Evidence for phosphatidylinositol 3-kinase—Akt—p70S6K pathway activation and transduction of mitogenic signals by platelet-derived growth factor in human meningioma cells

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.

Glutathione and Glutaredoxin in Redox Regulation and Cell Signaling of the Lens

The ocular lens has a very high content of the antioxidant glutathione (GSH) and the enzymes that can recycle its oxidized form, glutathione disulfide (GSSG), for further use. It can be synthesized in the lens and, in part, transported from the neighboring anterior aqueous humor and posterior vitreous body. GSH is known to protect the thiols of the structural lens crystallin proteins from oxidation by reactive oxygen species (ROS) so the lens can maintain its transparency for proper visual function. Age-related lens opacity or senile cataract is the major visual impairment in the general population, and its cause is closely associated with aging and a constant exposure to environmental oxidative stress, such as ultraviolet light and the metabolic end product, H2O2. The mechanism for senile cataractogenesis has been hypothesized as the results of oxidation-induced protein-thiol mixed disulfide formation, such as protein-S-S-glutathione and protein-S-S-cysteine mixed disulfides, which if not reduced in time, can change the protein conformation to allow cascading modifications of various kinds leading to protein-protein aggregation and insolubilization. The consequence of such changes in lens structural proteins is lens opacity. Besides GSH, the lens has several antioxidation defense enzymes that can repair oxidation damage. One of the specific redox regulating enzymes that has been recently identified is thioltransferase (glutaredoxin 1), which works in concert with GSH, to reduce the oxidative stress as well as to regulate thiol/disulfide redox balance by preventing protein-thiol mixed disulfide accumulation in the lens. This oxidation-resistant and inducible enzyme has multiple physiological functions. In addition to protecting structural proteins and metabolic enzymes, it is able to regulate the redox signaling of the cells during growth factor-stimulated cell proliferation and other cellular functions. This review article focuses on describing the redox regulating functions of GSH and the thioltransferase enzyme in the ocular lens.

Co-Targeting MAP Kinase and Pi3K-Akt-mTOR Pathways in Meningioma: Preclinical Study of Alpelisib and Trametinib

Simple Summary

Multi recurrent or high-grade meningiomas remain an unmet medical need in neuro-oncology. Several studies have highlighted the potential therapeutic efficacy of mTor inhibitors to control tumoral growth of meningiomas. However, a positive feedback on AKT oncogenic pathway from these drugs may explain the modest success. Our aim was to target Pi3kinase upstream mTor, and MAP kinase pathway, overactivated in meningiomas, alone or in combined targeting in comparison to mTor targeting. Our in vitro results obtained on three meningioma cell lines and on a large series of fresh human meningiomas, including 35 WHO grade 1, 23 grade 2, and five grade 3, showed that co-targeting Pi3kinase and MAP kinase seemed promising, opening new therapeutic strategies in these tumors.

Abstract

Recurrent or high-grade meningiomas are an unmet medical need. Recently, we demonstrated that targeting mTOR by everolimus was relevant both in vitro and in humans. However, everolimus induces an AKT activation that may impact the anti-proliferative effect of the drug. Moreover, the MAP kinase pathway was shown to be involved in meningioma tumorigenesis. We therefore targeted both the Pi3k-AKT-mTOR and MAP kinase pathways by using combinations of the Pi3k inhibitor alpelisib and the MEK inhibitor trametinib. Our study was performed in vitro on the human meningioma cell lines and on a large series of primary cultures providing from 63 freshly operated meningiomas including 35 WHO grade 1, 23 grade 2, and five grade 3, half of which presented a NF2 genomic alteration. Alpelisib induced a higher inhibitory effect on cell viability and proliferation than everolimus in all cell lines and 32 randomly selected tumors no matter the genomic status, the histological subtype or grade. Trametinib also strongly inhibited cell proliferation and induced AKT activation. Combined treatment with alpelisib plus trametinib reversed the AKT activation induced by trametinib and induced an additive inhibitory effect irrespective of the cell lines or tumor features. Co-targeting pathways seems promising and may be considered particularly for aggressive meningioma.

Advances in Molecular Biological and Translational Studies in World Health Organization Grades 2 and 3 Meningiomas: A Literature Review

The treatment of World Health Organization (WHO) grades 2 and 3 meningiomas remains difficult and controversial. The pathogenesis of high-grade meningiomas was expected to be elucidated to improve treatment strategies. The molecular biology of meningiomas has been clarified in recent years. High-grade meningiomas have been linked to NF2 mutations and 22q deletion. CDKN2A/B homozygous deletion and TERT promoter mutations are independent prognostic factors for WHO grade 3 meningiomas. In addition to 22q loss, 1p, 14p, and 9q loss have been linked to high-grade meningiomas. Meningiomas enriched in copy number alterations may be biologically invasive. Furthermore, several new comprehensive classifications of meningiomas have been proposed based on these molecular biological features, including DNA methylation status. The new classifications may have implications for treatment strategies for refractory aggressive meningiomas because they provide a more accurate prognosis compared to the conventional WHO classification. Although several systemic therapies, including molecular targeted therapies, may be effective in treating refractory aggressive meningiomas, these drugs are being tested. Systemic drug therapy for meningioma is expected to be developed in the future. Thus, this review aims to discuss the distinct genomic alterations observed in WHO grade 2 and 3 meningiomas, as well as their diagnostic and therapeutic implications and systemic drug therapies for high-grade meningiomas.

Synthesizing Molecular and Immune Characteristics to Move Beyond WHO Grade in Meningiomas: A Focused Review

No portion of this manuscript has previously been presented. Meningiomas, the most common primary intracranial tumors, are histologically categorized by the World Health Organization (WHO) grading system. While higher WHO grade is generally associated with poor clinical outcomes, a significant subset of grade I tumors recur or progress, indicating a need for more reliable models of meningioma behavior. Several groups have developed risk scores based on molecular or immunologic characteristics. These classification schemes show promise, with several models preliminarily demonstrating similar or superior accuracy to WHO grading. Improved understanding of immune system recognition and targeting of meningioma subtypes is necessary to advance the predictive power, as well as develop new therapies. Here, we characterize meningioma molecular drivers, predictive of recurrence and progression, and describe specific aspects of the immune response to meningiomas while highlighting critical questions and ongoing research. Relevant manuscripts of interest were identified using a systematic approach and synthesized into this focused review. Finally, we summarize the ongoing and completed clinical trials for immunotherapy in meningiomas and offer perspective on future directions.

mTOR Signaling and Potential Therapeutic Targeting in Meningioma

Meningiomas are the most frequent primary tumors arising in the central nervous system. They typically follow a benign course, with an excellent prognosis for grade I lesions through surgical intervention. Although radiotherapy is a good option for recurrent, progressive, or inoperable tumors, alternative treatments are very limited. mTOR is a protein complex with increasing therapeutical potential as a target in cancer. The current understanding of the mTOR pathway heavily involves it in the development of meningioma. Its activation is strongly dependent on PI3K/Akt signaling and the merlin protein. Both factors are commonly defective in meningioma cells, which indicates their likely function in tumor growth. Furthermore, regarding molecular tumorigenesis, the kinase activity of the mTORC1 complex inhibits many components of the autophagosome, such as the ULK1 or Beclin complexes. mTOR contributes to redox homeostasis, a vital component of neoplasia. Recent clinical trials have investigated novel chemotherapeutic agents for mTOR inhibition, showing promising results in resistant or recurrent meningiomas.

Chemotherapy and targeted therapies for meningiomas: what is the evidence?

