Activation of PI3K/mTOR pathway occurs in most adult low-grade gliomas and predicts patient survival

Low-Level Expression of p-S6 Is Associated with Nodal Metastasis in Patients with Head and Neck Cutaneous Squamous Cell Carcinoma

Cutaneous squamous cell carcinoma (cSCC) is the second most common form of skin cancer. The incidence of metastasis for cSCC is estimated to be around 1.2-5%. Ribosomal protein S6 (p-S6) and the p21 protein (p21) are two proteins that play central roles in other cancers. These proteins may be equally important in cSCC, and together, these could constitute a good candidate for metastasis risk assessment of these patients. We investigate the relationship of p-S6 and p21 expression with the impact on the prognosis of head and neck cSCC (cSCCHN). p-S6 and p21 expression was analyzed by immunohistochemistry on paraffin-embedded tissue samples from 116 patients with cSCCHN and associations sought with clinical characteristics. Kaplan-Meier estimators and Cox proportional hazard regression models were also used. The expression of p-S6 was significantly inversely associated with tumor thickness, tumor size, desmoplastic growth, pathological stage, perineural invasion and tumor buds. p21 expression was significantly inversely correlated with >6 mm tumor thickness, desmoplastic growth, and perineural invasion. p-S6-negative expression significantly predicted an increased risk of nodal metastasis (HR = 2.63, 95% CI 1.51-4.54; p < 0.001). p21 expression was not found to be a significant risk factor for nodal metastasis. These findings demonstrate that p-S6-negative expression is an independent predictor of nodal metastasis. The immunohistochemical expression of p-S6 might aid in better risk stratification and management of patients with cSCCHN.

Glioma-Induced Alterations in Excitatory Neurons are Reversed by mTOR Inhibition

Gliomas are highly aggressive brain tumors characterized by poor prognosis and composed of diffusely infiltrating tumor cells that intermingle with non-neoplastic cells in the tumor microenvironment, including neurons. Neurons are increasingly appreciated as important reactive components of the glioma microenvironment, due to their role in causing hallmark glioma symptoms, such as cognitive deficits and seizures, as well as their potential ability to drive glioma progression. Separately, mTOR signaling has been shown to have pleiotropic effects in the brain tumor microenvironment, including regulation of neuronal hyperexcitability. However, the local cellular-level effects of mTOR inhibition on glioma-induced neuronal alterations are not well understood. Here we employed neuron-specific profiling of ribosome-bound mRNA via 'RiboTag,' morphometric analysis of dendritic spines, and in vivo calcium imaging, along with pharmacological mTOR inhibition to investigate the impact of glioma burden and mTOR inhibition on these neuronal alterations. The RiboTag analysis of tumor-associated excitatory neurons showed a downregulation of transcripts encoding excitatory and inhibitory postsynaptic proteins and dendritic spine development, and an upregulation of transcripts encoding cytoskeletal proteins involved in dendritic spine turnover. Light and electron microscopy of tumor-associated excitatory neurons demonstrated marked decreases in dendritic spine density. In vivo two-photon calcium imaging in tumor-associated excitatory neurons revealed progressive alterations in neuronal activity, both at the population and single-neuron level, throughout tumor growth. This in vivo calcium imaging also revealed altered stimulus-evoked somatic calcium events, with changes in event rate, size, and temporal alignment to stimulus, which was most pronounced in neurons with high-tumor burden. A single acute dose of AZD8055, a combined mTORC1/2 inhibitor, reversed the glioma-induced alterations on the excitatory neurons, including the alterations in ribosome-bound transcripts, dendritic spine density, and stimulus evoked responses seen by calcium imaging. These results point to mTOR-driven pathological plasticity in neurons at the infiltrative margin of glioma - manifested by alterations in ribosome-bound mRNA, dendritic spine density, and stimulus-evoked neuronal activity. Collectively, our work identifies the pathological changes that tumor-associated excitatory neurons experience as both hyperlocal and reversible under the influence of mTOR inhibition, providing a foundation for developing therapies targeting neuronal signaling in glioma.

External auditory canal ectopic atypical meningioma: A case report and brief literature review

Meningiomas are tumours typically derived from the meningothelial cells of the arachnoid mater. They most often arise in intracranial, intraspinal, or orbital locations. Ectopic meningiomas, described as primary meningiomas with no intracranial involvement, are definitely unconventional. In fact, most of the extracranial meningiomas described in the literature, particularly in the outer ear, are effectively spreads of disease with primary intracranial localization. We describe a case of a primary external auditory canal meningioma with demonstrated absence of intracranial involvement, and we provide a full radiological, histological, immunohistochemical and molecular characterization of the lesion.

PI3K/AKT/mTOR signaling pathway activity in IDH-mutant diffuse glioma and clinical implications

BACKGROUND

IDH-mutant diffuse gliomas are heterogeneous, and improved methods for optimal patient therapeutic stratification are needed. PI3K/AKT/mTOR signaling activity can drive disease progression and potential therapeutic inhibitors of the pathway are available. Yet, the prevalence of PI3K/AKT/mTOR signaling pathway activity in IDH-mutant glioma is unclear and few robust strategies to assess activity in clinical samples exist.

METHODS

PI3K/AKT/mTOR signaling pathway activity was evaluated in a retrospective cohort of 132 IDH-mutant diffuse glioma (91 astrocytoma and 41 oligodendroglioma, 1p/19q-codeleted) through quantitative multiplex immunoprofiling using phospho-specific antibodies for PI3K/AKT/mTOR pathway members, PRAS40, RPS6, and 4EBP1, and tumor-specific anti-IDH1 R132H. Expression levels were correlated with genomic evaluation of pathway intrinsic genes and univariate and multivariate Cox proportional hazard regression models were used to evaluate the relationship with outcome.

RESULTS

Tumor-specific expression of p-PRAS40, p-RPS6, and p-4EBP1 was common in IDH-mutant diffuse glioma and increased with CNS WHO grade from 2 to 3. Genomic analysis predicted pathway activity in 21.7% (13/60) while protein evaluation identified active PI3K/AKT/mTOR signaling in 56.6% (34/60). Comparison of expression in male versus female patients suggested sexual dimorphism. Of particular interest, when adjusting for clinical prognostic factors, the level of phosphorylation of RPS6 was strongly associated with PFS (P < .005). Phosphorylation levels of both PRAS40 and RPS6 showed an association with PFS in univariate analysis.

CONCLUSIONS

Our study emphasizes the value of proteomic assessment of signaling pathway activity in tumors as a means to identify relevant oncogenic pathways and potentially as a biomarker for identifying aggressive disease.

Differential Regulation of the EGFR/PI3K/AKT/PTEN Pathway between Low- and High-Grade Gliomas

Gliomas represent 70% of all central system nervous tumors and are classified according to the degree of malignancy as low- or high-grade. The permanent activation of the EGFR/PI3K/AKT pathway by various genetic or post-translational alterations of EGFR, PI3KCA, and PTEN has been associated with increased proliferation and resistance to apoptosis. The present study aimed to analyze the molecular/genetic changes in the EGFR/PI3K/AKT/PTEN pathway between low-grade and high-grade gliomas in a sample of Colombian patients. A total of 30 samples were tested for PI3K and PTEN mutations, EGFR, PI3K, and AKT gene amplification, AKT, PI3K, BAX, Bcl2 expression levels, and phosphorylation of AKT and PTEN, EGFR and/or PI3K gene amplification was found in 50% of low-grade and 45% of high-grade ones. AKT amplification was found in 25% of the low-grade and 13.6% of the high-grade. The expression of PI3K, AKT, Bcl2, and BAX was increased particularly to a high degree. AKT phosphorylation was found in 66% of low-grade and 31.8% of high-grade. Increased phosphorylation of PTEN was found in 77% low-grade and 66% high-grade. Our results indicate that alterations in the EGFR/PI3K/AKT/PTEN pathway could be important in the initiation and malignant progression of this type of tumor.

Tyrosine phosphorylation of DEPTOR functions as a molecular switch to activate mTOR signaling

Metabolic dysfunction is a major driver of tumorigenesis. The serine/threonine kinase mechanistic target of rapamycin (mTOR) constitutes a key central regulator of metabolic pathways promoting cancer cell proliferation and survival. mTOR activity is regulated by metabolic sensors as well as by numerous factors comprising the phosphatase and tensin homolog/PI3K/AKT canonical pathway, which are often mutated in cancer. However, some cancers displaying constitutively active mTOR do not carry alterations within this canonical pathway, suggesting alternative modes of mTOR regulation. Since DEPTOR, an endogenous inhibitor of mTOR, was previously found to modulate both mTOR complexes 1 and 2, we investigated the different post-translational modification that could affect its inhibitory function. We found that tyrosine (Tyr) 289 phosphorylation of DEPTOR impairs its interaction with mTOR, leading to increased mTOR activation. Using proximity biotinylation assays, we identified SYK (spleen tyrosine kinase) as a kinase involved in DEPTOR Tyr 289 phosphorylation in an ephrin (erythropoietin-producing hepatocellular carcinoma) receptor–dependent manner. Altogether, our work reveals that phosphorylation of Tyr 289 of DEPTOR represents a novel molecular switch involved in the regulation of both mTOR complex 1 and mTOR complex 2.

