Erythropoietin and Erythropoietin Receptor Expression in Vestibular Schwannoma

Growth rate of vestibular schwannoma

Vestibular schwannoma (VS) is the most common tumor in the extra-axial posterior fossa compartment in adults. Growth rate is paramount to decision making regarding treatment and follow up of these tumors. We conducted a comprehensive review of the literature to answer four questions: What percentage of newly diagnosed VS will grow on follow-up? What factors correlate to tumor growth? What is the "normal" growth rate for sporadic VS? What factors characterize VS with rapid growth? Thirty-seven reports, with more than 4000 patients, fit our review criteria. One third of newly diagnosed VS will grow on follow-up of 1-3years. However, after 5years, up to one half will grow. Patient age and sex do not influence growth of VS. Hearing loss and vertigo at presentation do not predict tumor growth. It is unclear whether balance disturbance or tinnitus predict tumor growth. Tumor size and location do not predict tumor growth. Growth in the first year of observation is a strong predictor of tumor growth. The average growth rate of a VS is 0.99-1.11mm/year. However, the expected growth rate for VS that have been shown to grow at first follow-up is 3mm/year. Factors that may predict tumor growth of above 4mm/year are cystic and hemorrhagic features in the tumor, and hormonal treatment. VS grow at an average 1mm/year. VS that have been shown to grow at first follow-up should be considered for treatment, unless contraindicated. Long term follow-up is recommended for VS.

Tumor Biology of Vestibular Schwannoma: A Review of Experimental Data on the Determinants of Tumor Genesis and Growth Characteristics

OBJECTIVE

Provide an overview of the literature on vestibular schwannoma biology with special attention to tumor behavior and targeted therapy.

BACKGROUND

Vestibular schwannomas are benign tumors originating from the eighth cranial nerve and arise due to inactivation of the NF2 gene and its product merlin. Unraveling the biology of these tumors helps to clarify their growth pattern and is essential in identifying therapeutic targets.

METHODS

PubMed search for English-language articles on vestibular schwannoma biology from 1994 to 2014.

RESULTS

Activation of merlin and its role in cell signaling seem as key aspects of vestibular schwannoma biology. Merlin is regulated by proteins such as CD44, Rac, and myosin phosphatase-targeting subunit 1. The tumor-suppressive functions of merlin are related to receptor tyrosine kinases, such as the platelet-derived growth factor receptor and vascular endothelial growth factor receptor. Merlin mediates the Hippo pathway and acts within the nucleus by binding E3 ubiquiting ligase CRL4. Angiogenesis is an important mechanism responsible for the progression of these tumors and is affected by processes such as hypoxia and inflammation. Inhibiting angiogenesis by targeting vascular endothelial growth factor receptor seems to be the most successful pharmacologic strategy, but additional therapeutic options are emerging.

CONCLUSION

Over the years, the knowledge on vestibular schwannoma biology has significantly increased. Future research should focus on identifying new therapeutic targets by investigating vestibular schwannoma (epi)genetics, merlin function, and tumor behavior. Besides identifying novel targets, testing new combinations of existing treatment strategies can further improve vestibular schwannoma therapy.

Assessment of antiangiogenic effect of imatinib mesylate on vestibular schwannoma tumors using in vivo corneal angiogenesis assay

Object

Angiogenesis and the platelet-derived growth factor (PDGF) pathway are active in the pathogenesis of vestibular schwannomas (VSs). The purpose of this study was to test whether imatinib mesylate (Gleevec), a PDGF receptor (PDGFR) blocker, reduces angiogenic capacity in sporadic VS and in VS associated with neurofibromatosis Type 2 (NF2) using a corneal angiogenesis assay.

Methods

From 121 VS tissue samples stored in the tumor bank at the Marmara University Institute of Neurological Sciences, 10 samples (6 from sporadic cases, 4 from NF2-associated cases) were selected at random for use in this study. Expression of PDGF-A and PDGF-B and their receptors was evaluated in sporadic and NF2-associated VS as well as in glioblastoma (GBM) and normal brain tissue by means of immunohistochemistry and Western blot analysis. Corneal angiogenesis assay was then used to evaluate the angiogenic capacity of tissue specimens from sporadic and NF2-associated VS with and without imatinib treatment as well as positive and negative controls (GBM and normal brain tissue).