PURPOSE OF REVIEW

Although most meningiomas are slow growing tumors mainly controlled by surgery with or without radiotherapy, aggressive meningiomas that fail these conventional treatments constitute a rare situation, a therapeutic challenge and an unmet need in neuro-oncology.

RECENT FINDING

Mutational landscape in recurrent high-grade meningiomas includes mainly NF2 mutation or 22q chromosomal deletion, whereas telomerase reverse transcriptase promoter, BAP-1 and CDK2NA mutations were also found in aggressive meningiomas. Pi3K-Akt-mTOR pathway is currently the most relevant intracellular signaling pathway target in meningiomas with preliminary clinical activity observed. Assessment of drug activity with progression free survival rate at 6 months is challenging in regard to meningioma growth rate heterogeneity, so that 3-dimensional growth rate before and during treatment could be considered in the future to selected new active drugs.

SUMMARY

Despite a low evidence level, some systemic therapies may be considered for patients with recurrent meningioma not amenable to further surgery or radiotherapy. In recurrent high-grade meningioma, everolimus-octreotide combination, bevacizumab, sunitinib and peptide receptor radionuclide therapy exhibit a signal of activity that may justify their clinical use. Despite a lack of clear signal of activity to date, immunotherapy may offer new perspectives in the treatment of these refractory tumors.

Everolimus and Octreotide for Patients with Recurrent Meningioma: Results from the Phase II CEVOREM Trial

PURPOSE

Aggressive meningiomas that progress after surgery/radiotherapy represent an unmet medical need. Strong and constant expression of SSTR2A receptors and activation of the Pi3K/Akt/mTOR pathway have been demonstrated in meningiomas. The combination of everolimus, an mTOR inhibitor, and octreotide, a somatostatin agonist, has shown additive antitumor effect in vitro. The phase II CEVOREM trial investigated the efficacy of this combination on recurrent meningiomas.

PATIENTS AND METHODS

Patients with documented recurrent tumor progression ineligible for further surgery/radiotherapy were eligible to receive octreotide (30 mg/d, day 1) and everolimus (10 mg/d, days 1-28). The primary endpoint was the 6-month progression-free survival rate (PFS6). The secondary endpoints were overall survival, response rate, tumor growth rate according to central review, and safety.

RESULTS

A total of 20 patients were enrolled, including 2 with World Health Organization (WHO) grade I tumors, 10 with WHO grade II tumors, and 8 with WHO grade III tumors; furthermore, 4 patients harbored NF2 germline mutation. The overall PFS6 was 55% [95% confidence interval (CI), 31.3%-73.5%], and overall 6- and 12-month survival rates were 90% (95% CI, 65.6%-97.4%) and 75% (95% CI, 50.0%-88.7%), respectively. A major decrease (>50%) was observed in the growth rate at 3 months in 78% of tumors. The median tumor growth rate decreased from 16.6%/3 months before inclusion to 0.02%/3 months at 3 months (P < 0.0002) and 0.48%/3 months at 6 months after treatment (P < 0.0003).

CONCLUSIONS

The combination of everolimus and octreotide was associated with clinical and radiological activity in aggressive meningiomas and warrants further studies. Decrease in the tumor volume growth rate should be considered a complementary and sensitive endpoint to select potentially effective drugs for recurrent meningiomas.

An integrated genomic analysis of anaplastic meningioma identifies prognostic molecular signatures

Anaplastic meningioma is a rare and aggressive brain tumor characterised by intractable recurrences and dismal outcomes. Here, we present an integrated analysis of the whole genome, transcriptome and methylation profiles of primary and recurrent anaplastic meningioma. A key finding was the delineation of distinct molecular subgroups that were associated with diametrically opposed survival outcomes. Relative to lower grade meningiomas, anaplastic tumors harbored frequent driver mutations in SWI/SNF complex genes, which were confined to the poor prognosis subgroup. Aggressive disease was further characterised by transcriptional evidence of increased PRC2 activity, stemness and epithelial-to-mesenchymal transition. Our analyses discern biologically distinct variants of anaplastic meningioma with prognostic and therapeutic significance.

Advances in meningioma genetics: novel therapeutic opportunities

Meningiomas currently are among the most frequent intracranial tumours. Although the majority of meningiomas can be cured by surgical resection, ∼20% of patients have an aggressive clinical course with tumour recurrence or progressive disease, resulting in substantial morbidity and increased mortality of affected patients. During the past 3 years, exciting new data have been published that provide insights into the molecular background of meningiomas and link sites of tumour development with characteristic histopathological and molecular features, opening a new road to novel and promising treatment options for aggressive meningiomas. A growing number of the newly discovered recurrent mutations have been linked to a particular clinicopathological phenotype. Moreover, the updated WHO classification of brain tumours published in 2016 has incorporated some of these molecular findings, setting the stage for the improvement of future therapeutic efforts through the integration of essential molecular findings. Finally, an additional potential classification of meningiomas based on methylation profiling has been launched, which provides clues in the assessment of individual risk of meningioma recurrence. All of these developments are creating new prospects for effective molecularly driven diagnosis and therapy of meningiomas.

Global epigenetic profiling identifies methylation subgroups associated with recurrence-free survival in meningioma

Meningioma is the most common primary brain tumor and carries a substantial risk of local recurrence. Methylation profiles of meningioma and their clinical implications are not well understood. We hypothesized that aggressive meningiomas have unique DNA methylation patterns that could be used to better stratify patient management. Samples (n = 140) were profiled using the Illumina HumanMethylation450BeadChip. Unsupervised modeling on a training set (n = 89) identified 2 molecular methylation subgroups of meningioma (MM) with significantly different recurrence-free survival (RFS) times between the groups: a prognostically unfavorable subgroup (MM-UNFAV) and a prognostically favorable subgroup (MM-FAV). This finding was validated in the remaining 51 samples and led to a baseline meningioma methylation classifier (bMMC) defined by 283 CpG loci (283-bMMC). To further optimize a recurrence predictor, probes subsumed within the baseline classifier were subject to additional modeling using a similar training/validation approach, leading to a 64-CpG loci meningioma methylation predictor (64-MMP). After adjustment for relevant clinical variables [WHO grade, mitotic index, Simpson grade, sex, location, and copy number aberrations (CNAs)] multivariable analyses for RFS showed that the baseline methylation classifier was not significant (p = 0.0793). The methylation predictor, however, was significantly associated with tumor recurrence (p < 0.0001). CNAs were extracted from the 450k intensity profiles. Tumor samples in the MM-UNFAV subgroup showed an overall higher proportion of CNAs compared to the MM-FAV subgroup tumors and the CNAs were complex in nature. CNAs in the MM-UNFAV subgroup included recurrent losses of 1p, 6q, 14q and 18q, and gain of 1q, all of which were previously identified as indicators of poor outcome. In conclusion, our analyses demonstrate robust DNA methylation signatures in meningioma that correlate with CNAs and stratify patients by recurrence risk.