Upfront treatment with mTOR inhibitor everolimus in pediatric low-grade gliomas: A single-center experience

Pediatric low-grade gliomas (pLGGs) are the most frequent brain tumor in children. Adjuvant treatment, consisting in chemotherapy and radiotherapy, is often necessary if a complete surgical resection cannot be obtained. Traditional treatment approaches result in a significant long-term morbidity, with a detrimental impact on quality of life. Dysregulation of the mitogen-activated protein kinase (MAPK) pathway is the molecular hallmark of pLGGs and hyperactivation of the downstream mammalian target of rapamycin (mTOR) pathway is frequently observed. We report clinical and radiological results of front-line treatment with everolimus in 10 consecutive patients diagnosed with m-TOR positive pLGGs at the Bambino Gesù Children's Hospital in Rome, Italy. Median duration of treatment was 19 months (range from 13-60). Brain magnetic resonance imaging showed stable disease in 7 patients, partial response in 1 and disease progression in 2. Therapy-related adverse events were always reversible after dose reduction or temporary treatment interruption. To the best of our knowledge, this is the first report of everolimus treatment for chemo- and radiotherapy-naïve children with pLGG. Our results provide preliminary support, despite low sample size, for the use of everolimus as target therapy in pLGG showing lack of progression with a manageable toxicity profile.

A Profound Basic Characterization of eIFs in Gliomas: Identifying eIF3I and 4H as Potential Novel Target Candidates in Glioma Therapy

Simple Summary

Gliomas are brain tumors with currently limited therapy options. Glioma growth and proliferation is regulated by the mTOR pathway together with eukaryotic initiation factors (eIFs). In this work we show a profound basic characterization of eIFs in human gliomas and demonstrate increased mRNA and protein expressions of several eIFs in gliomas compared to healthy control brain tissue. Moreover, increased eIF3I and eIF4H levels seem to have a negative influence on the survival of patients. Our work suggests eIF3I and eIF4H as potential targets for future glioma therapy.

Abstract

Glioblastoma (GBM) is an utterly devastating cerebral neoplasm and current therapies only marginally improve patients’ overall survival (OS). The PI3K/AKT/mTOR pathway participates in gliomagenesis through regulation of cell growth and proliferation. Since it is an upstream regulator of the rate-limiting translation initiation step of protein synthesis, controlled by eukaryotic initiation factors (eIFs), we aimed for a profound basic characterization of 17 eIFs to identify potential novel therapeutic targets for gliomas. Therefore, we retrospectively analyzed expressions of mTOR-related proteins and eIFs in human astrocytoma samples (WHO grades I–IV) and compared them to non-neoplastic cortical control brain tissue (CCBT) using immunoblot analyses and immunohistochemistry. We examined mRNA expression using qRT-PCR and additionally performed in silico analyses to observe the influence of eIFs on patients’ survival. Protein and mRNA expressions of eIF3B, eIF3I, eIF4A1, eIF4H, eIF5 and eIF6 were significantly increased in high grade gliomas compared to CCBT and partially in low grade gliomas. However, short OS was only associated with high eIF3I gene expression in low grade gliomas, but not in GBM. In GBM, high eIF4H gene expression significantly correlated with shorter patient survival. In conclusion, we identified eIF3I and eIF4H as the most promising targets for future therapy for glioma patients.

Genomic Profiling Identified Novel Prognostic Biomarkers in Chinese Midline Glioma Patients

Background

Molecular characteristics are essential for the classification and grading of gliomas. However, diagnostic classification of midline glioma is still debatable and substantial molecular and clinical heterogeneity within each subgroup suggested that they should be further stratified. Here, we studied the mutation landscape of Chinese midline glioma patients in hope to provide new insights for glioma prognosis and treatment.

Methods

Tissue samples from 112 midline glioma patients underwent next-generation sequencing targeting 425 cancer-relevant genes. Gene mutations and copy number variations were investigated for their somatic interactions and prognostic effect using overall survival data. Pathway-based survival analysis was performed for ten canonical oncogenic pathways.

Results

We identified several currently established diagnostic and prognostic biomarkers of glioma, including TP53 (33%), EGFR (26%), TERT (24%), PTEN (21%), PIK3CA (14%), ATRX (14%), BRAF (13%), and IDH1/2 (6%). Among all genetic aberrations with more than 5% occurrence rate, six mutations and three copy number gains were greatly associated with poor overall survival (univariate, P < 0.1). Of these, TERT mutations (hazard ratio [HR], 3.00; 95% confidence interval [CI], 1.37–6.61; P = 0.01) and PIK3CA mutations (HR, 2.04; 95% CI, 1.08–3.84; P = 0.02) remained significant in multivariate analyses. Additionally, we have also identified a novel MCL1 amplification (found in 31% patients) as a potential independent biomarker for glioma (multivariate HR, 2.78; 95% CI, 1.53–5.08; P < 0.001), which was seldom reported in public databases. Pathway analyses revealed significantly worse prognosis with abnormal PI3K (HR, 1.81; 95% CI, 1.12–2.95; P = 0.01) and cell cycle pathways (HR, 1.97; 95% CI, 1.15–3.37; P = 0.01), both of which stayed meaningful after multivariate adjustment.

Conclusions

In this study, we discovered shorter survival in midline glioma patients with PIK3CA and TERT mutations and with abnormal PI3K and cell cycle pathways. We also revealed a novel prognostic marker, MCL1 amplification that collectively provided new insights and opportunities in understanding and treating midline gliomas.

N2M2 (NOA-20) phase I/II trial of molecularly matched targeted therapies plus radiotherapy in patients with newly diagnosed non-MGMT hypermethylated glioblastoma

Background

Patients with glioblastoma without O6-methylguanine-DNA methyltransferase (MGMT) promoter hypermethylation are unlikely to benefit from alkylating chemotherapy with temozolomide (TMZ). Trials aiming at replacing TMZ with targeted agents in unselected patient populations have failed to demonstrate any improvement of survival. Advances in molecular understanding and diagnostic precision enable identification of key genetic alterations in a timely manner and in principle allow treatments with targeted compounds based on molecular markers.

Methods

The NCT Neuro Master Match (N2M2) trial is an open-label, multicenter, phase I/IIa umbrella trial for patients with newly diagnosed isocitrate dehydrogenase (IDH) wildtype glioblastoma without MGMT promoter hypermethylation to show safety, feasibility, and preliminary efficacy of treatment with targeted compounds in addition to standard radiotherapy based on molecular characterization. N2M2 is formally divided into a Discovery and a Treatment part. Discovery includes broad molecular neuropathological diagnostics to detect predefined biomarkers for targeted treatments. Molecular diagnostics and bioinformatic evaluation are performed within 4 weeks, allowing a timely initiation of postoperative treatment. Stratification for Treatment takes place in 5 subtrials, including alectinib, idasanutlin, palbociclib, vismodegib, and temsirolimus as targeted therapies, according to the best matching molecular alteration. Patients without matching alterations are randomized between subtrials without strong biomarkers using atezolizumab and asinercept (APG101) and the standard of care, TMZ. For the phase I parts, a Bayesian criterion is used for continuous monitoring of toxicity. In the phase II trials, progression-free survival at 6 months is used as endpoint for efficacy.

Results

Molecular diagnostics and bioinformatic evaluation are performed within 4 weeks, allowing a timely initiation of postoperative treatment. Stratification for Treatment takes place in 5 subtrials, including alectinib, idasanutlin, palbociclib, vismodegib, and temsirolimus as targeted therapies, according to the best matching molecular alteration. Patients without matching alterations are randomized between subtrials without strong biomarkers using atezolizumab and asinercept (APG101) and the standard of care, TMZ. For the phase I parts, a Bayesian criterion is used for continuous monitoring of toxicity. In the phase II trials, progression-free survival at 6 months is used as endpoint for efficacy.

Discussion

Molecularly informed trials may provide the basis for the development of predictive biomarkers and help to understand and select patient subgroups who will benefit.

