related oxidative stress, and that photoreceptor cells are even selectively diminished by phototoxins of the alkylating agent N-Methyl-N-nitrosourea (MNU). Unexpectedly, we discovered that of all the NDRG family members, NDRG2, but not the originally hypothesized NDRG1 or other NDRG subtypes, was selectively expressed and specifically responded to retinal damaging conditions in photoreceptor cells. Furthermore, functional experiments proved that NDRG2 was essential for photoreceptor cell viability, which could be attributed to NDRG2 control of the photo-oxidative stress, and that it was the suppression of NDRG2 which led to photoreceptor cell loss in damaging conditions. More importantly, NDRG2 preservation contributed to photoreceptor-specific cell maintenance and retinal protection both in vitro and in vivo. Our findings revealed a previously unrecognized role of NDRG2 in mediating photoreceptor cell homeostasis and established for the first time the molecular hallmark of photoreceptor-specific cell death as NDRG2 suppression, shedding light on improved understanding and therapy of retinal degeneration.

mTORC2 contributes to the metabolic reprogramming in EGFR tyrosine-kinase inhibitor resistant cells in non-small cell lung cancer

Non-small cell lung cancer (NSCLC) patients with activating EGFR mutations are often successfully treated with EGFR tyrosine kinase inhibitor (TKI) such as erlotinib; however, treatment resistance inevitably occurs. Given tumor metabolism of glucose and therapeutic response are intimately linked, we explored the metabolic differences between isogenic erlotinib-sensitive and -resistant NSCLC cell lines. We discovered that the growth of erlotinib-resistant cells is more sensitive to glucose deprivation. Seahorse metabolic assay revealed erlotinib-resistant cells have lower spare respiratory capacity (SRC), an indicator of metabolic flexibility, compared to erlotinib-sensitive cells. Additionally, we found downstream components of mTORC2 signaling to be phosphorylated in erlotinib-resistant cells. Knockdown of an mTORC2 component, Rictor, enhanced the SRC and rescued the growth rate of erlotinib-resistant cells during glucose deprivation. Among NSCLCs with activating EGFR mutations, gene sets involved in glucose metabolism were enriched in patients with high expression of p-NDGR1, a readout of mTORC2 activity. Furthermore, overall survival was negatively correlated with p-NDRG1. Our work uncovers a link between mTORC2 and metabolic reprogramming in EGFR TKI-resistant cells and highlights the significance of mTORC2 in the progression of EGFR-mutated NSCLC.

NDRG1 regulates neutral lipid metabolism in breast cancer cells

Background

Altered lipid metabolism is an emerging hallmark of aggressive breast cancers. The N-myc downstream regulated gene (NDRG1) gene plays a critical role in peripheral nervous system myelination, as inactivating mutations cause severe demyelinating neuropathy. In breast cancer, elevated NDRG1 expression has been linked to clinical outcomes, but its functional role in breast cancer physiology has remained unclear.

Methods

A meta-analysis of NDRG1 expression in multiple large publicly available genomic databases was conducted. Genome-wide expression correlation and Cox proportional hazards and Kaplan-Meier modeling of clinical outcomes associated with elevated expression were assessed. To study NDRG1 function, gene silencing and overexpression phenotypic studies were carried out in a panel of cell lines representing all major breast cancer molecular subtypes. Changes in cell proliferation, morphology, and neutral lipid accumulation due to altered NDRG1 expression were assessed by high throughput, quantitative microscopy. Comprehensive lipidomics mass spectrometry was applied to characterize global changes in lipid species due to NDRG1 silencing. Labeled fatty acids were used to monitor cellular fatty acid uptake and subcellular distribution under nutrient replete and starvation culture conditions.

Results

NDRG1 overexpression correlated with glycolytic and hypoxia-associated gene expression, and was associated with elevated rates of metastasis and patient mortality. Silencing NDRG1 reduced cell proliferation rates, causing lipid metabolism dysfunction including increased fatty acid incorporation into neutral lipids and lipid droplets. Conversely, NDRG1 expression minimized lipid droplet formation under nutrient replete and starvation conditions.