STAT3 activation and risk of recurrence in meningiomas

Several studies have suggested that activation of signal transducer and activator of transcription 3 (STAT3) is associated with initiation, progression and metastasis of numerous types of malignancy. However, the role of the Janus kinase-interleukin 6-STAT3 signaling pathway in the pathogenesis and recurrence of meningiomas is unknown. The present study evaluated STAT3 activation by western blotting and immunohistochemistry and assessed its association with Ki-67 labeling in 13 cases of meningioma in which frozen tissue and ≥5.5-year follow-up information were available, and in formalin-fixed meningioma tissues from 14 cases with an 8.4-year follow-up. The results of the western blot analysis indicated that STAT3 phosphorylation was markedly higher in grade II meningiomas compared with that in grade I, with mean densitometric values of 8.6 and 1.7 following normalization to actin, respectively. High STAT3 phosphorylation/activation was identified in 2 of 3 recurrent World Health Organization (WHO) grade I meningiomas and 0 of 3 non-recurrent meningiomas. Strong STAT3 phosphorylation/activation signal was also found in 2 of 4 recurrent grade II meningiomas and 1 of 3 non-recurrent cases. According to the immunohistochemistry results, phospho-STAT3 was not increased in WHO grade II tumors compared with that in grade I tumors, and was not significantly different between recurrent and non-recurrent cases. Ki-67 labeling was significantly increased in grade II vs. grade I tumors, and was also significantly increased in recurrent compared with non-recurrent grade I meningiomas. The results of the current study suggest that, while detection of phosphorylated/activated STAT3 may be useful in isolated cases, identifying activation may be of little value in predicting recurrence.

Biology and clinical management challenges in meningioma

Meningiomas are the most frequently occurring intracranial tumors. They are characterized by a broad spectrum of histopathologic appearance. Molecular alterations driving meningioma development, which affect the NF2 gene, are found in roughly 50% of patients. Rare genetic events in benign meningiomas are mutations in TRAF7, KLF4, AKT1, and SMO; all of these mutations are exclusive of NF2 alterations. Progression to a clinically aggressive meningioma is linked to inactivation of CDKN2A/B genes, and a plethora of signaling molecules have been described as activated in meningiomas, which supports the concept of successful clinical use of specific inhibitors. Established treatments include surgical resection with or without radiotherapy delivered in a single fraction, a few large fractions (radiosurgery), or multiple fractions (fractionated radiotherapy). For recurrent and aggressive tumors, inhibitors of the vascular endothelial growth factor (VEGF) pathway, such as vatalinib, bevacizumab, and sunitinib, showed signs of activity in small, uncontrolled studies, and prospective clinical studies will test the efficacy of the tetrahydroisoquinoline trabectedin and of SMO and AKT1 inhibitors.

Role of Merlin/NF2 inactivation in tumor biology

Merlin (Moesin-ezrin-radixin-like protein, also known as schwannomin) is a tumor suppressor protein encoded by the neurofibromatosis type 2 gene NF2. Loss of function mutations or deletions in NF2 cause neurofibromatosis type 2 (NF2), a multiple tumor forming disease of the nervous system. NF2 is characterized by the development of bilateral vestibular schwannomas. Patients with NF2 can also develop schwannomas on other cranial and peripheral nerves, as well as meningiomas and ependymomas. The only potential treatment is surgery/radiosurgery, which often results in loss of function of the involved nerve. There is an urgent need for chemotherapies that slow or eliminate tumors and prevent their formation in NF2 patients. Interestingly NF2 mutations and merlin inactivation also occur in spontaneous schwannomas and meningiomas, as well as other types of cancer including mesothelioma, glioma multiforme, breast, colorectal, skin, clear cell renal cell carcinoma, hepatic and prostate cancer. Except for malignant mesotheliomas, the role of NF2 mutation or inactivation has not received much attention in cancer, and NF2 might be relevant for prognosis and future chemotherapeutic approaches. This review discusses the influence of merlin loss of function in NF2-related tumors and common human cancers. We also discuss the NF2 gene status and merlin signaling pathways affected in the different tumor types and the molecular mechanisms that lead to tumorigenesis, progression and pharmacological resistance.

Group I Paks as therapeutic targets in NF2-deficient meningioma

Neurofibromatosis type 2 (NF2) is an autosomal dominant disorder characterized by the development of multiple tumors in the central nervous system, most notably schwannomas and meningiomas. Mutational inactivation of NF2 is found in 40-60% of sporadic meningiomas, but the molecular mechanisms underlying malignant changes of meningioma cells remain unclear. Because group I p21-activated kinases (Paks) bind to and are inhibited by the NF2-encoded protein Merlin, we assessed the signaling and anti-tumor effects of three group-I specific Pak inhibitors - Frax597, 716 and 1036 - in NF2-/- meningiomas in vitro and in an orthotopic mouse model. We found that these Pak inhibitors suppressed the proliferation and motility of both benign (Ben-Men1) and malignant (KT21-MG1) meningiomas cells. In addition, we found a strong reduction in phosphorylation of Mek and S6, and decreased cyclin D1 expression in both cell lines after treatment with Pak inhibitors. Using intracranial xenografts of luciferase-expressing KT21-MG1 cells, we found that treated mice showed significant tumor suppression for all three Pak inhibitors. Similar effects were observed in Ben-Men1 cells. Tumors dissected from treated animals exhibited an increase in apoptosis without notable change in proliferation. Collectively, these results suggest that Pak inhibitors might be useful agents in treating NF2-deficient meningiomas.

Medical management of meningiomas

The efficacy of surgery and radiation has been well validated in the treatment of meningiomas, with efficacy depending on tumor pathology, size, symptomatology and rate of progression. The role of medical therapy has the least amount of data but is being increasingly investigated for tumors that are inoperable or those tumors that recur and/or progress despite standard therapy. In this review, current data on the use of chemotherapeutic agents in the management of meningiomas will be reviewed, including cytotoxic, biologic, targeted molecular and hormonal agents.

MKP-3 regulates PDGF-BB effects and MAPK activation in meningioma cells

Autocrine platelet derived growth factor-BB (PDGF-BB) and cerebrospinal fluid, which also contains PDGF, stimulate proliferation of leptomeningeal and meningioma cells, in part, by activation of the Raf-1-MEK-1-MAPK pathway. The negative regulators of this activation are not known. However, PDGF receptors and p44/42 MAPK are regulated, in part, by mitogen activated kinase phosphatase 3 (MKP-3) and Src homology carboxyl terminus protein (SHP-2). Six fetal and one adult human leptomeninges specimens and 22 meningiomas were evaluated for MKP-3, SHP-2, and phospho-SHP-2 as well as activation/phosphorylation of MEK1/2, p44/42 MAPK, Akt and signal transducer and activator of transcription 3 (STAT3) by western blot and MKP3 expression by polymerase chain reaction. PDGF-BB and cerebrospinal fluid effects on these phosphatases and signaling were also studied in vitro. MKP-3 and phospho-p44/42 MAPK were detected in all or six of seven leptomeninges, respectively. MKP-3 was detected in six of eight World Health Organization grade I and II meningiomas. Three of four grade I and five of five grade II with no or low MKP-3 had high levels of phospho-p44/42MAPK. MKP3 was not detected in four of six grade III meningiomas. These had high levels of phospho-p44/42MAPK. SHP2 was found in all leptomeninges and meningiomas while phospho-SHP-2 was found in 11 to 33% of grade I-III meningiomas. Reduced MKP-3 may facilitate PDGF-BB autocrine and paracrine mitogenic effects in a subpopulation of higher grade meningiomas by increasing phospho-p44/42 MAPK.