PI3K/mTOR inhibition of IDH1 mutant glioma leads to reduced 2HG production that is associated with increased survival

70-90% of low-grade gliomas and secondary glioblastomas are characterized by mutations in isocitrate dehydrogenase 1 (IDHmut). IDHmut produces the oncometabolite 2-hydroxyglutarate (2HG), which drives tumorigenesis in these tumors. The phosphoinositide-3-kinase (PI3K)/mammalian target of rapamycin (mTOR) pathway represents an attractive therapeutic target for IDHmut gliomas, but noninvasive indicators of drug target modulation are lacking. The goal of this study was therefore to identify magnetic resonance spectroscopy (MRS)-detectable metabolic biomarkers associated with IDHmut glioma response to the dual PI3K/(mTOR) inhibitor XL765. ¹H-MRS of two cell lines genetically modified to express IDHmut showed that XL765 induced a significant reduction in several intracellular metabolites including 2HG. Importantly, examination of an orthotopic IDHmut tumor model showed that enhanced animal survival following XL765 treatment was associated with a significant in vivo ¹H-MRS detectable reduction in 2HG but not with significant inhibition in tumor growth. Further validation is required, but our results indicate that 2HG could serve as a potential noninvasive MRS-detectable metabolic biomarker of IDHmut glioma response to PI3K/mTOR inhibition.

Jinlong capsule inhibits migration and invasion in human glioblastoma cells via the modulation of mTOR/S6 signaling pathway

Aim: To investigate the anticancer effects of Jinlong capsule (JLC) against human glioblastoma cells and the possible underlying mechanism. Methods: Cell Counting Kit-8 and colony formation assay were adopted for the analysis of cell viability. Cell invasion and migration were evaluated by transwell and wound healing assays. Then, the expression level of mammalian target of rapamycin (mTOR), phosphorylated mTOR (p-mTOR), S6 and phosphorylated S6 (p-S6) were determined by western blotting. Results: The results showed that JLC significantly inhibited human glioblastoma cell proliferation, invasion and migration in a dose-dependent manner. The expressions of p-mTOR and p-S6 were dramatically suppressed by JLC. Furtherly, inhibition of mTOR reduced the cell migration and invasion, while the mTOR agonist (MHY1485) could partially reverse the anti-migration and anti-invasion activity of JLC. Conclusion: The above results suggested that JLC would be a potential candidate for the treatment of glioblastoma.

Akt and mTORC1 signaling as predictive biomarkers for the EGFR antibody nimotuzumab in glioblastoma

Glioblastoma (GB) is the most frequent primary brain tumor in adults with a dismal prognosis despite aggressive treatment including surgical resection, radiotherapy and chemotherapy with the alkylating agent temozolomide. Thus far, the successful implementation of the concept of targeted therapy where a drug targets a selective alteration in cancer cells was mainly limited to model diseases with identified genetic drivers. One of the most commonly altered oncogenic drivers of GB and therefore plausible therapeutic target is the epidermal growth factor receptor (EGFR). Trials targeting this signaling cascade, however, have been negative, including the phase III OSAG 101-BSA-05 trial. This highlights the need for further patient selection to identify subgroups of GB with true EGFR-dependency. In this retrospective analysis of treatment-naïve samples of the OSAG 101-BSA-05 trial cohort, we identify the EGFR signaling activity markers phosphorylated PRAS40 and phosphorylated ribosomal protein S6 as predictive markers for treatment efficacy of the EGFR-blocking antibody nimotuzumab in MGMT promoter unmethylated GBs. Considering the total trial population irrespective of MGMT status, a clear trend towards a survival benefit from nimotuzumab was already detectable when tumors had above median levels of phosphorylated ribosomal protein S6. These results could constitute a basis for further investigations of nimotuzumab or other EGFR- and downstream signaling inhibitors in selected patient cohorts using the reported criteria as candidate predictive biomarkers.

Grade II and III Oligodendroglioma and Astrocytoma

In the 2016 WHO classification of diffuse glioma, the diagnosis of an (anaplastic) oligodendroglioma requires the presence of both an IDH mutation (mt) and 1p/19q codeletion, whereas (anaplastic) astrocytoma are divided in IDH wild-type and IDHmt tumors. Standard of care for grade II and III glioma consists of resection. For patients with tumors that require postoperative treatment, radiotherapy and chemotherapy are recommended. Trials in newly diagnosed grade II and III glioma have shown survival benefit of the addition of chemotherapy to radiotherapy compared with initial treatment with radiotherapy alone; both temozolomide and PCV have been shown to improve survival.

Precision Medicine for Primary Central Nervous System Tumors: Are We There Yet?

In recent years, technologic advances have increased tremendously our understanding of the molecular characteristics and genetic drivers of a variety of brain tumors. These discoveries have led to paradigm shifts in the treatment of these tumor entities and may therefore have a considerable impact on the outcome of affected patients in the near future. Here, we provide a broad overview of recently discovered clinically actionable mutations that have been identified in three different primary brain tumors: gliomas, meningiomas, and craniopharyngiomas. We furthermore highlight the diagnostic and therapeutic implications of these findings and summarize recently published and ongoing trials.

Cerebellar Ganglioglioma in Childhood: Histopathologic Implications for Management During Long-term Survival: A Case Report

We report the case of a 19-year-old female with cerebellar ganglioglioma that was diagnosed at 4 years of age. Despite treatment with partial resection, radiation, and chemotherapy, residual tumor slowly expanded into the brainstem and upper cervical cord, resulting in nocturnal hypopnea, progressive tetraparesis, and feeding difficulty during 8-10 years of age. Initiation of temozolomide and bevacizumab was effective in preventing further expansion of the tumor, and the patient has been treated at home and in school with noninvasive positive pressure ventilation and gastrostomy. Histopathologic examination of the resected tumor tissue revealed phospho-S6-positive tumor cells of either neuronal or astroglial appearance. This suggests that a higher proportion of cells of glial lineage could be linked to the progression of cerebellar ganglioglioma in childhood. Possible treatment options with mammalian target of rapamycin inhibitors are discussed.

Overexpression of mTOR and p(240-244)S6 in IDH1 Wild-Type Human Glioblastomas Is Predictive of Low Survival

PI3K/Akt/mTOR pathway activation is a hallmark of high-grade gliomas, which prompted clinical trials for the use of PI3K and mTOR inhibitors. However, the poor results in the original trials suggested that better patient profiling was needed for such drugs. Thus, accurate and reproducible monitoring of mTOR complexes can lead to improved therapeutic strategies. In this work, we evaluated the expression and phosphorylation of mTOR, RAPTOR, and rpS6 in 195 human astrocytomas and 30 normal brain tissue samples. The expression of mTOR increased in glioblastomas, whereas mTOR phosphorylation, expression of RAPTOR, and expression and phosphorylation of rpS6 were similar between grades. Interestingly, the overexpression of total and phosphorylated mTOR as well as phosphorylated rpS6 (residues 240-244) were associated with wild-type IDH1 only glioblastomas. The expression and phosphorylation of mTOR and phosphorylation of rpS6 at residues 240-244 were associated with a worse prognosis in glioblastomas. Our results suggest that mTOR and rpS6 could be used as markers of overactivation of the PI3K-mTOR pathway and are predictive factors for overall survival in glioblastomas. Our study thus suggests that patients who harbor IDH1 wild-type glioblastomas might have increased benefit from targeted therapy against mTOR.

The atypical protein kinase RIOK3 contributes to glioma cell proliferation/survival, migration/invasion and the AKT/mTOR signaling pathway

The RIO (right open reading frame) protein kinases include RIOK1, RIOK2 and RIOK3. Emerging evidence has suggested an important role of RIO kinases in cancer cell proliferation, apoptosis, migration and invasion. However, the expression profile and specific roles of RIOK3 are largely unknown during glioma progression. In the current study, quantitative real-time PCR, Western blot, and immunohistochemical analysis showed that RIOK3 was upregulated in glioma tissues. Available database analysis revealed that higher levels of RIOK3 were associated with poorer survival outcome in glioma patients. Flow cytometry, CCK8 and EdU assays showed that downregulation of RIOK3 arrested cell cycle progression and inhibited glioma cell proliferation. Wound healing, transwell and gelatin zymography assays revealed that silencing RIOK3 decreased glioma cell migration and invasion. Furthermore, the downregulation of RIOK3 significantly decreased the activity of AKT/mTOR signaling and induced apoptosis in glioma cells. Overexpression of RIOK3 showed the opposite effects on glioma cell proliferation, migration, invasion and the AKT/mTOR pathway. These results indicate that high RIOK3 levels in gliomas appear to contribute to the growth and expansion of this cancer, and may thus serve as a novel therapeutic target.