Results

The angiogenic potential of the sporadic and NF2-associated VS tumor tissue differed significantly from that of the positive and negative control tissues (p <0.05). Furthermore, NF2-associated VS showed significantly lower angiogenic potential than sporadic VS (p <0.05). Imatinib treatment significantly reduced the angiogenic potential in both the sporadic VS and the NF2-associated VS groups. The level of PDGF-A and PDGFR-α as well as PDGF-B and PDGFR-β expression in sporadic VS and NF2-associated VS also differed significantly (p <0.05) from the levels in controls. Additionally the level of PDGFR-β was significantly higher in sporadic VS than in NF2-associated VS (p <0.05).

Conclusions

The findings of this study indicate that NF2-associated VS has significantly more angiogenic potential than sporadic VS and normal brain tissue. Additionally, imatinib reduces the angiogenic activity of both sporadic and NF2-associated VS. The authors conclude that imatinib may be a potential treatment for VS, especially for NF2-associated lesions that cannot be cured with resection or radiosurgery.

EGF and bFGF promote invasion that is modulated by PI3/Akt kinase and Erk in vestibular schwannoma

OBJECTIVES

Vestibular schwannomas (VSs) are slow-growing benign tumors but, on rare occasion, can invade adjacent cranial nerves, causing significant morbidity, especially in association with neurofibromatosis 2 (NF2). We aimed to determine the role of the growth factors EGF, bFGF, and the hormone, Epo, in promoting such invasive behavior in VS, as well as their mechanisms of action.

METHODS

Immunohistochemical staining showed expression of EGFR, bFGF, Epo, EpoR in archived VS tissue. Western blots and immunofluorescence showed expression of EGFR, EpoR and FGF in HEI-193, an immortalized cell line derived from human NF2-related VS. Matrigel invasion assays were used to study the effect of Epo, FGF and bFGF on invasive behavior in HEI-193. Western blotting showed levels of phospho-Akt and phospho-Erk in HEI-193 upon addition of growth factors plus PI3K or MEK inhibitors. Quantitative RT-PCR was performed to determine the expression of MMP2 and MMP9 after treatment with growth factors.

RESULTS

EGFR, bFGF, Epo and EpoR were expressed in VS tissue and HEI193. Addition of EGF and bFGF increased cellular invasion by 10 and 3.5-fold, respectively. Epo had minimal effect on invasion. Results indicated that Erk is involved in bFGF but not EGF-induced invasion, while Akt is involved in both pathways. EGF treatment moderately induced MMP9, but is unlikely to account for the observed invasion.

CONCLUSION

Activation of EGFR and FGFR may promote invasive behavior in VS through ERK and Akt signaling pathways. Further investigation will be necessary to elucidate their potential as useful targets in the treatment of VS.

Human schwannomas express activated platelet-derived growth factor receptors and c-kit and are growth inhibited by Gleevec (Imatinib Mesylate)

Schwannomas, although benign, can be fatal or give rise to significant morbidity due to an unpredictable growth rate. They can reoccur after surgery or radiation, current treatments each with significant inherent risks. These risks are further amplified in neurofibromatosis type 2 (NF2), a germ line predisposition syndrome characterized by multiple schwannomas, underlying the need for biological targeted therapies. Gleevec (STI571, imatinib mesylate), in addition to the bcr-abl oncogene in chronic myelogenous leukemia, inhibits c-kit and platelet-derived growth factor receptor (PDGFR) signaling, thereby expanding its use to several malignant and benign human diseases. In the present study, we show that human sporadic and NF2-associated schwannomas have increased expression along with activation of PDGFR-alpha, PDGFR-beta, and c-kit receptors, compared with normal or traumatic nerve. Using the human NF2-null HEI-193 schwannoma cell line, Gleevec inhibited schwannoma viability, proliferation, and anchorage-independent growth, as well as induced apoptosis in a dose-dependent manner (IC(50) 5-10 micromol/L). These antitumorigenic effects were correlated to inhibition of PDGFR-alpha, PDGFR-beta, and c-kit activation/phosphorylation and major downstream signaling pathways. Lack of robust xenograft or transgenic models of schwannomas prevents extension of these studies in vivo. However, the established long track record and tolerable toxicity of Gleevec already in clinical use and our preclinical data lead us to propose that Gleevec should be evaluated in human schwannomas with shown progressive growth.