Conclusions

Here we report that NDRG1 contributes to breast cancer aggressiveness by regulating the fate of lipids in cells that exhibit an altered lipid metabolic phenotype. In line with its role in promoting myelination and its association with altered metabolism in cancer, our findings show that NDRG1 is a critical regulator of lipid fate in breast cancer cells. The association between NDRG1 and poor prognosis in breast cancer suggests it should play a more prominent role in patient risk assessment. The function of NDRG1 in breast cancer lipid metabolism may represent a promising therapeutic approach in the future.

Electronic supplementary material

The online version of this article (10.1186/s13058-018-0980-4) contains supplementary material, which is available to authorized users.

Chemoresistance‑related long non‑coding RNA expression profiles in human breast cancer cells

Breast cancer is the most commonly diagnosed cancer and the leading cause of cancer death in females worldwide. Chemoresistance has been a major reason for the drug therapy failure. The present study performed a microarray analysis between MCF-7 and MCF-7/adriamycin (ADR) cells, and intended to identify long non-coding (lnc)RNA expression character in drug resistant breast cancer cells. MCF-7/ADR cells were induced from MCF-7 cells via pulse-selection with doxorubicin for 4 weeks, and the resistance to doxorubicin of ADR cells was confirmed by MTT assay. Microarray analysis was performed between MCF-7 and MCF-7/ADR cells. Total RNA was extracted from the two cell lines respectively and was transcribed into cDNA. The results of the microarray were verified by reverse transcription-quantitative polymerase chain reaction (RT-qPCR). Gene Ontology (GO) and pathways analysis were conducted to enrich the dysregulated lncRNAs presented in the microarray results. Compared to the MCF-7 cells, 8,892 lncRNAs were differentially expressed in MCF/ADR cells (absolute fold-change >2.0). A total of 32 lncRNAs were selected for RT-qPCR by fold-change filtering, standard Student's t-test, and multiple hypothesis testing. Among the dysregulated lncRNAs, AX747207 was prominent because its associated gene RUNX3 was previously reported to be relative to malignant tumor chemoresistance. GO analysis results also indicated some biological processes and molecular functions linked to chemoresistance. The pathway enrichment results provided some potential pathways associated with chemoresistance. In the present study, the authors intended to identify lncRNA expression character in drug resistant cell line MCF-7/ADR, corresponding to the parental MCF-7 cell line. In addition, the study identified the lncRNA AX747207, and its potential targeted gene RUNX3, may be related to chemoresistance in breast cancer. These results may new insights into exploring the mechanisms of chemoresistance in breast cancer.

PTRF suppresses the progression of colorectal cancers

As a key component of caveolae structure on the plasma membrane, accumulated evidence has suggested that Polymerase I and Transcript Release Factor (PTRF) plays a pivotal role in suppressing the progression of human malignances. However, the function of PTRF in the development of colorectal cancers is still unclear. Here we report that the expression of PTRF is significantly reduced in tumor tissues derived from human patients with colorectal cancers, and that the downregulation of PTRF correlates to the advanced stage of the disease. In addition, we found that the expression of PTRF negatively regulates the tumorigenic activities of colorectal cell lines (Colo320, HT29 and CaCo2). Furthermore, ectopic PTRF expression caused significant suppression of cellular proliferation, and anchorage-independent colony growth of Colo320 cells, which have the lowest expression level of PTRF in the three studied cell lines. Meanwhile, shRNA mediated knockdown of PTRF in CaCo2 cells significantly promoted cellular proliferation and anchorage-independent colony growth. In addition, in vivo assays further revealed that tumor growth was significantly inhibited in xenografts with ectopic PTRF expression as compared to untreated Colo320 cells, but was markedly enhanced in PTRF knockdown CaCo2 cells. Biochemical studies revealed that overexpression of PTRF led to the suppression of the AKT/mTOR pathway, as evidenced by reduced phosphorylation of AKT, mTOR, and downstream MMP-9. Thus, these findings, for the first time, demonstrated that PTRF inhibits the tumorigenesis of colorectal cancers and that it might serve as a potential therapeutic target for human colon cancer patients.