TET1 exerts its tumour suppressor function by regulating autophagy in glioma cells

DNA methylation and demethylation play a critical role in the regulation of the molecular pathogenesis of gliomas. Tet methylcytosine dioxygenase 1 (TET1) catalyses the sequential oxidation of 5-methylcytosine (5mC) to 5-hydroxymethylcytosine, (5hmC) leading to eventual DNA demethylation. It has been reported that TET1 is a tumour suppressor in several cancers. However, whether TET1 plays a role in glioma development is largely unclear. Different glioma specimens and corresponding normal controls were collected to analyse the expression of TET1. At the same time, TET1 of glioma U251 cells was knocked down or overexpressed to observe its effect on glioma cell proliferation and invasion as well as autophagy level. Here, we reported that the expression of TET1 in glioma tissue was significantly lower than the corresponding non-tumour normal tissues, and the concentration of TET1 is negatively correlated with the glioma WHO classification. When TET1 gene in glioma U251 cells was knocked down by CRISPR/Caspase-9 system, the proliferation and invasive ability of U251 increased remarkably. But when TET1 was overexpressed in U251 cells, the proliferation and invasion were impaired. Following the down-expression of TET1, the level of autophagy in U251 cells decreased accordingly.However, when TET1 was overexpressed in U251 cells, the level of autophagy incraesed. Furthermore, bafilomycin A1 (Baf-A1) but not 3-methyladenine (3-MA) could decrease the autophagy level of TET1^−/− U251 cells as the wild-type controls. It suggests that the tumour suppressor effect of TET1 seems to be mediated by regulating the level of autophagy, and the regulation of TET1 on autophagy is at an early stage.

High LC3/Beclin Expression Correlates with Poor Survival in Glioma: a Definitive Role for Autophagy as Evidenced by In Vitro Autophagic Flux

Recent studies suggest the role of autophagy, an evolutionarily conserved catabolic process, in determining the response of gliomas to treatment either positively or negatively. The study attempts to characterize autophagy in low and high-grade glioma by investigating the autophagic flux and clinical significance of autophagy proteins (LC3 and beclin 1) in a group of glioma patients. We evaluated the expression of autophagic markers in resected specimens of low-grade glioma (LGG) and high-grade glioma (HGG) tissues, by immunohistochemistry and Western blotting. Our results show that expression of autophagy proteins were more prominent in HGG than in LGG. Increased level of autophagic proteins in HGG can be due to an increased rate of autophagy or can be because of blockage in the final degradation step of autophagy (defective autophagy). To distinguish these possibilities, the autophagic flux assay which helps to determine the rate of degradation/synthesis of autophagic proteins (LC3-II and p62) over a period of time by blocking the final degradation step of autophagy using bafilomycin A1 was used . The assessment of autophagic flux in ex vivo culture of primary glioma cells revealed for the first time increased turnover of autophagy in high grade compared to low grade-glioma. Though autophagic markers were reduced in LGG, functionally autophagy was non defective in both grades of glioma. We then investigated whether autophagy in gliomas is regulated by nutrient sensing pathways including mTOR and promote cell survival by providing an alternate energy source in response to metabolic stress. The results depicted that the role of autophagy during stress varies with tissue and has a negative correlation with mTOR substrate phosphorylation. We also evaluated the expression of LC3 and beclin 1 with progression free survival (PFS) using Kaplan-Meier survival analysis and have found that patients with low LC3/beclin 1 expression had better PFS than those with high expression of LC3/beclin 1 in their tumors. Together, we provide evidence that autophagy is non-defective in glioma and also show that high LC3/beclin 1 expression correlates with poor PFS in both LGG and HGG.

Functional network analysis of gene-phenotype connectivity associated with temozolomide

Rationale

Glioma has a poor survival rate in patients even with aggressive treatment. Temozolomide (TMZ) is the standard chemotherapeutic choice for treating glioma, but TMZ treatment consistently leads to high resistance.

Aim

To investigate the underlying mechanisms of TMZ action with new therapeutic regimens in glioma.

Methods and results

The biological effects of TMZ mainly depend on the three following DNA repair systems: methylguanine methyltransferase (MGMT), mismatch repair (MMR) and base excision repair (BER). Based on related genes in these three systems, web-based tools containing data compiled from open-source databases, including DrugBank, STRING, WebGestalt and ClueGO, were queried, and five common genes along with the top fifteen pathways, including the glioma pathway, were identified. A genomic analysis of the six genes identified in the glioma pathway by cBioPortal indicated that TMZ might exert biological effects via interaction with the tumor protein P53(TP53) signaling axis. Finally, a survival analysis with the six genes in glioma cases (low-grade glioma and glioblastoma multiforme) was conducted using OncoLnc, which might provide directions for the future exploration of prognosis in glioma.

Conclusions

This study indicates that a functional network analysis resembles a "BioGPS", with the ability to draw a web-based scientific map that can productively and cost-effectively associate TMZ with its primary and secondary biological targets.

Hypomethylation of CNTFRα is associated with proliferation and poor prognosis in lower grade gliomas

Ciliary neurotrophic factor receptor α subunit (CNTFRα) and CNTF play important roles in neuron survival, glial differentiation and brain tumor growth. However, the molecular mechanisms of CNTFRα regulation and its clinical significance in glioma remain largely unknown. Here, we found CNTFRα was overexpressed in lower grade gliomas (LGG) compared with glioblastoma (GBM) and normal brain specimens in TCGA datasets and in an independent cohort. Bioinformatics analysis revealed a CpG shore of the CNTFRα gene regulated its mRNA expression in TCGA datasets. This observation was further validated with clinical specimens and functionally verified using demethylating agents. Additionally, we observed that independent of IDH mutation status, methylation of CNTFRα was significantly correlated with down-regulated CNTFRα gene expression and longer LGG patient survival. Interestingly, combination of CNTFRα methylation and IDH mutation significantly (p < 0.05) improved the prognostic prediction in LGG patients. Furthermore, the role of CNTFRα in glioma proliferation and apoptosis through the PI3K/AKT pathways was demonstrated by supplementation with exogenous CNTF  in vitro and siRNA knockdown in vivo. Our study demonstrated that hypomethylation leading to CNTFRα up-regulation, together with autocrine expression of CNTF, was involved in glioma growth regulation. Importantly, DNA methylation of CNTFRα might serve as a potential epigenetic theranostic target for LGG patients.

Probing the phosphatidylinositol 3-kinase/mammalian target of rapamycin pathway in gliomas: A phase 2 study of everolimus for recurrent adult low-grade gliomas

BACKGROUND

Activation of the phosphatidylinositol 3-kinase (PI3K)/mammalian target of rapamycin (mTOR) pathway is common in patients with low-grade gliomas (LGGs), but agents that inhibit this pathway, including mTOR inhibitors, have not been studied in this population.

METHODS

Fifty-eight patients with pathologic evidence of recurrence after they had initially been diagnosed with World Health Organization (WHO) grade II gliomas were enrolled into a prospective phase 2 clinical trial and received daily everolimus (RAD001) for 1 year or until progression. Tissue at the time of enrollment was analyzed for markers of PI3K/mTOR pathway activation. Thirty-eight patients underwent serial multiparametric magnetic resonance imaging, with the tumor volume and the perfusion metrics (the fractional blood volume [fBV] for capillary density and the transfer coefficient [K_ps ] for vascular permeability) measured during treatment. The primary endpoint was progression-free survival at 6 months (PFS-6) in patients with WHO II disease at enrollment.

RESULTS

For patients with WHO II gliomas at enrollment, the PFS-6 rate was 84%, and this met the primary endpoint (P < .001 for an improvement from the historical rate of 17%). Evidence of PI3K/mTOR activation by immunohistochemistry for phosphorylated ribosomal S6^Ser240/244 (p-S6^Ser240/244 ) was associated with worse progression-free survival (PFS; hazard ratio [HR], 3.03; P = .004) and overall survival (HR, 12.7; P = .01). Tumor perfusion decreased after 6 months (median decrease in fBV, 15%; P = .03; median decrease in K_ps , 12%; P = .09), with greater decreases associated with improved PFS (HR for each 10% fBV decrease, 0.71; P = .01; HR for each 10% K_ps decrease, 0.82; P = .04).

CONCLUSIONS

Patients with recurrent LGGs demonstrated a high degree of disease stability during treatment with everolimus. PI3K/mTOR activation, as measured by immunohistochemistry for p-S6, was associated with a worse prognosis. Tumor vascular changes were observed that were consistent with the antiangiogenic effects of mTOR inhibitors. These results support further study of everolimus for LGGs. Cancer 2017;123:4631-4639. © 2017 American Cancer Society.

Phosphorylated ribosomal protein S6 correlation with p21 expression and inverse association with tumor size in oral squamous cell carcinoma

BACKGROUND

The purpose of this study was to investigate the clinical relevance of phosphorylated ribosomal protein S6 (p-S6), a surrogate marker of mammalian target of rapamycin (mTOR) activation, and p21 in a series of 125 patients with oral squamous cell carcinomas (OSCCs).

METHODS

Immunohistochemical analysis was performed to ascertain the phosphorylation status of p-S6 at Ser235/236 and Ser240/244, p21, and p53 protein expression.

RESULTS

Expression of phosphorylated S6 protein on either serine 235/236 or serine 240/244 was detected in 83% and 88% tumors, respectively, and both of them were inversely and significantly correlated with the tumor size and local infiltration. Positive p21 expression was found in 91.5% of the cases, and was inversely correlated with tumor size. In OSCC, p21 expression correlates with p-S6 levels, a surrogate marker of mTOR activation, independently of p53 status.