Expression of bcl-2 is associated with microvessel density in olfactory neuroblastoma

Erythropoietin (Epo) expression is regulated via hypoxia-inducible factor (HIF)-1alpha-directed gene transcription. Activation of the erythropoietin receptor (EpoR) by Epo leads to elevated expression of the anti-apoptotic protein, bcl-2, which has recently been shown to promote angiogenesis in malignant tumors. Expression of HIF-1alpha, Epo, EpoR, and bcl-2 was studied by immunohistochemistry in a series of 20 olfactory neuroblastoma (ONB) samples. Data were correlated with microvessel density, proliferative activity, and apoptosis in the specimens and survival analysis was performed to investigate the prognostic value of the examined factors. Immunohistochemical analysis revealed robust expression of HIF-1alpha, Epo, EpoR, and bcl-2 in ONB. Ninety percent of the samples showed HIF-1alpha immunoreactivity and in 60% of the cases, bcl-2 immunoreactivity was observed. A significant positive correlation between the expression levels of HIF-1alpha and bcl-2 and the microvessel density was found. Survival analysis did not reveal any prognostic significance for the tested factors. Expression of HIF-1alpha, Epo, Epo-R, and bcl-2 may play a functional role in ONB pathogenesis. Our data suggest that bcl-2 may act as a stimulator of angiogenesis in ONB, and thus represents a novel target for anti-angiogenic treatment strategies in the therapy of ONB.

The erythropoietin receptor in normal and cancer tissues

The hormone erythropoietin (EPO) is essential for the survival, proliferation and differentiation of the erythrocytic progenitors. The EPO receptor (EPO-R) of erythrocytic cells belongs to the cytokine class I receptor family and signals through various protein kinases and STAT transcription factors. The EPO-R is also expressed in many organs outside the bone marrow, suggesting that EPO is a pleiotropic anti-apoptotic factor. The controversial issue as to whether the EPO-R is functional in tumor tissue is critically reviewed. Importantly, most studies of EPO-R detection in tumor tissue have provided falsely positive results because of the lack of EPO-R specific antibodies. However, endogenous EPO appears to be necessary to maintain the viability of endothelial cells and to promote tumor angiogenesis. Although there is no clinical proof that the administration of erythropoiesis stimulating agents (ESAs) promotes tumor growth and mortality, present recommendations are that (i) ESAs should be administered at the lowest dose sufficient to avoid the need for red blood cell transfusions, (ii) ESAs should not be used in patients with active malignant disease not receiving chemotherapy or radiotherapy, (iii) ESAs should be discontinued following the completion of a chemotherapy course, (iv) the target Hb should be 12 g/dL and not higher and (v) the risks of shortened survival and tumor progression have not been excluded when ESAs are dosed to target Hb <12 g/dL.

Molecular studies of vestibular schwannomas: a review

PURPOSE OF REVIEW

To summarize advances in understanding the molecular biology of vestibular schwannomas over the past year.

RECENT FINDINGS

The role of the neurofibromatosis type 2 protein, denoted as merlin or schwannomin, in embryonic development, cellular adherence, and in cell proliferation has become better elucidated in the past year. Likewise, the role of merlin in Schwann cell-axon interaction has been studied. Additionally, two comprehensive analyses of the spectrum of human neurofibromatosis type 2 mutations have been compiled which make up a valuable resource in understanding critical regions of the neurofibromatosis type 2 gene. Neurofibromatosis type 2 screening guidelines for young patients with solitary vestibular schwannomas have been published. The role of electromagnetic radiation via cellular and portable telephones as a predisposing factor to vestibular schwannoma formation has also been the topic of several studies. Based on increased knowledge of the pathways in which merlin functions and the available transgenic and xenograft mouse models, preliminary data regarding directed pharmacotherapy are also summarized.

SUMMARY

With increased knowledge of the pathologic mechanisms and interacting proteins associated with merlin, the research community is poised to begin trials of targeted interventions in vitro and in the current mouse models.