Overexpression of TFEB Drives a Pleiotropic Neurotrophic Effect and Prevents Parkinson's Disease-Related Neurodegeneration

The possible implication of transcription factor EB (TFEB) as a therapeutic target in Parkinson's disease has gained momentum since it was discovered that TFEB controls lysosomal biogenesis and autophagy and that its activation might counteract lysosomal impairment and protein aggregation. However, the majority of putative direct targets of TFEB described to date is linked to a range of biological processes that are not related to the lysosomal-autophagic system. Here, we assessed the effect of overexpressing TFEB with an adeno-associated viral vector in mouse substantia nigra dopaminergic neurons. We demonstrate that TFEB overexpression drives a previously unknown bona fide neurotrophic effect, giving rise to cell growth, higher tyrosine hydroxylase levels, and increased dopamine release in the striatum. TFEB overexpression induces the activation of the mitogen-activated protein kinase 1/3 (MAPK1/3) and AKT pro-survival pathways, phosphorylation of mTORC1 effectors 4E-binding protein 1 (4E-BP1) and S6 kinase B1 (S6K1), and increased protein synthesis. We show that TFEB overexpression prevents dopaminergic cell loss and counteracts atrophy and the associated protein synthesis decline in the MPTP mouse model of Parkinson's disease. Our results suggest that increasing TFEB activity might prevent neuronal death and restore neuronal function in Parkinson's disease and other neurodegenerative diseases through different mechanisms.

Slowing down glioblastoma progression in mice by running or the anti-malarial drug dihydroartemisinin? Induction of oxidative stress in murine glioblastoma therapy

Influencing cancer metabolism by lifestyle changes is an attractive strategy as - if effective - exercise-induced problems may be less severe than those induced by classical anti-cancer therapies. Pursuing this idea, clinical trials evaluated the benefit of e.g. different diets such as the ketogenic diet, intermittent caloric restriction and physical exercise (PE) in the primary and secondary prevention of different cancer types. PE proved to be beneficial in the context of breast and colon cancer.Glioblastoma has a dismal prognosis, with an average overall survival of about one year despite maximal safe resection, concomitant radiochemotherapy with temozolomide followed by adjuvant temozolomide therapy. Here, we focused on the influence of PE as an isolated and adjuvant treatment in murine GB therapy.PE did not reduce toxic side effects of chemotherapy in mice administered in a dose escalating scheme as shown before for starvation. Although regular treadmill training on its own had no obvious beneficial effects, its combination with temozolomide was beneficial in the treatment of glioblastoma-bearing mice. As PE might partly act through the induction of reactive oxygen species, dihydroartemisinin - an approved anti-malarial drug which induces oxidative stress in glioma cells - was further evaluated in vitro and in vivo. Dihydroartemisinin showed anti-glioma activity by promoting autophagy, reduced the clonogenic survival and proliferation capacity of glioma cells, and prolonged the survival of tumor bearing mice. Using the reactive oxygen species scavenger n-acetyl-cysteine these effects were in part reversible, suggesting that dihydroartemisinin partly acts through the generation of reactive oxygen species.

LSD1 mediates MYCN control of epithelial-mesenchymal transition through silencing of metastatic suppressor NDRG1 gene

Neuroblastoma (NB) with MYCN amplification is a highly aggressive and metastatic tumor in children. The high recurrence rate and resistance of NB cells to drugs urgently demands a better therapy for this disease. We have recently found that MYCN interacts with the lysine-specific demethylase 1 (LSD1), a histone modifier that participates in key aspects of gene transcription. In cancer cells, LSD1 contributes to the genetic reprogramming that underlies to Epithelial-Mesenchymal Transition (EMT) and tumor metastasis. Here, we show that LSD1 affects motility and invasiveness of NB cells by modulating the transcription of the metastasis suppressor NDRG1 (N-Myc Downstream-Regulated Gene 1). At mechanistic level, we found that LSD1 co-localizes with MYCN at the promoter region of the NDRG1 gene and inhibits its expression. Pharmacological inhibition of LSD1 relieves repression of NDRG1 by MYCN and affects motility and invasiveness of NB cells. These effects were reversed by overexpressing NDRG1. In NB tissues, high levels of LSD1 correlate with low levels of NDRG1 and reduced patients survival. Collectively, our findings elucidate a mechanism of how MYCN/LSD1 control motility and invasiveness of NB cells through transcription regulation of NDRG1 expression and suggest that pharmacological targeting of LSD1 represents a valuable approach for NB therapy.