CONCLUSION

Expression of both p21 and p-S6 was found to inversely associate with tumor size but not survival outcomes in patients with OSCC.

Treatment of Adult Lower-Grade Glioma in the Era of Genomic Medicine

By convention, gliomas are histopathologically classified into four grades by the World Health Organization (WHO) legacy criteria, in which increasing grade is associated with worse prognosis and grades also are subtyped by presumed cell of origin. This classification has prognostic value but is limited by wide variability of outcome within each grade, so the classification is rapidly undergoing dramatic re-evaluation in the context of a superior understanding of the biologic heterogeneity and molecular make-up of these tumors, such that we now recognize that some low-grade gliomas behave almost like malignant glioblastoma, whereas other anaplastic gliomas have outcomes comparable to favorable low-grade gliomas. This clinical spectrum is partly accounted for by the dispersion of several molecular genetic alterations inherent to clinical tumor behavior. These molecular biomarkers have become important not only as prognostic factors but also, more critically, as predictive markers to drive therapeutic decision making. Some of these, in the near future, will likely also serve as potential therapeutic targets. In this article, we summarize the key molecular features of clinical significance for WHO grades II and III gliomas and underscore how the therapeutic landscape is changing.

Genetic alterations related to BRAF-FGFR genes and dysregulated MAPK/ERK/mTOR signaling in adult pilocytic astrocytoma

Pilocytic astrocytomas occur rarely in adults and show aggressive tumor behavior. However, their underlying molecular-genetic events are largely uncharacterized. Hence, 59 adult pilocytic astrocytoma (APA) cases of classical histology were studied (MIB-1 LI: 1%-5%). Analysis of BRAF alterations using qRT-PCR, confirmed KIAA1549-BRAF fusion in 11 (19%) and BRAF-gain in 2 (3.4%) cases. BRAF-V600E mutation was noted in 1 (1.7%) case by sequencing. FGFR1-mutation and FGFR-TKD duplication were seen in 7/59 (11.9%) and 3/59 (5%) cases, respectively. Overall 36% of APAs harbored BRAF and/or FGFR genetic alterations. Notably, FGFR related genetic alterations were enriched in tumors of supratentorial region (8/25, 32%) as compared with other locations (P = 0.01). The difference in age of cases with FGFR1-mutation (Mean age ± SD: 37.2 ± 15 years) vs. KIAA1549-BRAF fusion (Mean age ± SD: 25.1 ± 4.1 years) was statistically significant (P = 0.03). Combined BRAF and FGFR alterations were identified in 3 (5%) cases. Notably, the cases with more than one genetic alteration were in higher age group (Mean age ± SD: 50 ± 12 years) as compared with cases with single genetic alteration (Mean age ± SD: 29 ± 10; P = 0.003). Immunopositivity of p-MAPK/p-MEK1 was found in all the cases examined. The pS6-immunoreactivity, a marker of mTOR activation was observed in 34/39 (87%) cases. Interestingly, cases with BRAF and/or FGFR related alteration showed significantly lower pS6-immunostatining (3/12; 25%) as compared with those with wild-type BRAF and/or FGFR (16/27; 59%) (P = 0.04). Further, analysis of seven IDH wild-type adult diffuse astrocytomas (DA) showed FGFR related genetic alterations in 43% cases. These and previous results suggest that APAs are genetically similar to IDH wild-type adult DAs. APAs harbor infrequent BRAF alterations but more frequent FGFR alterations as compared with pediatric cases. KIAA1549-BRAF fusion inversely correlates with increasing age whereas FGFR1-mutation associates with older age. Activation of MAPK/ERK/mTOR signaling appears to be an important oncogenic event in APAs and may be underlying event of aggressive tumor behavior. The findings provided a rationale for potential therapeutic advantage of targeting MAPK/ERK/mTOR pathway in APAs.

Evaluation of Akt and RICTOR Expression Levels in Astrocytomas of All Grades

The mammalian target of rapamycin (mTOR) binds to several protein partners and forms two complexes, termed mTOR complexes 1 and 2 (mTORC1/2), that differ in components, substrates, and regulation. mTORC2 contains the protein Rapamycin-insensitive companion of mTOR (RICTOR); phosphorylates kinases of the AGC family, such as Akt; and controls the cytoskeleton. Even though the regulation of mTORC2 activity remains poorly understood, the hyperactivation of this signaling pathway has been shown to contribute to the oncogenic properties of gliomas in experimental models. In this work, we evaluated expression and phosphorylation of Akt, and expression of RICTOR and Ki-67 in 195 human astrocytomas of different grades (38 cases of grade I, 49 grade II, 15 grade III, and 93 grade IV) and 30 normal brains. Expression and phosphorylation of Akt increased with histological grade and correlated with a worse overall survival in glioblastomas (GBMs). RICTOR was overexpressed in grade I and II astrocytomas and demonstrated a shift to nuclear localization in GBMs. Nuclear RICTOR was associated to increased proliferation in GBMs. Our results point to an increase in total and phosphorylated Akt in high-grade gliomas and to a possible role of RICTOR in proliferations of high-grade GBM cells.

Immunohistochemical evaluation of the mTOR pathway in intra-oral minor salivary gland neoplasms

OBJECTIVES

The aim of this study was to investigate the expression of upstream and downstream molecules of the oncogenic mTOR signaling pathway in intra-oral minor salivary gland tumors (SGTs).

MATERIALS AND METHODS

Tissue samples consisted of 39 malignant and 13 benign minor SGTs, and 8 controls of normal minor salivary glands (NMSG). An immunohistochemical analysis for phosphorylated Akt, 4EBP1 and S6 (total and phosphorylated), and eIF4E was performed.

RESULTS

Expression of pAkt and 4EBP1 was observed in all SGTs and in most NMSG. p4EBP1 was detected in almost all SGT cases, NMSG being negative. S6 immunoreactivity was observed in 37.5% of NMSG, 92.3% of benign and 100% of malignant SGTs, while pS6 expression was observed in 77% of benign and 95% of malignant SGTs, but not in NMSG. Finally, eIF4E was expressed in 12.5% of NMSG, 69.2% of benign, and 76.9% of malignant tumors. All molecules studied had statistically significantly lower expression in NMSG compared with SGTs. Moreover, malignant neoplasms received higher scores compared with benign tumors for all molecules with the exception of eIF4E.

CONCLUSION

The mTOR signaling pathway is activated in SGTs, especially in malignancies. Therefore, the possible therapeutic role of targeting the mTOR pathway by rapamycin analogs in SGTs needs further investigation.

mTORC1 signaling in primary central nervous system lymphoma

Background:

Mammalian target of rapamycin (mTOR) complex 1 (mTORC1) acts as a downstream effector of phosphatidyl-inositol-3 kinase, which is frequently hyperactivated in glioblastoma multiforme and links to cell signaling in cellular proliferation, differentiation, metabolism, and survival. Although many studies have suggested the importance of mTORC1 in tumorigenesis, its role remains unclear in brain tumors other than glioblastoma.

Methods:

In the present study, we evaluated the activation of mTORC1 in 24 cases of primary central nervous system lymphoma (PCNSL).

Results:

Immunohistochemical analysis showed overexpression of Rheb, which is immediately upstream of mTORC1, in 20 cases of PCNSL. Immunohistochemical analysis also showed overexpression of phospho-4E-BP1 (Thr37/46) and phospho-S6 (Ser235/236), which are increased after mTORC1 activation as mTORC1 downstream effectors in 17 and 21 cases, respectively.

Conclusion:

Our data suggest that abnormal activation of the mTORC1 signaling pathway may cause tumor growth in patients with PCNSL.

AKT inhibition overcomes rapamycin resistance by enhancing the repressive function of PRAS40 on mTORC1/4E-BP1 axis

The mTORC1 inhibitors, rapamycin and its analogs, are known to show only modest antitumor activity in clinic, but the underlying mechanisms remain largely elusive. Here, we found that activated AKT signaling is associated with rapamycin resistance in breast and colon cancers by sustained phosphorylation of the translational repressor 4E-BP1. Treatment of tumor cells with rapamycin or the AKT inhibitor MK2206 showed a limited activity in inhibiting 4E-BP1 phosphorylation, cap-dependent translation, cell growth and motility. However, treatment with both drugs resulted in profound effects in vitro and in vivo. Mechanistic investigation demonstrated that the combination treatment was required to effectively inhibit PRAS40 phosphorylation on both Ser183 and Thr246 mediated by mTORC1 and AKT respectively, and with the combined treatment, dephosphorylated PRAS40 binding to the raptor/mTOR complex was enhanced, leading to dramatic repression of mTORC1-regulated 4E-BP1 phosphorylation and translation. Knockdown of PRAS40 or 4E-BP1 expression markedly reduced the dependence of tumor cells on AKT/mTORC1 signaling for translation and survival. Together, these findings reveal a critical role of PRAS40 as an integrator of mTORC1 and AKT signaling for 4E-BP1-mediated translational regulation of tumor cell growth and motility, and highlight PRAS40 phosphorylation as a potential biomarker to evaluate the therapeutic response to mTOR/AKT inhibitors.