Molecular genetics of meningiomas: Building the roadmap towards personalized therapy

New advances have recently been made in the field of molecular genetics and mouse modeling of meningiomas, opening new perspectives for future treatments. Recent genome-wide genotyping and exome sequencing studies have confirmed the pivotal role of NF2 in meningioma tumorigenesis, concerning roughly half of the tumors, and unraveled new mutations in non-NF2 meningiomas concerning AKT1, SMO, KLF4 and TRAF7. The molecular mechanisms underlying tumorigenesis of high histological grades have been progressively deciphered with the recent discovery of TERT promoter mutations in progressing tumors. A better understanding of the genetics and clinical behavior of high-grade meningiomas is mandatory in order to better design future clinical trials. New genetically engineered mouse models of benign and histologically aggressive meningioma represent a substantial resource for the establishment of relevant pre-clinical trials. By studying the mechanisms underlying these new tumorigenesis pathways and the corresponding mouse models, we should be able to offer personalized chemotherapy to patients with surgery- and radiation-refractory meningiomas in the near future.

Complex interactions between the components of the PI3K/AKT/mTOR pathway, and with components of MAPK, JAK/STAT and Notch-1 pathways, indicate their involvement in meningioma development

We investigated the significance of PI3K/AKT/mTOR pathway and its interactions with MAPK, JAK/STAT and Notch pathways in meningioma progression. Paraffin-embedded tissue from 108 meningioma patients was analysed for the presence of mutations in PIK3CA and AKT1. These were correlated with the expression status of components of the PI3K/AKT/mTOR pathway, including p85α and p110γ subunits of PI3K, phosphorylated (p)-AKT, p-mTOR, p-p70S6K and p-4E-BP1, as well as of p-ERK1/2, p-STAT3 and Notch-1, clinicopathological data and patient survival. A mutation in PIK3CA or AKT1 was found in around 9 % of the cases. Higher grade meningiomas displayed higher nuclear expression of p-p70S6K; higher nuclear and cytoplasmic expression of p-4E-BP1 and of Notch-1; lower cytoplasmic expression of p85αPI3K, p-p70S6K and p-ERK1/2; and lower PTEN Histo-scores (H-scores). PTEN H-score was inversely correlated with recurrence probability. In univariate survival analysis, nuclear expression of p-4E-BP1 and absence of p-ERK1/2 expression portended adverse prognosis, whereas in multivariate survival analysis, p-ERK1/2 expression emerged as an independent favourable prognostic factor. Treatment of the human meningioma cell line HBL-52 with the PI3K inhibitor LY294002 resulted in reduction of p-AKT, p-p70S6K and p-ERK1/2 protein levels. The complex interactions established between components of the PI3K/AKT/mTOR pathway, or with components of the MAPK, JAK/STAT and Notch-1 pathways, appear to be essential for facilitating and fuelling meningioma progression.

High-grade meningiomas: new avenues for drug treatment?

PURPOSE OF REVIEW

For standard first-line treatment of high-grade meningiomas, surgical resection and radiotherapy are regarded as standard of care. In the recurrent setting after exhaustion of all local treatment options, no effective therapies are known and several drugs have failed to show efficacy, but novel compounds may offer hope for better disease control.

RECENT FINDINGS

Upregulation of proangiogenic molecules and dysregulation of some signaling pathways such as the platelet-derived growth factor and mammalian target of rapamycin are recurrently found in high-grade meningiomas. Furthermore, in-vitro studies and single patient experience indicate that trabectedin may be an effective therapy in this tumor type. Unfortunately, so far there is a lack of conclusive clinical trials to draw definite conclusions of efficacy of these approaches.

SUMMARY

There remains a significant unmet need for defining the role of medical therapy in recurrent high-grade meningioma, and more basic research and multicentric well designed trials are needed in this rare and devastating tumor type. Potentially promising novel therapeutics include antiangiogenic drugs, molecular inhibitors of signaling cascades, immunotherapeutics or trabectedin. However, more basic research is required to identify more promising drug targets.

VIDEO ABSTRACT AVAILABLE

See the Video Supplementary Digital Content 1 (http://links.lww.com/CONR/A22).

AKT2 expression in histopathologic grading and recurrence of meningiomas

BACKGROUND

AKT2 (protein kinase B), an important protein in PI3K signaling pathway, is overexpressed in a variety of malignant tumors. However, in patients with meningiomas, the potential correlation between AKT2 and clinical outcome remains unknown.

METHODS

The expression of AKT2 and Ki-67 in meningioma tissues were evaluated immunohistochemically in 94 patients with meningiomas. The correlation of AKT2 immunoreactivity with clinicopathological features and the prognostic value of AKT2 in patients were also analyzed.

RESULTS

In this study, we examined the expression of AKT2 in meningiomas and unveiled its possible relationship with the clinical outcome. Immunohistochemical analysis revealed high AKT2 expression in 46 patients (46/94, 48.9%) and low AKT2 expression in the remaining 48 patients (48/94, 51.1%). There was a positive correlation between AKT2 and Ki-67 immunoreactivity (r = 0.35, P = 0.01). Clinicopathological evaluation suggested that AKT2 expression was associated with pathological grade and recurrence (P < 0.05). Univariate and Cox analysis indicated a significant correlation between high levels of AKT2 immunoreactivity and high rates of tumor recurrence (P < 0.05).

CONCLUSIONS

We conclude that AKT2 may play an important role in the development of meningioma. High AKT2 labeling index indicates higher grade of meningioma, and therefore AKT2 may be a useful molecular marker for predicting the prognosis of meningioma.

From stem cell niche environments to engineering of corneal epithelium tissue

Studies on stem cells (SC) show that SC functions are determined by the extracellular microenvironment, known as the "niche", and by intrinsic genetic programs in the SCs; both are involved in regulating the delicate balance of self-renewal and differentiation. We have identified an animal model of limbal SC (LSC) deficiency and transplantation of SC-containing limbal tissue to treat the LSC deficiency, which could not only replace LSCs by providing new healthy corneal epithelial cells but also restore the lost niche of the limbal stromal layer, causing the regression of vessels and rearrangement of the corneal stromal lamellae. The purpose of the ex-vivo expansion technique is to develop a method that will enable culture of a small number of SCs which could than be expanded in a defined cultured system while preserving the original characteristics and properties of the SCs. In addition, SC characteristics will continue to be maintained when the cultured cells are transplanted back into the host. Bromodeoxyuridine-retaining, ΔNp63, ABCG2, p120, and N-cadherin immunoreactive studies of LSC cultured on an amniotic membrane have been performed. Pathological studies have been conducted for cases with preexisting central corneal stromal opacity treated by transplantation of LSCs followed by penetrating keratoplasty. The results indicate that the amniotic membrane can provide the niche environment for cultured LSCs and maintain the limbal-like environment for the transplanted area of cornea.

Novel therapies for meningiomas

Although advances in surgery, radiation therapy and stereotactic radiosurgery have significantly improved the treatment of meningiomas, there remains an important subset of patients who remain refractory to conventional therapy. Treatment with chemotherapeutic agents such as hydroxyurea and alpha-interferon has provided minimal benefit. In this review, the role of newly emerging novel therapies for meningiomas, with a focus on targeted molecular agents, will be discussed.

Cucurbitacin I blocks cerebrospinal fluid and platelet derived growth factor-BB stimulation of leptomeningeal and meningioma DNA synthesis

Background

Currently, there are no consistently effective chemotherapies for recurrent and inoperable meningiomas. Recently, cucurbitacin I (JSI-124), a naturally occurring tetracyclic triterpenoid compound used as folk medicines has been found to have cytoxic and anti-proliferative properties in several malignancies thru inhibition of activator of transcription (STAT3) activation. Previously, we have found STAT3 to be activated in meningiomas, particularly higher grade tumors.