Prognostic relevance of miRNA-155 methylation in anaplastic glioma

The outcome of patients with anaplastic gliomas varies considerably depending on single molecular markers, such as mutations of the isocitrate dehydrogenase (IDH) genes, as well as molecular classifications based on epigenetic or genetic profiles. Remarkably, 98% of the RNA within a cell is not translated into proteins. Of those, especially microRNAs (miRNAs) have been shown not only to have a major influence on physiologic processes but also to be deregulated and prognostic in malignancies.To find novel survival markers and treatment options we performed unbiased DNA methylation screens that revealed 12 putative miRNA promoter regions with differential DNA methylation in anaplastic gliomas. Methylation of these candidate regions was validated in different independent patient cohorts revealing a set of miRNA promoter regions with prognostic relevance across data sets. Of those, miR-155 promoter methylation and miR-155 expression were negatively correlated and especially the methylation showed superior correlation with patient survival compared to established biomarkers.Functional examinations in malignant glioma cells further cemented the relevance of miR-155 for tumor cell viability with transient and stable modifications indicating an onco-miRNA activity. MiR-155 also conferred resistance towards alkylating temozolomide and radiotherapy as consequence of nuclear factor (NF)κB activation.Preconditioning glioma cells with an NFκB inhibitor reduced therapy resistance of miR-155 overexpressing cells. These cells resembled tumors with a low methylation of the miR-155 promoter and thus mir-155 or NFκB inhibition may provide treatment options with a special focus on patients with IDH wild type tumors.

Glioblastoma in elderly patients: solid conclusions built on shifting sand?

Management of glioblastoma in the elderly population is challenging. In the near future, more than half of patients with this tumor will be over the age of 65. Clinicians have been historically reluctant to treat such patients with the same intensity as younger patients. Due to upper age limits or poor accrual of elderly patients in clinical trials, randomized data for this patient population have been relatively sparse until recently. In this review, we will discuss the concept of an elderly patient population, describe evidence for molecular differences in glioblastoma of elderly versus young patients, evaluate recent first-line trials studying glioblastoma in elderly patients, and discuss best therapeutic practices including the value of molecular testing.

mTOR Cross-Talk in Cancer and Potential for Combination Therapy

The mammalian Target of Rapamycin (mTOR) pathway plays an essential role in sensing and integrating a variety of exogenous cues to regulate cellular growth and metabolism, in both physiological and pathological conditions. mTOR functions through two functionally and structurally distinct multi-component complexes, mTORC1 and mTORC2, which interact with each other and with several elements of other signaling pathways. In the past few years, many new insights into mTOR function and regulation have been gained and extensive genetic and pharmacological studies in mice have enhanced our understanding of how mTOR dysfunction contributes to several diseases, including cancer. Single-agent mTOR targeting, mostly using rapalogs, has so far met limited clinical success; however, due to the extensive cross-talk between mTOR and other pathways, combined approaches are the most promising avenues to improve clinical efficacy of available therapeutics and overcome drug resistance. This review provides a brief and up-to-date narrative on the regulation of mTOR function, the relative contributions of mTORC1 and mTORC2 complexes to cancer development and progression, and prospects for mTOR inhibition as a therapeutic strategy.

mTOR inhibition as an adjuvant therapy in a metastatic model of HPV+ HNSCC

Effective treatments for recurrent/metastatic human papillomavirus-positive (HPV+) head and neck squamous cell cancer (HNSCC) are limited. To aid treatment development, we characterized a novel murine model of recurrent/metastatic HPV+ HNSCC. Further analysis of the parental tumor cell line and its four recurrent/metastatic derivatives led to preclinical testing of an effective treatment option for this otherwise fatal disease. Reverse phase protein arrays identified key signaling cascades in the parental and recurrent/metastatic cell lines. While protein expression profiles differed among the recurrent/metastatic cell lines, activated proteins associated with the mTOR signaling cascade were a commonality. Based on these data, mTOR inhibition was evaluated as an adjuvant treatment for recurrent/metastatic disease. mTOR activity and treatment response were assessed in vitro by western blot, Seahorse, proliferation, clonogenic, and migration assays. Standard-of-care cisplatin/radiation therapy (CRT) versus CRT/rapamycin were compared in vivo. Low-dose rapamycin inhibited mTOR signaling, decreasing proliferation (43%) and migration (62%) while it enhanced CRT-induced cytotoxicity (3.3 fold) in clonogenic assays. Furthermore, rapamycin re-sensitized CRT-resistant, metastatic tumors to treatment in vivo, improving long-term cures (0-30% improved to 78-100%, depending on the recurrent/metastatic cell line) and limiting lymph node metastasis (32%) and lung metastatic burden (30 fold). Studies using immune compromised mice suggested rapamycin's effect on metastasis is independent of the adaptive immune response. These data suggest a role of mTOR activation in HPV+ HNSCC recurrent/metastatic disease and that adjuvant mTOR inhibition may enhance treatment of resistant, metastatic cell populations at the primary site and limit distant metastasis.