Glioblastoma: pathology, molecular mechanisms and markers

Recent advances in genomic technology have led to a better understanding of key molecular alterations that underlie glioblastoma (GBM). The current WHO-based classification of GBM is mainly based on histologic features of the tumor, which frequently do not reflect the molecular differences that describe the diversity in the biology of these lesions. The current WHO definition of GBM relies on the presence of high-grade astrocytic neoplasm with the presence of either microvascular proliferation and/or tumor necrosis. High-throughput analyses have identified molecular subtypes and have led to progress in more accurate classification of GBM. These findings, in turn, would result in development of more effective patient stratification, targeted therapeutics, and prediction of patient outcome. While consensus has not been reached on the precise nature and means to sub-classify GBM, it is clear that IDH-mutant GBMs are clearly distinct from GBMs without IDH1/2 mutation with respect to molecular and clinical features, including prognosis. In addition, recent findings in pediatric GBMs regarding mutations in the histone H3F3A gene suggest that these tumors may represent a 3rd major category of GBM, separate from adult primary (IDH1/2 wt), and secondary (IDH1/2 mut) GBMs. In this review, we describe major clinically relevant genetic and epigenetic abnormalities in GBM-such as mutations in IDH1/2, EGFR, PDGFRA, and NF1 genes-altered methylation of MGMT gene promoter, and mutations in hTERT promoter. These markers may be incorporated into a more refined classification system and applied in more accurate clinical decision-making process. In addition, we focus on current understanding of the biologic heterogeneity and classification of GBM and highlight some of the molecular signatures and alterations that characterize GBMs as histologically defined. We raise the question whether IDH-wild type high grade astrocytomas without microvascular proliferation or necrosis might best be classified as GBM, even if they lack the histologic hallmarks as required in the current WHO classification. Alternatively, an astrocytic tumor that fits the current histologic definition of GBM, but which shows an IDH mutation may in fact be better classified as a distinct entity, given that IDH-mutant GBM are quite distinct from a biological and clinical perspective.

What is New in the Management of Epilepsy in Gliomas?

OPINION STATEMENT

Seizures represent a common symptom in low- and high-grade gliomas. Tumor location and histology influence the risk for epilepsy. Some molecular factors (BRAF V 600E mutations in glioneuronal tumors and IDH1/2 mutations in diffuse grade II and III gliomas) are molecular factors that are relevant for diagnosis and prognosis and have been associated with the risk of epilepsy as well. Glutamate plays a central role in epileptogenicity and growth of glial and glioneuronal tumors, based on the release of glutamate from tumor cells that enhances excitotoxicity, and a downregulation of the inhibitory GABAergic pathways. Several potential targets for therapy have been identified, and m-TOR inhibitors have already shown activity. Gross total resection is the strongest predictor of seizure freedom in addition to clinical factors, such as preoperative seizure duration, type, and control with antiepileptic drugs (AEDs). Radiotherapy and chemotherapy with alkylating agents (procarbazine, CCNU, vincristine, temozolomide) are effective in reducing the frequency of seizures in patients with pharmacoresistant epilepsy. Newer AEDs (in particular levetiracetam and lacosamide) seem to be better tolerated than the old AEDs (phenobarbital, phenytoin, carbamazepine), but randomized clinical trials are needed to prove their superiority in terms of efficacy.

A preclinical orthotopic model for glioblastoma recapitulates key features of human tumors and demonstrates sensitivity to a combination of MEK and PI3K pathway inhibitors

Current therapies for glioblastoma multiforme (GBM), the highest grade malignant brain tumor, are mostly ineffective, and better preclinical model systems are needed to increase the successful translation of drug discovery efforts into the clinic. Previous work describes a genetically engineered mouse (GEM) model that contains perturbations in the most frequently dysregulated networks in GBM (driven by RB, KRAS and/or PI3K signaling and PTEN) that induce development of Grade IV astrocytoma with properties of the human disease. Here, we developed and characterized an orthotopic mouse model derived from the GEM that retains the features of the GEM model in an immunocompetent background; however, this model is also tractable and efficient for preclinical evaluation of candidate therapeutic regimens. Orthotopic brain tumors are highly proliferative, invasive and vascular, and express histology markers characteristic of human GBM. Primary tumor cells were examined for sensitivity to chemotherapeutics and targeted drugs. PI3K and MAPK pathway inhibitors, when used as single agents, inhibited cell proliferation but did not result in significant apoptosis. However, in combination, these inhibitors resulted in a substantial increase in cell death. Moreover, these findings translated into the in vivo orthotopic model: PI3K or MAPK inhibitor treatment regimens resulted in incomplete pathway suppression and feedback loops, whereas dual treatment delayed tumor growth through increased apoptosis and decreased tumor cell proliferation. Analysis of downstream pathway components revealed a cooperative effect on target downregulation. These concordant results, together with the morphologic similarities to the human GBM disease characteristics of the model, validate it as a new platform for the evaluation of GBM treatment.

Ciliary transport regulates PDGF-AA/αα signaling via elevated mammalian target of rapamycin signaling and diminished PP2A activity

Primary cilia are built and maintained by intraflagellar transport (IFT), whereby the two IFT complexes, IFTA and IFTB, carry cargo via kinesin and dynein motors for anterograde and retrograde transport, respectively. Many signaling pathways, including platelet- derived growth factor (PDGF)-AA/αα, are linked to primary cilia. Active PDGF-AA/αα signaling results in phosphorylation of Akt at two residues: P-Akt(T308) and P-Akt(S473), and previous work showed decreased P-Akt(S473) in response to PDGF-AA upon anterograde transport disruption. In this study, we investigated PDGF-AA/αα signaling via P-Akt(T308) and P-Akt(S473) in distinct ciliary transport mutants. We found increased Akt phosphorylation in the absence of PDGF-AA stimulation, which we show is due to impaired dephosphorylation resulting from diminished PP2A activity toward P-Akt(T308). Anterograde transport mutants display low platelet-derived growth factor receptor (PDGFR)α levels, whereas retrograde mutants exhibit normal PDGFRα levels. Despite this, neither shows an increase in P-Akt(S473) or P-Akt(T308) upon PDGF-AA stimulation. Because mammalian target of rapamycin complex 1 (mTORC1) signaling is increased in ciliary transport mutant cells and mTOR signaling inhibits PDGFRα levels, we demonstrate that inhibition of mTORC1 rescues PDGFRα levels as well as PDGF-AA-dependent phosphorylation of Akt(S473) and Akt(T308) in ciliary transport mutant MEFs. Taken together, our data indicate that the regulation of mTORC1 signaling and PP2A activity by ciliary transport plays key roles in PDGF-AA/αα signaling.

Epidermal growth factor-like module containing mucin-like hormone receptor 2 expression in gliomas

Epidermal growth factor (EGF) module-containing mucin-like receptor 2 (EMR2) is a member of the seven span transmembrane adhesion G-protein coupled receptor subclass. This protein is expressed in a subset of glioblastoma (GBM) cells and associated with an invasive phenotype. The expression pattern and functional significance of EMR2 in low grade or anaplastic astrocytomas is unknown and our goal was to expand and further define EMR2's role in gliomas with an aggressive invasive phenotype. Using the TCGA survival data we describe EMR2 expression patterns across histologic grades of gliomas and demonstrate an association between increased EMR2 expression and poor survival (p < 0.05). This data supports prior functional data depicting that EMR2-positive neoplasms possess a greater capacity for infiltrative and metastatic spread. Genomic analysis suggests that EMR2 overexpression is associated with the mesenchymal GBM subtype (p < 0.0001). We also demonstrate that immunohistorchemistry is a feasible method for screening GBM patients for EMR2 expression. Protein and mRNA analysis demonstrated variable expression of all isoforms of EMR2 in all glioma grades, however GBM displayed the most diverse isoforms expression pattern as well as the highest expression of the EGF1-5 isoform of EMR2. Finally, a correlation of an increased EMR2 expression after bevacizumab treatment in glioma cells lines is identified. This observation should serve as the impetus for future studies to determine if this up-regulation of EMR2 plays a role in the observation of the diffuse and increasingly invasive recurrence patterns witnessed in a subset of GBM patients after bevacizumab treatment.