Methods

Primary leptomeningeal cultures were established from 17, 20 and 22 week human fetuses and meningioma cell cultures were established from 6 World Health Organization (WHO) grade I or II meningiomas. Cells were treated with cerebrospinal fluid from patients without neurologic disease. The effects of cucurbitacin I on cerebrospinal fluid stimulation of meningioma cell DNA synthesis phosphorylation/activation of JAK1, STAT3, pMEK1/2, p44/42MAPK, Akt, mTOR, Rb and caspase 3 activation were analyzed in human leptomeningeal and meningioma cells.

Results

Cerebrospinal fluid significantly stimulated DNA synthesis in leptomeningeal cells. Co-administration of cucurbitacin I (250 nM) produces a significant blockade of this effect. Cucurbitacin I alone also produced a significant reduction in basal DNA synthesis. In grade I and II meningiomas, cerebrospinal fluid also significantly stimulated DNA synthesis. Co-administration of cucurbitacin I (250 nM) blocked this effect.

In the leptomeningeal cultures, cerebrospinal fluid stimulated STAT3 phosphorylation but not p44/42MAPK, Akt or mTOR. Cucurbitacin I had no effect on basal STAT3 phosphorylation but co-administration with cerebrospinal fluid blocked cerebrospinal fluid stimulation of STAT3 phosphorylation in each. In the grade I meningiomas, cerebrospinal fluid stimulated phosphorylation of STAT3 and decreased MEK1/2 and cucurbitacin I had no effect on basal STAT3, p44/42MAPK, Akt, JAK1, mTOR, or Rb phosphorylation. In the grade II meningiomas, cerebrospinal fluid stimulated STAT3 phosphorylation in all and reduced phosphorylation of MEK1/2 in all and p44/42MAPK in one. Cucurbitacin I had no effect on basal phosphorylation of STAT3 but reduced phorphorylated p44/42 MAPK in 2 grade II meningioma cells lines.

Conclusions

These studies raise the possibility that cucurbitacin I might have value as an adjunct chemotherapy. Additional studies are warranted to evaluate the effects of cucurbitacin I on meningiomas in vivo.

mTORC1 inhibitors suppress meningioma growth in mouse models

PURPOSE

To evaluate the mTORC1 (mammalian target of rapamycin complex 1) pathway in meningiomas and to explore mTORC1 as a therapeutic target in meningioma cell lines and mouse models.

EXPERIMENTAL DESIGN

Tissue microarrays (53 meningiomas of all WHO grades) were stained for phosphorylated polypeptides of mTOR, Akt, and the mTORC1 targets 4EBP1 and p70S6K, the latter being the consensus marker for mTORC1 activity. Expression of proteins and mRNAs was assessed by Western blotting and real-time PCR in 25 tumors. Cell lines Ben-Men-1 (benign), IOMM-Lee and KT21 (malignant), and pairs of merlin-positive or -negative meningioma cells were used to assess sensitivity toward mTORC1 inhibitors in methyl-tetrazolium and bromodeoxyuridine (BrdUrd) assays. The effect of temsirolimus (20 mg/kg daily) on tumor weight or MRI-estimated tumor volume was tested by treatment of eight nude mice (vs. 7 controls) carrying subcutaneous IOMM-Lee xenografts, or of eight (5) mice xenotransplanted intracranially with IOMM-Lee (KT21) cells in comparison to eight (5) untreated controls.

RESULTS

All components of the mTORC1 pathway were expressed and activated in meningiomas, independent of their WHO grade. A significant dosage-dependent growth inhibition by temsirolimus and everolimus was observed in all cell lines. It was slightly diminished by merlin loss. In the orthotopic and subcutaneous xenograft models, temsirolimus treatment resulted in about 70% growth reduction of tumors (P < 0.01), which was paralleled by reduction of Ki67 mitotic index (P < 0.05) and reduction of mTORC1 activity (p70S6K phosphorylation) within the tumors.

CONCLUSION

mTORC1 inhibitors suppress meningioma growth in mouse models, although the present study did not measure survival.

Chemotherapy: What is its role in meningioma?

While strong evidence exists for the standard therapy for meningiomas, inclusive of surgery and/or radiation therapy, for those tumors which recur, progress or are inoperable, the optimal medical therapies are yet to be elucidated. This article reviews the current literature for chemotherapeutic options for this subset of tumors, including cytotoxic agents, biologic agents, targeted molecular agents and hormonal agents. At this point in time, the most data is with hydroxyurea and somatostatin, although further trials with combination and targeted molecular therapies are still underway.

Sunitinib targets PDGF-receptor and Flt3 and reduces survival and migration of human meningioma cells

The multitargeted tyrosine-kinase inhibitor sunitinib is a highly effective anti-angiogenic and cytostatic agent in the therapy of various tumours. While malignant gliomas have been shown to be responsive to sunitinib, detailed studies analysing human meningiomas are missing. We therefore analysed the effects of sunitinib in two benign (BenMen-1, HBL52) and two malignant (IOMM-Lee, KT21MG) human meningioma cell lines and found that DNA synthesis was significantly (p ≤ 0.001) inhibited following 1, 2 or 5 μM sunitinib, with IC(50) values between 2 and 5 μM in all cell lines. This effect was associated with a G(2)M-arrest at 10 μM for BenMen-1, HBL52 and IOMM-Lee, and 20 μM in KT21MG cells. Nuclear bisbenzimide staining revealed chromatin condensation following treatment with sunitinib concentrations of 10 μM or higher. Corresponding, cell viability assays showed a significant (p ≤ 0.001) short term decrease of viable cells (24h) only for high sunitinib concentrations with IC(50)-values between 10 and 20 μM. However, pre-irradiated meningioma cells (5 Gy) showed a sensitivity shift towards IC(50)-values around 5 μM sunitinib. We also found that 5 μM strongly reduced meningioma cell migration in vitro. Western blot analyses showed abolished platelet derived growth factor receptor (PDGFR)-autophosphorylation after sunitinib. Interestingly, the drug also inhibited the autophosphorylation of the receptor tyrosine kinase fms-like tyrosine kinase 3 (Flt3) in a dose-dependent manner. Taken together, the present data show that micromolar sunitinib has strong cytostatic and anti-migratory effects on human meningioma cells.

Phase II study of Gleevec® plus hydroxyurea (HU) in adults with progressive or recurrent meningioma

We prospectively evaluated the efficacy and safety of imatinib plus hydroxyurea in patients with progressive/recurrent meningioma. A total of 21 patients with progressive/recurrent meningioma were enrolled in this dual center, single-arm, phase II trial. All patients received 500 mg of hydroxyurea twice a day. Imatinib was administered at 400 mg/day for patients not on CYP3A enzyme inducing anti-epileptic drugs (EIAEDs) and at 500 mg twice a day for patients on EIAEDs. The primary endpoint was progression-free survival at 6 months (PFS-6) and secondary endpoints were safety, radiographic response rate, and overall survival (OS). Best radiographic response was stable disease and was observed in 14 patients (67%). PFS-6 for all patients, those with grade I tumors (n = 8) and those with grade II or III tumors (n = 13) was 61.9, 87.5 and 46.2%, respectively. Patients with grade II or III tumors had poorer PFS and OS than those with grade I tumors, (P = 0.025 and P = 0.018) respectively. The only grade 3 or greater adverse event occurring in ≥ 10% of patients was anemia (10%). Imatinib plus hydroxyurea is well tolerated among patients with meningioma but has modest anti-tumor activity for this indication.