A new immunohistochemistry prognostic score (IPS) for recurrence and survival in resected pancreatic neuroendocrine tumors (PanNET)

Pancreatic neuroendocrine tumor (PanNET) is a neoplastic entity in which few prognostic factors are well-known. Here, we aimed to evaluate the prognostic significance of N-myc downstream-regulated gen-1 (NDRG-1), O6-methylguanine DNA methyltransferase (MGMT) and Pleckstrin homology-like domain family A member 3 (PHLDA-3) by immunohistochemistry (IHC) and methylation analysis in 92 patients with resected PanNET and follow-up longer than 24 months. In multivariate analyses, ki-67 and our immunohistochemistry prognostic score (IPS-based on MGMT, NDRG-1 and PHLDA-3 IHC expression) were independent prognostic factors for disease-free-survival (DFS), while age and IPS were independent prognostic factors for overall survival (OS). Our IPS could be a useful prognostic biomarker for recurrence and survival in patients following resection for PanNET.

Oncogenic Signalling through Mechanistic Target of Rapamycin (mTOR): A Driver of Metabolic Transformation and Cancer Progression

Throughout the years, research into signalling pathways involved in cancer progression has led to many discoveries of which mechanistic target of rapamycin (mTOR) is a key player. mTOR is a master regulator of cell growth control. mTOR is historically known to promote cell growth by enhancing the efficiency of protein translation. Research in the last decade has revealed that mTOR’s role in promoting cell growth is much more multifaceted. While mTOR is necessary for normal human physiology, cancer cells take advantage of mTOR signalling to drive their neoplastic growth and progression. Oncogenic signal transduction through mTOR is a common occurrence in cancer, leading to metabolic transformation, enhanced proliferative drive and increased metastatic potential through neovascularisation. This review focuses on the downstream mTOR-regulated processes that are implicated in the “hallmarks” of cancer with focus on mTOR’s involvement in proliferative signalling, metabolic reprogramming, angiogenesis and metastasis.

DEPTOR suppresses the progression of esophageal squamous cell carcinoma and predicts poor prognosis

As a naturally occurring inhibitor of mTOR, accumulated evidence has suggested that DEPTOR plays a pivotal role in suppressing the progression of human malignances. However, the function of DEPTOR in the development of esophageal squamous cell carcinoma (ESCC) is still unclear. Here we report that the expression of DEPTOR is significantly reduced in tumor tissues derived from human patients with ESCC, and the downregulation of DEPTOR predicts a poor prognosis of ESCC patients. In addition, we found that the expression of DEPTOR negatively regulates the tumorigenic activities of ESCC cell lines (KYSE150, KYSE510 and KYSE190). Furthermore, ectopic DEPTOR expression caused a significant suppression of the cellular proliferation, migration and invasion of KYSE150 cells, which has the lowest expression level of DEPTOR in the three cell lines. Meanwhile, CRISPR/Cas9 mediated knockout of DEPTOR in KYSE-510 cells significantly promoted cellular proliferation, migration and invasion. In addition, in vivo assays further revealed that tumor growth was significantly inhibited in xenografts with ectopic DEPTOR expression as compared to untreated KYSE150 cells, and was markedly enhanced in DEPTOR knockout KYSE-510 cells. Biochemical studies revealed that overexpression of DEPTOR led to the suppression of AKT/mTOR pathway as evidenced by reduced phosphorylation of AKT, mTOR and downstream SGK1, indicating DEPTOR might control the progression of ESCC through AKT/mTOR signaling pathway. Thus, these findings, for the first time, demonstrated that DEPTOR inhibits the tumorigenesis of ESCC cells and might serve as a potential therapeutic target or prognostic marker for human patients with ESCC.