Medical therapy of gliomas

Medical therapies are an important part of adjunctive therapy for gliomas. In this chapter we will review the chemotherapeutic and targeted agents that have been evaluated in clinical trials in grade II-IV gliomas in the last decade. A number of randomized phase III trials were completed and reported. There has been a clear success in oligodendroglial tumors and low grade glioma. Although some progress has been made in glioblastoma, considerable work involving the multidisciplinary collaboration of basic science, translational and clinical investigators needs to be done to improve the outcome of patients with anaplastic astrocytoma and glioblastoma. In addition, tailoring treatment based on molecular cytogenetic characteristics is a major focus of research into precision based medicine for glioma.

Targeting class IA PI3K isoforms selectively impairs cell growth, survival, and migration in glioblastoma

The phosphoinositide 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) pathway is frequently activated in human cancer and plays a crucial role in glioblastoma biology. We were interested in gaining further insight into the potential of targeting PI3K isoforms as a novel anti-tumor approach in glioblastoma. Consistent expression of the PI3K catalytic isoform PI3K p110α was detected in a panel of glioblastoma patient samples. In contrast, PI3K p110β expression was only rarely detected in glioblastoma patient samples. The expression of a module comprising the epidermal growth factor receptor (EGFR)/PI3K p110α/phosphorylated ribosomal S6 protein (p-S6) was correlated with shorter patient survival. Inhibition of PI3K p110α activity impaired the anchorage-dependent growth of glioblastoma cells and induced tumor regression in vivo. Inhibition of PI3K p110α or PI3K p110β also led to impaired anchorage-independent growth, a decreased migratory capacity of glioblastoma cells, and reduced the activation of the Akt/mTOR pathway. These effects were selective, because targeting of PI3K p110δ did not result in a comparable impairment of glioblastoma tumorigenic properties. Together, our data reveal that drugs targeting PI3K p110α can reduce growth in a subset of glioblastoma tumors characterized by the expression of EGFR/PI3K p110α/p-S6.

Prognostic role of phospho-PRAS40 (Thr246) expression in gastric cancer

INTRODUCTIONS

Phospho-PRAS40(Thr246) (phosphorylated proline-rich Akt substrate of 40 kilodaltons at Thr246) is a biomarker for phosphatidylinositol 3-kinase (PI3K) pathway activation and AKT inhibitors sensitivity.

MATERIAL AND METHODS

In this study, we immunohistochemically investigated the expression of phospho-PRAS40(Thr246) in 141 gastric cancer tumors, and evaluated its clinicopathological and prognostic significance.

RESULTS

Sixty-four cases (45.4%) were defined as phospho-PRAS40(Thr246) positive. Phospho-PRAS40(Thr246) correlated positively with lymph node metastasis, lymphatic infiltration, vascular infiltration and shorter survival. Furthermore, phospho-PRAS40(Thr246) is an independent prognostic factor for gastric cancer.

CONCLUSIONS

Our data suggest that phospho-PRAS40(Thr246) was frequently expressed in gastric cancers, and correlated with malignant progression and poor prognosis of patients. PI3K pathway-targeted therapies should be considered in the future treatment of gastric cancers.

Expression of PTEN and mTOR in sacral chordoma and association with poor prognosis

Sacral chordoma is an aggressive, locally invasive neoplasm, and has a poor prognosis. However, the molecular basis for the clinical behavior remains unknown. The purpose of this study was to investigate the expression of phosphatase and tensin homolog deleted on chromosome 10 (PTEN) and mammalian target of rapamycin (mTOR) in sacral chordoma, and explore their roles in the prognosis. PTEN and mTOR were detected immunohistochemically in 40 sacral chordoma tissues and 10 adjacent normal tissues. Correlations between PTEN and mTOR expression and clinicopathological factors were analyzed. Kaplan-Meier survival curves and log-rank test were used to analyze the continuous disease-free survival time (CDFS). The expression of PTEN in sacral chordoma was significantly lower than that in adjacent normal tissues, while the levels of mTOR expression in sacral chordoma were significantly higher than that in adjacent normal tissues (P = 0.000, P = 0.030). The positive expression of mTOR appears to correlate with the negative expression of PTEN in sacral chordoma (P = 0.021). PTEN-negative expression and mTOR-positive expression were associated with tumor invasion into the surrounding muscles (P = 0.038, P = 0.014). Log-rank test showed that PTEN-negative and mTOR-positive expressions had an important impact on the patients' CDFS (P = 0.011, P = 0.015). Our results suggest that PTEN and mTOR might play an important role in the local invasiveness of sacral chordoma. PTEN and mTOR might be recognized as important prognostic predictors of recurrence and could be used as potential therapeutic targets for the treatment for sacral chordoma.

Phase I study of vinblastine and sirolimus in pediatric patients with recurrent or refractory solid tumors

BACKGROUND

The combination of vinblastine and mammalian target of rapamycin (mTOR) inhibitor sirolimus inhibits the growth of neuroblastoma xenografts through pro-apoptotic and anti-angiogenic mechanisms. This phase I study aimed to explore the safety and toxicity of this combination in pediatric patients with advanced solid tumors.

PROCEDURE

Patients ≤21 years of age with recurrent/refractory solid tumors (including CNS) were eligible. Sirolimus was administered daily by mouth or nasogastric (NG) tube, with doses adjusted to achieve a target trough concentration of 10-15 ng/ml, with weekly intravenous vinblastine (dose escalated 4-6 mg/m(2)/dose according to 3 + 3 phase I design).

RESULTS

Fourteen patients were enrolled (median age 8.7 years; range 2.3-19) of whom 12 were evaluable for toxicity and 11 for response. One patient experienced a dose-limiting toxicity (grade 3 mucositis) at the highest vinblastine dose level. Myelosuppression was the most common toxicity. Dose-adjusted sirolimus trough concentrations were significantly lower in patients receiving drug via NG tube (1.50 ± 0.75 ng/ml/mg vs. 2.25 ± 1.07 ng/ml/mg for oral administration). Correlative biomarker analysis demonstrated a significant reduction in serum concentration of soluble vascular endothelial growth factor receptor (sVEGFR2) at 28 days compared to baseline consistent with inhibition of angiogenesis. One patient had a partial response and three had stable disease for more than 3 months.

CONCLUSIONS

The combination of mTOR inhibitor and vinblastine given over an extended continuous schedule is safe, associated with a reduction in circulating angiogenic factor (CAF) VEGFR2 and resulted in clinical responses. Future studies using the intravenously administered mTOR inhibitor temsirolimus are planned.

Generation of a patient-derived chordoma xenograft and characterization of the phosphoproteome in a recurrent chordoma

OBJECT

The management of patients with locally recurrent or metastatic chordoma is a challenge. Preclinical disease models would greatly accelerate the development of novel therapeutic options for chordoma. The authors sought to establish and characterize a primary xenograft model for chordoma that faithfully recapitulates the molecular features of human chordoma.

METHODS

Chordoma tissue from a recurrent clival tumor was obtained at the time of surgery and implanted subcutaneously into NOD-SCID interleukin-2 receptor gamma (IL-2Rγ) null (NSG) mouse hosts. Successful xenografts were established and passaged in the NSG mice. The recurrent chordoma and the derived human chordoma xenograft were compared by histology, immunohistochemistry, and phospho-specific immunohistochemistry. Based on these results, mice harboring subcutaneous chordoma xenografts were treated with the mTOR inhibitor MLN0128, and tumors were subjected to phosphoproteome profiling using Luminex technology and immunohistochemistry.

RESULTS

SF8894 is a novel chordoma xenograft established from a recurrent clival chordoma that faithfully recapitulates the histopathological, immunohistological, and phosphoproteomic features of the human tumor. The PI3K/Akt/mTOR pathway was activated, as evidenced by diffuse immunopositivity for phospho-epitopes, in the recurrent chordoma and in the established xenograft. Treatment of mice harboring chordoma xenografts with MLN0128 resulted in decreased activity of the PI3K/Akt/mTOR signaling pathway as indicated by decreased phospho-mTOR levels (p = 0.019, n = 3 tumors per group).

CONCLUSIONS

The authors report the establishment of SF8894, a recurrent clival chordoma xenograft that mimics many of the features of the original tumor and that should be a useful preclinical model for recurrent chordoma.

The molecular landscape of diffuse glioma and prospects for biomarker development

INTRODUCTION

High-throughput molecular profiling is transforming long-standing conceptions of diffuse gliomas, the most common primary brain tumors. Indeed, comprehensive genomic, transcriptomic and epigenomic analyses have not only provided striking mechanistic insights into the pathogenesis of diffuse gliomas but also greatly enriched the pool of potential biomarkers for prognostic and predictive patient stratification.

AREAS COVERED

This article summarizes significant recent developments in the molecular characterization of diffuse gliomas, focusing on implications for biomarker development and application. In doing so, we will also address relevant high-throughput molecular profiling technologies and both the opportunities and challenges implicit in their widespread incorporation into disease management workflows.