AR42, a novel histone deacetylase inhibitor, as a potential therapy for vestibular schwannomas and meningiomas

Neurofibromatosis type 2 (NF2) is an autosomal-dominant disease that results in the formation of bilateral vestibular schwannomas (VSs) and multiple meningiomas. Treatment options for NF2-associated tumors are limited, and to date, no medical therapies are FDA approved. The ideal chemotherapeutic agent would inhibit both VS and meningiomas simultaneously. The objectives of this study are (1) to test the efficacy of AR42, a novel histone deacetylase inhibitor, to inhibit VS and meningioma growth and (2) to investigate this drug's mechanisms of action. Primary cultures of human VS and meningioma cells were established. Nf2-deficient mouse schwannoma and benign human meningioma Ben-Men-1 cells were also cultured. Cells were treated with AR42, and the drug's effects on proliferation and the cell cycle were analyzed using a methanethiosulfonate assay and flow cytometry, respectively. Human phospho-kinase arrays and Western blots were used to evaluate the effects of AR42 on intracellular signaling. The in vivo efficacy of AR42 was investigated using schwannoma xenografts. Tumor volumes were quantified using high-field, volumetric MRI, and molecular target analysis was performed using immunohistochemistry. AR42 inhibited the growth of primary human VS and Nf2-deficient mouse schwannoma cells with a half maximal inhibitory concentration (IC(50)) of 500 nM and 250-350 nM, respectively. AR42 also inhibited primary meningioma cells and the benign meningioma cell line, Ben-Men-1, with IC(50) values of 1.5 µM and 1.0 µM, respectively. AR42 treatment induced cell-cycle arrest at G(2) and apoptosis in both VS and meningioma cells. Also, AR42 exposure decreased phosphorylated Akt in schwannoma and meningioma cells. In vivo treatment with AR42 inhibited the growth of schwannoma xenografts, induced apoptosis, and decreased Akt activation. The potent growth inhibitory activity of AR42 in schwannoma and meningioma cells suggests that AR42 should be further evaluated as a potential treatment for NF2-associated tumors.

Medical therapies for meningiomas

Meningiomas are the most common primary brain tumor in adults. Although the majority of these tumors can be effectively treated with surgery and radiation therapy, an important subset of patients have inoperable tumors, or develop recurrent disease after surgery and radiotherapy, and require some form of medical therapy. There are increasing numbers of studies evaluating various medical therapies but the results remain disappointing. Chemotherapies and hormonal therapies have been generally ineffective, although somatostatin analogues may have therapeutic potential. There is also increasing interest in targeted molecular therapies. Agents inhibiting platelet derived growth factor receptors and epidermal growth factor receptors have shown little efficacy, but molecular agents inhibiting vascular endothelial growth factor receptors appear to have some promise. As with other tumors, advances in the medical therapies for meningiomas will require improved understanding of the molecular pathogenesis of these tumors, more predictive preclinical models, and efficient mechanisms for conducting clinical trials, given the small population of eligible patients.

Lopinavir inhibits meningioma cell proliferation by Akt independent mechanism

Recent studies suggest that HIV-1 protease inhibitors may have anti-neoplastic effects on some malignancies. The anti-neoplastic effects of lopinavir have not been established or studied in brain tumors. Primary cultures of three fetal leptomeninges and 18 meningiomas were treated with lopinavir alone or with PDGF-BB. DNA synthesis was assessed by CyQUANT. Lopinavir effects on basal and PDGF-stimulated phosphorylation of the Akt-mTOR, MEK1/2-MAPK and STAT3 pathways, phosphorylation of Rb, Caspase 3 activation and reductions in survivin were assessed by Western blots. Lopinavir produced a significant reduction in PDGF-BB stimulation of DNA synthesis in a leptomeningeal culture (P = 0.0013) and 1 of 6 WHO grade I and 1 of 4 grade II meningiomas at 24 h and in 3 of 6 WHO grade I, 4 of 4 grade II and 1 of 1 grade III cell cultures (P = 0.0001) at 72 h. Lopinavir reduced PDGF-BB stimulation of phosphorylation/activation of MAPK in the 22 week fetal leptomeningeal cell cultures and in cells from 1 grade I meningioma at 24 h, but in none of 4 grade I and 5 grade II meningiomas at 6 h. Lopinavir had no notable effect on basal or PDGF-stimulated p-mTOR, p-MEK1/2, or p-STAT3, activation of Caspase 3 or survivin levels. Lopinavir treatment for 24 h had no effect on basal Rb phosphorylation but reduced Rb phosphorylation in all four meningioma cultures. These studies suggest that lopinavir may inhibit meningioma growth, and does so in part by cell cycle arrest. Additional evaluation of lopinavir as a potential adjunct chemotherapy is warranted.

Fibroblast growth factor receptor-3 expression in meningiomas with stimulation of proliferation by the phosphoinositide 3 kinase-Akt pathway

OBJECT

Fibroblast growth factor receptors (FGFRs)-1, -2, and -3 are expressed in the developing brain and may participate in CNS neoplasia. Fibroblast growth receptor-3 has not been demonstrated in the human CNS or its tumors. Nonetheless, it has been implicated in the pathogenesis of several other forms of neoplasia.

METHODS

Twenty-four human meningiomas were evaluated using Western blot analysis for expression of FGFR3, its ligand acidic FGF, and concomitant phosphorylation/activation of p44/42 mitogen-activated protein kinase (MAPK), Akt, and STAT3. Mutations in exons 7 and 10 of the FGFR3 gene were analyzed by polymerase chain reaction in 10 meningiomas. Primary meningioma cells cultured from 10 human meningiomas were also treated with acidic FGF and evaluated for cell proliferation or activation/phosphorylation of p44/42 MAPK, Akt, and STAT3.

RESULTS

Immunoblotting demonstrated the presence of FGFR3 in 12 (71%) of 17 primarily fibroblastic and transitional WHO Grade I meningiomas. The FGFR3 was detected in 4 (80%) of 5 WHO Grade II, and 2 of 2 Grade III tumors. Acidic FGF was detected in 3 (18%) of 17 Grade I, 1 (20%) of 5 Grade II, and 1 (50%) of 2 Grade III meningiomas. In WHO Grade I meningiomas, 3 of 6 tumors with no detectable FGFR3 had no detectable p-STAT3. In WHO Grades II and III meningiomas, FGFR3 expression was associated with p-STAT3, p-Akt, and p-p44/42 MAPK expression. No mutations were demonstrated in exons 7 or 10 by polymerase chain reaction in any meningioma. Treatment with acidic FGF, a ligand for FGFR3, stimulated meningioma cell proliferation and activation of Akt and STAT3 in primary meningioma cell cultures.

CONCLUSIONS

These findings suggest that FGFR3 and acidic FGF are expressed in adult human leptomeninges as well as WHO Grades I and II meningiomas. Fibroblast growth factor receptor-3 activation stimulates meningioma cell proliferation by activation of the phosphoinositide 3 kinase-Akt-PRAS40-mTOR and STAT3 pathways.

Increased STAT-3 and synchronous activation of Raf-1-MEK-1-MAPK, and phosphatidylinositol 3-Kinase-Akt-mTOR pathways in atypical and anaplastic meningiomas

The intracellular events promoting meningioma cell proliferation in high grade tumors are not established. In this study we compared 45 WHO grade I and 35 grade II or III meningiomas by Western blot or immunohistochemistry for phosphorylation/activation of the MEK-1-MAPK, PI3 K-Akt-mTOR-PRAS40 and STAT3 pathways. By Western blot, STAT3 activation was detected in 75% of grade I compared to 100% of grade II and III meningiomas. By immunohistochemistry p-STAT3 was detected in 28% of grade I compared to 65 or 66% of grade II and III meningiomas, respectively. Phosphorylated MEK-1 and p-MAPK were activated in nearly all grade I, II and III tumors. Phosphorylated Akt was also detected in the majority of meningiomas of each grade although downstream pathway component activation was less widespread. These findings suggest that there is increased STAT3 activation in WHO grade II and III meningiomas compared with grade I tumors. Moreover, each of the three major growth regulatory pathways is concomitantly activated in higher grade meningiomas.