SI113, a SGK1 inhibitor, potentiates the effects of radiotherapy, modulates the response to oxidative stress and induces cytotoxic autophagy in human glioblastoma multiforme cells

Glioblastoma multiforme (GBM) is the most aggressive CNS tumor and is characterized by a very high frequency of clinical relapse after therapy and thus by a dismal prognosis, which strongly compromises patients survival. We have recently identified the small molecule SI113, as a potent and selective inhibitor of SGK1, a serine/threonine protein kinase, that modulates several oncogenic signaling cascades. The SI113-dependent SGK1 inhibition induces cell death, blocks proliferation and perturbs cell cycle progression by modulating SGK1-related substrates. SI113 is also able to strongly and consistently block, in vitro and in vivo, growth and survival of human hepatocellular-carcinomas, either used as a single agent or in combination with ionizing radiations. In the present paper we aim to study the effect of SI113 on human GBM cell lines with variable p53 expression. Cell viability, cell death, caspase activation and cell cycle progression were then analyzed by FACS and WB-based assays, after exposure to SI113, with or without oxidative stress and ionizing radiations. Moreover, autophagy and related reticulum stress response were evaluated. We show here, that i) SGK1 is over-expressed in highly malignant gliomas and that the treatment with SI113 leads to ii) significant increase in caspase-mediated apoptotic cell death in GBM cell lines but not in normal fibroblasts; iii)enhancement of the effects of ionizing radiations; iv) modulation of the response to oxidative reticulum stress; v) induction of cytotoxic autophagy. Evidence reported here underlines the therapeutic potential of SI113 in GBM, suggesting a new therapeutic strategy either alone or in combination with radiotherapy.

Silencing of ECHDC1 inhibits growth of gemcitabine-resistant bladder cancer cells

Combined gemcitabine and cisplatin (GC) treatment is a first line chemotherapy for bladder cancer. However, acquired resistance to GC has been a major problem. To address the mechanism of gemcitabine resistance, and to identify potential biomarkers or target proteins for its therapy, we aimed to identify candidate proteins associated with gemcitabine resistance using proteomic analysis. We established gemcitabine-resistant human bladder cancer cell lines (UMUC3GR and HT1376GR) from gemcitabine-sensitive human bladder cancer cell lines (UMUC3 and HT1376). We compared the protein expression of parental and gemcitabine-resistant cell lines using isobaric tags for relative and absolute quantification (iTRAQ) and liquid chromatography tandem mass spectrometry. Among the identified proteins, ethylmalonyl-CoA decarboxylase (ECHDC1) expression was significantly increased in both of the gemcitabine-resistant cell lines compared to the respective parental cell lines. Silencing of ECHDC1 reduced ECHDC1 expression and significantly inhibited the proliferation of UMUC3GR cells. Furthermore, silencing of ECHDC1 induced upregulation of p27, which is critical for cell cycle arrest in the G1 phase, and induced G1 arrest. In conclusion, ECHDC1 expression is increased in gemcitabine-resistant bladder cancer cells, and is involved in their cell growth. ECHDC1, which is a metabolite proofreading enzyme, may be a novel potential target for gemcitabine-resistant bladder cancer therapy.

[MACF1 knockdown in glioblastoma multiforme cells increases temozolomide-induced cytotoxicity]

OBJECTIVE

To investigate the role of microtubule-actin crosslinking factor 1 (MACF1) in the response of glioma cells to temozolomide (TMZ).

METHODS

TMZ was applied to a human gliomablastoma cell line (U87) and changes in the protein expression and cellular localization were determined with Western blot, RT-PCR, and immunofluorescence. The responses of the cells with MACF1 expression knockdown by RNA interference to TMZ were assessed. TMZ-induced effects on MACF1 expression were also assessed by immunohistochemistry in a nude mouse model bearing human glioblastoma xenografts.

RESULTS

TMZ resulted in significantly increased MACF1 expression (by about 2 folds) and changes in its localization in the gliomablastoma cells both in vitro and in vivo (P<0.01). Knockdown of MACF1 reduced the proliferation (by 45%) of human glioma cell lines treated with TMZ (P<0.01). TMZ-induced changes in MACF1 expression was accompanied by cytoskeletal rearrangement.

CONCLUSION

MACF1 may be a potential therapeutic target for glioblastoma.