EXPERT OPINION

Although the number of validated biomarkers guiding diffuse glioma management is currently quite small, rapidly progressing molecular annotation continues to provide a steady stream of clinically relevant candidates, many of which show promise for predictive capabilities in the context of specific targeted therapeutics. Such potential now requires rigorous validation in well-designed clinical trials supported by robust molecular profiling assays operative from standard clinical material.

Antiproliferative effects of γ-secretase inhibitor, a Notch signalling inhibitor, in multiple myeloma cells and its molecular mechanism of action

OBJECTIVES

To investigate the effects of γ-secretase inhibitor (GSI), a Notch signalling inhibitor, on the proliferation of multiple myeloma cells in vitro and its molecular mechanism of action.

METHODS

RPMI 8226 cells were treated with increasing concentrations of GSI (0-20 µmol/l) for 24-72 h. Proliferation was measured using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromide (MTT) assay. Cell-cycle analysis was performed on RPMI 8226 cells treated with 0-10 µmol/l GSI for 48 h using flow cytometry. Expression of Notch signalling proteins (Notch1, Jagged 1 and Jagged 2), Bcl-2 and phosphorylated Akt (p-Akt) was determined using Western blotting in RPMI 8226 cells treated with various concentrations of GSI for various time periods.

RESULTS

GSI inhibited proliferation of RPMI 8226 cells in a concentration- and time-dependent manner by inducing G0/G1 cell-cycle arrest. GSI-mediated antiproliferative effects were associated with significant reductions in the expression of Notch1, Jagged1, Jagged2, p-Akt and Bcl-2.

CONCLUSION

Inhibition of the Notch signalling pathway by GSI may be a promising therapeutic approach for the treatment of multiple myeloma.

The combination of novel targeted molecular agents and radiation in the treatment of pediatric gliomas

Brain tumors are the most common solid pediatric malignancy. For high-grade, recurrent, or refractory pediatric brain tumors, radiation therapy (XRT) is an integral treatment modality. In the era of personalized cancer therapy, molecularly targeted agents have been designed to inhibit pathways critical to tumorigenesis. Our evolving knowledge of genetic aberrations in pediatric gliomas is being exploited with the use of specific targeted inhibitors. These agents are additionally being combined with XRT to increase the efficacy and duration of local control. In this review, we discuss novel agents targeting three different pathways in gliomas, and their potential combination with XRT. BRAF is a serine/threonine kinase in the RAS/RAF/MAPK kinase pathway, which is integral to cellular division, survival, and metabolism. Two-thirds of pilocytic astrocytomas, a low-grade pediatric glioma, contain a translocation within the BRAF gene called KIAA1549:BRAF that causes an overactivation of the MEK/MAPK signaling cascade. In vitro and in vivo data support the use of MEK or mammalian target of rapamycin (mTOR) inhibitors in low-grade gliomas expressing this translocation. Additionally, 15-20% of high-grade pediatric gliomas express BRAF V600E, an activating mutation of the BRAF gene. Pre-clinical in vivo and in vitro data in BRAF V600E gliomas demonstrate dramatic cooperation between XRT and small molecule inhibitors of BRAF V600E. Another major signaling cascade that plays a role in pediatric glioma pathogenesis is the PI3-kinase (PI3K)/mTOR pathway, known to be upregulated in the majority of high- and low-grade pediatric gliomas. Dual PI3K/mTOR inhibitors are in clinical trials for adult high-grade gliomas and are poised to enter studies of pediatric tumors. Finally, many brain tumors express potent stimulators of angiogenesis that render them refractory to treatment. An analog of thalidomide, CC-5103 increases the secretion of critical cytokines of the tumor microenvironment, including IL-2, IFN-γ, TNF-α, and IL-10, and is currently being evaluated in clinical trials for the treatment of recurrent or refractory pediatric central nervous system tumors. In summary, several targeted inhibitors with radiation are currently under investigation in both translational bench research and early clinical trials. This review article summarizes the molecular rationale for, and the pre-clinical data supporting the combinations of these targeted agents with other anti-cancer agents and XRT in pediatric gliomas. In many cases, parallels are drawn to molecular mechanisms and targeted inhibitors of adult gliomas. We additionally discuss the potential mechanisms underlying the efficacy of these agents.

Overcoming resistance to rapalogs in gliomas by combinatory therapies

Glioblastoma is the most common and aggressive brain tumor type, with a mean patient survival of approximately 1year. Many previous analyses of the glioma kinome have identified key deregulated pathways that converge and activate mammalian target of rapamycin (mTOR). Following the identification and characterization of mTOR-promoting activity in gliomagenesis, data from preclinical studies suggested the targeting of mTOR by rapamycin or its analogs (rapalogs) as a promising therapeutic approach. However, clinical trials with rapalogs have shown very limited efficacy on glioma due to the development of resistance mechanisms. Analysis of rapalog-insensitive glioma cells has revealed increased activity of growth and survival pathways compensating for mTOR inhibition by rapalogs that are suitable for therapeutic intervention. In addition, recently developed mTOR inhibitors show high anti-glioma activity. In this review, we recapitulate the regulation of mTOR signaling and its involvement in gliomagenesis, discuss mechanisms resulting in resistance to rapalogs, and speculate on strategies to overcome resistance. This article is part of a Special Issue entitled: Inhibitors of Protein Kinases (2012).

PTEN promoter methylation and activation of the PI3K/Akt/mTOR pathway in pediatric gliomas and influence on clinical outcome

The signaling pathways that underlie the pathogenesis of pediatric gliomas are poorly understood. We characterized the PI3K/Akt/mTOR pathway in pediatric gliomas of all grades. Using immunohistochemistry, we assessed activation of the PI3K/Akt/mTOR pathway by evaluating the downstream signaling molecules phospho(p)-S6, phospho(p)-4BP1, and phospho(p)-PRAS40; PTEN; and PTEN promoter methylation, as well as the MIB labeling index. We correlated these findings with the clinical outcomes of 48 children with gliomas. Eighty percent of high-grade gliomas (12/15) showed activation of the PI3K/Akt/mTOR pathway based on p-S6 and p-4EBP1 expression. The majority of high-grade gliomas were negative for PTEN expression (10/15), and 50% had PTEN promoter methylation (grade III: 2/4; grade IV: 3/6). Low-grade gliomas demonstrated PI3K/Akt/mTOR pathway activation in 14/32 (43.8%) by p-S6 and 16/32 (50%) by p-4EBP1. Over 50% of grade I (6/11) and almost all grade II tumors (6/7) showed PTEN promoter methylation. Tumor grade correlated negatively with PTEN expression and positively with expression of p-S6 and p-4EBP1 (PTEN: P = .0025; pS6: P = .0075; p-4EBP1: P = .0066). There was a trend toward inverse correlation of methylation of the PTEN promoter with expression of PTEN protein (P= .0990) and direct correlation of expression of p-S6 and p-4EBP1 with poorer clinical outcome, as measured by progression-free survival (p-S6: P= .0874; p-4EBP1: P= .0475). Tumors with no PTEN expression had a higher MIB labeling index (P= .007). The majority of pediatric gliomas show activation of the PI3K/Akt/mTOR pathway, with methylation of the PTEN promoter occurring commonly in these tumors.

The PI3K/AKT/mTOR signalling pathway is active in salivary gland cancer and implies different functions and prognoses depending on cell localisation

OBJECTIVES

The PI3K/AKT/mTOR signalling axis controls cell proliferation and survival and has achieved major importance as a target for cancer therapy. This investigation evaluated the expression of the major components P-AKT, P-mTOR, PI3K and P-S6rp in salivary gland cancer.

MATERIALS AND METHODS

Immunohistochemical expression of P-AKT, P-mTOR, PI3K and P-S6rp was evaluated and correlated to clinicopathological parameters and survival of 272 patients with salivary gland carcinomas.

RESULTS AND CONCLUSION

Analysis of all tumours together revealed an increased expression of all components of the pathway in comparison to normal salivary gland control tissue. Nuclear expression of P-AKT was associated with young age, localised tumour stage, absence of lymph node metastases and favourable prognosis. On the contrary, cytoplasmic P-AKT displayed unfavourable tumour characteristics like high-grade malignancy, and worse overall survival. In comparison to cytoplasmic/membrane mTOR expression, nuclear P-mTOR was associated with absence of lymph node metastases and higher survival rates. PI3K and P-S6rp were exclusively found in the cytoplasm. Expression of P-S6rp was correlated to increased age, advanced tumour size and lymph node metastases. In all tumours together, nuclear P-AKT positively correlated with nuclear P-mTOR, whereas P-S6rp was associated with expression of PI3K and cytoplasmic P-AKT. In acinic cell carcinoma, cytoplasmic expression of P-AKT, P-mTOR, PI3K and P-S6rp was positively associated with each other. In conclusion, PI3K/AKT/mTOR signalling is active in salivary gland cancer and might function as a target for personalised therapy. P-AKT and P-mTOR possess distinct molecular functions with impact on prognosis depending on their cellular localisation.