Imatinib mesylate enhances therapeutic effects of gemcitabine in human malignant mesothelioma xenografts

PURPOSE

Platelet-derived growth factor receptor beta (PDGFRbeta), frequently activated in malignant mesothelioma, is a promising cancer therapeutic target. Imatinib mesylate (STI571; Glivec) is a selective inhibitor of tyrosine kinases as bcr-abl, c-kit, c-fms, and PDGFRbeta and enhances tumor drug uptake by reducing the interstitial fluid pressure. We previously showed that imatinib mesylate synergizes with gemcitabine and pemetrexed in PDGFRbeta-positive mesothelioma cells. Here, we aimed at investigating these combined treatments in a novel mesothelioma model.

EXPERIMENTAL DESIGN

REN mesothelioma cells, infected with a lentiviral vector carrying the luciferase gene, were injected in the peritoneum of severe combined immunodeficient mice. This model allowed imaging of live animals treated with pemetrexed or gemcitabine chemotherapeutics, or with imatinib mesylate alone, as well as with a combination of gemcitabine and imatinib mesylate.

RESULTS

We show here that, consistent with our previous in vitro studies, gemcitabine inhibited tumor growth, whereas pemetrexed was ineffective, even at the highest dosage tested. Compared with monotreatment, the combination of gemcitabine with imatinib mesylate led to a further tumor growth inhibition and improved mice survival, by a decrease rate of tumor cell proliferation and an increase in number of apoptotic tumor cells.

CONCLUSIONS

Imatinib mesylate enhances the therapeutic response to gemcitabine, in accordance with our previous in vitro data. These in vivo results validate imatinib mesylate and gemcitabine as a combination treatment of malignant mesothelioma, also in view of its known positive effects on tumor drug uptake. These evidences provide the rationale for the currently ongoing clinical trials.

Meningioma

Meningiomas are mostly benign tumours originating from the arachnoid cap cells, represent 13-26% of all intracranial tumours. They are more common in older age and in females. Deletion in NF2 gene and exposure to ionizing radiation are established risk factors, while the role of sex hormones is yet not clarified. Five-year survival for typical meningiomas exceeds 80%, but is poorer (5-year survival <60%) in malignant and atypical meningiomas. Papillary and haemangiopericytic morphology, large tumour size, high mitotic index, absence of progesterone receptors, deletions and loss of heterozygosity are poor prognostic factors. Complete surgical excision is the standard treatment. Radiotherapy is currently used in the clinical practice in atypical, malignant or recurrent meningioma at a total dose of 45-60Gy. However, the role of adjuvant irradiation is still controversial and has to be compared in a randomised prospective setting with a policy of watchful waiting. Radiosurgery has gained more and more importance in the management of meningiomas, especially in meningiomas that cannot be completely resected as for many skull base meningiomas. Medical therapy for patients with recurrent, progressive and symptomatic disease after repeated surgery, radiosurgery and radiotherapy is investigational. Hormonal therapy with progesterone antagonists has shown modest results, while chemotherapy with hydroxyurea appears moderately active.

Targeted drug therapy for meningiomas

✓ Although advances in surgery, radiation therapy, and stereotactic radiosurgery have significantly improved the treatment of meningiomas, there remains an important subset of patients whose tumors are refractory to conventional therapy. Treatment with traditional chemotherapeutic agents has provided minimal benefit. In this review, the role of targeted molecular therapies for recurrent or progressive meningiomas is discussed.

New prospects for management and treatment of inoperable and recurrent skull base meningiomas

Skull base, including optic nerve, cavernous sinus, clival and foramen magnum tumors represent a major challenge for neurosurgeons and neuro-oncologists. Growth regulatory signaling pathways for these tumors are of increasing interest as potential targets for new chemotherapy. Those differentially activated in various grades of meningiomas are currently being identified as well. This article reviews some recent findings pathways that appear to regulate meningioma growth. Potential targets for novel therapies are also discussed.

CXC receptor and chemokine expression in human meningioma: SDF1/CXCR4 signaling activates ERK1/2 and stimulates meningioma cell proliferation

Recent evidence indicates that cancer cells express chemokine (CK) receptors and that their signaling is crucial for tumor proliferation, migration, and angiogenesis. The profiles of expression of CXC CK receptors (CXCR1-5) and their main ligands (growth-related oncogene, GRO1-2-3/CXCL1-2-3; interleukin 8, IL-8/CXCL8; monokine-induced gamma-interferon MIG/CXCL9; gamma-interferon-inducible-protein-10, IP-10/CXCL10; stromal cell-derived factor-1, SDF1/CXCL12; B-cell activating CK-1, BCA-1/CXCL13) were analyzed by reverse transcription polymerase chain reaction (RT-PCR) in surgical samples of human meningiomas. All the five receptors displayed high percentages of positive cases: 92% CXCR1, 89% CXCR2, 83% CXCR3, 78% CXCR4, and 94% CXCR5. Conversely, their ligands showed a lower pattern of expression: 40% IL-8, 42% GRO1-3, 42% IP-10, 28% MIG, 53% SDF1, and 3% BCA-1. SDF1/CXCR4 interaction plays a pivotal role in cancer proliferation. Thus, the signaling mechanisms activated by the exclusive binding between SDF1 and CXCR4 was investigated in 12 primary cultures from meningioma tissues. CXCR4 was functionally coupled as demonstrated by the significant increase of DNA synthesis in meningioma cells in response to SDF1, measured by [3H]-thymidine uptake. In three primary cultures, the SDF1-dependent mitogenic activity was associated with a marked phosphorylation of extracellular signal-regulated kinase (ERK1/2) as evaluated by Western blots. PD98059 (a MEK inhibitor) significantly reduced ERK1/2 activation, thus linking the SDF1/CXCR4 pathway to meningioma cell proliferation via ERK1/2 signal transduction. We demonstrate, for the first time in human meningiomas, the simultaneous expression of CXCR1-5 and their CKs and the mitogenic activity of SDF1/CXCR4, suggesting a pivotal role of these receptor-ligand pairs in meningeal tumors.

Preliminary data suggestive of a novel translational approach to mesothelioma treatment: imatinib mesylate with gemcitabine or pemetrexed

BACKGROUND

Malignant mesothelioma is a cancer which is refractory to current treatments. Imatinib mesylate is a selective inhibitor of tyrosine kinases such as bcr-abl, c-Kit, c-Fms and platelet derived growth factor receptor beta (PDGFRbeta). PDGFRbeta is often overexpressed in mesothelioma cells and is a therapeutic target for imatinib in some solid tumours. A study was undertaken to assess whether imatinib alone or combined with chemotherapeutic agents may be effective for treating mesothelioma.

METHODS

Cultures from mesothelioma MMP, REN and ISTMES2 cell lines were treated with imatinib alone or in combination with a chemotherapeutic agent.

RESULTS

Imatinib induced cytotoxicity and apoptosis selectively on PDGFRbeta positive mesothelioma cells via blockade of receptor phosphorylation and interference with the Akt pathway. Of the chemotherapeutic agents tested in combination with imatinib, a synergistic effect was obtained with gemcitabine and pemetrexed.