NDRG1 inhibition sensitizes osteosarcoma cells to combretastatin A-4 through targeting autophagy

Combretastatin A-4 (CA-4), a tubulin-depolymerizing agent, shows promising antitumor efficacy and has been under several clinical trials in solid tumors for 10 years. Autophagy has an important pro-survival role in cancer therapy, thus targeting autophagy may improve the efficacy of antitumor agents. N-myc downstream-regulated gene 1 (NDRG1) is a significant stress regulatory gene, which mediates cell survival and chemoresistance. Here we reported that CA-4 could induce cell-protective autophagy, and combination treatment of CA-4 and autophagy inhibitor chloroquine (CQ) exerted synergistic cytotoxic effect on human osteosarcoma (OS) cells. Meanwhile, CA-4 or CQ could increase the expression of NDRG1 independently. We further performed mechanistic study to explore how CA-4 and CQ regulate the expression of NDRG1. Using luciferase reporter assay, we found that CA-4 transcriptionally upregulated NDRG1 expression, whereas CQ triggered colocalization of NDRG1 and lysosome, which subsequently prevented lysosome-dependent degradation of NDRG1. Further, we showed that knockdown of NDRG1 caused the defect of lysosomal function, which accumulated LC3-positive autophagosomes by decreasing their fusion with lysosomes. Moreover, NDRG1 inhibition increased apoptosis in response to combination treatment with CA-4 and CQ. Taken together, our study revealed abrogation of NDRG1 expression sensitizes OS cells to CA-4 by suppression of autophagosome–lysosome fusion. These results provide clues for developing more effective cancer therapeutic strategies by the concomitant treatment with CA-4 and clinical available autophagy inhibitors.

A Pan-Cancer Proteogenomic Atlas of PI3K/AKT/mTOR Pathway Alterations

Molecular alterations involving the PI3K/AKT/mTOR pathway (including mutation, copy number, protein, or RNA) were examined across 11,219 human cancers representing 32 major types. Within specific mutated genes, frequency, mutation hotspot residues, in silico predictions, and functional assays were all informative in distinguishing the subset of genetic variants more likely to have functional relevance. Multiple oncogenic pathways including PI3K/AKT/mTOR converged on similar sets of downstream transcriptional targets. In addition to mutation, structural variations and partial copy losses involving PTEN and STK11 showed evidence for having functional relevance. A substantial fraction of cancers showed high mTOR pathway activity without an associated canonical genetic or genomic alteration, including cancers harboring IDH1 or VHL mutations, suggesting multiple mechanisms for pathway activation.

Tweety-Homolog 1 Drives Brain Colonization of Gliomas

Early and progressive colonization of the healthy brain is one hallmark of diffuse gliomas, including glioblastomas. We recently discovered ultralong (>10 to hundreds of microns) membrane protrusions [tumor microtubes (TMs)] extended by glioma cells. TMs have been associated with the capacity of glioma cells to effectively invade the brain and proliferate. Moreover, TMs are also used by some tumor cells to interconnect to one large, resistant multicellular network. Here, we performed a correlative gene-expression microarray and in vivo imaging analysis, and identified novel molecular candidates for TM formation and function. Interestingly, these genes were previously linked to normal CNS development. One of the genes scoring highest in tests related to the outgrowth of TMs was tweety-homolog 1 (TTYH1), which was highly expressed in a fraction of TMs in mice and patients. Ttyh1 was confirmed to be a potent regulator of normal TM morphology and of TM-mediated tumor-cell invasion and proliferation. Glioma cells with one or two TMs were mainly responsible for effective brain colonization, and Ttyh1 downregulation particularly affected this cellular subtype, resulting in reduced tumor progression and prolonged survival of mice. The remaining Ttyh1-deficient tumor cells, however, had more interconnecting TMs, which were associated with increased radioresistance in those small tumors. These findings imply a cellular and molecular heterogeneity in gliomas regarding formation and function of distinct TM subtypes, with multiple parallels to neuronal development, and suggest that Ttyh1 might be a promising target to specifically reduce TM-associated brain colonization by glioma cells in patients.SIGNIFICANCE STATEMENT In this report, we identify tweety-homolog 1 (Ttyh1), a membrane protein linked to neuronal development, as a potent driver of tumor microtube (TM)-mediated brain colonization by glioma cells. Targeting of Ttyh1 effectively inhibited the formation of invasive TMs and glioma growth, but increased network formation by intercellular TMs, suggesting a functional and molecular heterogeneity of the recently discovered TMs with potential implications for future TM-targeting strategies.

K27M-mutant histone-3 as a novel target for glioma immunotherapy

Mutation-specific vaccines have become increasingly important in glioma immunotherapy; however, shared neoepitopes are rare. For diffuse gliomas, a driver mutation in the gene for isocitrate dehydrogenase type-1 has been shown to produce an immunogenic epitope currently targeted in clinical trials. For highly aggressive midline gliomas, a recurrent point mutation in the histone-3 gene (H3F3A) causes an amino acid change from lysine to methionine at position 27 (K27M). Here, we demonstrate that a peptide vaccine against K27M-mutant histone-3 is capable of inducing effective, mutation-specific, cytotoxic T-cell- and T-helper-1-cell-mediated immune responses in a major histocompatibility complex (MHC)-humanized mouse model. By proving an immunologically effective presentation of the driver mutation H3K27M on MHC class II in human H3K27M-mutant gliomas, our data provide a basis for the further clinical development of vaccine-based or cell-based immunotherapeutic approaches targeting H3K27M.

mTORC1 and mTORC2 in cancer and the tumor microenvironment

The mammalian target of rapamycin (mTOR) is a crucial signaling node that integrates environmental cues to regulate cell survival, proliferation and metabolism, and is often deregulated in human cancer. mTOR kinase acts in two functionally distinct complexes, mTOR complex 1 (mTORC1) and 2 (mTORC2), whose activities and substrate specificities are regulated by complex co-factors. Deregulation of this centralized signaling pathway has been associated with a variety of human diseases including diabetes, neurodegeneration and cancer. Although mTORC1 signaling has been extensively studied in cancer, recent discoveries indicate a subset of human cancers harboring amplifications in mTORC2-specific genes as the only actionable genomic alterations, suggesting a distinct role for mTORC2 in cancer as well. This review will summarize recent advances in dissecting the relative contributions of mTORC1 versus mTORC2 in cancer, their role in tumor-associated blood vessels and tumor immunity, and provide an update on mTOR inhibitors.

Biological Role and Therapeutic Targeting of TGF-β3 in Glioblastoma

Transforming growth factor (TGF)-β contributes to the malignant phenotype of glioblastoma by promoting invasiveness and angiogenesis and creating an immunosuppressive microenvironment. So far, TGF-β₁ and TGF-β₂ isoforms have been considered to act in a similar fashion without isoform-specific function in glioblastoma. A pathogenic role for TGF-β₃ in glioblastoma has not been defined yet. Here, we studied the expression and functional role of endogenous and exogenous TGF-β₃ in glioblastoma models. TGF-β₃ mRNA is expressed in human and murine long-term glioma cell lines as well as in human glioma-initiating cell cultures with expression levels lower than TGF-β₁ or TGF-β₂ in most cell lines. Inhibition of TGF-β₃ mRNA expression by ISTH2020 or ISTH2023, two different isoform-specific phosphorothioate locked nucleic acid (LNA)-modified antisense oligonucleotide gapmers, blocks downstream SMAD2 and SMAD1/5 phosphorylation in human LN-308 cells, without affecting TGF-β₁ or TGF-β₂ mRNA expression or protein levels. Moreover, inhibition of TGF-β₃ expression reduces invasiveness in vitro Interestingly, depletion of TGF-β₃ also attenuates signaling evoked by TGF-β₁ or TGF-β₂ In orthotopic syngeneic (SMA-560) and xenograft (LN-308) in vivo glioma models, expression of TGF-β₃ as well as of the downstream target, plasminogen-activator-inhibitor (PAI)-1, was reduced, while TGF-β₁ and TGF-β₂ levels were unaffected following systemic treatment with TGF-β₃ -specific antisense oligonucleotides. We conclude that TGF-β₃ might function as a gatekeeper controlling downstream signaling despite high expression of TGF-β₁ and TGF-β₂ isoforms. Targeting TGF-β₃in vivo may represent a promising strategy interfering with aberrant TGF-β signaling in glioblastoma. Mol Cancer Ther; 16(6); 1177-86. ©2017 AACR.