CONCLUSIONS

This study provides a rationale for a novel translational approach to the treatment of mesothelioma which relies on enhancement of tumour chemosensitivity by inhibition of Akt.

Signaling-transduction pathways required for ex vivo expansion of human limbal explants on intact amniotic membrane

PURPOSE

Ex vivo expansion of limbal epithelial progenitor cells on amniotic membrane (AM) without 3T3 fibroblasts is a new surgical approach to treat limbal stem cell deficiency. Such expansion requires NGF-TrkA-mediated signaling, and this study was conducted to delineate the downstream signaling pathways.

METHODS

The human corneolimbal ring was cut into explants and cultured on intact human AM. At day 0 or 10, low-molecular-weight inhibitors were added, whereas the control group received dimethyl sulfoxide (DMSO). The epithelial outgrowth rate was monitored for 17 days, and the epithelial cells were collected for Western blot analysis.

RESULTS

In the control, most expansion of human limbal epithelial cells started from the limbus from days 5 to 7 and reached approximately 80% confluence at day 17. Compared with the control, the outgrowth was completely inhibited by 50 microM LY294002 or 50 microM SR13668 and was significantly suppressed by 10 microM U0126, but was not affected by 10 microM of either SB203580 or JNK inhibitor 1. The inhibition of outgrowth by LY294002, SR13668, and U0126 was reversible. Western blot analysis showed that phosphorylation of Akt and FKHRL1was abolished by LY294002 and SR13668, but downregulated by U0126, which also abolished phosphorylation of p44/42 mitogen-activated protein kinase (MAPK). The phosphorylation of p38 and JNK MAPK were downregulated or abolished during ex vivo expansion.

CONCLUSIONS

Ex vivo expansion of human limbal epithelial progenitor cells on intact AM is mediated by the survival signaling pathway mediated by PI3K-Akt-FKHRL1 and by the mitogenic MAPK pathway mediated by p44/42 at the expense of p38 and JNK MAPK.

Mitogenic Signal Transduction Pathways in Meningiomas: Novel Targets for Meningioma Chemotherapy?

The roles of growth factor receptors and numerous downstream growth regulatory pathways are of increasing interest in neuro-oncology. These pathways have been extensively studied in gliomas but only recently analyzed in meningiomas. This article reviews current research on the growth factor receptor-Ras-Raf-1-MEK-1-MAPK, PI3K-Akt/PKB, PLC-gamma1-PKC, phospholipase A2-cyclooxygenase, and TGF-beta receptor-Smad pathways that appear to regulate meningioma growth and inhibit apoptosis. Sites along these receptor/kinase cascades that might be targeted by novel therapies are also discussed.

Immunocytochemical detection of 14-3-3 in primary nervous system tumors

14-3-3 proteins have attracted much recent interest in the etiopathogenesis of human cancers owing to their involvement in the prevention of apoptosis. However, the expression of 14-3-3 in primary nervous system tumors has not been previously characterized. In this paper, Immunohistochemistry using a specific anti-14-3-3 antibody was performed on formalin-fixed, paraffin embedded archival tissue from 124 primary human nervous system tumors and 10 normal brain tissues. In the normal control brains, 14-3-3 immunoreactivity was localized mainly in the neuronal somata and processes, and some glial cells showed only weak immunoreactivity. However, 14-3-3 immunoreactivity was seen in the majority of astrocytomas [grade I (9/11), II (16/21), III (13/17), IV (17/21)]. There was no difference between the positive expression rates of 14-3-3 in different grades of astrocytomas (P = 0.968). But the intensity and degree of 14-3-3 immunoreactivity in diffuse astrocytomas, anaplastic astrocytoma, and glioblastoma multiformes showed trends with tumor grade, with glioblastomas having the highest positivity (P = 0.048). The 14-3-3 immunoreactivity was also seen in the majority of other gliomas [oligodendroglioma (2/3), anaplastic oligodendroglioma (4/4), ependymoma (1/2), anaplastic ependymoma (2/2), choroid plexus papilloma (3/3), pineocytoma (2/2), medulloblastoma (5/8)]. All meningiomas [syncytical (3), fibrous/fibroblastic (4), angiomatous (4), transitional/mixed (3)] were intensely and diffusely positive. All schwannomas (4), neurofibromas (2), pituitary adenomas (6) and craniopharyngiomas(4) also showed intense positive staining. These results showed that 14-3-3 is expressed in the majority of the primary human nervous system tumors. The up-regulated expression of 14-3-3 may be a common mechanism for evading apoptosis in most primary human nervous system tumors, and targeting 14-3-3 may be a novel promising strategy for the treatment of these tumors, especially for malignant tumors.

Different Activation of Mitogen-Activated Protein Kinase and Akt Signaling Is Associated with Aggressive Phenotype of Human Meningiomas

PURPOSE

Activation of intracellular signaling cascades has been implicated in the growth control of benign meningiomas, but their role for meningioma progression and outcome is unknown. Here we determined the expression and function of proteins involved in mitogen-activated protein kinase (MAPK) and phosphinositol-3 kinase (PI3K)/Akt signaling in benign, atypical, and malignant meningiomas and studied their association with clinicopathologic data including meningioma recurrence.

EXPERIMENTAL DESIGN

Expression of various MAPK and PI3K signaling proteins was determined in 70 primary meningiomas and, if present, in recurrent tumors by immunohistochemistry and Western blotting. The expression patterns in primary and recurrent tumors were related to clinical data. The effect of MAPK and PI3K pathway inhibition on cell proliferation and apoptosis was determined using a primary malignant meningioma cell culture.

RESULTS

Atypical and malignant meningiomas showed higher levels of phospho-Akt compared with benign tumors, and their proliferation could be inhibited by PI3K blocking using wortmannin. PI3K inhibition did not induce apoptosis in malignant meningioma cells. In contrast, expression of phospho-Raf and phospho-MAPK was decreased in aggressive meningiomas compared with benign tumors, but MAPK inhibition by PD98059 resulted in tumor cell apoptosis and decreased proliferation. Reduced MAPK activation was associated with meningioma recurrence, and PI3K activation was associated with poor preclinical condition and brain invasion of malignant meningiomas.

CONCLUSIONS

Both MAPK and PI3K/Akt pathways are activated at different levels in benign and malignant meningiomas. Activation of PI3K/Akt signaling contributes to the aggressive behavior of malignant meningiomas, whereas MAPK activation is involved in both proliferation and apoptosis of malignant meningiomas.

Meningioma: Current treatment options and future directions

Benign meningiomas can be observed if not symptomatic or growing. When treatment is indicated, the options are surgery, radiosurgery, fractionated radiation therapy, or a combination of these modalities. Except in certain cases, such as large tumors that require debulking for relief of symptoms, we do not recommend the routine use of combination therapy. Intracranial meningiomas have usually been treated with surgical resection with an expected durable local control of 80% to 90% when a gross total resection (GTR) is obtained. Patients who have inoperable disease, refuse surgery, undergo less than a GTR, or who have aggressive histology should instead be considered candidates for radiation therapy or radiosurgery. While benign meningiomas can be successfully treated definitively or postoperatively with either fractionated radiation therapy or single fraction radiosurgery, atypical or malignant lesions are best treated with fractionated radiation therapy with conventional dosimetric margins. The role of systemic therapy is not yet defined, but multiple agents are being investigated in early phase trials for patients with recurrent or progressive disease after standard therapy has failed.